JPH045354B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a "Passive Interrogator Label System" (PILS). The passive interrogator label system includes an interrogator that sends an interrogation signal and one or more "labels" or It includes a passive transponder and a receiving and decoding system that receives the response signal and decodes the information contained therein.

A passive interrogator label system of the type of the present invention is disclosed in U.S. Pat. No. 4,058,217 to Cole. The simplest forms of the systems disclosed in these patents include a radio frequency transmitter capable of sending RF pulses of electromagnetic energy. These pulses are received by the passive transponder's antenna and applied to a piezoelectric "launch" transducer that converts the electrical energy received at the antenna into sound waves within the piezoelectric material. When pulsed, the sound waves generated within the piezoelectric material are sent along a defined sound path. Other "tap" transducers or reflectors placed at regular intervals along this path convert the sound waves into electrical energy or direct the sound waves back to the launch transducer. Either convert it back into electrical energy. The presence of a tap transducer or reflector at a determined location along the sound path determines whether a response pulse is sent with a certain time delay in response to the interrogation pulse. This determines the information code contained in the transponder's response.

When the acoustic pulses are reconverted into electrical signals, the electrical signals are fed to the transponder's antenna and transmitted as radio frequency electromagnetic energy. This energy is received by a receiver and decoder, preferably co-located with the interrogator transmitter. The information contained in this response is then decoded.

The transponder of a passive interrogator label system operates in the "time domain" and produces a response signal containing one or more pulses of radio frequency energy upon receipt of each burst or pulse of radio frequency electromagnetic energy. The presence or timing of a response pulse to a sent interrogation pulse determines the information code contained in the response.

Passive interrogator label systems of the type described above have a number of drawbacks. The signal-to-noise ratio of these systems is not easily improved. This is because these systems are subject to interference in both wide and narrow bands. Furthermore, these systems require extensive signal processing of the transponder response signals to determine the information code. Normally, this signal processing must be performed on the receiver side. This is because the information is contained in a relatively wide band signal. Transmission to a distant signal processing unit may require transmission of wideband signals.

It is an object of the present invention to provide an interrogator which only requires the transmission of low power interrogation signals.
To provide a transponder system.

Another object of the present invention is to provide an interrogation transponder system with a high signal-to-noise ratio.

Another object of the invention is to provide an interrogator-transponder system having a signal decoder that is simpler and less expensive than decoders currently used in systems of this type.

These objects, as well as further objects that will become apparent from the description below, are to provide a device for sending a first interrogation signal having a first frequency that sequentially takes on the values of a plurality of frequencies within a defined frequency range. This is achieved according to the present invention. This first frequency is, for example, in the range 905-925 MHz, in a frequency band freely used throughout the world for short-range transmissions.

A remote transponder associated with a system according to the invention receives as input the first signal and produces as output a second response signal. Signal conversion means within the transponder convert the first signal into a second signal and include:

(1) A "signal conditioning element" coupled to receive the first signal. Each signal conditioning element provides an intermediate signal having a known amount of delay and a known amplitude modulation relative to the first signal.

(2) A "signal combining element" coupled to all signal conditioning elements to combine these intermediate signals to create a second signal. A known information code is provided, which code identifies and is associated with a particular passive transponder.

The system of the present invention provides a second
The apparatus further includes an apparatus for receiving the signal and a mixer for receiving both the first and second signals or a signal extracted therefrom, mixing the two signals, and thereby producing another signal. This further signal may include a sum frequency and a difference frequency of the first signal and the second signal.

Finally, the system according to the invention includes a signal processor that responds to the further signal produced by the mixer, detects the frequencies contained in that further signal, and thereby determines the information code associated with the passive transponder. Contains.

A system according to the invention is disclosed in the above-mentioned US patent
It has several advantages over passive interrogator label systems of the type disclosed in 3273146 and 3706094. Because there is little interference in both wide and narrow areas, the system of the present invention is more effective than known systems.
The signal-to-noise ratio has been improved. The present invention does not require a complex signal processor to decipher the information code. Since the main part of the processing of the signal takes place in the radio frequency (RF) part of the system, conventional algorithms for Fourier analysis can be used in the signal processor.

Furthermore, the output of the mixer (as described above) which mixes the first (interrogating) signal and the second (response) signal, or the signals extracted therefrom, is such that the frequency and its band are acoustically Because it is within the wave range, it can be sent over regular telephone lines. Therefore, the signal processor may be located far from the RF interrogator/receiver and mixer. This allows a relatively expensive computer to be used to perform Fourier analysis of one or more remote interrogators/receivers without requiring an expensive signal transmission chain from the remote location to the computer.

Finally, the radio frequency technology used in the system of the invention is simpler than that of known devices of this type. This is because radio frequency signals are used directly to carry information codes. More specifically, this is because it is included in the frequency and phase of the transponder's response signal (second signal) with respect to the interrogation signal (first signal).

Embodiments of the invention will be described in detail below with reference to the accompanying drawings.

Next, preferred embodiments of the present invention will be described with reference to FIGS. 1 to 24 of the accompanying drawings.
Identical elements in each figure are designated by the same reference numerals.

FIG. 1 shows the overall configuration of an interrogator-transponder system according to the present invention. The system includes a signal source such as a voltage controlled oscillator 10. This voltage controlled oscillator 10 receives a control signal V from a control element 12 . The voltage V determines the frequency of the signal generated by the oscillator. This output signal of the oscillator is amplified by a power amplifier 14 and applied to an antenna 16 for transmission to a transponder. The transmitted signal is designated as S ₁ .

The signal S ₁ is transmitted to the antenna 18 of the transponder 20
The signal is received by the passive signal converting element 22 and passed through the passive signal converting element 22. This signal converter converts input signal S ₁ into output signal S ₂
Convert to The output signal S ₂ is passed to the same antenna 18 or to a different antenna 24 for retransmission to the interrogator/receiver device.

The signal conversion carried out by the signal conversion element 22 will be explained in detail below with reference to _FIG . It would be sufficient to simply explain that it is included.

Signal S ₂ is received by antenna 26, which may be the same antenna as transmitting antenna 16 or a different antenna. This signal is then passed to circuit element 28 which converts signal S ₂ to signal S ₄ .

Similarly, the output of VOC 10 is passed to circuit element 30 which generates signal _S3 . These two signals
S ₃ and S ₄ are added to a mixer (4 channel multiplier) 32.

Circuit elements 30 and 28 receive respective input signals S ₁ and S ₂
may or may not include means for generating the respective output signals S ₃ and S ₄ by changing the output signals S 3 and S 4 . for example,
The element 30 may be simply a non-blocking electrical circuit or wire, such as a small conversion signal of the transmitted signal S ₁ from the signal S ₃ . Similarly, circuit element 28 receives signal S ₄
It may simply be an amplifier, such that S 2 is substantially the same as signal S ₂ but has a higher signal level. Other variations of circuit elements 30 and 28 are discussed below. However, in general, signal S ₃ is extracted from signal S ₁ and is therefore a function of the frequency and phase of signal S ₁ , whereas signal S ₄ is derived from signal S ₂ . It is therefore a function of the frequency and phase of the signal _S2 .

Signals S ₃ and S ₄ are mixed or heterodyned in mixer 32 to generate signal S ₅ . this signal
S ₅ includes both the sum frequency and the difference frequency of the frequencies included in signals S ₃ and S ₄ . Signal S ₅ is passed to signal processor 34 . This signal processor 3
4 determines, measures or detects at least some of the frequencies contained in the signal S ₅ . In particular, signal processor 34 uses Fourier analysis (transform) to determine some of the difference frequencies _fi in signal S ₅ after signal S ₅ is sampled and digitized. Preferably, the signal processor also includes:
Determine the amplitude a _i of frequency component f _i and φ _i in each phase.
Here, the phase φ _i is measured with respect to one frequency component f _p .

The information determined by the signal processor 34 is sent to a microcomputer consisting of a storage device 36 and a microprocessor 38. This microcomputer continuously analyzes frequency, amplitude and phase information and makes decisions based on this information. For example, this microcomputer can determine the identity of transponder 20.

FIG. 2 explains the nature and operation of transponder 20. This transponder may be a completely passive component or may include a power source and one or more active components. As understood,
The signal conversion element 22 shown in the block diagram of FIG. 1 includes N+1 signal processing elements 40 and signal coupling elements 4.
It consists of 2. Each of the signal processing elements 40 is coupled to the antenna 18 and receives a transmission interrogation signal S ₁ . As will be appreciated, each processing element 40 produces as output a respective intermediate signal I ₀ , I ₁ , . . . , I _N . These intermediate signals are transmitted to a combining element 42 which combines (eg, additive, multiplicative, etc.) these intermediate signals to produce an output signal _S2 .

As seen in FIG. 2, each signal processing element 40 consists of a known delay T _i and a known amplitude adjustment A _i (either attenuation or amplification).
The respective delay T _i and amplitude adjustment A _i may be a function of the frequency of the received signal S ₁ or may be independent of frequency, providing a constant delay and a constant amplitude adjustment, respectively.

In this embodiment of the invention, the delay element T _i , the amplitude adjustment element A _i and the intermediate signal coupling element 42 are strictly passive elements, i.e. they do not require a power supply to operate and the signals being processed are Not amplified. However, the principles and concepts of the invention are also applicable to active devices. As detailed below,
The delay elements are realized by elements that generate, transmit and receive surface acoustic waves, or by optical fibers or optical waveguides that transmit infrared or optical radiation. The amplitude adjustment element may be either a passive element consisting of a resistor and/or a reactance in order to attenuate the signal. As is clear from FIG. 2, the order of the delay elements and amplitude adjustment elements may be reversed, ie, the amplitude element A _i may come before the delay element T _i .

The signal processor 34 shown in FIG.
Determine some of the frequencies f _i included in S ₅ . As shown, signal S ₅ passes through a bandpass filter 44 having an audio orange passband (eg, 1-3 KHz). This bandpass filter passes a portion of the signal S ₅ having a frequency different from that of the signals S ₃ and S ₄ and removes extremely low frequency noise. The output of the bandpass filter is provided to a sample and hold circuit 48 via an anti-aliasing filter 46. The analog signal is thus sampled at a sampling rate determined by clock 50. This sampling rate is twice the upper frequency of the breadth pass filter 44. The output period of the sampled signal in the sample and hold circuit is the period during which the sampled signal is digitized by the analog/digital (A/D) converter 52. Ultimately, this digitized sample is sent from the A/D converter to a dedicated computer 54, which repeatedly stores the samples output during a defined period of time and analyzes these signals. Perform a Fourier transform. The computer 54 thus generates a digital output defining the frequency f _i contained in the original signal S ₅ . If necessary, the computer 54
, each amplitude a _i at each frequency f _i
and the phase φ _i may be determined.

4 and 5 show the signal processor 3
FIG. 4 is a frequency diagram representing a typical output of 4; These outputs carry an information code provided by the signal transformer 22 of the transponder 20, so that the identification of the particular transponder corresponding to this code is carried out.

Here, in the device shown in Figure 1 again, VCO10
shall be controlled so that the frequency of the signal _S1 becomes a plurality of consecutive frequency values within a defined frequency range. For example, ramping up the control voltage between the minimum and maximum voltages,
Alternatively, it may be lowered to move the frequency continuously within the limits of a defined frequency range. Alternatively, the voltage V may be stepped from one value to the next between a minimum and maximum voltage such that the signal S ₁ has a number of discrete frequency values within a defined frequency range. You can also do it. This frequency range is
905 to 925 MHz is preferred and the frequency band is freely available throughout the world for short range transmission.

If the signal _S1 successively takes on a plurality of frequency values, the output of the signal processor is
The configuration shown in the figure and FIG. 5 is obtained. As shown in FIG. 4, a large number of discrete frequencies f ₀ , f ₁ , f ₂ ... f ₁₀ included in the signal S ₅ have different amplitudes (magnitudes) a ₀ , a ₁ ... a ₁₀ and phases φ ₀ , φ ₁ ... φ ₁₀ (the phases φ ₁ ... φ ₁₀ of the frequencies f ₁ ... f ₁₀ are all based on the phase φ ₀ of the frequency f ₀ ).

The measured phase φ ₀ ... φ ₁₀ depends on the distance from the transmitter to the transponder, so radially inward about the transmitter and receiver,
The outward movement of the transponder can be measured by repeatedly measuring each phase. FIG. 5 shows that the transmitter/
It shows how much the phases φ ₀ ...φ ₁₀ are rotated (for example, 45°) with respect to each phase in FIG. 4 due to the different distances from the receiver to the transponder.

The different frequencies contained in the signal S ₅ are due to the characteristics of the transponder as well as the frequencies contained in the transmitted signal S ₁ .

It is assumed that VCO 10 is controlled to give a linear sweep in frequency. The transponder is also configured such that the signal conversion component can be designed as a delay line filter as shown in FIG. This filter has an initial delay T ₀ followed by equal delays ΔT. Each delay section 55
The output from has undergone a phase shift φ _i (i=0 to N). The phase left φ _i −φ _i-1 is the center frequency (915M
Hz) to one of four values: 0, ±90° or 180°. The transponder code information is carried by these phase differences.
The purpose of this system is to search for patterns of phase differences as unique identification information for a particular transponder.

Output signal from each delay component I ₀ ...I _N (intermediate signal)
are summed to form signal _S2 . This signal S ₂ is fed to the common antenna of the transponders.

Furthermore, the signals S ₃ and S ₄ in this system are
Assuming that signals S ₁ and S ₂ are related in terms of frequency and phase (but not amplitude) at the transmitter and receiver, respectively, the response signal S ₄ is
When mixed with the transmitted signal S ₃ at , a beat is generated due to the delay in the transponder. In fact, each intermediate signal I ₀ ... _IN creates its own unique beat frequency. By comparing the phases of adjacent beat frequencies, the information phase encoded in the transponder can be recovered.

Therefore, the VCO frequency changes from the minimum frequency ω ₀ to the maximum frequency ω ₀ +△ at a constant rate of ω = radians per second.
Assuming that it is swept up to ω, the time during which this sweep is performed is τ=Δω/ω〓. Note that ω=2πf radians.

This signal S ₁ can be expressed as a frequency modulated cosine wave.

S ₁ (t)=COS(ω ₀ t+1/2ω〓t ² ) The instantaneous frequency of this signal is ω ₀ +ω〓t. The initial phase can be set to zero. This is simply an arbitrary question of where to choose the time origin. The amplitude can be 1. Although the sweep time is naturally finite, this constraint is ignored in the present analysis. Although there is an "edge effect" created by the finite sweep time, the primary operation of the system is most clearly understood by ignoring this edge effect.

The transponder intermediate signal I _i has the same form as the transmitted signal S ₁ with the following exceptions.

(1) T _c +T ₀ +i△T delayed. where T _c is the round trip transmission time from transmitter to transponder to receiver.

(2) θ _i phase is shifted. and (3) the amplitude is reduced to A (all equal for all intermediate signals).

Therefore, the composite response signal _S2 is given by the following equation.

S ₂ (t)=A _N 〓 ⁱ⁼⁰ S ₁ (t-T _c -T ₀ -i△T)θ _i =A _N 〓 ⁱ⁼⁰ cos{ω ₀ (t-T _c -T ₀ -i ΔT) +1/2ω〓(t−T _c −T ₀ −iΔT) ² +θ _i } The useful output of the mixer 32 can then be represented by the product of different components of the following frequencies:

S ₅ (t)=S ₁ (t)×S ₂ (t) When this algebraic expression is solved, it is expressed as follows.

S ₅ (t)=A _N 〓 〓 ⁱ⁼⁰ cos{ω〓t(i△T+T _c +T _p )+ω ₀ (i△T+T _c +
T _p ) −1/2ω〓(T _c ² +T _p ² +(i△T) ² +2T _c T _p +2i
△T (T _c + T _p )) − θ _i } This is the amplitude A, the instantaneous frequency ω (i△T + T _c +
T _p ), consisting of frequency lines with inclusive phase φ _i (N+1)
It will be recognized as a book comb spectrum.
If we perform spectrum analysis on the signal S ₅ (t) so that many frequency lines do not interfere with each other, we get
The amplitude A and phase φ _i can be retrieved for each line separately. (In fact, Fourier analysis yields parallel coordinates for each line, which requires further processing to convert to polar coordinates and obtain the phase φ _i .) Figures 4 and 5 show the propagation It shows how the phase φ _i changes as a result of a change in the delay T _c . By calculating the phase φ _i of the frequency line at different times and comparing the results of each calculation, it is then possible to determine whether the transponder has moved radially with respect to the transmitting and receiving system. This comparison may be performed in a simple manner by appropriate programming of the microprocessor 38.

FIG. 7 shows a typical type of transponder disclosed in _U.S. Pat. It converts that sound wave energy back into an electrical signal _S2 . In particular, the signal transducing element of the transponder consists of a substrate 58 of piezoelectric material, such as a lithium niobate (LiNGO ₃ ) crystal. A layer of metal such as aluminum is deposited on the surface of this substrate, forming a pattern as shown in FIG. For example, the pattern may consist of two bus bars 60 and 62 connected to dipole antenna 56, a delivery transducer 64, and a plurality of tap transducers 66. Bars 60 and 62 form a transmission path 68 for sound waves originating from the delivery transducer and propagating substantially linearly to the tap transducers in turn. This tap transducer reconverts the sound waves collected and summed by busbars 60 and 62 into electrical energy. This electrical energy is then converted into electromagnetic radiation by activating the dipole antenna 56.
It is propagated as signal _S2 .

In the acoustic transducer disclosed in U.S. Pat. No. 3,706,094, the presence or absence of a tap transducer at each equidistant transducer location provides an information code in the transmitted response signal. Thus, a single pulse or burst signal of radio frequency energy (first signal S 1 ) transmitted to the transponder results in one or more response pulses (second signal S ₁ ) depending on the presence or absence of the tap transducer of the sonic device. signal S ₂ ).

In a preferred embodiment of the invention, taps are placed at equal intervals along the acoustic wave path 68, as shown in FIG.
A transducer 66 is provided and the information code is applied by providing a selected number of "delay pads 70" between the tap transducers. This delay pad, shown in more detail in FIG. 8, is preferably made of the same material and is preferably co-located with bus bars 60, 62 and transducers 64, 66. Each delay pad has an operating frequency (approximately 915MHz)
One tap transducer 66 by 1/4 or 90° for a sound wave that is not delayed at
is wide enough to delay the propagation of sound waves from one transducer to the next. By placing these delay pads between successive tap transducers, the delay received by the next tap transducer 66B is determined relative to when the sound wave passes below the previous tap transducer 66A. Preferably, the phase φ of the sound wave is controlled to allow the following four phase states:

1. When there is no pad between tap transducers 66A and 66B, φ=-90°; 2. When there is one pad between tap transducers 66A and 66B, φ=0°. , 3 When there are two pads between tap transducers 66A and 66B, φ=90°; 4 When there are three pads between tap transducers 66A and 66B, φ=180° It is.

Referring to FIG. 6, phase information φ ₀ (the signal discarded by the first tap transducer in the line) and phase information φ ₁ , φ _{2 .}
The signal picked up by the transducer) is fed to a combiner (adder), which in the embodiment of FIG. 7 comprises bus bars 60 and 62. This location information is sent as signal _S2 by antenna 56 and contains the information code of the transponder.

FIG. 9 shows another example of the general class of transponders shown in FIG. In this example, combination or combination element 42 includes adder 72 and mixer 7.
4. This example also uses a known delay T _N =0 and a known amplitude modification A _N
=1.

The effect of mixing (heterodyning) the received signal S ₁ with the output signal from the summing device 72 is:
The purpose is to double the frequency of the output signal _S2 . The output of mixer 74 will contain the sum and difference frequencies of its two inputs, the two inputs being the frequencies of signal S ₁ . transmitted (radiated) if the antenna is initially tuned to radiate a signal at the sum frequency and not the difference frequency
Signal S ₂ has twice the frequency of signal S ₁ . Therefore, the receiving device of the system is tuned to receive a frequency one octave higher than the frequency of the transmitting device;
It makes it possible to transmit the signal S ₁ and receive the signal S ₂ . This device eliminates the problem of clutter and echoes from targets reflecting the transmitted signal _S1 .

Figures 10 and 11 show acoustic wave devices implementing the transponder of Figure 9. The device includes conventional busbars 60 and 62 on a piezoelectric substrate 58. The bus bar 60 is split vertically at one point,
Diode 76 and RF choke 77 are coupled across the gap to provide a single unbalanced mixer that doubles the frequency of output signal _S2 .

In this embodiment, delay pad 78 takes the configuration shown in FIG. 11 to provide not only a phase delay of the acoustic wave, but also a selected attenuation (amplitude modulation). This configuration provides an additional means of encoding, ie the code consists of amplitude as well as phase information.

Referring to FIG. 11, the delay pad inserted between tap transducers 66 includes a specially designed amplitude modulation pad 80. Patsudo 80 is
It has a cut edge perpendicular to the path of the persistent acoustic wave travel 68. Thus, this cut edge has two edge surfaces 82 in the wave.
and 84 are shown. Edge 82 has a length "a" while edge 84 has a length "b". Edge 82 has two edges 82 and 84
The difference in delay given by pads in
180°, extending parallel to edge 84 at a distance D apart. With this constraint, Edge 8
The portion of the wave that crosses edge 84 is moved out of phase by the portion of the wave that crosses edge 84, thereby providing cancellation.

Attenuation W can be calculated by comparing the associated edge lengths a and b.

W=(a-b)/(a+b) If length b=0, there is no attenuation (W=1).
When a=b, there is maximum attenuation (W=0).

Signals conveyed by the transponder of Figure 9
Since the frequency of S ₂ is twice the frequency of signal S ₁ , the decoding system must be modified accordingly. In Figure 12, a multiple of the frequency f of the signal generated by the VCO (for example, 2
The portion of the system shown in FIG. 1 is shown having a frequency multiplier (e.g., a doubler) coupled to the output of VCO 10 to provide a signal S ₃ having a frequency Mf that is . The signal S ₃ , which is then mixed with the augmented signal S ₂ received from the transponder, has a frequency that approximates the frequency of the signal S ₂ .

FIG. 13 shows yet another modification of the decoding system according to the invention. In this case, the signals S ₃ and S ₄ are created by heterodyne reception with the separately created signals S ₆ and S ₇ , respectively. Signals S ₆ and S ₇ must be the same or related synchronization signals to produce synchronization outputs S ₃ and S ₄ .

The shape shown in FIG. 13 may serve to reduce the frequency of signals S ₃ and S ₄ , thus facilitating system design.

In Fig. 14, how does the frequency f of the signal generated by the VCO of the device shown in Fig. 1 fall within the specified frequency range (905-925MHz)?
It shows what can be changed in steps. In this example, the control unit 12 is configured such that the frequency f is the lowest frequency 905M of 128 equal steps.
Hz to the maximum frequency of 925MHz,
Apply step voltage V to VCO10. After reaching 925MHz, the frequency is lowered again to 128 steps and the process is repeated.

FIG. 15 shows the device of FIG. 1 with three additional features:

(1) A ramp or sawtooth signal generator to vary the frequency of the VCO.

(2) A clock generator and a switch to toggle back and forth between transmit and receive modes.

(3) A synchronous pulse generator to select the sampling time and thereby compensate for nonlinearities in the frequency sweep.

The apparatus of FIG. 15 includes a ramp generator 90 for providing a sawtooth waveform to the VCO 92. The VCO is
An output signal with a frequency f whose slope changes linearly and repeatedly from 905 MHz to 925 MHz is generated. This signal is amplified by an RF amplifier 94 to transmit the signal to a transmit power amplifier 98 or a decoding mixer 100.
is supplied to a transmit-receive switch 96 which leads to a transmitter-receive switch 96. Switch 96 is controlled by a 100 KHz square wave signal generated by clock 102. The output signal S ₁ from power amplifier 98 is provided to an external circuit or transmit/receive (TR) switch 104 and transmitted as electromagnetic radiation by antenna 106.

A transponder response signal S ₂ is received by antenna 106 and provided through a circulator or TR switch 104 to a receiver amplifier 108 . The output of this amplifier S ₄ is mixed with the signal S ₃ provided intermittently by switch 96.

The output S ₅ of the mixer 100 includes the sum and difference of frequencies of the signal S ₃ and the signal S ₄ , and this output S ₅ is
It is fed to a bandpass waver 110 having a passband between 1KHz and 3KHz. The output of this waver is provided through an anti-aliasing waver 112 to a sample and hold device 114 .

A sample and holding device 114 provides each sample to an analog-to-digital (A/D) converter 116. This A/D converter provides the count value of each sample to an element 118 which analyzes the frequencies contained in the signal by means of fast Fourier transform. Sample and holding device 114 and A/D converter 11
6 is activated by a sampling signal derived from the signal generated by VCO 92. This sampling signal compensates for the non-linearity with respect to time of the monotonically increasing frequency f of the VCO output signal.

As shown in FIG. 15, the signal generated by VCO 92 is amplified and passed through a delay element 120 having a fixed signal delay time Ts. A signal in which both the delayed and undelayed signals contain both sums and differences of frequencies
It is fed to a mixer 122 which generates S ₇ . Signal S ₇
is supplied to a low-pass waver 124 that passes only the frequency difference portion of this signal. The output of this low pass waver is provided to a zero crossing detector 126 which generates a pulse at each positive going (or negative going) zero crossing. Each of these pulses is
Sample and holding device 114 and A/D converter 1
16.

16-18 illustrate the operation of the circuit shown in FIG. 15. 16 shows the 100 KHz output from clock 102, and FIG. 17 shows the frequency sweep of the signal generated by VCO 92. In FIG. 18, the solid line 128
indicates the frequency of the transmitted signal S ₁ by the dashed line 130
shows the frequency of the signal S ₂ received from the transponder by. As you can see from the drawing, dashed line 1
The signal indicated at 30 is received during the interval of transmission of the signal indicated by solid line 128. These interval periods are
It is chosen to be approximately equal to the one-round travel delay time between the transmission of the signal S ₁ to the transponder and the reception of the signal from the transponder. As shown by the multiple dashed lines, the response signal from the transponder can be arbitrarily generated as a result of the combined (in the example summed) intermediate signals with different delay times (T ₀ , T ₁ , ...T _N ). may contain a large number of frequencies in a given period of time.

Figures 19-22 illustrate a further preferred embodiment of the invention, which uses radiation generated from a laser. As shown in FIG. 19, laser 132 is energized and, in response to the controller,
Generate radiation at a series of different frequencies (eg, in the infrared or visible light spectrum). This radiation forms signal S ₁ , which is transmitted to transponder ₁₃₄ . Transponder 134 receives signal S ₁ , (1) generates a response signal S ₂ in response to signal S ₁ , and (2) reflects signal S ₁ by mirror 136 . The reflected signal S ₁ is received by the photocell (PC) 138 in the same manner as the response signal S ₂ and is sent to the photocell 138.
converts these radiation signals into electrical signals.
The output of the photocell 138 is a signal S ₁ of a different frequency.
and _S2 , and is supplied to a signal processing device 140 of the type shown in FIG.

The transponder 134 for the interrogation, reception and encoding device shown in FIG.
It is possible to take one of the forms shown in FIGS. 21 and 22. FIG. 20 shows a plurality of optical fibers of different lengths, which receive the signal S ₁ and transmit the reflected signal S ₂ . Signal S ₂ therefore includes all signals coming out of all optical fibers. In this configuration, each optical fiber receives the signal S ₁ , introduces it from one end, reflects, and directs the signal S ₁ again to its receiving end.

In the embodiment of FIG. 21, a single optical fiber is used to generate signal _S2 . In this case, the many taps or notches 142 in the optical fiber serve to reflect some of the radiation back to the receiving end.

FIG. 22 shows an optical waveguide with an integrated optic delay line doped into the optical substrate. The waveguide consists of a receiving guide 146, a transmitting guide 148, and a plurality of taps 150 between the receiving and transmitting guides. Therefore, this optical waveguide operates in exactly the same manner as the notched optical fiber shown in FIG.

Figures 23 and 24 show how multiple transceiver systems are used to obtain range and bearing to the transponder TP. In FIG. 23, two transmitters, receivers, and mixers are used with antennas 152 and 154 separated by a distance L. Signals from antennas 152 and 154 respectively
Mixers 156 and 158 receiving S ₂ also receive a common signal S ₃ derived from the transmitted signal S ₁ . The signal S ₅ produced by these mixers contains the encoded phase information received from the transponder. By comparing the phase φ ₀₁ of the signal received by one antenna 152 with the phase φ ₀₂ of the signal received by the other antenna 154 using, for example, a comparator 160, the phase difference Δφ is determined.
can be decided.

From the arrangement shown in FIG. 23, it can be seen that θ=tam ^-1 △φ/φL φ _L =KL=2πL/λ φ _L =2πfL/c.

Therefore, the orientation θ to the transponder can be measured.

FIG. 24 shows how the distances R ₁ and R ₂ of two sets of devices of the type shown in FIG. 23 placed at known locations and from these locations to the transponder can be determined. In this case, the first azimuth angle θ ₁ is measured by the first instrument system 162 and the azimuth angle θ ₂ is measured by the second instrument system 1
Measured at 64. The distances R ₁ and R ₂ are the angles θ ₁ , θ ₂ and the distance L ₀ , and the two equipment systems 162
It can be calculated from the angle θ ₀ between and 164.

Although a novel system for passive transponder interrogation has been disclosed, and a system has been disclosed which satisfies all of the objects and desired effects thereof, variations, modifications, and uses of the present invention are contemplated by the present specification, drawings, and the like. It will be apparent that many variations can be made upon study of the embodiments by those skilled in the art. All such various modifications are included in the present invention without departing from the gist of the present invention as defined in the claims.

[Brief explanation of drawings]

FIG. 1 is a block diagram of an interrogator transponder system according to the present invention. FIG. 2 is a block diagram of a transponder used in the system of FIG. FIG. 3 is a block diagram of a signal processor used in the system of FIG. 4 and 5 are frequency graphs of information obtained by the signal processor of the system of FIG. FIG. 6 is a block diagram of a passive transponder in accordance with one preferred embodiment of the present invention. FIG. 7 is a diagram showing the actual configuration of the embodiment of FIG. 6. FIG. 8 is an enlarged view of a portion of FIG. 7. FIG. 9 is a block diagram of a passive transponder in accordance with another preferred embodiment of the present invention. FIG. 10 is a diagram showing the actual configuration of the embodiment of FIG. 9. Figure 11 is the first
FIG. 2 is a diagram showing details of the standing acoustic wave device used in the one shown in FIG. FIG. 12 is a block diagram of one preferred embodiment of the interrogator/receiver of FIG. Figure 13 shows the interrogator shown in Figure 1/
FIG. 3 is a block diagram of another preferred embodiment of the receiver. FIG. 14 is a frequency versus time graph illustrating one preferred form of frequency variation in the system of FIG. FIG. 15 is a detailed block diagram of one preferred embodiment of the interrogation, reception and decoding portions of the system of the present invention. FIG. 16 is a timing diagram representing the clock output of the device of FIG. 15. FIG. 17 is a frequency versus time diagram representing the transmitted signal of the device of FIG. 15. FIG. 18 is a frequency versus time diagram representing both the transmitted and received signals in the apparatus of FIG. 15. FIG. 19 is a block diagram of the transmitter and receiver of the infrared or optical interrogator/transponder system of the present invention. FIG. 20 represents one preferred embodiment of a passive transponder for use with the system of FIG. 19. FIG. 21 represents another preferred embodiment of a passive transponder for use with the system of FIG. 19. FIG. 22 shows a third preferred embodiment of a passive transponder for use with the system of FIG. 16. FIG. 23 is a topological diagram illustrating how to orient to a transponder using the passive interrogator/transponder system of the present invention. FIG. 24 is a topological diagram illustrating how to range a transponder using the passive interrogator/transponder system of the present invention. In the figure: 10: voltage controlled oscillator, 14: power amplifier, 16; 18: antenna, 20: transponder, 28: signal conversion circuit element, 30: signal generation circuit element.

Claims (1)

[Scope of Claims] 1. A device for interrogating a transponder carrying encoded information, comprising: a.
A device comprising the following components: b, c, d, e, f, and g. (a) at least one transponder means for receiving a first signal and transmitting a second signal in response; The means includes signal converting means that receives the first signal as an input and generates the second signal as an output, the means for: (1) converting the first signal by a known amount; (2) a plurality of signal conditioning means, each of which generates an intermediate signal that is delayed and whose amplitude is varied by a known amount; a signal combining means for producing a signal of
Said signal conditioning means and signal combining means are associated with said second transponder means.
give a known information code to the signal. (b) transmitting means for transmitting said first signal having a first frequency; The first frequency sequentially takes values of a plurality of frequencies within a predetermined frequency range wide enough to temporally distinguish the known delay amounts of each of the plurality of signal conditioning means. (c) said second from said transponder means;
receiving means for receiving signals. (d) means connected to said transmitting means for generating a third signal derived from said first signal; (e) means connected to said receiving means for generating a fourth signal derived from said second signal; (f) Mixing means for receiving the third signal and the fourth signal and mixing these signals to generate a fifth signal. (g) signal processing means responsive to said fifth signal for detecting at least some of the frequencies contained in said fifth signal and thereby determining said information code associated with said transponder means; 2. The apparatus of claim 1, wherein said emitting means comprises means for generating said first frequency as a plurality of individual frequency values within said predetermined frequency range. 3. The apparatus of claim 1, wherein said emitting means comprises means for generating said first frequency as a plurality of individual frequency values within said predetermined frequency range. 4. The device according to claim 1, wherein the transmitting means comprises means for generating the first signal as an electromagnetic wave. 5. Apparatus according to claim 4, wherein the transmitting means is a radio transmitter and the frequency range is within the radio frequency spectrum. 6. Apparatus according to claim 4, wherein the transmitting means is a coherent optical radiation source. 7. The device according to claim 6, wherein the frequency range is in the infrared range. 8. The apparatus of claim 1, wherein the transmitting means and the receiving means share one antenna. 9. The apparatus of claim 1, wherein the transmitting means includes switch means for intermittently interrupting transmission of the first signal, thereby creating repeat periods for receiving the second signal. 10 The switching means includes a clock signal generator and, responsive to the clock signal, a first clock signal at a clock signal rate.
10. The apparatus of claim 9, further comprising an electronic switch for blocking the signal. 11 The switching means transmits the first signal to the means for generating a third signal derived from the first signal.
10. The apparatus of claim 9, wherein the signal is sent alternately when not being transmitted by the transmitting means. 12. The signal exchange means according to claim 1, comprising a substrate that determines a plurality of travel paths for sound waves on its surface, and electric circuit means that transmits the surface sound waves from the start end to the end end of the travel paths each having a different length. The device described. 13. Said electrical circuit means includes at least one launch transducer disposed on the substrate surface for exchanging a first signal with a surface acoustic wave propagating along the travel path and a launch transducer disposed on the surface of the substrate for converting the acoustic wave into an output signal. a plurality of tap transducers spaced along the substrate surface and an electrical circuit coupled to the tap transducers for combining the output signals to form a second signal; 13. Apparatus according to claim 12. 14 determining a plurality of transducer locations equidistantly along the travel path, disposing tap transducers at at least some of these transducer locations, and disposing the tap transducer at these locations; 14. The apparatus of claim 13, wherein the presence or absence creates an information code in the second signal. 15. The apparatus of claim 12, wherein a plurality of sound wave delay pads are disposed on the substrate surface along the travel path to adjust the propagation time of the sound wave along the travel path. 16. Claim 15: All delay pads have the same width in the direction of propagation of the sound wave, so that the presence or absence of the pads changes the propagation time of the sound wave by a predetermined amount.
The device described in. 17. The apparatus of claim 15, wherein the delay pad is shaped to vary the amplitude of the sound wave by a predetermined amount, the amplitude of the sound wave being at least part of the information code. 18. The device of claim 12, wherein the substrate is a lithium niobate ( _LiNbO3 ) crystal. 19 The signal converting means includes at least one optical waveguide that determines the traveling path of the light wave, a means for injecting the light wave into one end of the waveguide, and a means for injecting the light wave into the one end of the waveguide at a distance along the waveguide. 2. Apparatus as claimed in claim 1, further comprising tapping means for determining when the point at which the point has been placed is reached. 20. The apparatus of claim 19, wherein the optical waveguide comprises at least one optical fiber. 21. The apparatus of claim 19, wherein the optical waveguide comprises an integrated optical waveguide. 22. The apparatus of claim 19, wherein the tapping means includes means for producing a second signal. 23. The apparatus of claim 22, wherein the transmitting means propagates the first signal as a beam of light. 24. The apparatus of claim 23, wherein the tapping means includes means for propagating the second signal as optical radiation. 25. The apparatus of claim 23, wherein the tapping means includes means for propagating the second signal as radio frequency electromagnetic radiation. 26 The mixing means (1) receives the third and fourth signals;
and (2) producing a fifth signal through only the portion of said output signal that includes the difference frequency. and a frequency filter forming a frequency filter. 27. The apparatus of claim 1, wherein the fifth signal is an analog signal and the signal processing means includes an analog-to-digital converter for converting the fifth signal into a digital signal. 28. The apparatus of claim 27, wherein the signal processing means includes means coupled to the analog-to-digital converter to perform a fast Fourier transform on the digital signal.