Batteryless sensor used in security applications

1 2

button igniter, similar to those in a commercial gas BATTERYLESS SENSOR USED IN SECURITY barbecue, could be mounted in a special set of hydraulic APPLICATIONS cylinders and used to generate sufficient energy to radi

ate a VHF signal to a remotely-located repeater. This DESCRIPTION OF THE PRIOR ART 5 Pascal cylinder arrangement is used to trade force for

1. Field of the Invention displacement, the equivalent of a mechanical transThis invention relates to a batteryless and unattended former. Four pounds of force, as well as a § inch dis

sensor which can be used in security system applica- placement, is required to trip the spring-loaded igniter,

tions to, for example, determine remotely, the opening/- A human stepping on the sensor buried in sand four

closing of a door or a window without the use of hard 10 inches below the surface results in about 40 pounds of

wiring. force applied to the igniter. The mechanical advantage

2. Description of Prior Art provided by the Pascal cylinders is used to reduce the The concept of a batteryless sensor was initially de- displacement in about the same proportion. These inex

veloped and patented for use as a vehicle traffic sensor pensive sensors can be used to seed a preferred corridor

[Reference lj. The basic idea of the initial batteryless 15 of entry much like a mine field except here, a signal is

sensor is very simple. It consists of two opposing mag- radiated instead of an explosion,

nets mounted on iron pads and separated by a soft iron The magnetic sensor placed in the roadway produces

connecting rod. The rod serves as the core for a sole- an EMF by changing the reluctance of the magnetic

noid. When a ferromagnetic body, such as the under path. This, in turn, varies the flux lines passing through

carriage of a vehicle, passes over the buried sensor a 20 a solenoid generating the voltage required to power the

voltage, V, is produced by the solenoid in accordance VHF oscillator. The movement of the ferromagnetic

with Faraday's Law. This law states that automobile causes the generation action; the magnet

and the solenoid are stationary.

v - N d^ 25 *n tne batteryless low tire pressure sensor, the EMF is

_ *' generated by a magnet mounted on a cantilever rod

surrounded by a solenoid. Both the magnet and the

where N is the number of turns and d<J> the differential solenoid rotate together with tire motion; only when

flux lines cut by the vehicle in a given time increment there is acceleration (deceleration) is there a relative

dt. The output voltage is an oscillatory transient of velocity between the magnet and the coil causing an sufficient magnitude to power a VHF transmitter with 3U EMF t0 be generated. This then powers a VHF oscilla

an effective range of a few hundred feet. In the initial tor which activates under low tire pressure,

sensor, the radiated signal was produced when the am- For personnel detection, an EMF is generated by a

phtude of the signal was positive The duration and piezoeiectric transducer which is activated by an in

amplitude of the oscillatory burst depended upon the ... {qq rim ^ format of ^ ^ a hi h

speed and heigh of the vehicle. An oscillator using he * , ^ ... he ( 3Q k/and 5Q *

output of thesolenoid as an ersatz power supply (ycc) *tivel y Hen5( convHerting tjfe signal t0 a

radiated a VHF signal to a traffic pole a few hundred t. , ,7 , ^ -fl «s • < A

, . , °. TM,. v . , ^ _ , tional Vec supply voltage with sufficient duration to

feet away and then to a CPU for processing data. To be „ . .7 ,. ., , _„

t.- 1 * u • operate a coded signal (e.g., 12 V and 20 ms respec

effective, however, the vehicle must be in motion over ..v . . . , . * > e". . . , , the sensor 40 tively) is the task. The piezoelectnc device and mount

In the same year, a second member of the class of in* structure remain fixedbatteryless sensors was developed to monitor tire pres- OBJECTS OF THE INVENTION

sure on large trucks based on the energy available from ... - , •

a rotating wheel [Reference 2], Large trucks contain as An obJect of the sulfct TM<x*xoxi is to create a batmany as 32 very expensive tires. Tires wear very 45 teryless energy source for converting either a rotational quickly when tire pressure is too low. Here, the EMF, or a translational motion applied to the sensor into elecnecessary to power an oscillator source, is generated by tncal enerSv sufficient to power a VHF oscillator, a resonant mechanical system excited by cyclic acceler- 11 ls another object of the invention to make the duraations of the tire. A switch attached to the tire fill valve t,on of the ersatz v« ener8v suPPlv created by the mocloses when the tire pressure is less than a preset thresh- 50 tion sufficient to radiate a coded signal to a selective old. The VHF oscillator signal is radiated to a display in receiver located typically up to one mile distant from the cab which indicates when tire pressure is too low. the sensor.

This is also a safety feature. 11 is a further object to require no wiring to or from

In 1984, a third member of the class of batteryless the sensor, and that the installation be covert in the sensors was developed for use by the Immigration and 55 sense that its presence is not obvious under general Naturalization Service (INS), Department of Justice inspection.

[Reference 3] There, the task was to detect the pres- SUMMARY OF THE INVENTION

ence of illegal immigrants crossing certain sections of

our border with Mexico. The above objectives and advantages are achieved in

Since people are not ferromagnetic targets, a new 60 a preferred embodiment of the present invention. A concept was necessary. The advantages of a batteryless small and concealed permanent magnet motor operated sensor, as before, are that there is no maintenance or as a generator and when placed, in one example, in a battery replacement costs and the possibility of theft of door jamb is used to convert the rotational energy availthe sensor itself is minimized; installation costs are mini- able from opening/closing a door or, in another exammal. 65 pie, the translational energy from opening/closing a

For the INS application, a piezoelectric energy window to an ersatz Vcc transient power supply via a source was chosen. After a considerable amount of pulley and spring arrangement; the regulated 10 volt experimentation, it was found that an ordinary push supply has a duration of about 150 ms. The duration of 3 4

the power supply is sufficient to radiate a coded VHF pulley 1 can be seen in conjunction with transmitter oscillator signal to a repeater or central processing unit electronics 5 described in the next section. Subminiature located as far as one mile from the sensor. The receiver componentry for sensor 7 is now commercially availis able to interrogate a multiplicity of sensor units over able to fit most window and door frames, a given time period. It is shown how the covertness of 5 One embodiment of the subject invention uses a mothe sensor can be further improved by using opposing tor/generator and associated gear train 4 manufactured magnets mounted both in the door and jamb. by Buehler Products, Inc., Raleigh, N.C., and identified DESCRIPTION OF THE DRAWINGS as 18 V dc, part #1.61.01.347-5 068. The gear train

accompanying the motor/generator 4 requires modifi

FIG. la shows a side view of a batteryless sensor. io cation for this application. A number of intermediate

FIG. lb shows a front view of the batteryless sensor. spur gears ^ removed. A spacer is added so that the

FIG. 2 shows an electronic block diagram of the drive gear directly drives the gear that was previously

pr2SJB? e1mb0dlment 0f , lnv5ntl0n- J , at the end of the chain. In this manner, an approximately

FIG. 3 shows an array of coded sensors and a central Qne mch displacement of the rod 3 mounted m the door

re??!Y,er', , _ . 15 jamb 8 turns the pulley 1 about J turn at a sufficient

FIG. 4 shows a covert permanent magnet approach J {e ^ 1Q ^ acrQss a Jk Qhm ^

for driving the permanent magnet generator of the bat- ^ * d m ^ ^se duration of 150 milli

teryless sensor. , *: . . ■ .

FIG. 5 shows a micropower receiver block diagram. seconds (ms) is produced

FIG. 6 is a vector representation of physical van- 20 T^/otal cost off the components including the

ajjjes motor/generator and gear tram 4 and the electronics 5

FIG. 7 shows a step up gear arrangement. is « the order of tens of dollars for the batteryless sen

sor 7; this does not include the cost of receiver 6 of FIG.

DESCRIPTION OF THE PREFERRED 3, which is estimated in the range of hundreds of dollars.

EMBODIMENT
1. The Energy Source

25 2. The Integrated Sensor

, , , , An electronic block diagram of the preferred embodi

In the batteryless sensor described m the subject m- ment of the source 5 is shown in HG 2 Rod 3

vention, the intruder spins the armature of a small per- ^ 2Q and „ j tum ^ ator/ train 4 shaft

manent magnet dc motor and gear tram. Either the field fe maki h ica, ... whh the doQr lg m shQwn

or the magnets are moved relative to each other by the 30' £ ^ ^ of generator brushes 9,

motion of the intrusion that generates the EMF. Trans- . * ra\M\r um- rj* T>cm»*

lation energy here is converted to rotary motion and a PeTManent magne (PM) field 19 is applied to a DF02M,

pulley and a gear reduction scheme is used to provide 1 amPere' 200-volt full-wave bridge rectifier Wproduc

the proper duration signal. ,n8 »?, "regulated 0 volt peak signal. A 100 tfd, 25

A dc motor, acting as a generator, converts motion to 35 TMU TM" capacitor 11 and a 5 volt type 1078L05 regu

a transient electrical power supply. For example, the lator \2 provides TM ^ +5 TMlt SUPPv'^hlch 18 ^

rotational energy of a door closure/opening motion is stant during the 150 ms pulse burst of VHF energy. The

converted to the transient electrical power supply. In 5 volt V<* suPPlv ls connected to both a tone generator

another example, the linear motion of a double hung 17 (MX503 or 258TC) and a modulator and VHF oscil

window being opened is converted to the transient 40 lator 18 whlch feeds an essentially resonant dipole 16

electrical power supply. The gear train spins the motor, 0-e > depending on length constraints m the door appli

which acts as the generator, at a high speed for a small cation). The signal radiated by the MC2833 oscillator

linear displacement of a rod located in the frame of the chip 18 is set at 49.845 MHz and receives tones from

door or window. One approach is to use a rack and tone generator 17 from 600 to 2,295 Hz. Four different

pinion gear arrangement to convert the linear transla- 45 tones were selected for experimentation and monitored

tionofa rod mounted in the door frame or window into by receiver 6. The MC2833 oscillator chip 18 is de

a momentary rotational movement of the generator scribed on page 2-20 of the Motorola Telecommunica

shaft. This was replaced in later models by a simple tions Catalogue, DL136 Revision 2, 1989.

pulley and spring arrangement as the preferred mount- In FIG- 2> the tone generator 17 supplies a sinusoidal

ing arrangement for the sensor. An analysis of the 50 tone frequency depending upon the digital code se

door/rod/pulley and gear train requirements will fol- lected, as shown in Table I, as set by small switches Do

low. through D3. One such switch setting is assigned to each

A typical example showing the invention is shown in batteryless/window sensor 7. In FIG. 3, a central re

FIGS. la and lb. Referring to FIG. la, a batteryless ceiver 6 distal to the sensors 7 receives the radiated

sensor 7 is encased in a door jamb 8. When a plunger 55 signals.

rod 3 is pushed in by the closing of a door 15, a timing TABLE I

belt 20 attached to the rod 3 by a collar 40 turns a pulley ■ ~ ~. ^

. . . * » ■ 1 r TONE MODULATOR TABLE.

1 which rotates a motor/generator 4. A spring 2 applies _ :—„ . „ —

the proper tension to belt 20 to reset the rod 3 when the Input Tone (f° m ^ BmaryCodg inputs

door 15 opens, again turning pulley 1 and rotating mo- 60 —

tor/generator 4 in the opposite direction. A stop collar 500 0000

41 fastened to rod 3 is stopped by an inner surface of a gg2 0010

container 42 to limit the motion of rod 3. A rubber 1023 001 1

grommet 43 cushions the rod 3 at the bottom. One end 1164 0100

of spring 2 is anchored to a block 44, which is fastened 65 1305 0101

,„ 1446 0110

to container 42. ]Jg7 0 1 1 1

In the front view of the sensor 7 shown in FIG. lb, 1728 1000

the motor/generator and gear train assembly 4 and 1869 1001

5 6

TABLE I-continued ^'s ... by antenna 22 and filtered by input band

pass filter 23. After amplification in low noise RF ampli

. T Tone MODULATOR TABLE^ fier 24, the signal is further filtered by bandpass filter 25

Input Tone Frequency (f0m Hz)* Bmary Coded Inputs ^ ^ to ^ Mit of ... ...

MX013QA Dj D2 D, D0 $ ^telfeIence.

The filtered RF signal is then fed to a micropower RM receiver chip 27 (Motorola MC 3367) which consists of an internal downconverter (controlled by local oscillator crystal 28), IF amplifier, quadrature detector 10 and lower power audio stages. Filtering is accom

Toi****. ±20 Hz (Minimum) plished fl{ the mtennediate frequency (IF) of 456 kHz

. „ . ^ . . , it_ through the use of external resonators 26.

The experimentally-measured current drams for the ° . . r

. „ „*__ . J , . _ ., XT The audio output from the micropower receiver 27 is

various components are as shown in Table II. .. f . , _„ ...

r then passed to a tone decoder 29, an MX-COM MX-013

TABLE II 15 MetroPageTM decoder chip. A reference frequency

Current Drain @ 5 Volts Regulated. for the tone decoder is generated by an internal oscilla

Component # Component Type Current (ma) tor controlled by external ceramic resonator 30. Upon

n MX503 3 receiving a narrowband FM, RF emission having the

12 78L05 0.5 correct tone (FM modulation frequency), the decoder

2! MC2833 12 output 31 contains a four-bit digital word containing the

ID of the signal, and Data Valid line 32 goes high to The total current drain of the sensor, when activated, indicate that a valid tone has been received, is 6.5 ma, corresponding to an actual load of 770 ohms, Hexadecimal switch 34 is used to select one of the 16 as compared to our original value of 750 ohms used in possible tone frequencies. If the output 31 from tone the initial testing of the Vcc source. The chips for the RF detector 29 matches the setting of switch 34, a logical modulator/oscillator 18 and tone generator 17 were one Detection Output signal 35 is generated by the selected to coordinate with the receiver 6 design. The comparator 33 to activate a monitor 36. frequency deviation of the FM transmission was mea- Receiver 6 power is obtained from a set of three (3) sured to be 2500 Mz. D-size lithium batteries (not shown). The entire rein FIG. 4 a more covert application suggests the use ceiver 6, as described above, draws approximately 2 of two opposing magnets 13 and 14 in the door 15 and mA at 3.6 Volts.

the door jamb 8 respectively. Then when the door 15 The batteryless sensor 7 being used operates on a

closes, the opposing magnets 13 and 14 would cause the spring-loaded pulley system which produces a voltage

rod 3 connected to one of the magnets 14 to drive the 3J signal used to power a transmitter chip. It is important

gear train 4 and, in turn, the generator 4 of sensor 7. The to determine the minimum rotational (angular) velocity

selection of magnets 13 and 14 and the cosmetic design required to cause the generator to produce some mini

of the door 15 and jamb 8 to facilitate this concept mum supply voltage Vs.

would be used where covertness is important. In FIG. 6, it can be seen that an applied rotational

FIG. 3 shows one receiver 6 monitoring a large num- velocity, to* initiated by a door 54 closure/opening

ber, fl through fn, of coded sensors 7. The dipole 16 motion will translate to a certain related tangential ve

transmits the coded rf signals to antenna 22 of receiver locity Vm as follows: 6.

3. Primary Power Requirements

It can be shown that to achieve a range of one mile 45 vm=vdcos ... 0 (1) requires an effective radiated power of about 10 mW.

Assuming the gain of the non-resonant dipole 16 of At first it would appear that a generator's 60 velocity

FIG. 2 (because of the extended length required) to be depends only on the angle 6 of the door 54 opening,

about unity, the dc primary power required for a mea- However, upon further examination, it can be shown

sured 40 percent oscillator efficiency is about 25 mW. 50 that id, the width of door 54, also varies with 6 in a way

For a Vcc of 5 volts, this corresponds to an equivalent that diminishes the dependence of the velocity on the

load resistance of angle of the door 54 opening. That is, since:

rrf=r„sec 9, (2)

n _ <V*& _ 25 _1Ln 55

Primary Power 25 x 10-3 ft ... from (}) ^

Allowing for some power to operate the tone genera- ... cos e=a^n- (3) tor used for coding and modulator/transmitter 18, a

RL=750 ohms was used for initial testing. For a rod 3 60 Therefore, the relationship between the generator having a length of 1 inch and a 120 degree rotation of pulley's 56 rotational velocity (o>m) and the door's rotathe shaft of the generator 4 in a half second, a signal tional velocity, tad, is given by: duration of 150 ms is radiated; a minimum signal duration of 20 ms is required for successful detection. vm=a>mrm. (4)

4. The Receiver 65 Then> by setting (3) equal t0 (4)) the following ratio of

A block diagram of the receiver 6 is provided in FIG. rotational velocities is obtained: 5. The radiated VHF signal from the batteryless sensor