WO2004055661A1

WO2004055661A1 - Device for transmitting/receiving acoustic waves in a plate, and method for making same

Info

Publication number: WO2004055661A1
Application number: PCT/FR2003/003703
Authority: WO
Inventors: Jean-Pierre Nikolovski
Original assignee: Intelligent Vibrations
Priority date: 2002-12-12
Filing date: 2003-12-12
Publication date: 2004-07-01
Also published as: FR2848700B1; FR2848700A1; AU2003300593A1

Abstract

The invention concerns a device for transmitting/receiving acoustic waves comprising a set of piezoelectric sensors PZTO to PZT4 bonded to a plate, said sensors capable of being independently transmitters or receivers of acoustic waves propagated in the plate and said device comprising filtering means adapted to define at least two independent spectral bands, one in the audio domain, the other in the ultrasound domain. Said device is characterized in that a set of at least three sensors among the four sensors PZTO to PZT3 operates in reception mode in the audio and ultrasound bands and enables the device to operate as impact-sensitive or microphonic faceplate, one sensor at least among the four sensors PZTO to PZT3 operates in transmission or reception mode in the ultrasound band while at least one sensor PTZ4 operates in transmission mode simultaneously in the audio band.

Description

"DEVICE FOR TRANSMITTING / RECEIVING ACOUSTIC WAVES IN A PLATE, AND METHODS OF MAKING SUCH DEVICES"

The present invention relates generally to interactive communication devices between a user and a machine.

More specifically, the invention relates to a device for collecting, transmitting and processing acoustic waves transmitted by a user or a sensor to a plate serving as an interface with a machine, said device being endowed with functionalities allowing it to on the one hand, to analyze the propagation times of the acoustic waves in the plate in particular to measure the coordinates x _r , y _r of impacts, on the other hand, to emit or receive an audible sound, in particular the voice, using the plate as a microphone membrane or as a speaker. Thus, being able to locate small impacts made with objects such as fingernails, keys, rings or pens makes it possible to transform the plate into a giant “impactile” surface, the term “impactile” being a neologism created by analogy with the word “ tactile ”and whose meaning throughout this description will be“ who reacts to an impact ”.

WO 96 11378 discloses a device for acquiring coordinates x _r , y _r of the point of a rigid plate from which a source punctually emits wave packets, by analysis of the propagation time of the waves in the plate in two directions x and y of the plate.

Also known from patent EP 1 141 884 A is an acquisition device where two pairs of transducers are associated respectively with each direction x, y, the position of the source in each direction being determined by measuring the time differential. arrival of the wave packets on the two respective pairs of transducers from said direction.

Both acquisition devices are particularly suitable for the selective detection, dlun Lamb acoustic mode- in a plate ^{^"of"} isotropic glass. In particular, the device of patent EP 1 141 884 A proposes a method of collecting the voice of a user mechanically exciting the glass plate. The present invention shows how to further improve this result, by transforming the plate in audio transceiver, half duplex and programmable using one or more sensors glued to the plate as transmitters of acoustic waves in the ambient air which amounts to using the plate as a speaker in a frequency band limited to part of the audible band while simultaneously using other sensors in receiver mode in a different spectral band, in particular in the ultrasonic frequency spectrum, in order to be able to simultaneously detect the position of a possible impact on the plate controlling for example the stopping the current emission in the audible spectrum and the consecutive emission of another audible message. In addition, the devices described in the patents cited above lack flexibility when transforming a glazing into an interactive screen simply because the gains of the receiver amplifiers must be able to be optimized from one device to another and d '' one channel to another depending on the type and quality of bonding of the sensors or the dispersion of the properties of the electronic components used generating a variation in analog noise on each amplification channel. The present invention therefore proposes the following improvement consisting in introducing a range of gains that can be programmed digitally for each of the channels and independently of the other channels, as well as an algorithm for automatically searching for the optimal gain for each detection channel. In addition, since the plate has a certain number of sensors that can be damaged during installation or after several years of use, it may prove necessary to be able to check the condition of the electrical connections and easily identify the faulty connections. For this, the invention shows a method for checking the state of the electrical connections of the sensors consisting in measuring the equivalent capacity of the piezoelectric sensors.

Another object of the present invention is also to improve the electrical bandwidth _: acoustics of the glass plate when it is used as a loudspeaker, in particular to correct the bandwidth of the glass plate at low frequencies and allow it by using a dynamic compression function to emit an acoustic sound of sufficient amplitude and quality allowing to hear correctly, even in urban areas where there is in practice a relatively high ambient acoustic noise.

To achieve these goals, the invention proposes, according to a first aspect, an acoustic wave transmitter-receiver device comprising a set of piezoelectric sensors bonded to a plate, said sensors being able to be independently transmitters or receivers of acoustic waves propagated in the plate. and said device comprising filtering means capable of defining at least two independent spectral bands, one in the audible range, the other in the ultrasonic range, device characterized in that a set of at least three sensors taken among four sensors operates in reception mode in the audible and ultrasonic bands and allows operation of the device in a touch screen, at least one sensor taken from among four sensors operates in transmission or reception mode in the ultrasonic band while at least one sensor operates in transmission mode simultaneously and independently in the audible band.

Advantageously, it constitutes a device for acquiring coordinates of points of interaction of an acoustic source with the surface of the plate, of finite dimensions, comprising a set of acoustic sensors each formed by two piezoelectric transducers located opposite -screw on either side of the plate, or of a transducer in the form of a piezoelectric plate with alternating polarization, bonded to the edge of the plate, the device comprising processing means for determining the coordinates of said interaction point by analyzing the difference in propagation time of the acoustic waves emitted by the source to the various sensors, device characterized in that the processing means comprise, in association with each sensor, a respective electronic circuit comprising in cascade means for performing a wideband pre-amplification with digital gain adjustment on four bits, i.e. 16 gay values ns possible, means for selective amplification centered on a first frequency ^"determined, means for detecting the head of the wave packet and means for switching the transmitter or receiver sensors to automatically determine the distance between the different sensors, from the knowledge of the speed of sound of acoustic waves in the plate, and also carry out an integrity check of the plate by regularly carrying out a new measurement of this distance which is compared with the values measured during the first configuration of the plate . The device also comprises at least one piezoelectric transducer intended for the production of sound in ambient air by using the plate as a coupling surface, said coupling surface playing the role of loudspeaker membrane, the interesting feature being that the mechanical excitation of the plate produced by a small piezoelectric transducer propagates in the plate at a speed 10 times greater than the speed of propagation of the sound in the air which allows to distribute the sound to be transmitted on a surface of large transmission, typically several square meters. The effect produced is then a feeling of uniformity of the sound produced whatever the position of the user in front of the plate, as well as the absence of decrease of the signal when the user moves away from the plate. Such an interface can thus be installed on shop windows, or bus shelters, but also on glazing making up partitions, glass doors, flat or slightly curved windows such as those found in passenger windows. of automobile cars.

Preferred but non-limiting aspects of the device according to the invention are the following:

- The sensors are four in number and consist of an assembly of two piezoelectric transducers of square shape, rectangle, disc, half disc or quarter disc of piezoelectric ceramics bonded on either side of the plate, so that four sensors form the vertices of a rectangle whose center constitutes the origin of the coordinates. A sensor is formed by two half-discs when it is glued to more than three diameters from the corner of a rectangular plate, the edge of the half-disc being collinear and directly above the edge of the plate, while the connections electrics are made in antiparallel. It is formed by two quarter discs when glued to the corner of a plate, the two perpendicular edges of each quarter disc being aligned with those of the corners of the plate. The shape of the transducer piezoelectric is arbitrary when it is intended to mechanically excite the plate so that it transmits in the ambient air an audible sound.

- The sensors are four in number and are in the form of a rectangular piezoelectric plate bonded to the polished edge of the plate, the width of a plate being equal to the thickness of the plate, while the length of a plate is chosen so that the fundamental longitudinal resonance of the wafer along this length is close to 100 kHz, which corresponds in practice to a length of the order of 20 mm. In addition, the wafer is alternately polarized, the plane delimiting the polarization reversal being coplanar with the median plane of the plate, so that the wafers will be particularly well suited to the detection of antisymmetric Lamb waves, in particular in the case of double-glazed type glass plates. In this case, the four sensors are glued to the edges of the plate intended to serve as a user interface, that is to say intended to receive the impacts. These sensors are particularly well suited to glass plates at least 10 mm thick.

- The rectangle whose vertices corresponds to the location of the four sensors is divided into four quadrants, each quadrant being associated with the triplet of sensors closest to the center of the quadrant responsible for detecting the coordinates of an impact in this quadrant, the measurement accuracy being theoretically better than that which would be obtained by other triplets,

- The piezoelectric ceramic discs have a silver back allowing electrical connections to be made on the same face of the disc,

- In the case of sensors bonded to the faces, the electrical connections of the two piezoelectric transducers of each sensor are connected in antiparallel, the polarization vectors being mounted symmetrically with respect to the median plane of the plate so that the symmetrical modes, more are discriminated and the asymmetric modes are slower and preferred,

- The location of an impact point on a plate in one of the four quadrants defined by the pair of bits (g _y , g _x ) consists in measuring the difference in flight times between two sensors, taken from a triplet of sensors , defining a first direction and two sensors, taken from the same triplet of sensors, defining a second direction perpendicular to the first, so that the Cartesian coordinates of the point of impact (x _r , y _r ) on the plate are given by the formula:

•

gv ² At »g (- p ² -ι-v ² At» g (Atxg- Atra)) Atre + ^, Vp ^{2 2} (4 ² - r 'Atxg ² ) (g ² + 4g ² - v ² ÇAtxg- Atγtf ) ² ) Atyt) ² (4 g ² - v ² Atyt ïr = (-) ^r 4 (çr ² ιr ² txg ² ₊ p ² (-4 g + _U ² Atyg ² ))

- Where, p and q are positive numbers representing respectively the abscissa and the ordinate of the position of the sensors relative to the center of the rectangle defined by the sensors, v the speed of the acoustic plate mode detected, that is to say -to say, for an isotropic lens, that of the Lamb mode A ₀ , Δt _xg , (respectively Δt _yg ) the difference in the propagation times of the wave packet generated by the impact, between the sensors of the first pair located in the half-rectangle g _x (respectively of the second pair located in the half-rectangle g _y ),

- The determination of the triplet of sensors associated with a given impact is carried out according to an algorithm seeking the largest difference in flight time available between the sensors in two perpendicular directions,

- The electronic circuits associated with the sensors for the localization of an impact include in cascade a broadband preamplifier stage, an amplifier stage digitally programmable on four bit, a selective amplifier stage adjustable in an ultrasonic band located between 20 kHz and 150 kHz , a square rise stage, a peak detector stage with discharge resistance, an operational amplifier integrator stage with a resistive bridge with high input polarization impedances so that the integrator is saturated at a level opposite to that towards which it would presently saturate with a positive signal, an adaptation stage at a logic level constituting a synchronization signal intended for calculating the position of an impact,

- The electronic circuits associated with the sensors for recording audio sound recovered by the plate bathed in the ambient air and operating in microphone mode include a bypass at the output of the amplifiers with programmable gains towards a high impedance input follower stage, a floor summing amplifier of the selected channels, a high-pass first order filter of cutoff frequency of 30 Hz, a low-pass filter 6 ^ee cutoff frequency order of 5000 Hz, an analog switch to an audio output on connector Jack mono 3 5 mm intended to be connected to the microphone input of a sound card of a PC. The analog switch is in high impedance mode when the plate is operating in speaker mode.

- The electronic circuits associated with the sensor for the production of sound by the plate comprise an amplifier stage, a low pass filter stage of the first order with a cutoff frequency around 2.3 kHz, a low pass stage of the 6 ^th order with a cut-off frequency of 5 kHz, a signal dynamic compression stage with a square root function, a high-voltage output amplifier stage to an RCA-type output connector, a branch to a logic level adapter stage putting the microphone function output switch under high impedance. - At least one of the sensors is capable of being switched into the transmitter of an ultrasonic wave packet detected by the other sensors whose positions are to be determined in order to trigger a plate integrity test, by measuring the difference in propagation time of the wave packet between the different sensors,

- The management of all the steps of measurement, processing and data transfer by a serial communication interface, either to an LCD display, or to an interface for musical instruments (MIDI interface), or to a more powerful computer such a microcomputer via its RS232 or USB port is governed by a microcontroller,

- The device constitutes a peripheral interface with a machine which receives the signals from the processing means and which, depending on the said signals, controls the execution of files contained in the computer by various peripherals of known types connected to the computer such as for example without limitation, a video projector, a video camera, loudspeakers, a modem, an intercom, a printer, or even an automation unit controlling a mechanical action such as closing a protective curtain, l orientation of a camera, control of a process, According to a second aspect, the invention provides a method for developing an acoustic wave transmitter-receiver device with localization functions by measuring the propagation of ultrasound and acoustic transduction in the audible range, characterized in that '' it includes the following stages: - providing a plate of given solid material;

- Arrange on the plate a set of piezoelectric sensors (PZTO to PZT4) bonded to the plate, these sensors being able to emit and / or receive acoustic waves propagated in the plate;

- in association with the sensors, provide a circuit for processing the signals received and / or emitted by the sensor comprising filtering means capable of defining two independent spectral bands, one in the ultrasonic domain and the other in the audible domain, these two bands being delimited between them by a cut-off frequency, and

- choose the frequencies of the ultrasonic band according to the type of solid material of the plate.

In one embodiment, the method includes providing a plastic plate and choosing the ultrasonic band around about 30 kHz.

In another embodiment, the method includes providing a glass or metal plate and choosing the ultrasonic band around about 100 kHz.

According to a third aspect, the invention provides a method for developing an acoustic wave transmitter-receiver device with localization functions by measuring the propagation of ultrasound and acoustic transduction in the audible range, characterized in that '' it includes the following stages:

- provide a plate of given solid material;

- Arrange on the plate a set of piezoelectric sensors glued to the plate, these sensors being able to emit and / or receive acoustic waves propagated in the plate; - provide, in association with the sensors, circuitry for processing the signals received and / or emitted by the sensor, comprising filtering means capable of define two independent spectral bands, one in the ultrasonic domain and the other in the audible domain, these two bands being delimited between them by a cut-off frequency, and

- choose a type of arrangement of the piezoelectric sensors according to the type of solid material of the plate.

In a first embodiment, the method comprises providing a plastic plate and choosing an arrangement of the individual sensors on only one face of the plate.

In a second embodiment, the method comprises providing a glass or metal plate and choosing an arrangement of the individual sensors in pairs on either side of the plate.

Finally, the invention provides a device for transmitting and receiving acoustic waves, characterized in that it comprises a set of piezoelectric sensors bonded to one side of a plastic plate and suitable for at least some of them to detect acoustic waves. ultrasonic propagated in the plate according to the symmetrical mode, in that at least one of said sensors is capable of emitting and / or receiving sound waves in the audible range, and in that it further comprises means of filtering capable of defining at least two independent spectral bands, one in the ultrasonic domain, the other in the audible domain, and means for processing the signals filtered independently in the two bands.

Other aim and advantages aspects of the present invention will appear better on reading the following detailed description of preferred embodiments thereof, given by way of nonlimiting example and made with reference to the appended drawings, in which:

Figure 1 is a schematic view of a rectangular impact plate with loudspeaker function and reduced active surface, giving the location and the coordinates of the sensors in the particular case where these are in the form of a semi-disc and form the vertices of a rectangle. The actual coordinate system, the identification of the four quadrants, the propagation times of the acoustic waves, and the actual coordinates (x _r , y _r ) of an impact on the plate are also given. Figure 2 has a schematic top view in section of a rectangular impact plate giving the location and positioning of four sensors in the shape of a quarter disc glued opposite and intended for the measurement of the coordinates of impacts brought to the plate. Figure 3 includes a schematic top view in section of a rectangular plate made impactable on only a portion of its total surface, the portion also being in the form of a rectangle whose vertices are given by the location and positioning of four sensors in the form of a half disc glued opposite and intended for the measurement of the coordinates of impacts carried to the plate.

Figure 4 is a schematic sectional view from above of the placement and the electrical connections connecting two piezoelectric silver-return transducers, in the form of a quarter disc, mounted vis-à-vis in the square corner of a plate . Figure 5 is a schematic sectional view from above of the placement and electrical connections connecting two piezoelectric transducers with silvering feedback, in the form of a half-disc, mounted vis-à-vis the edge of a plate.

FIG. 6 is a schematic view from above and in section of a rectangular impact plate with reduced active surface, the sensors being alternately polarized ceramics bonded to the polished edges of the plate.

Referring first to Figure 1, there is shown a PLQ plate comprising four sensors PZTO, PZT1, PZT2, PZT3 formed of pairs of piezoelectric transducers. As shown in FIG. 4, the two transducers of each pair are identified by the indices t for the upper face and b for the lower face. They are in the form of a half-disc, indicated by the index s and are fixed vis-à-vis on the two opposite faces of the plate, for example by gluing, to collect the acoustic waves circulating in the plate. The choice of the shape of the transducer is imposed by the reflection of the acoustic waves on the sides of the plate. Indeed, the reflection of an elastic wave, in a solid, at the interface of a free surface results in a superposition of the incident wave and the reflected waves, the reflected waves being able to be of very different nature due of mode conversion phenomenon, which however and despite the conversions produces almost a doubling of the mechanical displacement collected by the ceramic. Thus, a quarter disc will be chosen when the sensors are glued to the square corners of a plate, according to the assembly in FIG. 3, and in the form of a half disc when they are glued away from a corner, in practice more than three sensor diameters. The direction of the electrical polarizations and of the electrical connections are respectively symmetrical with respect to the median plane of the plate and antiparallel so as to discriminate any symmetrical propagation mode and to favor any antisymmetrical propagation mode. The making of the electrical connections is facilitated by a return of silvering RA from one face to the other of the half-discs so as to have the two electrodes on the same face. The four sensors constitute the vertices of a rectangle. An orthogonal coordinate system x, y of origin O is associated with the plate PLQ, the origin O being physically located at the point of intersection of the diagonals of the rectangle defined by the four sensors. The x and y axes intersect the midpoints of the sides of the rectangle defined by the sensors. The PZTO, PZT1, PZT2, PZT3 sensors have the respective coordinates (-ρ, -q) and (p, -q), (-p, q), (p, q). Acoustic waves can be generated by the impact of an object on the plate or by compression waves propagating in the ambient air and mechanically exciting the surface of the plate, such as voice. The plate is an isotropic material, for example glass, which may have undergone a quenching process to increase its impact resistance. When the material is monolithic glass, an impact of the nail plate on the surface of the plate essentially generates two acoustic modes, one corresponding to an elastic deformation of the glass due to the shock wave, asymmetrical with respect to the median plane of the plate, the other corresponding to an elastic strain wave. symmetrical with respect to the median plane of the plate. These modes are respectively Lamb's A0 and S0 modes. The relative proportion of the two modes depends on the frequency, the nature of the impact and the materials colliding. In the case ^" of an impact carried by a fingernail, for example that of the index finger, struck flat on a plate, which will be described by the term flick, the A0 mode is generated predominantly by compared to S0 mode in a glass plate monolithic. The use of a pair of transducers glued vis-à-vis on both sides of the plate and electrically connected in antiparallel allows to selectively detect the asymmetric mode A0, slower to propagate in the plate than the symmetrical mode S0 . The plate may be made of a material other than glass. This can be a sheet of aluminum or steel or made of a metal alloy. The plate can also be made of plastic, for example plycarbonate or polymethyl methacrylate. In the case of plastics, the relative proportion of the modes generated by the flicker changes in favor of the S0 mode. In addition, while the acoustic propagation speeds are comparable between glass and a metal such as aluminum, it is quite different for plastics which have acoustic propagation speeds two to four times lower and a much more acoustic attenuation. big. In the case of plastics, such as polycarbonate, it is preferable to detect the fast mode S0 rather than the slow mode A0. For this, it suffices to stick the transducers only on one side of the plate without vis-à-vis on the other side. The plate also comprises a fifth PZT4a sensor, appearing in FIG. 1 in the form of a piezoelectric disc with silver feedback, but which can be of any shape, its function being to mechanically excite the plate only in the spectral band audible used in telephony, typically 300 Hz-3300 Hz, so that it becomes a giant loudspeaker, without interfering with the functioning of the plate as an impactile panel. The fifth PZT4a sensor can also be in the form of two piezoelectric transducers mounted facing each other according to FIGS. 4 or 5, the advantage being to increase the transverse excitation power of the plate. The useful impact surface is located inside the rectangle defined by the location of the four sensors. This rectangle can cover only a portion of the total surface of the plate. In the case of shop windows whose total surface easily exceeds ten square meters, the ^" impactile ^" surface may be limited to the surface that a user can reach in a standing position, that is to say a little more than two meters in height . The sensors should preferably be hidden and protected from humidity and attack. We realize that using metal profiles with glazing beads and silicone seals incorporating the sensors. The dormant sections and the glazing beads may be made of an electrically conductive material such as aluminum. The sandwiching of the sensors constitutes a Faraday cage, that is to say an electromagnetic shielding, protecting the input amplifiers from certain untimely capacitive couplings with other devices such as plasma screens, LCD or other electronic or electrical devices.

The aim of the present invention is thus to show how these three functionalities, that is to say impactile panel, microphone and loudspeaker coexist and make it possible to transform the plate into a consumer communication terminal.

For this, if we stick to the signal processing described in French patent 98/16229 reporting a broadband amplification followed by a square rise followed by a peak detection then an integration , it appears that this process lacks flexibility in adjusting the gains of the amplifiers. Indeed, there is a certain dispersion on the values of the electrical components used, as well as on the quality of the bonding so that the optimal gain can vary from one channel to another and from one device to another.

To overcome this drawback, the present invention proposes a modification of the broadband amplifier stage by replacing the broadband amplifier with fixed gain by a programmable gain amplifier. Each of the four sensors is thus connected to a programmable gain amplifier, the gain value being defined by four bits allowing 16 possible gain values. The gain of the programmable amplifiers is then determined experimentally by an automated gain search procedure consisting, for each channel, from the maximum gain and decreasing it in successive stages until the background noise of the channel in the absence of any interactivity on the glass is sufficiently low to no longer inadvertently trigger the switching of the synchronization and adaptation transistors at a logic level.

The determination of the coordinates of an impact according to the assembly of FIG. 1, in fact only requires three sensors taken from PZTO, PZT1, PZT2, PZT3. Several configurations with 3 sensors forming a right triangle can be extracted from the 4-sensor configuration in Figure 1. The four configurations described below lead to identical mathematical solutions, except for the sign, for the coordinates of an impact (xr, yr). In addition, each of these configurations is better suited than the others, from the point of view of the accuracy of the measurement, if it is used only on a given quadrant of the active surface. A quadrant corresponds to a quarter of the active surface and represents the intersection of one of the two half-planes of positive or negative x coordinates with one of the two half-planes of positive or negative y coordinates.

Thus, for a given impact, the quadrant to which it belongs is first determined, then the coordinates (xr, yr) are calculated according to the formula associated with this quadrant.

The Cartesian coordinates of the sensors PZTO, PZT1, PZT2, PZT3 are respectively (-p, -q), (p, -q), (-p, + q), (+ p, + q). Acoustic waves travel at the speed v of the mode detected by the sensors (i.e. antisymmetric or symmetrical). The propagation times to the sensors of a wave packet generated by an impact at (xr, yr) are respectively tOO, tlO, tOl, tl 1.

The coordinates (xr, yr) are obtained by solving a system of equations, valid for a given quadrant. The four systems of equations are

(gy, gx). = (0.0). xr <0 and yr <0

(gy, gx). = (0.1). xr <0 and yr> 0

(gy, gx). = (1.0). xr> 0 and yr <0

(gy, gx). = (U). xr> 0 and yr> 0

The following formulas give the position of the impact (xr, yr). It suffices to replace gx and gy by the value 1 or 0 corresponding to the quadrant concerned.

Atxg (qp ² v ² <4 p ² -ir ² Atxg ² ) (* P ² ^ q ² - u ² (Atxg - At _ra ) ² ) Atyg ² (4 g ² - v ² Atyg ² ) “p ² ^ Atyg ² (-4 g ² ... v ² Atyg (-Atxg tc = (-l) ^ÏJt - p tïg (β ² v ² Atxg ² + p ² (-4 g? Ti ^ tra ² ))

_ _r _ _{1) S!} . gv ² Atxg (-4 p ² + ^ Atxg (Atxg - Atyg)) Atyg p ² ^ (4 ² - ² Atxg ² ) (4 g ² + 49 - Γ ² (Atxg - Atyg) ² ) Atyg ² (4 çr ² - v ² tyt

4 (g ² V ² Atxg ² + p ² (-4 q ² + V ² Atyg ² ))

The method for determining the coordinates of an impact on a plate described above makes it possible to transform a shop window or any other plate into glass or plastic or metal into an impactile surface. The source of impact can be a flick, that is to say an impact made with the dish of the nail on the glass plate. The characteristic of the impact is to create acoustic waves in a relatively wide spectral range and at an electronically exploitable level up to frequencies above 150 kHz. The detection of the ultrasonic spectral components makes it possible to properly measure the differences in propagation time between the different sensors. When using a glass or metal plate, the ultrasonic frequency useful for localizing the impact to the nearest centimeter is between 80 KHz and 120 kHz. In the case of plastic such as polycarbonate the useful ultrasonic frequency is between 20 kHz and 50 KHz. For this, the wave packet generated by an impact must be converted into an electrical signal for each of the PZTO to PZT3 sensors. Each of the four sensors PZTO to PZT3 is thus associated with an electronic processing channel responsible for extracting the high-frequency components from the wave packet generated by the impact. This is achieved by subjecting the electrical signal to various processing operations including connection to a switching block defining the input or output mode of the channel, followed for the input mode of a broadband amplifier stage with programmable gain, followed by an amplifier stage selective around a frequency 100 kHz for glass or metal and 30 kHz for polycarbonate and other plastics, a square rise stage, a peak detector stage with slow discharge resistance, an active integrator at output level saturated positively in the absence of signal thanks to a bridge of polarization resistors of values at least 10 times higher than the output impedance of the step-up squared, finally of a stage of adaptation to a logic level . The result of this treatment is that an impact on the plate generates a packet of waves which one will convert at the time of its reception into a single logical transition for all the head of the packet of waves, which will make it possible to accurately measure a difference in time of arrival of the wave packet towards the various sensors.

This treatment thus makes it possible to determine the coordinates of the impact using the above formula. However, it is not sufficient to produce a reliable interface, that is to say which is only triggered when a human action consisting for example of a flick on glass, metal, or plastic is carried out. Indeed, acoustic noise in the 30-150 kHz band can reach the plate via the coupling between the ground and the chassis. To prevent such signals from triggering a position measurement, the device performs a simultaneous analysis of the wave packet on at least one other spectral component, in practice in the vicinity of the upper limit of the audible spectrum, for example 12 KHz. For this, the output of one of the four programmable wideband amplifiers is diverted to a selective filter of the frequency to be controlled, in this case 12 KHz, the said filter being intended in combination with the selective filter at 100 kHz ( for glass), to characterize the impact, i.e. to define a frequency signature, by verifying the simultaneous presence of energy around these two frequencies, in a given proportion characteristic of the impact and therefore to discriminate the signals unwanted in the form of a packet of waves whose spectral content does not simultaneously present the required levels.

We thus obtain a more reliable impact tile. However, this is not enough. Indeed, it is common for electronic devices to fail after a certain number of hours of operation. It is often difficult and expensive to detect the failure. In addition, with the development of complexity systems, it happens that a bad connection or a giddiness is taken for a breakdown.

Another aspect of the present invention is to provide a system for assisting in the identification of faults. The most important fault diagnosis concerns the state of the electrical connections at the sensor levels. Indeed, the installation of an interactive showcase is often carried out during the renewal of a storefront. The sensors are then integrated into the frame and it would be costly to have to completely dismantle a storefront without knowing beforehand whether the fault comes from a break in the electrical contact on one of the sensors. The fault diagnosis on one of the sensors can be carried out using one of the characteristics of piezoelectric ceramics, ie their high dielectric permittivity which gives them a high value of static capacity, typically of several nanoFarads. The control of the state of the connections then consists in measuring the value of this static capacity for each of the four sensors PZTO to PZT4. When the sensors consist of two transducers mounted in parallel or antiparallel, the static capacity measured is the sum of the two capacities of the individual transducers. It is therefore very easy to identify the faulty sensor and if the fault simply concerns one or both transducers constituting the sensor. In practice, the measurement of the capacitance is carried out by measuring the discharge time of the static capacitance brought to a known potential, through a resistor of known value. For this, the switching blocks placed at the inputs of the analog channels are shared at the outputs. The sensors are then brought, for a short time, to a known potential difference. The charging current is limited by a resistance of a few hundred ohms. Once the charge has been completed, the switching blocks are placed under high impedance, and the capacitors discharge slowly through another resistor of the order of 100 kOhms while a timer is started. The timer stops when the voltage across the capacitor drops below a predefined threshold. For a static capacity of ^the OϋF, the discharge time is approximately equal to the product of the discharge resistor by the value of the static capacitance of the piezoelectric transducer, a millisecond. In the event of a break in the electrical connections at the sensors, there is a sharp decrease in discharge time. It will be noted here that the linear capacity of the coaxial cable connecting the sensors to the input amplifiers is only 100 picoFarad per meter. Thus the equivalent capacity of 10 meters of coaxial cable represents only one nanoFarad, barely 1% of the value of the static capacity of a piezoelectric sensor. There can therefore never be any confusion between the static capacity of a sensor and the capacity of the connecting cable.

We thus have a first function to assist in fault diagnosis. A second diagnostic aid function also consists in switching the switching block of one of the four sensors PZTO to PZT3 in output mode and in applying an electrical pulse of the order of 45 V, for a very short time decomposing in 5 μs rise time and 5 μs return to initial state. This has the consequence of generating a packet of acoustic waves in the plate. The three other sensors remaining in receiver mode, a measurement of the propagation time differences of the wave packet emitted by the excited sensor, for example PZT3, and the other sensors is simultaneously launched. Knowing then, the speed of propagation of the acoustic waves in the plate, either v = 3350 m / s for the asymmetric mode A0 in the glass or v = 1500 m / s for the symmetrical mode S0 in the polycarbonate, one obtains directly a measurement the length and width of the rectangle formed by the sensors. Indeed, the moment of excitation of the PZT3 sensor corresponds simultaneously to the moment of arrival of the wave which it generates at its location, so that tπ = 0. If the origin of time is that corresponding to the moment of excitation of the PZT3 transducer, then the length 2p and the width 2q of the rectangle formed by the four sensors are f2p = vxtιol given by the formulas: <>

[2q = vxtoιJ

We thus obtain a second very useful function which consists in installing the plate to measure the length and the width of the rectangle formed by the sensors and to periodically compare this saved value with other measurements made later, for example during a initialization process during each electrical connection of the impact tile or following each impact.

Another aspect of the present invention relates to the possibility of using the same PZTO to PZT3 sensors to transform the plate into a microphonic membrane. This is obtained by once again deriving the outputs of the four broadband programmable amplifiers to follower amplifiers, then to a summing amplifier stage of the signals coming from the follower amplifiers, a high pass filter stage of the first cut-off frequency 30 Hz, a low-pass filter stage of the first order cut-off frequency 2 kHz, a high-order low-pass filter stage, such as a Bessel or Chebyshev filter of order 6, cut-off frequency of 5000Hz, an analog switch of the microphone function, delivering on a load impedance of 560 Ohms. This load resistance arrives at the terminals of a 3.5 mm jack audio connector, which can then be connected to the microphone input of a PC sound card. In addition to the microphone function, the plate can be used as a loudspeaker. This function is provided by the PZT4a sensor. Since the same plate is used as a microphone or speaker, the two functions are mutually exclusive. In addition, one of the functions will take precedence over the other. In the case of this invention, priority is given to the loudspeaker function which, when activated, deactivates the microphone function by placing the analog switch of the microphonic function under high impedance. The loudspeaker function is thus called master, while the microphone function is called slave.

One of the advantages of the present invention resides in the fact that it is possible to ensure that the loudspeaker function does not disturb the impactile panel function. To do this, the PZT4a audio sensor is controlled by electronics with filtering functions. In particular, any audio signal coming from a high fidelity storage medium and in general, any audio source intended to be retransmitted by the glass plate will undergo an ^" electronic processing comprising at least one amplifier stage, one compression stage dynamically consisting of a logarithmic amplification or elevated to the square root of the signal, followed by a filter stage lowpass 6 ^ee order 5000Hz cutoff frequency, followed by a high pass filter stage with 30Hz cutoff frequency, followed by a power amplifier stage for mechanical excitation of the PZT4a audio transducer. Dynamic compression makes it possible to enhance certain sounds of low amplitude which could only be heard well in calm environments where high fidelity listening is possible. This is not the case for shop windows which bathe most of the time in a noisy ambient sound environment. The dynamic compression by the square root function is constructed in such a way that the loudest sounds remain unchanged, while a weak sound will be amplified. For example, a recording for which the loudest sound is 1 Volt peak to peak, but lasts only one second over a total recording length of 30 seconds containing almost only sounds with amplitude 10 mV, will have after dynamic compression, always the same loudest sound of 1 Volt peak to peak, but the sounds of 10 mV will have been amplified to 100 mV. Thus, by making the loudspeaker function independent of the impactile slab function, an impact at a given location on an impactile plate can trigger an action implementing the loudspeaker function while this same loudspeaker function can be stopped. during its execution by an impact on the plate produced at another location on the plate. The impactile slab function will thus have priority and will be called master over the loudspeaker function which will be called slave.

For this, the processes for calculating impact coordinates, as well as characterizing the impact by simultaneously checking the presence of energy in sufficient proportion at the two frequencies 12 KHz and 100 kHz (for glass or metal and 30 KHz for polycarbonate and other plastics), as well as the programmable gain functions, automatic search for optimal gain or fault diagnosis, are controlled by a microcontroller with an arithmetic and logic unit with several input ports - outputs capable of generating interruptions on rising or falling edge, of several timers, of a real time clock, of a system clock, of a watchdog function, of program and data memories, as well as of communication functions of series type or parallel allowing it to exchange commands and data with a master microcomputer.

The microcomputer will itself be equipped with hardware and software means enabling it to execute certain computer files and activate certain peripherals such as and in a non-exhaustive manner, a video projector, an Internet video camera, a modem, a sound card, printer, compact disc player, depending on the position of an impact on a predetermined area of the glass plate.

The microcomputer can itself be connected to the Internet via a service provider possibly using high-speed communication means and depend on a central server, so that a simple glass plate equipped with the invention can be used as a multimedia communication terminal.

Claims

claims

1. Acoustic wave transmitter-receiver device comprising a set of piezoelectric sensors (PZTO to PZT4) bonded to a plate, said sensors being able to be independently transmitters or receivers of acoustic waves propagated in the plate and said device comprising means filter capable of defining at least two independent spectral bands, one in the audible range, the other in the ultrasonic range, device characterized in that a set of at least three sensors taken from among four sensors (PZTO to PZT3 ) operates in reception mode in the audible and ultrasonic bands and allows operation of the device in a touch screen, at least one sensor taken from among four sensors (PZTO to PZT3) operates in transmission or reception mode in the ultrasonic band while at least one sensor (PZT4a) operates in transmission mode simultaneously and independently in the audible band.

2. Device according to claim 1, characterized in that the sensors operating in the ultrasonic band are capable of determining the position of an impact applied to the plate by measuring the difference in propagation time of the acoustic waves between the different sensors, said acoustic waves being generated by the impact of an object such as the nail plate, a key, the tip of a pen, etc.

3. Device according to claim 2 characterized in that the frequencies of the ultrasonic band are chosen according to the material of the plate.

4. Device according to one of claims 2 and 3, characterized in that each sensor is associated with an electronic processing channel comprising a switching block defining the input or output mode of the channel, followed for the input mode of a wideband amplifier with programmable gain, followed by a selective amplifier around a frequency chosen according to the material of the plate, a square rise stage, a peak detector stage with slow discharge resistance, an active integrator with positively saturated output level in the absence of signal, finally an adaptation stage at a logic level and for the output mode, of a stage making it possible to apply to the terminals of the sensors and for a short time, a potential difference with resistors for limiting the charge and discharge current, the discharge time measured being proportional to the product of the resistance of discharge, of known value, by the value of the static capacity of the piezoelectric transducer and serving to measure this value of static capacity of the piezoelectric sensor and therefore to check the good condition of an electrical connection on the sensors.

5. Device according to claim 4, characterized in that the output of at least one programmable broadband amplifier is diverted to a selective filter of a predetermined frequency located in the upper part of the audible band, said filter being intended for combination with the selective filter chosen according to the material of the plate, to characterize an impact by checking the simultaneous presence of energy around these two frequencies, in a given proportion, and therefore to discriminate the nuisance signals appearing in the form of wave packet whose spectral content does not present the required levels simultaneously, of signals resulting from impacts on the glass, the only ones capable of simultaneously producing the required signal level at the two determined frequencies.

6. Device according to claims 2 to 5, characterized in that the gain of the programmable amplifiers is determined by an automated gain search procedure consisting for each channel in decreasing by successive stages the value of the gain until the noise of bottom of the channel in the absence of any interactivity on the plate is sufficiently low to no longer inadvertently trigger the switching of the adaptation transistors at a logic level.

7. Device according to claim 1, characterized in that the sensors operating in the audible band are capable of recording or producing sound in ambient air by coupling with the plate playing the role of microphonic membrane in reception mode or loudspeaker in broadcast mode.

8. Device according to claim 7, characterized in that the audible band intended for recording or producing sound in the ambient air by coupling with the plate is limited by filtering to the band of approximately 30Hz to 5000 Hz.

9. Device according to claim 7, characterized in that the plate is made of a transparent material such as glass or transparent plastics such as polycarbonate or polymethyl methacrylate and constitutes a coupling surface of several square meters.

10. Device according to claims 1 to 9, characterized in that the sensors are located on the periphery of the plate and are protected and hidden by a frame and glazing beads with seals ensuring a seal against splashing water or other liquids.

11. Device according to claims 1 to 10, characterized in that the application of a potential difference to the audio transducer PZT4a intended for the production of sound in the ambient air by the plate, puts under high impedance, and therefore deactivates the receiver audio filter intended for receiving sound by coupling with the plate, so that the loudspeaker function is said to be master, while the microphone function is said to be slave.

12. Device according to claims 1 to 11, characterized in that the production of an audio sound in the ambient air by the plate is possibly interrupted by an impact on the plate, the said impact being validated by exceeding the threshold levels required by the discrimination filters of the upper part of the audible band and of the discrimination of the ultrasonic band chosen as a function of the material of the plate, so that the plate in impactile interface mode is said to be master, while the production of audible sound is said to be slave.

13. Device according to claim 7, characterized in that the plate is in a flat rectangular shape such as those that can be found in shop windows, partitions, glass doors, windows or slightly curved such that those that can be found in the window panes of passengers in motor cars or public transport shelters or display furniture in commercial sales spaces.

14. Device according to claims 1 to 13, characterized in that for glass in monolithic plate and metal in monolithic plate, the piezoelectric sensors PZTO to PZT4 consist of two piezoelectric transducers PZTt and PZTb bonded opposite and on the other side of the plate and are in the form of half-discs with silver backing when glued to the side of a plate, the edge of the disc being collinear and in line with the edge of the plate or in the form of a quarter disc with silver back when glued to the corners of the rectangular plate, the two perpendicular sections being aligned with those of the plate, while the electrical connections are made in antiparallel, and for plastics such as polycarbonate, the sensors Piezoelectric PZTO to PZT4 consist of a single piezoelectric transducer, all glued on the same side or the side opposite to the side receiving the impact.

15. Device according to claims 1 to 14, characterized in that the sensors are piezoelectric ceramic plates with alternating polarization of rectangular shape, bonded to the polished edge of the plate, the plane of separation of the alternating polarization being coplanar with the plane median of the glass plate.

16. Device according to claims 1 to 15, characterized in that it comprises means for compressing the dynamics, according to a law chosen from the group of logarithmic and square root laws, of signals from high-fidelity audio recordings such as compact discs and intended to be played using an interactive showcase in its speaker function.

17. Method for developing an acoustic wave transmitter-receiver device with localization functions by measuring the propagation of ultrasound and acoustic transduction in the audible range, characterized in that it comprises the following steps:

- provide a plate of given solid material;

- in association with the sensors, provide a circuit for processing the signals received and / or emitted by the sensor, comprising filtering means capable of defining two independent spectral bands, one in the ultrasonic domain and the other in the audible domain, these two bands being delimited between them by a cut-off frequency, and - choose the frequencies of the ultrasonic band according to the type of solid material of the plate.

18. The method of claim 17, characterized in that it comprises providing a plastic plate and choosing the ultrasonic band around about 30 kHz.

19. The method of claim 17, characterized in that it comprises providing a glass or metal plate and choosing the ultrasonic band around about 100 kHz.

20. Method for developing an acoustic wave transmitter-receiver device with localization functions by measuring the propagation of ultrasound and acoustic transduction in the audible range, characterized in that it comprises the following steps:

- provide a plate of given solid material;

21. The method of claim 20, characterized in that it comprises providing a plastic plate and choosing an arrangement of the individual sensors on only one side of the plate.

22. The method of claim 20, characterized in that it comprises providing a glass or metal plate and choosing an arrangement of the individual sensors in pairs on either side of the plate.

23. Acoustic wave transmitter-receiver device, characterized in that it comprises a set of piezoelectric sensors (PZTO to PZT4) bonded to only one side of a plastic plate and able for at least some to detect ultrasonic acoustic waves propagated in the plate according to the symmetrical mode, in that at least one of said sensors is capable of emitting and / or receive sound waves in the audible range, and in that it further comprises filtering means capable of defining at least two independent spectral bands, one in the ultrasonic field, the other in the audible field, and means for processing the signals filtered independently in the two bands.