US3214631A

US3214631A - Tube having target with store and/or non-store sections

Info

Publication number: US3214631A
Application number: US214877A
Authority: US
Inventors: Robert H Anderson
Original assignee: Tektronix Inc
Current assignee: Tektronix Inc
Priority date: 1962-08-06
Filing date: 1962-08-06
Publication date: 1965-10-26
Anticipated expiration: 1982-10-26
Also published as: NL142820B; DE1439716A1; DE1439659A1; GB992178A; NL6409585A; SE317452B; US3325673A; NL296317A; NL144770B; US3214516A; GB1036859A; DE1439634A1; NL298991A; GB992177A; DE1439634C2; DE1439634B2; CH418391A

Description

Oct. 26, 1965 R. H. ANDERSON TUBE HAVING TARGET WITH STORE AND/OR NON-STORE SECTIONS 2 Sheets-Sheet 1 Filed Aug. 6, 1962 Fig. I

Fig. 5 52 IN VE N 70R.

ROBERT H. ANDERSON BUCKHORN, CHEATHAM a BLORE ATTORNEYS R. H. ANDERSON TUBE HAVING TARGET WITH STORE AND/0R NON-STORE SECTIONS 2 Sheets-Sheet 2 &

//V VE N TOR.

ROBERT H. ANDERSON ll I.

E R O L B 8 M A H m E H C R O H m AT TORNE Y Oct. 26, 1965 Filed Aug. 6, 1962 United States Patent 3,214,631 TUBE HAVING TARGET WITH STORE AND/ OR NON-STORE SECTIONS Robert H. Anderson, Portland, Oreg., assignor to Tektronix, Inc., Beaverton, 0reg., a corporation of Oregon Filed Aug. 6, 1962, Ser. No. 214,877 17 Claims. (Cl. 315-12 The subject matter of the present invention relates generally to cathode ray storage tubes, and in particular to direct viewing bistable storage tubes which employ a thin integral layer of secondary emissive phosphor material as the storage dielectric of the storage target in such tubes. The phosphor layer has a thickness within a critical range of thicknesses over which the phosphor material can function both to store a bistable electrical charge image for an indefinite controllable time and to emit a visible light image corresponding to such charge image. The storage target of the present invention also employs a coating of light transparent electrically conductive material beneath the phosphor layer to apply target voltages thereto. In addition the integral phosphor layer is provided with a sufliciently porous structure to enable the transmission of secondary electrons through such layer which are emitted from one side of the phosphor layer and are collected by the conductive coating target electrode on the opposite side of such layer, as described in my copending U.S. patent application, Serial No. 180,457, hereafter referred to.

In order to enable the phosphor layer of the storage target to store a bistable charge image, the target voltage applied to the conductive coating must be within a stable range of voltages. This stable range'is between a lower limit retention threshold voltage below which storage is not possible, and an upperlimit fade positive voltage" above which the flood electrons, normally used to maintain the charge image produced by a writing beam, produce a uniform charge over the target dielectric so that a charge image is not possible. The conductive coating is separated into a plurality of spaced conductive areas which may be connected to different potentials in order to provide a split screen storage target so that some portions of the phosphor layer over such areas will store, and other portions will not store a charge image. Thus one portion of the storage target may be used for merely viewing an electrical signal applied to the storage tube without storing such signal, while another portion of such target may be used to view and store the image of this or another signal. In this manner several different signal waveforms may be stored side by side for comparison purposes without the danger of obscuring the waveform traces. Still other portions of the storage target over different conductive areas may be employed to display characters which correspond to different positions of switches which control the operation of such storage tube, for example, the vertical gain and the horizontal sweep speed switches of a cathode ray oscilloscope.

The storage tube of the present invention is especially useful in a cathode ray oscilloscope to display and store the waveforms of electrical signals received by such oscilloscope. However, the new storage tube may also be employed as part of a sonar or radar installation, an electronic computer or other apparatus which ordinarily employs a storage tube. Since the storage tube of the present invention is an improvement over the tube described by the same inventor in copending US. patent application Serial No. 180,457 filed on March 19, 1962, by Robert H. Anderson, and entitled Electron Discharge Display Device, the disclosure of this copending application is hereby incorporated into the present application in order to avoid unnecessary duplication. The present storage tube has several advantages over the previous storage tube since it employs a storage target which is constructed to enable portions of the target to operate in a bistable storage mode while other portions of such target operate in a nonstorage mode. This allows a portion of the target to be employed as a previewing area for the electrical signal under investigation, while another target portion can be employed as a storage area so that adjustment errors in vertical gain, horizontal sweep speed, or triggering can be corrected by displaying the trace in the previewing area before moving it to the storage area. This previewing eliminates the necessity for erasing the stored image of an incorrect trace which would be caused by such an adjustment error. The split screen storage target also allows two or more traces to be stored side by side for comparison without danger of obscuring the traces due to one incorrect trace, which can save much time ordinarily lost due to repeated erasing of the storage target or to repeated assembly and disassembly of the different arrangements of the apparatus under test.

Another advantage of the present storage tube is the construction of separate target areas as a character display which may be used to visually indicate directly on the storage target the positions of switches employed to control the operation of the storage tube. The switch position character display is located at the outer edge of the storage target so that photographs of waveforms presented on the storage target are automatically labeled as to the control voltage and time units for the vertical and horizontal axes, respectively, of the graticule scale on the face plate of such tube. A further advantage of displaying the switch positions directly on the storage target is that they may be viewed at the same time as the signal waveform, thereby eliminating the need for movement of the observers eyes from the viewing screen of the storage tube to the control switches to determine the graticule scale units.

Still another advantage of the storage tube of the present invention is that it employs an envelope having a ceramic funnel portion which is provided with a plurality of spaced ridges on the outer surface thereof extending from a point adjacent the larger end of such funnel portion which is sealed to the glass face plate portion of such envelope, to a point remote from such face plate where the funnel portion is of reduced diameter. Conductive lead strips are provided over the tops of the ridges on the exterior of the envelope, which are electrically connected to different conductive areas of the storagev target and to various conductive wall coatings on the inner surface of the funnel envelope portion inside such envelope. A connector socket in the shape of a collar sleeve is provided around the small end of such funnel envelope portion so that spring contacts in such socket engage the lead strips to connect the electrodes attached to such strips to different voltage sources connected to such contacts. This allows a large number of electrical connections to be made in the region of the face plate, such as would be necessary if a switch position character display is employed as part of the target, without increasing substantially the space occupied by the storage tube.

It is therefore one object of the present invention to provide an improved cathode ray storage tube.

A further object of the invention is to provide an improved storage tube which is capable of producing a storage display and a nonstorage display simultaneously.

Another object of the invention is to provide an improved direct viewing storage tube of the type having a storage target which also functions as the viewing screen of such tube and in which the storage target is divided into a plurality of separate independent target areas which can be employed either as storage or nonstorage areas to provide both a storage display and a nonstorage display simultaneously on the same target.

A still further object of the invention is to provide an improved storage tube which is capable of producing both a character display and a signal display simultaneously.

Still another object of the present invention is to provide an improved direct viewing, bistable storage tube which has a character display area on its storage target for indicating positions of controls employed to vary the vertical gain, horizontal sweep speed or other characteristics of such storage tube.

An additional object of the present invention is to provide an improved storage target in which a thin dielectric layer of secondary emissive phosphor material is employed to store an electrical charge image and to emit a visible light image corresponding to such charge image, and in which a light transparent coating of electrically conductive material positioned beneath such dielectric layer is employed as a plurality of independently controlled target electrodes by separating such coating into a plurality of spaced conducting areas which may be connected to different target voltages in order to enable the portions of such dielectric layer above such conducting areas to store a charge image for an indefinite controllable time or to operate in a nonstorage manner depending upon the magnitude of such target voltages.

Another object of the present invention is to provide an improved storage tube in which an envelope having a ceramic funnel portion with a plurality of conductively coated of spaced ridges on the exterior surface of such funnel portion is employed along with a connector socket collar to electrically connect a plurality of separate conductive areas on the storage target and wall coatings inside such tube to voltage sources outside the tube.

Other objects and advantages of the storage tube of the present invention will be apparent in the following detailed description of a preferred embodiment thereof and in the attached drawings of which:

FIG. 1 is a side view of one embodiment of the storage tube of the present invention with parts broken away to show internal structure;

FIG. 2 is a front view of the storage tube of FIG. 1;

FIG. 3 is a vertical section view taken along the line 33 of FIG. 1 with parts broken away to show the internal structure of the storage target;

FIG. 4 is a partial vertical section view taken along the line 4-4 of FIG. 3;

FIG. 5 is an enlarged view of a corner of the character display portion of one embodiment of the storage target of the present invention with parts broken away to show internal structure;

FIG. 6 is a partial vertical section view taken along the line 6-6 of FIG. 5;

FIG. 7 is an enlarged view of part of another embodiment of the storage target of the present invention;

FIG. 8 is an oblique vertical section view taken along the line 88 of FIG. 7;

FIG. 9 is an oblique sectional view similar to FIG. 8 showing a third embodiment of the storage target of the present invention; and

FIG. 10 is an oblique sectional view similar to FIG. 8 showing a fourth embodiment of the storage target of the present invention.

One embodiment of the storage tube of the present invention is shown in FIG. 1 to include, briefly, a storage target 10 supported on the inner surface of a light transparent face plate 12 of glass material which is sealed to the large end of a hollow, funnel shaped envelope portion 14 of ceramic material to form part of the envelope of such storage tube. The ceramic funnel portion 14 may be sealed at its small end to a hollow tubular neck portion 16 of glass material which contains the electron gun structure of the writing gun 17 and the flood guns 18 disclosed in my copending US. patent application Serial No. 180,457 previously referred to. The electrostatic deflection plates of the writing gun 17 as well as the isolation shield between such deflection plates may be connected to conventional vertical amplifier, horizontal sweep generator and high voltage supply circuits (not shown) by means of metal lead pins 19 extending through the side of the neck portion 16 of the envelope. The remaining gun structure of the writing gun 17 and the flood guns 18 may be connected by means of lead pins 20 extending through the rear end of such neck portion and held in proper spaced relationship by a plug 22 of insulating material. The writing gun produces a narrow beam of high velocity electrons which is moved across the storage target in accordance with an input signal applied to the vertical deflection plates of such writing gun to produce a charge image on such target. This charge image is stored or maintained by the low velocity electrons emitted by the flood guns which are substantially uniformly distributed over the storage target.

As shown in FIGS. 2, 3 and 4, the storage target 10 of the present invention differs from the storage target of the previously referred to application in that the light transparent coating of conductive material, such as tin oxide, employed in such target is divided into a plurality of separate

conductive areas

24, 26, and 28. These conductive areas are coated over the inner surface of the glass face plate 12 and are separated by horizontal gaps and 32 in the conductive coating. A secondary emissive dielectric layer 34 of phosphor material, such as P-l type phosphor, is provided over the

conductive areas

24, 26 and 28 on the face plate 12 by a decalcomania technique. This is an integral semicontinuous phosphor layer 34 which has a sufliciently porous structure to enable the transmission of secondary electrons through such layer for collection by the conductive areas, and a thickness that is within a critical range of thicknesses over which the particular phosphor material employed is capable of storing a bistable electrical charge image for an indefinite controllable time in the manner disclosed in my above mentioned copending application. Thus the phosphor layer 34 serves two primary functions-first, to store the electrical charge image produced by the writing gun 17 and maintained by the flood guns 18 of the storage tube; and second, to emit a visible light image corresponding to such charge image so that an optical readout is obtained from the storage tube. It should be noted here that the storage tube of the present invention, along with my previous storage tube, is also capable of electrical readout since an output signal is obtained from the

conductive areas

24, 26 and 28 when a reading beam is moved across the charged surface of phosphor layer 34. Thus if the conductive areas are electrically connected to the Z-axis input of a TV monitor tube and the raster signal of such TV monitor is transmitted to the deflection plates of the writing gun during electrical readout, an electrical readout signal corresponding to the stored charge image including the character display mentioned above, can be reproduced on the TV monitor or other electrical display device since such writing gun can also be employed as the reading gun of the storage tube if desired.

An edge lighted graticule scale 36 may be provided on the inner surface of the flat glass face plate 12 either in the form of the scribed lines shown in FIG. 4, or as glass frit lines which are deposited on the inner surface of such face plate and fused thereto. While any scale can be employed, the graticule scale 36 shown is made up of vertical and horizontal lines which divide up the viewing area over the conducting

areas

24, 26 and 28 into one centimeter squares to form a scale having a rectangular shape of 8 centimeters by 10 centimeters which has its horizontal axis centered over gap 30.

Since the target voltages on the conductive areas 24 and 26 determine whether the portions of the phosphor layer 34 overlying such conductive areas operate in a storage mode or a non-storage mode, one portion of the phosphor layer can be employed as a conventional fluorescent viewing screen for producing a visual image of the electric signal waveform under investigation without storing such image, while the other portion of phosphor layer can be used as a storage dielectric for storing the image. This allows the waveform to be previewed by the operator on one portion of the storage target before it is stored on another portion of such target. Connecting one of the conductive areas 24 and 26 to a voltage that is within the stable range of target voltages causes that portion of the phosphor layer over such one conductive area to store a charge image for an indefinite controllable time, while connecting the other area to a voltage below the retention threshold voltage of such layer prevents that portion of the layer over such other area from storing such a charge image. Thus, the use of two separate conductive areas 24 and 26, rather than one, allows a portion of the storage target to operate in the storage mode and another portion of such target to operate in a nonstorage mode merely by properly selecting the target voltages applied to such conductive areas. This split screen storage target is of great convenience when comparing two different signal waveforms side by side since errors in vertical gain, horizontal sweep speed or sweep triggering can be corrected before storage by previewing the waveform on the non-storage target area and then moving such waveform to the storage area by adjustment of the vertical position control. The vertical position control may be provided with a scale which is calibrated in terms of the horizontal graticule lines in order to allow more exact location of the stored image on the storage area of the target.

The electrical connections to the

conductive areas

24, 26 and 28 may be accomplished by extending their conductive coatings of tin oxide up to the edge of the glass face plate 12 so that they extend through the glass frit seal 38 connecting such face plate to the ceramic funnel portion 14, as shown in FIG. 4. This funnel portion of the tube envelope may be provided with a plurality of spaced ridges 40 which extend longitudinally from a point adjacent the face plate at the large end of such funnel back toward the neck portion 16 to a point near the small end of such funnel portion. Each of these ridges 40 may be provided with a fired lead strip 42 of conductive material, such as silver, which extends along the top of such ridges and is connected by a conductor coating 43 with the lead portions of the conducting

areas

24, 26 and 28 that extend through the glass seal 38. The metal lead strips 42 can be applied to the top of the ridges 40 before sealing the ceramic funnel 14 to the glass face plate 12 by rolling a roller coated with silver paint over such ridges, or the lead strips may be painted in the grooves between the ridges if it is desired. After sealing, the conductor coating 43 is applied over the glass seal 38 to electrically connect the lead strips 42 to the conductive areas. Of course, if all of the ridges are not used as supports for lead strips, as is true of the embodiment shown, the unused ridges may be covered with a suitable masking material before the lead strips are applied to the remaining ridges.

The inner surface of the funnel portion 14 of the envelope may be provided with a plurality of axially spaced

wall coatings

44, 46, 48 and 50 of conductive material, such as silver, which function as focusing, collimating and collecting electrodes for the primary electrons emitted by the writing gun 17 and the flood guns 18 and for the secondary electrons emitted by the storage target 10. Each of these wall coatings may be connected to the exterior of the funnel portion of the envelope by a hole through the side of such funnel portion. The inner surface of the hole is coated with a connector layer 52 of conductive material, such as silver paint, and then the hole is filled by a plug 54 of glass frit material, as shown in FIG. 3. The connector layer 52 is continued over the top of the glass plug 54 up the side of the adjacent ceramic ridge 40 into contact with the lead strip 42 on the top of such ridge in order to complete the electrical connection of the wall coating to the exterior of the envelope. The first wall coating 50 nearest the storage target 10 is spaced from the phosphor layer 34 and the second wall coating 48 by narrow gaps to electrically insulate such first wall coating from these two elements. In order to obtain more uniform background illumination of the storage target, the first wall coating 50 may be split into four

separate portions

56, 58, 60 and 62 which are separated with four spacer gaps adjacent the ends of

gaps

30 and 32 between the

conductive areas

24, 26 and 28, and the wall coating portions are each connected by dilferent connector layers 52 and lead strips 42 to an external voltage source for independently controlling the voltages applied thereto in a manner hereafter described.

The lead strips 42 are connected to different voltage sources by means of a connector socket 64 shown in FIG. 1 which consists of a hollow frustro-conical sleeve 66 of insulating material which fits as a collar around the small end of the funnel portion 14 of the envelope. A plurality of leaf spring contacts 68 are attached at circumferentially spaced points on the inner surface of the collar sleeve 66 so that each of such spring contacts extends radially inward into engagement with one of a plurality of notches 70 in the end of the envelope ridges 40 adjacent neck envelope portion 16. The spring contacts 68 are fastened to the collar sleeve 66 by metal eyelet rivets 72 which may be soldered to lead wires 74 that are electrically connected to different voltage sources. Thus the spring contacts 68 electrically connect the lead strips 42 to the voltage sources in order to apply different voltages to the wall coatings and to the conductive target areas of the storage tube. The collar sleeve 66 of the connector socket 64 may be provided with

annular flanges

75 and 76 which extend inwardly from the opposite ends of such sleeve to serve as stops to limit axial movement of such connector socket in a direction toward the face plate 12. The smaller diameter flange 76 must have an opening large enough to clear the lead pins 18 when such connector socket is moved over the neck portion of the envelope into its proper position. A keyway (not shown) may be provided in larger diameter flange 75 of the collar sleeve 66, which engages one of the ridges 40 to prevent rotation of the connector socket after it is properly positioned.

The storage target 10 of the present invention may also have a character display structure that may include a vertical gain display 77 and a horizontal sweep speed display 78 which enable the switch positions of the controls employed to vary the vertical gain and horizontal sweep speed, respectively, of the storage tube to be displayed directly on the storage target within the graticule scale 36 so that they are automatically recorded in photographs of the graticule area of the target. These character displays 77 and 78 may include a plurality of numbers, letters and other symbols which are formed by providing separate independent storage areas for each character. This is accomplished in one embodiment of the storage target shown in FIGS. 3, 5 and 6 by separating the conductive coating area 28 into a plurality of spaced areas 76 which are shaped in the form of the characters to be displayed. Each of these character areas 76 includes a lead portion which extends through the glass seal 38 to the edge of the face plate 12 into electrical contact with a conductor layer 43 and a lead strip 42 on one of the ridges 40. i

In order to prevent that portion of the phosphor layer 34- which overlies the lead portion of the character areas 76 from storing and producing a light image of the lead, a lead cover layer 79 of dielectric material is provided over the lead portions of the character areas. As shown in FIG. 6, the lead cover layer increases the total thickness of the target dielectric over the lead portion of the character area 76 so that it is greater than that of the remaining phosphor storage dielectric over such character area. This allows the retention threshold voltage of the thicker dielectric region to be above the fade positive voltage of the thinner phosphor region so that a voltage may be applied to the conductive character area 76, which makes the thinner region fade positive to a uniformly illuminated condition to light the character and allows the thicker region to remain negative in an unwritten or dark condition to prevent the lead portion from lighting up. The lead cover layer 79 may be P1 type phosphor material similar to that of the phosphor layer 34 so that it may be provided merely as a thickened portion of such phosphor layer if desired. Another way of covering the lead portions of the character areas 76 to prevent the light image of such lead areas from being seen would be to provide a masking layer of light opaque material as the lead cover layer 79. This would not prevent the portion of the phosphor layer 34 over the lead cover layer from lighting up but would prevent the light image of the lead from being transmitted through the face plate.

If the phosphor layer 34 is about .0015 inch thick, it will have a retention threshold voltage of about +250 volts DC. and a fade positive voltage of approximately +350 volts DC. with respect to the flood gun cathode. Therefore, when the character area 76 is switched to a voltage greater than +350 volts that portion of the phosphor layer 34 about the character area will immediately change into a written storage condition in which the entire portion of the phosphor layer is illuminated in the character shape of the underlying conductive area. However, if the lead cover layer 78 is P-l phosphor, .001 inch thick, the total thickness of the phosphor region above the lead portion of the conductive character area 76 is .00l5+.00l or about .0025 inch. This thicker phosphor region will have a retention threshold voltage of about +450 volts D0. which must be exceeded before storage is possible in this region. Therefore, if the character area 76 is maintained at a voltage between +350 and +450 volts, such as +400 volts, the character region of the overlying phosphor layer will be illuminated while the lead region of such phosphor layer will remain in a dark or unilluminated condition. Since the retention threshold voltage of the phosphor layer 34 is about +250 volts when such layer is .0015 inch thick, some of the characters in the

displays

77 and 78 can be illuminated by merely switching such character areas 76 to +400 volts, while connecting the other characters to a voltage below +250 volts. For example, if the characters 50 v./cm. of the character display 77 and the characters .2 a sec./ cm. of the character display 78 are illuminated, the voltage gain switch is set at 50 volts per centimeter uncalibrated and the sweep speed switch is set at .2 microsecond per centimeter calibrated.

In order to achieve the most desirable results the background or dark voltage on the character areas which are not to be illuminated, is set to some intermediate voltage between 0 and +250 volts, for example about +145 volts, rather than merely being reduced to 0. This dark voltage prevent a large negative charge from accumulating on regions of the phosphor layer which are adjacent the character regions desired to be illuminated, thereby overcoming a coplanar grid elfect caused by the negatively charged phosphor regions which would deflect the flood electrons inward at the edges of the character areas and cause the character image to be distorted and unevenly illuminated. This coplanar grid effect is also apparent between the phosphor region over conductive area 26 and the top of the characters. In order to Overcome this defect, a guard band 80 of tin oxide is provided around the character displays 77 and 78 as a separate part of the conductive area 28. .The guard band is spaced from and shaped to conform to the top of the character areas 76 and is also spaced from the bottom conductive area 26 by gap 32. A portion of the guard band 80 extends between the voltage gain character display 77 and the sweep speed character display 78 to the edge of the face plate 12 into electrical contact with one of the lead strips 42 on the ridges 40 at the bottom of such face plate. In a similar manner to the dark or unilluminated character areas, the guard band is connected to a dark voltage of about volts D.C. in order to insure uniform illumination of the selected characters.

Another effect similar to the coplanar grid effect is also observed on the portions of the phosphor layer 34 overlying the corners of the conductive areas 24 and 26 adjacent the gap 30 when the first wall coating 50 is provided as one continuous coating. Thus, if target portion corresponding to the conductive area 26 is operated in a storage condition, while that corresponding to the conductive area 24 is operated in a non-storage condition, the phosphor region over the upper conductive layer 24 becomes more negatively charged than the phosphor region over the lower conductive area 26. This together with the +50 volts D.C. potential on the wall coating 50 causes the flood electrons directed at the upper corners of the conductive area 26 to be deflected downward so that the phosphor over these corners has a lower background illumination than the remainder of the phosphor layer overlying such conductive area. This non-uniform illumination can be corrected by splitting the first wall coating 50 into the four

parts

56, 58, 60 and 62 and raising the potential of the wall coating part 56 which is adjacent the upper conductive area 26 to volts, while maintaining the voltage of

wall coating portions

58 and 62 adjacent the lower conductive area at +50 volts. The same effect is present to a lesser extent at the lower corners of the conductive area 26 since they are adjacent the guard band 80 and the phosphor layer overlying such guard band is negatively charged in a similar manner to the conductive area 24. Thus the wall coating portion 60 surrounding such guard band may be provided with an operating potential which isadjustable over the range of 0 to +150 volts D.C.

Another embodiment of the character display portion of the storage target is shown in FIGS. 7 and 8 to include tin oxide character areas 82 which are similar to character areas 76 except that they are not formed in the shape of the characters, but may be of the generally rectangular shape shown in dotted lines. As shown in FIG. 8, an intermediate phosphor layer 84 is provided over the surface of the character areas 82 before the phosphor layer 34 is applied. This intermediate phosphor layer 84 is provided with character shaped holes which are positioned to fall on the character areas 82. As a result the second phosphor layer 34 is depressed into the character shaped holes of the intermediate phosphor layer 84 so that the total thickness of the phosphor is less in such holes than it is in the surrounding background regions. The intermediate phosphor layer 84 can also be extended down over the lead portion of the conductive character areas 82 so that it replaces the lead cover layer 79 of FIG. 6. Therefore, if the intermediate phosphor layer 84 is about .001 inch thick, the same thickness as the lead cover layer 79, only that portion of the phosphor layer 34 which is depressed into the character shaped holes in the intermediate layer will be illuminated when the conductive area is connected to +400 volts DC. The reason for this is that the thicker background region has a retention threshold voltage of +450 volts since it is the same thickness as that of the phosphor region over the lead cover layer 79 previously referred to.

A third embodiment of the character display portion of the storage target 10 is shown in FIG. 9 to be similar to that shown in FIGS. 7 and 8 except that the intermediate phosphor layer 84 is replaced with a light opaque masking layer 86 having character shaped holes over the conductive character areas 82. The masking layer 86 may be any light opaque material such as aluminum, silver or other suitable metals, or a white ceramic powder which can be fused either directly to the glass face plate 12 or over the conductive areas 82 and has an advantage over metal in that it is substantially invisible when viewing on a background of P-l phosphor. Here the thickness of the masking layer 86 is not important except to the extent that it is opaque. While the entire phosphor region over the character area 82 may be charged to a storage condition and illuminated, the only light transmitted through the glass face plate 12 is that which passes through the character shaped holes in the masking layer 86. Thus only the character image is visible from the front end of the storage tube.

A fourth embodiment of the display portion of the storage target is shown in FIG. 10 to include a glass layer 88 having character shaped holes therein, which extends over the upper portion of the conductive character areas 82, but not over the lead portion of such character areas. This glass layer may be powdered glass frit which is fused to the face plate 12 over the conductive areas 82. The character shaped holes in the glass layer 88 are filled with phosphor material to the same thickness as the glass layer, for example, by the use of a squeegee to spread a solution of the phosphor material over such glass layer. In this embodiment the phosphor layer forming the signal display portion of the storage target may be terminated below the conductive area 26 before it covers the glass layer 88 so that such phosphor layer 34 would not extend over the lead portion of the character areas 82. Of course, then there would be no problem as far as unwanted illumination of the character leads because the phosphor material over the leads has been removed.

While the conductive target coating has been shown to be split into two equal signal display areas 24 and 26, it is obvious that these conductive areas may be of different dimensions. Thus if it is desirable to store several traces on the bottom area 26, this area may be made twice as wide as the top area 24 which could be then used as a preview area for observing the signal waveforms before storage. If this were done, the vertical position knob of the cathode ray oscilloscope could be provided with a scale calibrated in accordance with the graticule scale, as discussed previously, for moving waveform trace from the previewing area 24 to the exact position desired on the storage area 26. Another modification of the storage target of the present invention could be made by providing a large plurality of horizontal strips of conductive material in place of the two conductive areas 24 and 26. The electrical leads to these strips could then be connected to a suitable selector switch on the front panel of the oscilloscope in order to interconnect any number of strips into different sized groups. This would allow the position of the nonstorage area and the storage area to vary as well as the size of such target areas. For example, if sixteen strips were employed, the top six strips could be connected to +300 volts to function as a first storage area, the next four strips could be connected to +100 volts to function as a hon-storage area, and the bottom. six could be connected to +300 volts to function as a second storage area. The selector switch could also be calibrated in terms of either the horizontal graticule lines or in terms of the number of strips employed in order to accurately position the location of the gap or split between storage and nonstorage areas.

Of course all the signal display areas of the target including conductive areas 24 and 26 may be operated in a storage mode or a non-storage mode, rather than having both storage areas and non-storage areas. When target areas 24 and 26 are operated as storage areas, each may be erased independently of the other by raising the target voltage above the fade positive voltage and then lowering it below the retention threshold voltage in the manner disclosed in the patent application referred to above. This allows several different signal waveforms to be stored and erased successively for comparison with the same standard waveform which is stored on another target area.

In addition to the uses already described, the split screen storage target of the present invention can be employed to clip a signal waveform above or below a selected voltage magnitude by positioning such waveforms over the gap between adjacent storage and non-storage target areas, with the quiescent voltage trace a predetermined vertical distance from such gap which corresponds to such voltage magnitude. Thus, that portion of the waveform which is above or below the selected voltage, depending on the type of clipping employed, is positioned on the non-storage target area so that it is not stored. This would indicate which portion of the waveform is transmitted or rejected by the particular clipping circuit under investigation. It should be noted that it is possible that the waveform image may be lost when storing signals of very low amplitude if such waveform is positioned exactly in the gap 30 between the conductive areas 24 and 26 when the gap is in the form of a horizontal line. This can be avoided if the gap is in the form of a zigzag or sawtooth line.

In order to avoid the coplanar grid effect mentioned above, the conductive areas on the glass face plate 12 should be positioned close together in order to cover as much glass surface as possible to prevent a high negative charge from accumulating on such uncovered glass surface. Also the conductive areas of all non-storage regions of the target should be connected to a dark voltage in the neighborhood of volts D.C. rather than to 0 volts to avoid this effect. Since a thick phosphor layer of storage dielectric has a tendency to accumulate more of a negative charge than a thin phosphor layer, it may be necessary to provide a separate thin layer of phosphor over the character areas if a relatively thick layer of phosphor is employed over the conductive areas 24 and 26, to prevent the coplanar grid effect from blurring the character display. It should be noted that while the two character displays 77 and 78 indicated in FIG. 2 are those of the vertical gain and horizontal sweep speed, respectively, of the oscilloscope, other character displays may also be employed. In addition to the two character displays 77 and 78 another pair of character displays corresponding to the character displays shown, may be positioned along the top of the face plate 12 above the conductive area 26 if the storage tube is suitably modified so that it can be used in a dual trace or a dual beam type oscilloscope. This second pair of character displays would indicate the vertical gain and the horizontal sweep speed of the second input signal applied to the storage tube. Of course either the split screen portion of the storage target including conductive coating areas 24 and 26, or the character display portion of the storage target can be employed together or separately in the storage tube of my previously filed patent application, Serial No. 180,457.

Itwill be obvious to those having ordinary skill in the art that various changes may be made in the details of the above described preferred embodiment of the present invention without departing from the spirit of the invention. Therefore it is not intended to limit the scope of the present invention to the details of the preferred embodiment thereof and that scope should only be determined by the following claims.

I claim:

1. A direct viewing storage target for use in a cathode ray storage tube, comprising:

a support member of insulative material;

a first electrically conductive area on one portion of the surface of one side of said support member;

a second electrically conductive area on another portion of said surface of said support member and insulatingly spaced from said first area; and

a storage dielectric layer of phosphor maten'al supported on said one side of said support member over said first area and said second area, said dielectric layer being an integral layer of sufficiently porous structure to enable secondary electrons emitted from one side of the layer to be transmitted through said layer and collected by said conductor areas on the opposite side thereof so that said phosphor material can store an electrical charge image for an unlimited time over a stable range of target voltages applied to said first and second conductive areas, and will emit a light image corresponding to said charge image, when bombarded by electrons.

2. A direct viewing storage target for use in a cathode ray storage tube, comprising:

a support member of light transparent insulative material;

.a first light transparent film of electrically conductive material coated over one portion of the surface of one side of said support member;

a second light transparent film of electrically conductive material coated over another portion of said surface of said support member so that it is insulatingly spaced from said first film;

a storage dielectric layer of phosphor material supported on said one side of said support member over said first film and said second film, said dielectric layer being an integral layer of sufficiently porous structure to enable secondary electrons emitted from one side of the layer to be transmitted through said layer and collected by said conductive film on the opposite side thereof so that said phosphor material can store an electrical charge image for an indefinite, con trollable time over a stable range of target voltages applied to said first and second films, and will emit a light image corresponding to said charge image, when bombarded by electrons; and

means for applying a different target voltage to said first film than to said second film to allow one of these films to have a target voltage which is within said stable range and the other film to have a target voltage which is outside said stable range during the time charge images are formed on the portions of the dielectric over said films, so that the portion of said dielectric layer above said one film will store a charge image and the portion of said dielectric layer above said other film will not store a charge image.

3. A direct viewing bistable storage target for use in a cathode ray storage tube, comprising:

a support member of light transparent insulative material;

a first light transparent film of electrically conductive material coated over one portion of the surface of one side said support member;

a dielectric layer of phosphor material supported on said one side of said support member over said first film and said second film, said dielectric layer being semicontinuous and having a substantially uniform thickness that is within the range of thicknesses over which said phosphor material can store a bistable electrical charge image for an indefinite controllable time over a stable range of target voltages applied to said first and second films, and will emit a light image corresponding to said charge image, when bombarded by electrons; and

means for applying a different target voltage to said first film than to said second film to allow one of these films to have a target voltage which is within said stable range and the other film to have a target voltage which is outside said stable range during the formation of charge images on the portions of the dielectric layer over said films, so that the portion of said dielectric layer above said one film will store a charge image and the portion of said dielectric layer above said other film will not store a charge image. 4. A direct viewing bistable storage target for use in a cathode ray storage tube, comprising:

a support member of light transparent glass insulative material;

a graticule scale provided on the surface of one side of said support member;

a first light transparent layer of tin oxide conductive material coated over said graticule scale on one portion of the surface of said one side of said support member;

a second light transparent layer of tin oxide conductive material coated over said graticule scale on another portion of the surface of said one side of said support member and insulatingly spaced from said first layer;

a dielectric layer of phosphor material supported on said one side of said support member over said first layer and said second layer, said dielectric layer being semicontinuous and having a substantially uniform thickness that is within the range of thicknesses over which said phosphor material can store a bistable electrical charge image for an indefinite, controllable time over a stable range of target voltages on said first and second films, and will emit a light image corresponding to said charge image, when bombarded by electrons; and

means for applying different target voltages to said first and second layers to allow one of these conductive layers to have a target voltage which is within said stable range and the other conductive layer to have a target voltage which is outside said stable range during the formation of charge images on the portions of said dielectric layer over said conductive layers, so that the portion of said dielectric layer above said one conductive layer will store a charge image and the portion of said dielectric layer above said other conductive layer will not store a charge image in order to allow previewing on said storage target of an electrical signal applied to said storage tube before the image of said signal is stored on said storage target.

5. A viewing screen for use in a cathode ray tube which produces a character display on one portion of said screen, comprising:

a light transparent support member;

a plurality of spaced light transparent areas of electrically conductive material secured to one side of said support member in spaced, insulated relationship to each other;

a dielectric layer of phosphor material supported on said one side of said support member with a first portion remote from said conductive areas and a second portion over said conductive areas;

means supported by said support member, for causing the second portion of said dielectric layer to form a light image in the shape of a character over each of said conductive areas when the proper voltage is applied to said conductive areas; and

means for app-lying different voltages to said conductive areas.

6. A direct viewing bistable storage target for use in a storage tube which indicates the position of switches for controlling the operation of said storage tube, comprising:

a support member of light transparent insulative material;

a light transparent layer of electrically conductive material secured to one side of said support member;

a plurality of spaced light transparent areas of electrically conductive material secured to said one side of said support member in spaced, insulated relationship to each other and to said conductive layer;

a dielectric layer of phosphor material supported as a semicontinuous layer on said one side of said support member with a first portion over said conductive layer and a second portion over said conductive areas, said first portion of said dielectric layer having a sutficiently porous structure to enable the transmission of secondary electrons through the dielectric layer to said conductive layer so that said phosphor material can store a bistable electrical charge image for an indefinite controllable time over :a stable range of target voltages applied to said conductive layer and will emit a light image corresponding to said charge image, when bombarded by electrons;

means for causing the second portion of said dielectric layer to form a light image in the shape of a character over each of said conductive areas which correspond to the position of said switch when the proper voltage is applied to said conductive areas; and

means for applying different voltages to said conductive areas and said conductive layer.

7. A direct viewing bistable storage target for use in a a dielectric layer of phosphor material supported on said one side of said support member with a first portion over said conductive layers and a second portion over said guard band and said conductive areas, said first portion of dielectric layer having a substantially uniform thickness and at least some parts of said second portion of said dielectric layer having a thickness, which are within the range of thicknesses over which said phosphor material can store an electrical charge image for an indefinite controllable time over a stable range of collector voltages applied to said conductive layer and said conductive areas, and will emit a light image corresponding to said charge image, when bombarded by electrons; and

means for applying different collector voltages to said conductive areas, said conductive layers and said guard band.

9. A cathode ray tube, comprising:

an envelope of insulating material having a light transstorage tube which indicates the position of switches in a cathode ray oscilloscope employing said storage tube, comprising:

parent face plate portion secured to a funnel portion; a viewing screen including a plurality of spaced, light transparent areas of conductive material secured to a support member of light transparent insulative material; .a light transparent layer of electrically conductive matea portion of the inner surface of said face plate in spaced insulated relationship, and a dielectric layer of phosphor material supported on said inner surface of rial secured to one side of said support memb r; said face plate with a first portion remote from said a plurality of spaced light transparent areas f l conductive areas and a second portion over said concally Conductive material formed in the shape of ductive areas, and means for causing said portion of charaoters which correspond to different switch P said dielectric layer to form a light image in the shape tions and secured to said one side of said pp of a character over each of said conductive areas member in spaced, insulated relationship to each other h th proper Voltage i applied t aid conductive and to said conductive layer; areas;

a dielectric layer of P p material supported on a plurality of spaced conductive leads coated on the exsaid one side of said pp member with a first P terior of the funnel portion of said envelope with a n oVer said Conductive layer and a Second Portion difierent lead being electrically connected to each ever said Conductive areas, said first Portion of said one of said conductive areas inside said envelope; dielectric layer having a substantially uniform thickmeans for l i diff t Voltages t each f said ness and at least some parts of said second portion l d of said dielectric layer having a thickness, which is means for generating a beam of high velocity electrons within the range of thicknesses Over which said P and for deflecting said beam across the dielectric P material can Store an electrical charge image layer of said viewing screen in response to an elecfor an indefinite controllable time within a stable trical Signal to for an image f i i l on id range of target voltages on said conductive layer and di l i 1 d d Conductive and will emit a light image means for bombarding said dielectric layer with low corresponding to said charge image, when bombarded 4 velocity electrons to produce said character images. y electrons; and 10. A direct viewing storage tube, comprising:

means for pp y different Voltages to said conductive an envelope of insulating material having a light transareas and to said conductive layer so that the voltage parent f e plate portion secured to a f l portion; on som f a Conductive areas can be below said a storage target including a light transparent layer of stable range and the voltage on other of Said areas conductive material and a plurality of spaced, light a be above said Stdhie range in order to form a light transparent areas of conductive material formed in image in the Shape of said other areas on Said Second the shape of different characters, which are secured portion of said dielectric layer to indicate the position to h inner fac of said face plate in spaced of said switches. insulated relationship, and a storage dielectric layer 8. A direct viewing storage target for use in a storage of phosphor material supported on said inner tube to indicate the position of switches in a cathode ray f f said fa plate over id conductive layer OSCiiIOSCOPe p y g said storage tube, comprising? and said conductive areas, said dielectric layer being a PP member of light transparent insulative mate an integral layer of sufliciently porous structure to rial; enable the transmission of electrons through said a first light transparent layer of electrically conductive dielectric layer to said conductive layer so that said material secured to One S O said pp member; phosphor material can store a bistable electrical a second light tr ahsParent layer of electrically eohduo charge image for an indefinite controllable time over tive material secured to said one side spaced from a stable range f target voltages applied to said Said fi st Conductive y ductive layer and said conductive areas, and will emit a plurality of spaced light transparent areas of electri- 5 a light image corresponding to id charge i cally conductive material formed in the shape of when bombarded by electrons; Charac rs Which correspond to (iiiiereht switch p a plurality of spaced conductive lead strips each coated tions and lead portions connected to said characters, over the exterior f said f l portion f i secured to a One side of said Support member in velope and electrically connected to one of the con- P insulated relationship to each other and 7 ductive areas or to the conductive layer of said a d eOndnetiVe y storage target inside said envelope;

a guard band of electrically conductive material secured means f r applying different target voltages to each of to said one side of said support member positioned id l d t i between said areas and said second layer and spaced means for generating a beam of electrons and for detherefrom; 7 fleeting said beam across the dielectric layer of said storage target in response to an electrical signal to form a charge image of said signal on said dielectric layer; and

means for bombarding said dielectric layer substantially uniformly with electrons to retain said charge image when said beam no longer bombards said dielectric layer.

11. A direct viewing bistable storage tube, for use in a cathode ray oscilloscope, comprising:

an envelope of insulating material having a transparent glass face plate portion secured to a ceramic funnel portion by a seal portion, said funnel portion having a plurality of spaced ridges on the outer surface thereof extending from a point at the large end of said funnel portion adjacent said face plate to a point at the small end of said funnel portion remote from said face plate;

a storage target including a light transparent layer of conductive material and a plurality of spaced, light transparent areas of conductive material, which are secured to the inner surface of said face plate in spaced insulated relationship, and a storage dielectric layer of phosphor material supported on said inner surface of said face plate with a first portion over said conductive layer and a second portion over said conductive areas, said first portion and at least part of said second portion of said dielectric layer having a thickness which is within the range of thickness over which said phosphor material can store a bistable electrical charge image for an indefinite controllable time within a stable range of target voltages on said conductive layer and said conductive areas and will emit a light image corresponding to said charge image, when bombarded by electrons;

a plurality of spaced metal lead strips each coated over one of the ridges on the exterior of said envelope and electrically connected to one of the conductive areas or the conductive layer of said storage target inside said envelope;

means for applying different target voltages to each of said lead strips, including a connector socket in the form of a collar sleeve of insulating material surrounding the small end of said funnel portion and having a plurality of metal spring contacts supported on said collar so that they extend inwardly therefrom into contact with said lead strips;

means for generating a beam of electrons and for deflecting said beam across the dielectric layer of said storage target in response to an electrical signal to form a charge image of said signal on said first portion of dielectric layer; and

means for bombarding said dielectric layer with electrons to retain said charge image when said beam no longer bombards said dielectric layer.

12. A direct viewing bistable storage tube for use in a cathode ray oscilloscope, comprising:

an envelope of insulating material having a transparent glass face plate portion secured to a ceramic funnel portion by a seal portion, said funnel portion having a plurality of spaced ridges on the outer surface thereof extending from a point adjacent said face plate to a point remote from said face plate;

a graticule scale provided on the inner surface of said face plate;

a storage target including a plurality of spaced light transparent layers of conductive material and a plurality of spaced, light transparent areas of conductive material, which are secured to the inner surface of said face plate in spaced insulated relationship, and a storage dielectric layer of phosphor material supported on said inner surface of said face plate with a first portion over said conductive layers and a second portion over said conductive areas so that said first portion can display the signal waveforms of said oscilloscope and said second portion can display the switch positions of said oscilloscope, said first portion and at least part of said second portion of said dielectric layer having a thickness which is within the range of thicknesses over which said phosphor material can store a bistable electrical charge image for an indefinite controllable time within a stable range of target voltages on said conductive layer and said conductive areas and will emit a light image corresponding to said charge image, when bombarded by electrons;

a plurality of annular wall coatings of conductive material coated on the interior surface of said funnel portion of said envelope axially spaced along said envelope, one of said wall coatings nearest said face plate being split into a plurality of portions which are separated by spacing gaps adjacent the spacing gaps between the conductive layers and areas of said storage target;

a plurality of spaced metal lead strips each coated over one of the ridges on the exterior of said envelope and electrically connected to one of the wall coatings, wall coating portions, conductive areas or the conductive layers of said storage target inside said envelope;

means for applying different target voltages to each of said lead strips;

means for bombarding said dielectric layer substantially uniform with electrons to retain said charge image when said beam no longer bombards said dielectric layer.

13. An envelope structure for use in a cathode ray tube, comprising:

a hollow, tubular funnel member of ceramic material having a plurality of spaced ridges on the outer surface of said funnel member extending longitudinally from a point adjacent the larger end of said funnel member to a point adjacent the smaller end of said funnel member;

a flat face plate of light transparent glass material shaped to conform to the larger end of said funnel member;

a vacuum tight seal between said face plate and the larger end of said funnel member;

a plurality of lead strips of conductive material coated on said funnel member so that they are spaced apart by said ridges; and

means for electrically connecting each of said lead strips to one of a plurality of electrodes positioned inside said envelope.

14. The envelope structure of claim 13, in combination with a connector socket comprising:

a collar sleeve of insulating material adapted to fit around the outside of the smaller end of the funnel portion of said envelope;

a plurality of spring contacts of conductive material supported in spaced, insulated relationship on said collar sleeve so that they each extend inwardly into engagement with a notch in one of the ridges on said funnel portion and into electrical contact with the lead strip on said one ridge; and

means for connecting each of said contacts to a voltage source in order to apply different voltages to the electrodes inside said envelope.

15. A storage target comprising:

a common support member;

a plurality of storage dielectric areas supported on different portions of said support member; and

means for simultaneously applying different D.C. voltages to the dielectric areas during the formation of charge images on said areas to enable the operation of said dielectric areas independently in storage or nonstorage conditions so that at least one of said dielectric areas can store for a controllable time a charge image produced thereon while another of said dielectric areas cannot store a charge image, said voltages being substantially uniform along each dielectric area.

16. A storage tube comprising:

an evacuated envelope;

a storage target including a plurality of storage dielectric regions supported inside said envelope;

control means including a plurality of insulated areas of electrical conductive material adjacent different ones of said dielectric regions, and means for simultaneously applying different voltages to said conductive areas during the formation of charge images on said dielectric regions in order to operate said dielectric regions independently in storage or nonstorage conditions so that at least one of said dielectric regions can store bistably a charge image produced thereon while another of said dielectric regions cannot store a charge image, said voltages being sub stantially uniform along each conductive area;

Writing means for bombarding said storage target with high velocity electrons to produce charge images on said dielectric regions; and

holding means for bombarding said storage target with low velocity electrons to store the charge image on said one dielectric region Without necessarily storing the charge image on said other dielectric region.

17. A direct viewing storage tube comprising:

an evacuated envelope;

a storage target including a plurality of storage dielectric regions of phosphor material supported inside said envelope;

control means including a plurality of insulated areas of electrical conductive material adjacent different ones of said dielectric regions, and means for simultaneously applying different voltages to said conductive areas during the formation of charge images on said dielectric regions in order to operate said dielectric regions independently in storage or nonstorage conditions so that at least one of said dielectric regions can store for a controllable time a charge image produced thereon While another of said dielectric regions cannot store a charge image;

Writing means for bombarding said storage target with high velocity electrons to produce charge images on said dielectric regions and to emit light images from said dielectric regions corresponding to said charge images; and

holding means for bombarding said storage target with low velocity electrons to store the charge image on said one dielectric region without necessarily storing the charge image on said other dielectric regions.

References Cited by the Examiner UNITED STATES PATENTS 2,269,156 1/42 Kling 17450.52 2,623,090 12/52 Bohlke 174-5052 2,719,185 9/55 Sorg 174---50.53 2,872,613 2/59 Kalfaian 3l368 2,884,558 4/59 Smith 31368 DAVID G. REDINBAUGH, Primary Examiner.

DAVID J. GALVIN, Examiner.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No 3,214,631 October 26, 1965 Robert H Anderson r appears in the above numbered pat- It is hereby certified that erro s Patent should read as ent requiring correction and that the said Letter corrected below.

Column 2, line 2 for "control" read correct strike out "of", first occurrence; column column 3, line 28, line 2 for "about" read above Y line 59, for "prevent" read prevents column 16, line '53, for "uniform" read I uniformly Signed and sealed this th day of June 1966.

(SEAL) Attest:

ERNEST W. SWIDER Attesting Officer EDWARD J. BRENNER Commissioner of Patents

Claims

1. A DIRECT VIEWING STORAGE TARGET FOR USE IN A CATHODE RAY STORAGE TUBE, COMPRISING: A SUPPORT MEMBER OF INSULATIVE MATERIAL; A FIRST ELECTRICALLY CONDUCTIVE AREA ON ONE PORTION OF THE SURFACE OF ONE SIDE OF SAID SUPPORT MEMBER; A SECOND ELECTRICALLY CONDUCTIVE AREA ON ANOTHER PORTION OF SAID SURFACE OF SAID SUPPORT MEMBER AND INSULAINGLY SPACED FROM SAID FIRST AREA; AND A STORAGE DIELECTRIC LAYER OF PHOSPHOR MATERIAL SUPPORTED ON SAID ONE SIDE OF SAID SUPPORT MEMBER OVER SAID FIRST AREA AND SAID SECOND AREA, SIAD DIELECTRIC LAYER BEING AN INTEGRAL LAYER OF SUFFICIENTLY POROUS STRUCTURE TO ENABLE SECONDARLY ELECTRONS EMITTED FROM ONE SIDE OF THE LAYER TO BE TRANSMITTED THROUGH SAID LAYER AND COLLECTED BY SAID CONDUCTOR AREAS ON THE OPPOSITE SIDE THEREOF SO THAT SAID PHOSPHOR MATERIAL CAN STORE AN ELECTRICAL CHARGE IMAGE FOR AN UNLIMITED TIME OVER A STABLE RANGE OF TARGET VOLTAGES APPLIED TO SAID FIRST AND SECOND CONDUCTIVE AREAS, AND WILL EMIT A LIGHT IMAGE CORRESPONDING TO SAID CHARGE IMAGE, WHEN BOMBARDED BY ELECTRONS.