JPH0321876B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to an interrogation device that transmits an interrogation signal and one or more "labels" or passives that generate a response signal containing encoded information in response to the interrogation signal. The present invention relates to a "Passive Interrogation Label System" (PILS), which is a system comprising a digital transponder and a receiving/decoding device for receiving a response signal and decoding the information contained therein.

PRIOR ART A passive question labeling system of the type involved in the present invention is disclosed in U.S. Pat. No. 3,273,146 to Horwitz II;
Cole and Vaughan, U.S. Pat. No. 3,706,094;
Cole and Vaughan U.S. Pat. No. 3,755,803;
Vaughan and Cole, US Pat. No. 4,058,217. The systems disclosed in these patents, in their simplest form, include a radio frequency transmitter capable of transmitting RF pulses of electromagnetic energy. These pulses are received by the passive transponder's antenna and sent to the piezoelectric "launch" transducer. This transducer converts electrical energy received from an antenna into acoustic energy within a piezoelectric material. Upon receiving a pulse, a sound wave is generated within the piezoelectric material and sent along a defined sound wave path. Further "tap" transducers are placed in this path at certain defined intervals, and these transducers convert the sound waves back into electrical energy, which is then converted back into electrical energy by the launch transducer. The presence of a tap transducer at a defined location along the acoustic wave path determines whether a response pulse is transmitted with a particular time delay in response to the interrogation pulse. This determines the information code contained in the transponder's response.

When the sound wave pulse is reconverted into an electrical signal,
This electrical signal is sent to the transponder's antenna and transmitted as RF electromagnetic energy. This energy is received at a receiver/decoder, preferably co-located with the interrogation transmitter, to decode the information contained in this response to the interrogation.

In this general type of system, the energy contained in the response signal is substantially less than the energy sent as the transponder interrogation signal.

OBJECTS OF THE INVENTION It is an object of the invention to provide a compact passive transponder for use in an interrogation system to transmit a response signal containing encoded information in response to receiving an interrogation signal.

Another object of the present invention is to provide a substrate having a substrate surface defining a path of travel of a surface acoustic wave, and a surface of the substrate having a surface so as to convert between surface sound wave energy and electrical energy propagating along the path of travel. at least one transducer element disposed in the transducer element; and circuitry connected to the transducer element(s) for providing an interrogation signal to the transducer element and for receiving a response signal from the transducer element. passive transponder.

Yet another object of the invention is to provide a passive transponder of the above type in which insertion losses are minimized.

SUMMARY OF THE INVENTION The above object, as well as other objects that will become apparent from the following description, is that, according to the invention, surface acoustic waves are spaced apart along said path of travel for reflecting back surface acoustic waves directed toward a transducer element. This is achieved by providing a plurality of acoustic reflectors on the substrate surface.

Sonic reflectors can be very efficient - reflecting nearly 100% of the sound wave energy - so that virtually all of the sound wave energy produced by a transducer is reflected back to the transducer. , is reconverted into electrical energy. Therefore, theoretically, the total energy conversion loss is about 3 dB when emitting the sound wave and about 3 dB when converting the sound wave back into an electrical signal, for a total of 6 dB.
Various configurations of transducers and reflectors disposed on piezoelectric substrates are discussed in detail below.

For a more complete understanding of the invention, preferred embodiments of the invention will now be described in detail with reference to the accompanying drawings.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will now be described with reference to FIGS. 1-14, throughout which like elements are designated with like reference numerals.

1 to 7 show an interrogator-transponder system using a surface acoustic wave transponder according to the invention. The transmitter/receiver and decoder system shown in FIG. 1 includes a ramp signal generator 20 that provides a sawtooth wave to a voltage controlled oscillator (VCO) 22. VCO is frequency
An output signal with a frequency that repeatedly slopes linearly upward from 905 MHz to a frequency of 925 MHz is generated. This signal is amplified by an RF amplifier 24 and supplied to a transmit/receive switch 26. switch 2
6 directs the signal to either a transmitter power amplifier 28 or a decode mixer 30. Amplifier 2
The output signal S1 from 8 is sent to the external circuit, i.e.
It is sent to the reception (TR) switch 34 and is sent to the antenna 3.
6 as electromagnetic radiation.

A block diagram of a transponder associated with the system of FIG. 1 is shown in FIG. The transponder receives signal S1 at antenna 38 and sends this signal to a series of delay elements 40 with indicated delay times To and ΔT. After each successive delay, a portion of the signal Io, I1, T2...IN is taken out,
It is sent to addition element 42. The resulting signal
S2 (which is the sum of intermediate signals Io,...IN) is
It is fed back to antenna 38 and transmitted to antenna 36 of the system of FIG.

The response signal S2 of the transponder is sent to the antenna 3.
6 and the circulatory system i.e. TR switch 3
4 and is sent to the reception amplifier 44. The output S4 of the amplifier 44 is heterodyne coupled with the signal S3 intermittently provided by the switch 26 in the mixer 30.

The output S5 of mixer 30 contains the sum and difference frequencies of signals S3 and S4. This output is sent to a bandpass filter 46 with a passband of 1 to 3KHz. The output of this filter is sent to a sample and hold circuit 50 via an anti-aliasing filter 48.

A sample and hold circuit 50 sends each sample to an analog-to-digital (A/D) converter 52. The A/D converter then provides the digital values of the samples to processor 54, which analyzes the frequencies contained in the signal by Fourier transformation. The sample-and-hold device 50 and the A/D converter 52 are strobed by a sampling signal that serves to compensate for non-linearities in the momentary increasing frequency of the VCO output signal with respect to time.

To effect this compensation, the signal at the frequency generated by VCO 22 is passed through an isolation amplifier 56 to a delay element 58 which provides a constant signal delay Ts. Both the delayed and undelayed signals are sent to mixer 60, which mixes the signal containing the sum and difference frequencies.
Generate S7. This signal S7 is sent to a low pass filter 62 which passes only the portion of this signal that contains the difference frequency. The output of the low pass filter is sent to a zero crossing detector 64,
This detector generates a pulse at each positive (or negative) going zero crossing. These pulses are used to strobe sample and hold device 50 and A/D converter 52.

3 to 5 are for explaining the operation of the circuit shown in FIG. 1. Figure 3 shows the 100KHz output of the clock 32, and Figure 4 shows the output of the clock 32.
It shows the frequency sweep of the signal generated by VCO 22. In FIG. 5, the frequency of the transmitted signal S1 is shown by a solid line 66, and the frequency of the signal S2 received from the transponder is shown by a dotted line 68. As is clear from this figure, the signal 68 is
It is received during the interval between transmissions of signal 66. These intervals are selected to be approximately equal to the round trip delay time between sending the signal to the transponder and receiving the transponder's response. As indicated by the multiple dotted lines, the transponder response varies with different delay times (To,
To+ΔT, To+2ΔT, .

FIGS. 6 and 7 illustrate an embodiment of a passive transponder implementing the block diagram of FIG. This transponder converts the received signal S1 into a sound wave, and then reconverts this sound wave energy into an electrical signal S2 and transmits it to the die ball antenna 7.
It operates to transmit from 0. More specifically, the signal transducing element of the transponder consists of a substrate 72 of piezoelectric material, such as a niobic acid (LiNbO ₃ ) crystal.
Contains. A layer of metal, such as aluminum, is disposed on the surface of this substrate, forming a pattern as shown in detail in FIG. For example, this pattern includes two bus bars 74 and 76 connected to dipole antenna 70.
and a “launch (radiation)” transducer 78.
It consists of a plurality of "tap" transducers 80. Thus, busbars 74 and 76 provide a travel path 82 for surface sound waves generated by the launch transducers and propagating in a substantially straight line to reach each tap transducer in turn.
Define. The tap transducer converts the surface sound waves back into electrical energy, which is collected by busbars 74 and 76 and thus summed. This electrical energy then activates the dipole antenna 70,
It is converted into electromagnetic radiation and transmitted as signal S2.

Tap transducers 80 are equally spaced along a surface acoustic wave path 82 as shown in FIG. 6, and by providing a selected number of "delay pads" 84 between the tap transducers, An information code associated with the transponder is provided. These delay pads, shown in detail in FIG. 7, are preferably formed of the same material and disposed with bus bars 74, 76 and transducers 78, 80. Each delay pad is sufficient to retard the propagation of surface sound waves from one tap transducer 80 to the next by 1/4 cycle, or 90°, relative to undelayed sound waves at the operating frequency (approximately 915 MHz). It has a wide width. By providing locations for three delay pads between successive tap transducers, the phase φ of the surface sound waves received by the tap transducers can be reduced to
It can be controlled to give different types of phases.

1 When no pad is installed between successive tap transducers: -90° 2 When one pad is installed between successive tap transducers: 0° 3 When two pads are installed between successive tap transducers : +90°4 When three pads are installed between successive tap transducers: +180° To explain Figure 2, the phase information φo (for the first tap transducer in a line) (the phase of the signal picked up by the tap transducer) and φ1, φ2, ...φN (the phase of the signal picked up by the successive tap transducers)
is sent to a synthesizer (adder), which
The embodiment shown in FIG. 6 consists of bus bars 74 and 76. This phase information transmitted by antenna 70 as signal S2 contains the information code of the transponder.

Systems of the type described above operate satisfactorily when the number of tap transducers is eight or less, but as the number of tap transducers increases, the signal-to-noise ratio of the transponder response signal decreases significantly. This is because the tap transducer acts both as a launch transducer and as a partial reflector of the surface acoustic waves, resulting in a corresponding increase in spurious signals in the transponder response when increasing the number of tap transducers. This is to do so. This constraint on the number of tap transducers also imposes a constraint on the length of the information code provided in the transponder response.

The present invention provides a means to reduce spurious signals and insertion losses in passive transponders so that the size of the information code can be increased to the desired length. This effect is achieved by providing one or more surface acoustic wave reflectors in the surface acoustic wave path on the piezoelectric substrate to reflect the surface acoustic waves back toward the transducer for reconversion into electrical signals. be done.

FIG. 8 illustrates the general concept of the invention in which transducer 86 is used in a unique configuration with reflectors 88 and 90 in place of the arrangement of FIG. 6 having launch transducer 78 and tap transducer 80. . In particular, transducer 8
6 is configured to convert electrical energy received at terminals 92 and 94 into surface acoustic wave energy that propagates outward in both directions as indicated by arrows 96 and 98. The launch transducer is a well-known device in which individual electrode fingers are arranged between and connected to two busbars 100 and 102 to form an interdigital (comb-like) electrode assembly. It consists of a method. In the illustrated pattern, half of the fingers are connected to busbar 100 and the other half are connected to busbar 102. Each electrode is connected to one or the other busbar and extends toward the free end in the direction of the other busbar.

It will be apparent that the size of the transducer can be expanded arbitrarily by simply adding electrode fingers in the same pattern shown. The size of the transducer is therefore determined by the number of fingers arranged in parallel.

Also, according to well-known and conventional practice, the distance between successive fingers is 3λ/4. However, λ
is the center wavelength of the surface acoustic wave. This distance 3λ/
4 is measured between the centers of the individual electrodes. Furthermore, as can be seen, the length of the active area between the end of the electrode connected to busbar 100 and the end of the electrode connected to busbar 102 is Kλ. However, K
is a proportionality constant.

Surface acoustic waves traveling outward from transducer 86 in directions 96 and 98 are reflected by reflectors 88 and 90.
is encountered and reflected by these reflectors. These reflectors are connected to busbars 104 and 1 on both sides.
consists of individual electrode fingers extending between 06 and 06. As shown in FIG. 8, these electrodes are separated by a distance of λ/2 from center to center.

Reflectors 88 and 90 direct nearly 100% of the surface acoustic wave energy toward transducer 86.
That is, they serve to reflect in directions 108 and 110, respectively. Thus, after a pulse of surface acoustic energy is generated by transducer 86, this pulse is reflected by reflectors 88 and 90 and reconverted by transducer 86 into an electrical signal.

The arrangement of FIG. 8 includes one or more delay pads 11.
2, these pads control the phase of the surface acoustic waves received by transducer 86. In the case of a 90° phase delay (compared to the phase of the received surface sound wave without the delay pad present), the width of the delay pad is 1 of the width of the delay pad for the transponder configuration shown in Figures 6 and 7. Must be /2. This is because the surface acoustic wave traverses the delay pad twice (ie, in both directions).

FIG. 9 shows an entire transponder system using the concept shown in FIG. In FIG. 9, a plurality of transducers 114 are
It is connected to a common busbar 116 and 118, which in turn is connected to a dipole antenna (not shown) of the transponder. On either side of the arrangement are reflectors 120 and 122 that reflect the surface acoustic waves emitted by the transducer towards the transducer.

The transducers 114 are connected in parallel so that the high frequency interrogation pulse is received by all transducers simultaneously. These transducers therefore simultaneously generate surface sound waves that are transmitted outwardly in both directions.
With the particular configuration illustrated, the reflected surface acoustic waves are received at staggered intervals, with one interrogation pulse generating a series of response pulses after each delay time. FIG. 9 shows the time order of the reflected signals as 1, 2, 3, . . . 18, 19, and 20.

FIG. 10 shows a passive transponder with a transducer and reflector according to another preferred embodiment of the invention. In this case, four transducers 124 are electrically connected in series between bus bars 126. These transducers are interconnected by intermediate electrodes 128, and electrical circuit connections through each transducer are made by capacitive coupling. These transducers, when energized by an RF electrical signal, generate surface acoustic waves traveling in four parallel paths 130 simultaneously.

To the right of transducer 124 in FIG. 10 are four sets of reflectors 132, 134, 1
36 and 138 are arranged in the traveling path 130 of the surface acoustic waves. In the example shown, there are three reflectors 140 in each set, but the number of reflectors can vary. Position 132, 134, 13
If only one reflector is provided at each of 6 and 138, this reflector must be designed to reflect approximately 100% of the surface acoustic waves at the wavelength of the surface acoustic waves. If two or more reflectors are provided, these reflectors may be designed to reflect only a portion of the surface acoustic waves.

In the embodiment of FIG. 10, for example, each set has 3
If two reflectors are provided, the first and second
The reflectors must be able to send some sound wave energy through underneath them to the third and final reflector placed in line. In this way, when a pulse of surface acoustic energy is generated by transducer 124, some of it is reflected by the first transducer, some of it is reflected by the second reflector, and some of it is reflected by the second reflector;
A further portion is then reflected by a third reflector arranged in line.

If each reflector is designed to reflect only, say, 10% of the energy it receives, the first and second
and from the third reflector to the transducer 124
About 10%, 8.1% and 6.5% of the energy is returned to the

The first reflector receives 10% of the 100% energy received.
90% of the received energy reaches the second reflector, which reflects 10% of the received 90% energy, or 9%, back toward the transducer 124, but this 9% Of this, 8.1% passes through the first reflector. This is because the first reflector reflects back 10% of the energy received from the second reflector, or 0.9% of the total. The third reflector is the first incoming energy
It receives 81% and reflects 10% of it, or 8.1%.
The second and first reflectors each reflect 10% of the energy from the third reflector, resulting in 6.5% passing through the first reflector and transducer 12.
Head to 4. 72.9% passes through the third reflector, and any subsequent reflectors in this line will cause similar reflections.

The reflectance of each reflector can be adjusted by selecting the number of interdigitated pairs. Each pair of fingers reflects approximately 1 to 2 percent of the incoming surface sound wave energy.

FIG. 11 shows yet another preferred embodiment in which the transducers are placed between common busbars 140 and 142. These transducers 144 (designated "T" in FIG. 11)
generates surface sound waves in both directions indicated by arrows 146. These sound waves are reflected by reflector 148 (11th
(indicated by "R" in the figure) and is reflected back towards the transducer in the direction indicated by arrow 150. As shown in FIG. 11, the distances between transducer 144 and reflector 148 are staggered such that one interrogation pulse produces successive response pulses.

FIG. 12 shows a number of transducers 152 electrically connected in series and a number of reflectors 15.
4 shows yet another preferred embodiment of the invention, in which 4 are electrically connected in series. The transducers and reflectors are "tuned" to operate at different surface sound wave wavelengths such that a particular one of the transducers generates surface sound waves based on the particular frequency applied to terminal electrodes 156 and 160.
This surface acoustic wave travels to the right (in the direction of FIG. 12) and is reflected back by each reflector 154 tuned to the same wavelength as the corresponding transducer.

FIG. 13 shows the various frequency bands of the interrogation signal required for the transponder embodiment shown in FIG. As shown, there are five frequency bands 162, one for each of the five transducers 152 and corresponding reflectors 154.

In the embodiment of FIG. 12, transducer 15
The information code of the transponder is provided by providing a selected number of delay pads 164 between the transponder 2 and the reflector 154. These retardation pads change the phase of the surface acoustic waves that propagate toward reflector 154 and are returned to transducer 152.

FIG. 14 shows a further embodiment of a transponder according to the invention with separate launch and receive transducers. As can be seen, surface acoustic waves are generated by launch transducer 166 and propagate in the direction indicated by arrow 168. These surface sound waves pass under the receiving transducer 170 and follow the arrow 17
4 toward one or more reflectors 172. This sonic energy is reflected by reflector 172 and directed toward receiving transducer 170 in the direction indicated by arrow 176.

In the embodiment shown in FIG. 14, the launch and receive transducers can be connected to separate antennas. This is advantageous in some applications because separate antennas can receive and radiate energy in different directions.

As is clear from the above, the present invention does not use reflectors with nearly 100% reflection, but rather arranges a plurality of reflectors in a common line to reduce the amount of reflection for each reflector. The advantage of this configuration is that the area of the surface acoustic wave chip can be reduced, resulting in a compact transponder structure.

There has been shown and described a novel surface acoustic wave passive transponder having acoustic reflectors and achieving all objectives and advantages. However, many changes, modifications, and other uses may occur in light of the foregoing description and accompanying drawings disclosing preferred embodiments of the invention.
and applications will be apparent to those skilled in the art. All such changes, modifications, other uses, and applications that do not depart from the spirit and scope of the invention are intended to be covered by the claims.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a system for transmitting an interrogation signal, receiving a response signal, and decoding information encoded in the response signal. FIG. 2 is a block diagram of a passive transponder used in the system of FIG. , FIG. 3 is a timing diagram showing the clock output of the system of FIG. 1, FIG. 4 is a frequency versus time diagram showing the transmitted signal of the system of FIG.
6 is an enlarged top view of a particular embodiment of the transponder of FIG. 2; FIG. 6 is an enlarged plan view of a portion of the embodiment shown in FIG. 6; FIG. 8 is an enlarged plan view of a transducer and two reflectors of the type used in the invention; FIG. 9 is an enlarged plan view of a portion of the embodiment shown in FIG. Close-up top view of transducer/reflector pattern;
FIG. 10 is an enlarged plan view of a transducer/reflector pattern according to a second preferred embodiment of the present invention; FIG. 11 is an enlarged plan view of a transducer/reflector pattern according to a third preferred embodiment of the present invention; FIG. 12 is an enlarged plan view of a transducer/reflector pattern according to a fourth preferred embodiment of the present invention; FIG. 13 is a frequency diagram showing the frequency bands of each interrogation pulse in the configuration of FIG. 12; FIG. 2 is an enlarged plan view of a transducer/reflector pattern according to a fifth preferred embodiment of the present invention; FIG. 20... Gradient signal generator, 22... Voltage controlled oscillator (VCO), 24... RF amplifier, 26...
Transmission/reception switch, 28...Power amplifier, 30
...Decode mixer, 32...Clock, 34...
...Transmission/reception switch, 36, 38...Antenna, 40...Delay element, 44...Amplifier, 52...
... Analog-digital converter, 54 ... Processor, 56 ... Isolation amplifier, 60
...Mixer, 64...Zero crossing detector, 70...
Antenna, 72... Base, 74, 76... Bus bar, 78... Lunch transducer, 80...
Tap transducer, 82... Travel path, 86
...Transducer, 88,90...Reflector,
100, 102... Bus bar, 112... Delay pad, 116, 118... Common bus bar, 12
0,122...Reflector.

Claims (1)

[Claims] 1. In a passive transponder used in an interrogation system for transmitting a response signal containing coded information in response to reception of an interrogation signal, the substrate surface forms a plurality of travel paths for surface acoustic waves. a substrate having: a transducer means disposed on the surface of said substrate for converting between surface acoustic wave energy propagating along these paths and electrical energy; and transducer means for directing the surface acoustic wave energy back toward said transducer means. a plurality of acoustic wave reflectors disposed on the substrate surface along the travel path for reflecting the acoustic waves; circuit means for receiving a response signal from the transducer means, the travel path extending in at least one direction from the transducer means along at least one common line, and at least one of the reflectors proximate the transducer means. and reflects only a portion of the received sonic energy, while another portion of the sonic energy passes under one of the reflectors and reaches the next reflector along the common line. A passive transponder characterized by: