EP0040559A1 - Piezoelektrische Konvolutionseinrichtung mit elastischen Wellen - Google Patents

Piezoelektrische Konvolutionseinrichtung mit elastischen Wellen Download PDF

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Publication number
EP0040559A1
EP0040559A1 EP81400686A EP81400686A EP0040559A1 EP 0040559 A1 EP0040559 A1 EP 0040559A1 EP 81400686 A EP81400686 A EP 81400686A EP 81400686 A EP81400686 A EP 81400686A EP 0040559 A1 EP0040559 A1 EP 0040559A1
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EP
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Prior art keywords
guide
substrate
convolver
convolving
convoluting
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Granted
Application number
EP81400686A
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English (en)
French (fr)
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EP0040559B1 (de
Inventor
Hervé Gautier
Charles Maerfeld
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Thales SA
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Thomson CSF SA
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    • G—PHYSICS
    • G06—COMPUTING; CALCULATING OR COUNTING
    • G06G—ANALOGUE COMPUTERS
    • G06G7/00—Devices in which the computing operation is performed by varying electric or magnetic quantities
    • G06G7/12—Arrangements for performing computing operations, e.g. operational amplifiers
    • G06G7/19—Arrangements for performing computing operations, e.g. operational amplifiers for forming integrals of products, e.g. Fourier integrals, Laplace integrals, correlation integrals; for analysis or synthesis of functions using orthogonal functions
    • G06G7/195—Arrangements for performing computing operations, e.g. operational amplifiers for forming integrals of products, e.g. Fourier integrals, Laplace integrals, correlation integrals; for analysis or synthesis of functions using orthogonal functions using electro- acoustic elements

Definitions

  • the invention relates to convolvers using the propagation of acoustic waves in piezoelectric solids. Given two incident electrical signals of duration T and carrier frequency f, counterprogressive elastic waves which propagate in a region of the surface of the support where they interact non-linearly are excited at the ends of a support made of piezoelectric material. generate a double frequency electric field. This electric field is collected by an integrating electrode covering the interaction region and this collecting electrode provides an electric signal whose modulation represents the convolution function of the two incident electric signals. When the modulation function of one of the two incident signals has undergone a time inversion before being applied to one of the inputs of the convolver device, the emerging signal represents a correlation function.
  • the invention applies more particularly to convolvers capable of analogically processing signals characterized by a high f.T product.
  • the guide convolvers produced so far have a response which tends to deviate from the mathematical expression of the convolution integral. Indeed, when the length L of the collecting electrode becomes large with respect to the electromagnetic wavelength, which corresponds to a product fT of high value, it is necessary to take account of the electromagnetic losses which create disturbances at the level of interaction. The signal from the interaction is no longer spatially uniform. As the electric charges are no longer induced in phase, they do not add up in an equiphase manner in the interaction region. In addition, the resistance of the collecting electrode eventually becomes appreciable with respect to the output impedance of the convolutor, which leads to a deterioration of the response. It should also be mentioned that disturbances at the interaction level also appear, even if the length L of the collecting electrode is small compared to the electromagnetic wavelength, when the resistance-capacitance product of the guide is not small enough before period 1 / f.
  • the invention aims to collect the convolution signal by samples taken step by step along the interaction region of the counterprogressive elastic waves, without these samples being able to disturb by their presence the propagation of acoustic waves.
  • the interval between two successive samples is chosen so that the difference in uniformity of the interaction remains small when the samples are brought back to the outlet of the convolutor.
  • FIG. 1 represents the diagram of a convoluting device of known type.
  • a support made of piezoelectric material 10 are arranged at the two ends two transducers 11 and 12 in the form of interdigitated combs forming the two inputs e and e 2 of the convolutor.
  • the two signals for which the convolution function is to be obtained are modulated around a central carrier frequency f equal to several tens of megaherts. These two signals are sent to the inputs e, and e 2 so as to generate two counterprogressive elastic waves propagating in two directions opposite to the surface of the support 10 with more or less penetration depending on the type of waves generated.
  • the support 10 acts not only as a propagating medium but also as a non-linear medium where there is a non-linear interaction of the two waves which creates a signal of double carrier frequency.
  • This signal is nominally spatially uniform over the area of interaction and is detectable by means of a uniform electrode 15 placed on the interaction zone.
  • This electrode 15 forms a capacitor with a counter electrode consisting for example of two side plates 16 connected to each other by a connection 17 to the electrical ground.
  • the plate 15 thus collects the electric charges induced by the non-linear interaction of the two waves and provides at its output s a signal C (t) at the frequency 2f.
  • the two contraprogressive waves emitted are of the form: where x is the axis of propagation of the waves at speed v, w the pulsation 2 ⁇ f and k the number of waves w / v.
  • the modulation of the signal C (t) represents the convolution function of the signals F (t) and G (t) compressed in time by a ratio 2, and over a time interval corresponding to the duration during which the two signals interact over the entire length L of the plate 15.
  • These devices are capable of processing signals of several tens of Megahertz of bandwidth B and of a few tens of microseconds of duration T. They are of great interest by their great simplicity of implementation, their high processing speed, their volume and their very low consumption.
  • the waves must be guided in this width W and the plate 15 is simply used, the guidance being obtained by the effect of slowing down of the waves caused by the short-circuit of the acoustic field at the surface.
  • the device of FIG. 1 can be produced as follows.
  • the frequency f is equal to 156 MHz and the duration T to 12 s.
  • the beam compressors are produced by couplers with conductive bands.
  • the electrodes 15 and 16 constitute a portion of the electromagnetic transmission line in which the propagation speed of the electromagnetic waves v EM is low because of the high value of the permittivity of the substrate. Effects of propagation losses appear when the length L of the output plate is greater than about 0.1 of electromagnetic wavelength ⁇ EM equal to v EM / 2f. These effects introduce on the one hand phase shifts between the sources of the charges and the points of contact and on the other hand reflections at the points of discontinuity electric.
  • the condition L / ⁇ EM > 0.1 corresponds to: going is the speed of the acoustic waves.
  • the device described has a central frequency equal to 156 MHz for a band of 50 MHz.
  • the signal obtained at the output s is:
  • the factor M ( T ) a function of T , is due to the non-uniformity of the interaction and the signal H (t) no longer represents the convolution function of the two signals F (t) and G (t) .
  • the convolver device according to the invention illustrated in FIG. 2 comprises an output electrode 15 provided with several contacts distributed over its entire length along the axis of propagation of the acoustic waves and connected together to form the output s of the convolutor, the maximum interval between the contacts being chosen to obtain a low error of uniformity of the interaction.
  • the transmission line 20 comprises n equidistant sockets 21 connected at a common point by wires 22 introducing a negligible phase shift.
  • FIG. 4 represents the variations of I cc / I in amplitude, solid line, and in phase, dotted line, in the case where the half-distance between taps is equal to 0.075 ⁇ EM and for 3 values of the attenuation a by ⁇ EM in Neper.
  • the resistance R is given by if r is the plate resistivity and the capacitance C depends on the distance between the positive and negative electrodes and it can be adjusted.
  • the loss a is known and the maximum spacing between taps can be determined to obtain the required uniformity error.
  • the maximum distance between taps is of the order of 0.1 ⁇ a to 0.2 ⁇ a for a phase error and of limited amplitude respectively at 10 ° and 1 dB.
  • the contacts on the outlet plate must be made so as not to disturb the propagation of the acoustic waves. Given the high operating frequencies, the dimensions are very small, the plate being able to measure a few tens of microns in width, and several production techniques can be used.
  • the contacts are made by soldering or by direct bonding of a conductive wire 40 on the outlet plate 41 placed on the surface of the substrate 45.
  • the dimensions of the welding point 42 or the adhesive point 43 do not exceed one tenth of the acoustic wavelength.
  • welding is carried out either by thermocompression or by ultrasound. As for bonding, it is obtained cold using either indium or electrically conductive epoxy resin.
  • the contacts can be made by welding or gluing next to the plate so that you can increase the size of the welding point or the glue point. For this, the contacts are made at a distance from the plate such that the energy of the acoustic waves is practically zero, this distance being of the order of a few wavelengths.
  • connection blocks 52 are arranged along the plate 55 on the surface of the substrate. They are electrically connected to the plate by conductive strips 50 whose width is less than lal5 to disturb the propagation of the acoustic waves as little as possible, their length being equal to Z chosen to sufficiently distance the blocks from the plate. These bands are connected to the blocks by wider bands 51 making it possible to reduce the electrical resistance. Referring to Figure 7, the ground electrodes 54 are notched to receive the blocks 52, this discontinuity does not affect the uniformity of the interaction. These electrodes can also be distant enough from the plate to remain uniform if the width of the substrate allows it. These electrodes can also be placed on the lower surface of the substrate. The spots of solder or glue 53 made on the pavers can be produced using all the conventional techniques since there are no longer any dimensional constraints.
  • each metal strip 51 and each block 52 are placed on a thin layer of an electrically insulating material 60 such as resin or Si 0 2, thus significantly reducing the coupling between the substrate and the parts metallic.
  • an electrically insulating material 60 such as resin or Si 0 2
  • FIG. 9 shows another technique making it possible to suppress coupling by the conductive strips of connections 50.
  • Each strip is metallized on a material which is then eliminated so as to leave an air gap 70 between substrate and the strip. Note that this technique is known in particular for the production of an acoustic filter.
  • the guide 55, the strips 50 and 51 and the blocks 52 are for example metallized by deposition, by evaporation or spraying using a mask produced by photolithography.
  • Another embodiment consists in placing an electrode in the form of a plate opposite the guide and similar to the latter. The connections to the output circuit are made on this electrode.
  • FIG 10 shows in section an embodiment by capacitive coupling.
  • a first substrate 85 has on its surface the devices for generating the acoustic waves and the guide 80; it can also include the ground electrodes 82.
  • a second substrate 86 is applied to the surface of the first substrate 85.
  • the two substrates are preferably made of the same material.
  • the substrate 86 has a recess 83 provided with the output electrode 81 placed opposite the guide 80 and at a predetermined distance h. This distance h is chosen so as to capacitively couple the electrode to the guide without reducing the efficiency of the convolver. For this, the capacitance C brought back must be large compared to the capacitance C of the piezoelectric substrate.
  • the value of the capacitance C is of the order of the permittivity P of the substrate, while the value of the capacitance C is equal to where ⁇ o is the permittivity of the air, these values being counted per unit of length along the axis of propagation of the waves.
  • the condition C >> C p is therefore written .
  • the substrate 85 includes the recess such as 83 provided with the acoustic guide 80 while the other substrate is planar.
  • Figures 11 and 12 show two other alternative embodiments for which the guide is not metallized: either it is produced by profiling the substrate to give it a greater thickness opposite the output electrode as shown in Figure 11 at 90, either it is produced by modifying the structure of the substrate opposite the output electrode by an ion implantation as shown in FIG. 12 at 100.
  • the faces of the two piezoelectric substrates 85 and 86 are polished and brought into contact then maintained by gluing or mechanically by pressing, or else by adhesion obtained by optical seal.
  • FIG. 13 shows an embodiment comprising metal studs 110 produced between the metal guide and the outlet electrode.
  • the height of the recess 83 may be notably greater than for the constructions with capacitive coupling and it is therefore less critical.
  • the lateral dimension of each stud is small in front of ⁇ a, approximately 0.1 A; in addition, these studs 110 are distributed along the guide randomly to avoid cumulative effects, the average distance between studs being of the order of 100 ⁇ a .
  • the pads are produced beforehand either on the guide 80 or on the electrode 81, for example by photoengraving, the two substrates then being assembled according to one of the techniques seen above.
  • FIG. 14 An embodiment by profiled guide is shown in FIG. 14.
  • the guide 120 is profiled in thickness transversely to the axis of propagation of the waves to present a central zone 121 and two lateral zones 122.
  • the central zone has a thickness greater than the two lateral zones causing by mechanical loading effect on the substrate 125 a slower propagation speed under this central zone and consequently guiding the waves.
  • the speed in the free zone of the substrate 123 is also greater than that of the lateral zones by the effect of an electric short circuit on the surface of the substrate.
  • the lateral zones 122 are produced so as to present a large electrical conduction.
  • the profiling of the guide is obtained for example by ionic machining. It can also be obtained by adding a conductive or insulating material over a prior metallization.
  • the electrical contacts 124 are made at the outer edges of the lateral zones outside the zone of presence of the acoustic energy.
  • FIG. 15 An embodiment by homogeneous thickness guide is shown in Figure 15 in top view.
  • Guide 130 is uniform in thickness and has a structure transverse to the axis of propagation of the waves leading to, creating a central guiding zone 131 and two lateral zones on which the electrical connections are made.
  • the central zone is continuous while the two lateral zones are discontinuous and produced by cutting the guide into strips (132) perpendicular to its axis.
  • the central zone thus makes a total short-circuit on the surface of the substrate which slows down the waves relative to the lateral zones which make a partial short-circuit.
  • the spacing p between bands (132) is chosen to be less than ⁇ a / 2 to avoid the known effects of "stop band” and thus maintain a large bandwidth B.
  • the guide is for example obtained by photoengraving or photolithography.
  • the electrical contacts are. made at the ends of the bands.
  • the guide has a width W of 30 ⁇ and a length L of 35 mm. It has four equidistant sockets of 1, two of which are located at the ends so that the ratio l / ⁇ EM is close to 0.16, the frequency band being equal to 100 MHz.
  • Figures 16 and 17 schematically represent the convolver and output circuit assembly.
  • FIG. 17 makes it possible to distinguish the detail of the connections at the level of a socket.
  • the metallized studs 146 are connected to the guide 143 and are connected to each other and to the ends of the tracks 142 of the output circuit by gold wires a few millimeters in length 148.
  • the ground electrodes 147 are connected to the parts of the output circuit connected to ground at 149.
  • the arrangement of the tracks 142 makes it possible to connect the four sockets to the output cable 143, of impedance generally equal to 50 ⁇ , by connections of identical lengths, thus making it possible to add the signals from the sockets in phase. Note that this realization is possible because the speed of the electromagnetic waves in the guide is low compared to that of the conventional transmission lines constituted by the tracks 142.
  • the output circuit can also be produced on the acoustic substrate previously metallized and covered with a insulating layer with the lowest permittivity possible.
  • such an embodiment makes it possible to obtain a uniformity of the amplitude response of less than 1 dB and a uniformity of the phase of less than 15 °. With only the two extreme sockets connected, the result is amplitude uniformity to within 5 dB and phase uniformity between 80 and 90 degrees.

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  • Physics & Mathematics (AREA)
  • Mathematical Physics (AREA)
  • Engineering & Computer Science (AREA)
  • Theoretical Computer Science (AREA)
  • Acoustics & Sound (AREA)
  • Software Systems (AREA)
  • Computer Hardware Design (AREA)
  • General Physics & Mathematics (AREA)
  • Surface Acoustic Wave Elements And Circuit Networks Thereof (AREA)
  • Transducers For Ultrasonic Waves (AREA)
EP81400686A 1980-05-20 1981-04-30 Piezoelektrische Konvolutionseinrichtung mit elastischen Wellen Expired EP0040559B1 (de)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
FR8011225 1980-05-20
FR8011225A FR2483143B1 (fr) 1980-05-20 1980-05-20 Dispositif convoluteur piezoelectrique a ondes elastiques

Publications (2)

Publication Number Publication Date
EP0040559A1 true EP0040559A1 (de) 1981-11-25
EP0040559B1 EP0040559B1 (de) 1984-08-08

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EP81400686A Expired EP0040559B1 (de) 1980-05-20 1981-04-30 Piezoelektrische Konvolutionseinrichtung mit elastischen Wellen

Country Status (7)

Country Link
US (1) US4388599A (de)
EP (1) EP0040559B1 (de)
JP (1) JPS5718115A (de)
CA (1) CA1177126A (de)
DE (1) DE3165355D1 (de)
FR (1) FR2483143B1 (de)
NO (1) NO154365C (de)

Families Citing this family (16)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPS58196712A (ja) * 1982-05-12 1983-11-16 Nec Corp エラステイツク・コンボルバ
JPS598075U (ja) * 1982-07-07 1984-01-19 三菱電機株式会社 熱交換器
US4592009A (en) * 1983-11-17 1986-05-27 E-Systems, Inc. MSK surface acoustic wave convolver
US4870376A (en) * 1983-12-15 1989-09-26 Texas Instruments Incorporated Monolithic elastic convolver output circuit
US4584475A (en) * 1984-05-29 1986-04-22 Allied Corporation Surface acoustic wave infrared line imaging array
US4675839A (en) * 1985-04-10 1987-06-23 Allied Corporation Receiver for a spread spectrum communication system having a time-multiplexed convolver
JPS61296807A (ja) * 1985-06-25 1986-12-27 Clarion Co Ltd 弾性表面波装置
GB2197559B (en) * 1986-08-22 1990-03-28 Clarion Co Ltd Bias voltage circuit for a convolver
US4894576A (en) * 1987-04-10 1990-01-16 Clarion Co., Ltd. Surface-acoustic-wave convolver
JP2911893B2 (ja) * 1987-05-15 1999-06-23 クラリオン株式会社 弾性表面波装置
US5440155A (en) * 1987-10-15 1995-08-08 Electronic Decisions Incorporated Acoustic charge transport convolver, method of use and fabrication
JP2520136Y2 (ja) * 1988-02-15 1996-12-11 クラリオン株式会社 弾性表面波装置
JPH02199910A (ja) * 1989-01-27 1990-08-08 Clarion Co Ltd 弾性表面波装置
JPH03162103A (ja) * 1989-11-21 1991-07-12 Fujitsu Ltd 実効線路長が変更されたマイクロストリップライン
US5357225A (en) * 1992-12-23 1994-10-18 Alcatel Network Systems, Inc. Method and apparatus for adjusting the impedance of a microstrip transmission line
DE69525937D1 (de) 1995-06-09 2002-04-25 Canon Kk Akustische Oberflächenwellenanordnung und diese verwendendes Übertragungssystem

Non-Patent Citations (4)

* Cited by examiner, † Cited by third party
Title
ELECTRONICS LETTERS, vol. 8, no. 22, 2 novembre 1972 Hitchin Herts, GB S. LUDVIK et al.:"Nonlinear interaction of acoustic surface waves in epitaxial gallium arsenide", pages 551-552 *
IEEE PROCEEDINGS OF THE ULTRASONICS SYMPOSIUM, Monterey 5-7 novembre 1973 New York, US L.R. ADKINS: "Strip coupled A1N and Si on sapphire convolvers", pages 148-151 *
IEEE PROCEEDINGS OF THE ULTRASONICS SYMPOSIUM,Monterey,5/7-11-1973 New York, US W.R. SHREVE et al.: "Strip coupled acoustic convolvers", pages 145-147 *
PROCEEDINGS OF THE IEEE, mai 1976, vol. 64, no. 5, New York, US G.S. KINO: "Acoustoelectric interactions in acoustic-surface-wave devices", pages 724-748 *

Also Published As

Publication number Publication date
DE3165355D1 (en) 1984-09-13
NO154365B (no) 1986-05-26
US4388599A (en) 1983-06-14
JPS5718115A (en) 1982-01-29
EP0040559B1 (de) 1984-08-08
CA1177126A (en) 1984-10-30
FR2483143B1 (fr) 1988-02-05
NO811707L (no) 1981-11-23
FR2483143A1 (fr) 1981-11-27
JPH031847B2 (de) 1991-01-11
NO154365C (no) 1986-09-03

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