US3413481A - Spectral emission coding - Google Patents

Description

Nov. 26, 1968 J. w. BERRY SPECTRAL EMISSION CODING Filed Feb. 9, 1966 INVENTOR. JOHN W/LL/AM BERRY ATTORNEY United States Patent M 3,413,481 SPECTRAL EMISSION CODING John William Berry, Stamford, Conn., assignor to American Cyanamid Company, Stamford, Conn., a corporation of Maine Filed Feb. 9, 1966, Ser. No. 526,191 5 Claims. (Cl. 250--226) ABSTRACT OF THE DISCLOSURE Coded symbols are produced, the coding representing presence or absence of metals having sharp emission lines under spark discharge. The symbols, on a suitable substrate, are read out by passing each symbol through a spark discharge at a repetitive rate of sparks, detecting the sharp lines in a plurality of detectors, one for each metal, and sending the signals from the detectors through readout circuits responding to the presence or absence of the coded components. The detectors may be photomultiplier tubes or solid state detectors with limitations to the line to be detected, for example, sharp cutting interference filters. Preferably the light from the spark discharge is led to the detectors by fiber optics to permit a wider physical separation of detectors.

Background of the invention In the co-pending application of Freeman and Halverson, Ser. No. 596,366, filed Oct. 14, 1966, which is a continuation-in-part of an application Ser. No. 437,866, filed Mar. 8, 1965, now abandoned, both applications being assigned to the assignee of the present application, there is described a process for encoding and retrieving information by means of coded inks containing various combinations of components which fiuoresce under ultraviolet or short wave illumination at different wavelengths. Preferably there are included for at least some of the components chelated lanthanide ions which fiuoresce in very narrow bands. Coding can be in terms of presence or absence of particular components, and this permits a number of symbols equal to 2 -1 Where n is the number of components. For example, four components permit fifteen different symbols, six components 63, and the like. The coded symbols have the advantage that they do not depend on the shape of the symbol as is needed in other systems, for example bank check account numbers in magnetic inks and the like.

A problem is presented in the number of components Summary of the invention The present invention eliminates the problems of symbol number by using metals or metal compounds and reading out the coded inks or other symbol forms by subjecting the symbols to a spark discharge producing the spark spectra of the metal components present and detecting sharp lines which are unique for the particular components. The number of metals which are practical is very much greater than the number of photoluminescent materials available with the sharp fluorescent bands, and this is one of the principal advantages of the present invention, although for certain particular uses, such as personal identification and the like, the invention presents other advantages.

While, theoretically, it might be thought that any metal 3,413,481 Patented Nov. 26, 1968 could be present as a component in the coded symbols, as a matter of practical use the choice is somewhat more limited though the number of components is greater than with practical photoluminescent materials. Certain metals are not suitbale because of the enormous number of closely adjacent lines; typical examples of such metals are the transition metals, iron, nickel and cobalt. Other metals, such as for example silicon, sodium, potassium and the like, while they have reasonably intense lines sufficiently separated, are unsuitable because many substrates, such as for example paper, on which the coded symbols may be formed, are apt to contain such materials as impurities or as deliberately added components, for example, siliceous fillers in paper and the like. This leaves as the preferred metals bismuth, gallium, germanium, lithium, cadmium, lead, scandium, silver, mercury, tin, zinc and zirconium. It should be understood that the invention is not strictly limited in its broader aspects to these preferred metal components, because with a little care, for example in the choice of a substrate, it is possible to use some of the other metals, the limitation only being that they shall have strong lines sufficiently separated from other lines of other components to permit spectral separation and detection. In a more specific aspect, however, the present invention contains the limitation to the preferred metals set out above.

The form in which the metal components are mixed to produce the coding and applied to substrates or formed into symbols presents no problem. For example, inks may be made of solutions or dispersions of metal salts, always taking care that the anion of the salt does not itself emit lines on spark excitation which would be overlapping and hence confusing with the metal itself or with the metals of other components. It is also possible to precipitate relatively insoluble metal compounds or the metal itself on substrates. This is particularly readily effected with metals such as silver which can be transformed into the metallic state by exposure to light. Where there is no objection to visible evidence of the presence of particular components, this makes silver a very useful metal for one of the cornponents. It should be noted that in the present invention, just as with the photoluminescent coded inks of the Freeman and Halverson applications, it is sometimes desirable that the coded message be secret, that is to say that the symbols in the coded inks be colorless. For other uses, such as for example account numbers on the edge of bank checks, there is an advantage in having the symbols visible, which can easily be effected by including a suitable pigment. In such cases, the account number can be read either visually, if there has been no mutilation of the shape of some of the symbols, or by machine reading using spark excitation.

The present invention also permits a different physical form because the metals for the most part can be alloyed, and thus relatively strong and permanent articles can be produced, such as a rod, a metallic coating on a plastic identification card, and the like. When such an identification object is inserted in the reader at a plant gate or gnards desk, the readout will confirm the identity of the owner. Obviously of course the choice of metals for alloying are subject to some limitation, for example they must be capable of forming alloys and the alloys should be reasonably non-cornoding, thus for example lithium and mercury are less suitable for this last use than some of the other metals.

The nature of the readout mechanism for determining the presence of the particular metals can be quite varied, and the present invention is not limited. to any particular type of readout. Thus, for example, for readout machines which are permanent and adapted to read fairly low concentrations of the components in the coded symbols, photo-multiplier tubes as detectors present many advantages. Thus they are extremely fast, extraordinarily sensitive, and so even when used with extremely sharp cutting filters, such as for example low transmission interference filters, adequate signals are produced. On the other hand, where the readout is simpler and where space, portability or cost are more important, solid state radiation detectors, such as cadmium sulfide, lead sulfide and the like, may be preferred. Because of the lower sensitivity it will often be necessary to associate such detectors with preamplifiers or other electronic circuits which increase the signal to the desired level. Time constants of the detectors are also not necessarily without significance. Where very fast reading of symbols is required, short time constant detectors are of course needed, and this is another case where the high sensitivity photo-multiplier tubes have very advantageous characteristics. However, for identification machines where speed of reading is of little or no importance, the cheaper, more compact, and lower voltage devices, such as solid state detectors, may be preferred in spite of the fact that they have somewhat longer time constants, particularly at low signal levels, which makes them less suitable for extremely high speed reading. All in all, it is an advantage of the present invention that a wide range of detectors may be used so that the best combination of characteristics for any particular use may be chosen.

Spark production from conventional sources, such as Tesla coils, usually produce a series of sparks at very short repetition intervals. The resulting signals from the radiation detector are therefore suitable for amplification and other processing in AC electronic circuits which have many advantages, such as freedom from drift and the like. Of course the circuits used and the detectors must be suitable for the repetition rate of the sparks used in reading the coded information.

Brief description of the drawing The drawing is an isometric view of a readout apparatus.

Description of the preferred embodiments The invention will be described in greater detail in conjunction with the drawing, which illustrates, in semidiagrammatic form, a typical readout mechanism for six component coded symbols. A metallic table 1 is provided across which a coded object 2 such as a car-d or bank check is moved. At 3 an aluminum electrode extends in close proximity to the surface of the card. Repetitive spark discharges are produced by conventional spark discharge supply 4 shown as connected to the electrode and to the table by wires 5 and 6. Sparks are produced at a predetermined repetitive rate, and the radiation from the discharge is led through fiber optics light pipes 7 to six detectors. These detectors contain photomultiplier tubes and sharp cutting interference filters, and are labelled clockwise Zn for the 6362.3 A. line, Ag for the 328068 A. line of silver, In for the 4101.77 A. of indium, Ge for the 3039.06 A. of germanium, Ga for the 4172.06 A. of gallium, and Cd for the 6438.47 A. line of cadmium. The detectors are connected by wires (not numbered), to an electronic readout 8, which is shown diagrammatically as the circuits are conventional binary to digital conversion circuits.

Mention has been made of an aluminum electrode bebecause aluminum does not have strong emission lines in the visible, although it does have strong emission lines in the ultraviolet, which of course are easily eliminated from the detectors by the sharp cutting filters. Another metal which can be used for the electrode is lead, which also has most of its strong lines in the ultraviolet. Since we are concerned with the surface of the electrode which is in contact with the spark, it is of course perfectly possible to have a coating of lead or aluminum on another metal for the main electrode body.

I claim:

1. A coded ink symbol printing and information retrieval system using coded inks having metallic components and a readout mechanism comprising in combination,

(a) two electrodes with space therebetween for receiving an article with coded symbols,

(b) means for producing a series of sparks between the electrodes and through the coded symbols at a predetermined repetition rate,

(c) radiation detectors for the different metal components responding sharply only to a preselected strong line in the spark emission spectrum of each components, said detectors transforming radiation into electrical signals, and

((1) electronic means actuated by the signals from the detectors for reading out coded symbols.

2. A system according to claim 1 in which the detectors are photomultiplier tubes with sharp cutting filters.

3. A system according to claim 1 in which radiation detectors are solid state detectors with sharp cutting filters.

4. A system according to claim 1 in which the metals comprise a plurality of metals selected from the group consisting of bismuth, cadmium, lithium, gallium, germanium, indium, lead, mercury, silver, tin, zinc, and zirconium.

5. A system according to claim 2 in which the metals comprise a plurality of metals selected from the group consisting of bismuth, cadmium, lithium, gallium, germanium, indium, lead, mercury, silver, tin, zinc and zirconium.

References Cited UNITED STATES PATENTS 2,577,814 12/1951 Saunderson et al. 250-226 X 2,823,577 2/1958 Machler 8814 2,951,164 8/1960 Timms 25071 X 3,144,551 8/1964 Webb et al 88--14 X ARCHIE R. BORCHELT, Primary Examiner.

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