RU2533692C1 - Multiplexer acoustic array for "electronic nose" and "electronic tongue" analytical instruments - Google Patents

Abstract

FIELD: instrument engineering.

SUBSTANCE: multiplexer acoustic array includes flat parallel plate out of pieso-electric crystal with crystallographic axis lying in the plate plane and passing through conditional plate center, interdigital transducers positioned symmetrically in pairs at the work side of plate and forming acoustic channel system where directions of acoustic wave propagation intersect in the conditional plate center where a circular zone is made in the conditional plate center for a sample, acoustic channels can excite plate-shape mode family of vibrations in the plate, with wavelength not exceeding plate thickness.

EFFECT: enhanced selectivity of vibration modes with increase of number of sensors for excited modes.

8 cl, 12 dwg

Description

The invention relates to analytical instrumentation, and in particular to devices for physicochemical analysis of liquid and gaseous media using acoustic waves.

Since the mid-20th century, the development of the development of individual acoustic sensors that provide information about gas in the form of an electrical signal of high frequency [D.S. Balantine, R.M. White, S.J. Martin, et al. Acoustic wave sensors: Theory, design and physico-chemical applications - NY: Academic Press, p. 436, 1996]. These sensors have found their application. But, like sensors based on other physical principles, they are not able to single-handedly selectively detect individual gases in their mixture, since chemical coatings that react to one gas component and do not react to the rest cannot be created.

By analogy with biological systems of olfaction and taste perception, approaches were formulated to create electronic analogues - devices, now known as "electronic nose" and "electronic language", used to analyze mixtures of gases and liquids, respectively [H.T. Nagle, R. Gutierrez-Osuns, S.S. Schiffman // IEEE Spectrum, v. 35, no.9, p.22, 1998; W. Gopel. Sensors and Actuatoprs, v. B52, p. 125, 1998; U. Ewimar, W. Gopel Sensors and Actuators, v. B52, p. 143, 1998; SOUTH. Vlasov, A.V. Legin, A.M. Rudnitskaya // Abstracts of the All-Russian Conference with international participation "Sensors and Microsystems" 21-23.06.2000, p.32]. The main component of these devices is the multisensor lattice - it determines the accuracy, resolution (selectivity) and temporary stability of the entire device.

In the first-generation electronic nose industrial devices that appeared in the mid-90s of the 20th century, discrete sensors were used, which differ in both gas-sensitive materials and physical and technical principles of operation. In such devices, it was necessary to provide an additional circuit for pairing signals of different types of sensors, and long-term measurements of gas-sensitive materials, different for different types of sensors, required frequent recalibration of end devices. As a result, the operation of the device was unstable in time.

In the second generation electronic nose devices, for the unification of signals, multisensor systems of the same type, in particular acoustic sensors, located on the same chip were used. In this case, all sensors generate signals of the same type, and their coupling is not required, and the variation of the properties of the output characteristics is achieved again by changing the gas-sensitive coatings and / or operating conditions (for example, operating temperatures in the range of 200-500 ° C). However, here, the use of various coatings with different “aging” requires frequent recalibration and even complete replacement of the multisensor system. As a result, a fundamental contradiction arises: on the one hand, the more sensors are contained in the system and the more diverse they are, the more perfect is the work of the “electronic nose”. On the other hand, the more sensors and, therefore, the more gas-sensitive coatings, the less stable the operation of the entire device due to aging films.

A number of inventions are devoted to the possibilities of creating a multisensor system containing simultaneously a large number of various sensors and a small number of chemical coatings used in them. In US patent (US 4691714, Wong et al., 08/08/1987) describes an array of acoustic sensors designed to identify liquids by their viscosity and temperature. The device comprises a plate with plane-parallel faces made of fused silica, a 6.4 μm thick ZnO piezoelectric film located on the same face above a metal film, and pairs of interdigital transducers (IDT) with a period of λ = 25 μm located on top of the ZnO film . The test liquid is applied to the opposite side of the said composite plate. To carry out measurements, the IDT pair generates and receives two acoustic waves in the plate - surface (surfactant), which propagates along the face that does not come into contact with the liquid, and volumetric (SAW), which propagates deep into the plate, is reflected from the face with the liquid and again arrives at the first facet where the receiving IDT is recorded. The same IDT also records a surface acoustic wave. The simultaneous existence of two acoustic waves in such a device is ensured by the choice of the plate thickness h much longer than the period λ. IDT (h / λ≈25). In the device of the described construction, the fluid viscosity is determined by measuring the amplitude of the reflected body wave, and its temperature is determined by the change in the speed (phase) of the surface acoustic wave.

However, since the temperature of the test liquid may be different from that for the fused silica wafer, the mass of the liquid is much higher than the mass of the entire acoustic device so that the equilibrium temperature of the device-liquid system is as close as possible to the initial temperature of the liquid. The less "massive" the liquid, the worse the accuracy of the measurements and the greater the difference between the initial temperature of the liquid and the measured one. In addition, since the amplitude of the reflected body wave depends not only on the viscosity, but also on the temperature of the liquid, the viscosity measured for a small liquid also does not correspond to the real value, i.e. the design is not applicable for liquids with a volume of less than 100 μl. Finally, due to the use of only 2 acoustic waves in the device, the number of parameters by which the liquid is identified is also limited to two, which is not enough in most applications.

A multi-frequency acoustic sensor for analyzing liquids and gases is described (US 5235235, Martin et al., 08/10/1993). The sensor includes several IDT pairs with different periods, which are located in one line and generate surface acoustic and lamellar acoustic waves that differ in frequency. Based on the difference in the interaction of acoustic waves excited at different frequencies with mass, viscous and other plate loads, the device is able to identify a gas or liquid mixture by several parameters. However, the use of a large number of IDTs located in a line entails an increase in the dimensions of the device and undesirable distortions of those acoustic waves that, propagating in one direction, pass through a large number of IDTs in the internal part.

A sensor array is described which consists of a piezoelectric substrate and several parallel-mounted single-input resonators on a SAW with identical IDTs in each resonator (US 5325704, Mariani et al., 05.07.1994). The directions of propagation of surfactants in all sensors of such a lattice are parallel to each other, and, therefore, the properties of all surfactants excited in each sensor are identical. To ensure the required difference in sensors, gas sensitive coatings differing in properties are traditionally used. As a result of various aging coatings, there is a need for frequent recalibration of the entire device.

A sensor array is described for identifying a liquid also by viscosity and temperature (US 7398685 B2, Itoh et al., July 15, 2008). The lattice consists of a piezoelectric substrate and 2 surfactant sensors oriented orthogonally to each other. The test sample is applied to the overlap area of two surfactants excited in the lattice. Due to the use of a limited number of (two) sensors, such a lattice is also unsuitable for the analysis of multicomponent liquids.

Closest to the patented multisensor acoustic array is a SAW device described in the work "Integrated array of gas sensors" (VI Anisimkin, RG Kryshtal, AV Medved, E. Verona, VE Zemlyakov "Integrated array of gas sensors" // Electronics Letters, v .34, no.13, p.1360-1361, 1998 - the closest analogue). The device comprises a substrate of a piezoelectric single crystal, on the working surface of which there are four pairs of IDTs arranged in a circle with a common center, at certain angles to the crystallographic axis. The only gas-sensitive adsorbent film is located in the center of the circle. The periods λ of all IDTs are the same and much smaller than the thickness h of the substrate. Each IDT pair excites one surfactant and forms only one gas sensor, the response of which depends both on the change in the physical parameters of the film under the action of the test gas (the same for all sensors) and on the properties of the surfactant. The difference between the responses of the sensors in this design is ensured by the anisotropy of the 4 probe waves, which differently “read” the changes in the same film properties during adsorption.

However, the closest analogue has its drawbacks: its use is limited to gaseous analytes, because upon contact with the liquid, the surfactants completely decay; the maximum number of sensors is limited - it is equal to the number of excited waves, one in each acoustic channel.

The present invention is directed to a multi-sensor system for analyzing liquid and gaseous media, which simultaneously contains a large number of different sensors and a small number of chemical coatings used.

The patented multisensor acoustic array contains a plane-parallel plate of a piezoelectric crystal having a crystallographic axis lying in the plane of the plate and passing through the conditional center of the plate, which has a working and back sides. IDTs are placed symmetrically in pairs on the working side of the plate with the formation of a set of acoustic channels, the directions of propagation of acoustic waves in which intersect at the conditional center of the plate, there is a zone around the conditional center in the form of a circle for the sample,

The difference of the patented lattice is that the acoustic channels are capable of exciting in the plate a family of plate-like modes of oscillation with a wavelength of less than or equal to the thickness of the plate, while IDTs in different acoustic channels have different values of the period of the pins and / or angles between the crystallographic axis of the plate and the mentioned directions of propagation of acoustic waves.

The lattice can be characterized by the fact that plate modes of vibration include linearly polarized acoustic modes of quasi-longitudinal and quasi-vertical polarization, and also by the fact that the number of pairs of pins of interdigital transducers in a single acoustic channel satisfies the condition of frequency resolution of neighboring vibration modes with close velocities: (v _{n +1} -v _n ) / v _n ≤0.01, where v _n ; v _{n + 1} are the propagation velocities of vibration modes of n and n + 1 orders of magnitude, respectively.

The lattice can be characterized by the fact that in the center of the working side of the plate in the area around the conditional center there is a film of a substance sensitive to the composition of the gas sample, and also in the fact that in the center of the back side of the plate in the area around the conditional center there is a film of a substance sensitive to the composition of the gas sample and / or liquid sample.

The lattice can be characterized by the fact that the plate is made of ST-quartz and has a thickness h = 500 μm, as well as the fact that the plate is made of a 128 ° Y-LiNbO ₃ piezoelectric crystal and has a thickness h = 500 μm.

The lattice can be characterized by the fact that the plate is made of a 128 ° Y-LiNbO ₃ piezoelectric crystal in the form of a disk with a thickness of h = 500 μm, IDTs are located around the conditional center of the disk on three concentric circles at angles Θ ₁ = 0 °; Θ ₂ = 30 °; Θ ₃ = 60 ° and Θ ₄ = 90 ° to the crystallographic axis X of the said crystal, and the periods of the transducers from the periphery to the center decrease and amount to 500 μm, 300 μm, and 200 μm.

The technical result is an increase in selectivity due to a significant (more than an order of magnitude) increase in the number of sensors and applicability for both gases and liquids.

The invention is based on well-known provisions and experimental facts established by the applicant himself.

It is known [I.A. Victorov. Physical fundamentals of the application of Rayleigh and Lamb ultrasonic waves in technology. M .: Science. 1966; B.A. Auld, Acoustic Fields and Waves, New York-London-Sydney-Toronto: Wiley-Interscience Publication, 1973, vol.2], that in solid-state plates with free plane-parallel surfaces and with a thickness of the order of the length of the acoustic wave, a family of acoustic waves (acoustic plate modes) differing in polarization and propagation velocities. For isotropic plates, such modes are polarized either strictly parallel (SH modes) or strictly perpendicular (Lamb modes) to these surfaces. In anisotropic plates, mode polarization is usually more complex and in the general case is an ellipse whose plane is inclined both to the plate surface and to the direction of wave propagation.

Applicants have shown that, along with well-known modes in plates of anisotropic materials, there can also exist linearly polarized acoustic modes of quasi-longitudinal QL and quasi-vertical QSV polarization [Ivan V. Anisimkin "New type of an acoustic plate modes: quasi-longitudinal normal wave," Ultrasonics, vol .42, no.10, p.1095-1099, 2004; V.I. Anisimkin "New acoustic plate modes with quasi-linear polarizations", IEEE Trans. on Ultrason., Ferroelect., Freq. Contr., Vol. 59, no.10, p.2363-2367, 2012], which significantly expand the variety of plate modes, as well as their applicability to practical devices. So, in contrast to the previously known, new plate modes can be used to analyze both gases and liquids [I.V. Anisimkin and V.I. Anisimkin, "Attenuation of acoustic normal modes in piezoelectric plates loaded by viscous liquids", IEEE Trans. on Ultrason, Ferroelect., Freq. Contr., Vol. 53, no.8, p.1487-1492, 2006].

These modes may have an abnormally high coefficient of electromechanical coupling [V.I. Anisimkin and N.V. Voronova "Acoustic properties of the film / plate layered structure", IEEE Trans. on Ultrason, Ferroelect., Freq. Contr., Vol. 58, no.3, p. 578-584, 2011; IN AND. Anisimkin, N.V. Voronova et al. The structure of acoustic modes in piezoelectric plates with free and metallized surfaces // Radio Engineering and Electronics, vol. 57, No. 7, p. 808-812, 2012] and an anomalously large angle of deviation of the energy flux [V.I. Anisimkin, I.I. Pyataikin, and N.V. Voronova, 'Propagation of the Anisimkin Jr.' and Quasi-Longitudinal Acoustic Plate Modes in Low Symmetry Crystals of "Arbitrary" Orientation ", IEEE Trans. Ultrason, Ferroelect., Freq. Contr., Vol. 59, p. 806-810, April 2012]. The region of existence of new modes is not limited to crystals and directions with a high degree of symmetry [V.I. Anisimkin, "General properties of the Anisimkin Jr. plate modes", IEEE Trans. on Ultrason, Ferroelect., Freq. Contr., Vol. 57, no.9, p.2028-2034, 2010; V.I. Anisimkin, I.I. Pyataikin, and N.V. Voronova, 'Propagation of the Anisimkin Jr.' and Quasi-Longitudinal Acoustic Plate Modes in Low Symmetry Crystals of "Arbitrary" Orientation ", IEEE Trans. Ultrason, Ferroelect., Freq. Contr., Vol. 59, p.806-810, April 2012], which is characteristic of the previously known modes of Lamb and SH.

The invention is illustrated in the drawings, where:

figure 1 shows the topology of the functional areas of the substrate for the formation of a multisensor acoustic array;

figure 2 - design of a multisensor acoustic array using a set of IDT pairs;

figure 3 enlarged shows the design of a single IDT of a pair;

figure 4 - design of a simple multisensor acoustic array with two pairs of IDT on a substrate of ST-quartz;

figure 5 - amplitude-frequency characteristics of the acoustic plate modes excited in the multisensor lattice of figure 4;

6, 7 - relative phase change ("response") to temperature t relative humidity RH of the acoustic plate modes of different quasi-longitudinal QL and quasi-vertical QSV polarization, respectively;

Fig. 8 is a photograph of an experimental sample of a multisensor acoustic array made on a substrate of 128 ° Y-LiNbO ₃ ; for comparison - a coin of 1 ruble denomination;

Fig.9-12 - the amplitude-frequency characteristics of the acoustic plate modes excited in the design of the sample shown in Fig.8.

Figure 1-3 shows the topology and design of a multisensor acoustic array using several pairs of IDT, as well as an enlarged design of a single IDT.

The multi-sensor acoustic lattice is made on a substrate 1 of a piezoelectric crystal in the form of a plane-parallel plate having a supporting platform 2, which defines the crystallophysical axis 3, with respect to which a further lattice topology is constructed. The substrate 1 has a central part 4, zone 5, where pairs of electro-acoustic IDTs forming acoustic channels are located, and a central part 6 in the form of a circle around the indicated conditional center 61, where sensitive film can be placed. The substrate 1 is characterized by a thickness h, has a working 71 and a back 72 sides. Acoustic channels are configured to excite in each of them a family of plate modes of oscillations of n orders of magnitude with a wavelength λ less than or equal to the thickness h of the plate (λ≤h).

In zone 5, on the working 71 side of the substrate 1, acoustic channels are formed to excite and receive acoustic vibrations. The channels, as schematically shown in figure 2, are formed by IDT pairs 8.1, 8.2, 8.3 ... 8.8, and in total they can contain K on the substrate surface, and the number “ID” of IDT pairs can reach about 100 and can only be determined by technological capabilities and practicality .

Each IDT pair, consisting of two identical IDTs, is located on straight lines passing through the conditional center 61, and the individual IDT pairs themselves are respectively at equal distances from the conditional center 61. So, for explanation, it is shown that IDT pair 8.1 is located on a straight line 9.1, and IDT pair 8.7 on a straight line 9.7. In this case, the channels are deployed relative to the crystallophysical axis 3 (for example, X) at angles то, that is, the axial line 9. To each pair is placed at an individual angle Θ. However, a case is possible (as shown in Fig. 8) when several IDT pairs are placed on one straight line, i.e. have the same angle Θ.

Figure 3 shows the structure of a single Converter. The IDTs are formed by the contact pads 8.01, connected with the straight, opposed-placed pins 8.02, have a period λ and an aperture w. The direction of emission / reception is shown by arrows 8.03. The number of pins 8.02 of a pair of interdigital transducers in a single acoustic channel satisfies the condition for the frequency resolution of neighboring modes of oscillations with close speeds: (v _{n + 1} -v _n ): v _n ≤0.01, where v _n ; v _{n + 1} are the propagation velocities of vibration modes of n and n + 1 orders of magnitude, respectively.

The IDT characteristics in accordance with the patented invention are selected from the condition of excitation in the piezoelectric substrate 1 of acoustic plate modes (IDT periods λ≤h) and the frequency resolution of neighboring modes of oscillations with close velocities v _n and frequencies f _n = v _n / λ. (the number of IDT pin pairs ≥100 for fulfilling the condition (v _{n + 1} -v _n ): v _n ≤0.01, where v _n ; v _{n + 1} are the propagation velocities of the vibration modes of orders n and n + 1, respectively).

The examples demonstrate particular implementations of the multisensor acoustic array and the obtained characteristics.

Figure 4 shows the construction of a simple multisensor acoustic array consisting of a piezoelectric substrate 100 made of ST quartz (Euler angles 0 °; 132.75 °; Θ, where Θ is measured from the X axis) with a thickness of h = 500 μm and two pairs of IDT 8.001 and 8.002, forming two acoustic channels. The IDT orientation relative to the edges of the substrate 100 (crystallographic axis X, arrow) is Θ ₁ = 0 ° and Θ ₂ = 90 °. The periods of IDT pairs are equal and are λ ₁ = λ ₂ = 300 μm. The number of sensors in the array, equal to the number of excited modes, is 36, 18 for each IDT pair.

The amplitude-frequency characteristics of acoustic plate modes excited in a multisensor acoustic array (Fig. 5) along the X axis (Θ = 0 °) are shown in Fig. 5. Characteristics are determined using an HP 8753ES four-port analyzer. Peaks from left to right correspond respectively to two modes with quasi-shift-vertical polarization QSV (f _QSV-1 = 10.28 MHz, f _QSV-2 = 11.66 MHz), a mode with quasi-shift-horizontal polarization QSH (f _QSH = 17.358 MHz) and mode with quasi-longitudinal polarization QL (f _QL = 28.714 MHz, label 1).

An example of different sensitivity of the excited modes to the same external influences is shown in Fig.6, 7. Fig.6 shows the relative phase change ("response") of the acoustic plate mode QSV-1 to temperature t and relative humidity RH, and Fig.7 - same for QL plate mode. It is seen that for the QSV-1 mode, the “responses” to temperature and humidity at RH <80% have a comparable value, while for the QL mode, the temperature “response” is much larger than the “humidity” one.

Figure 8 shows a photograph of an experimental sample of another multisensor acoustic array made on a 128 ° Y-LiNbO ₃ piezoelectric crystal (Euler angles 0 °, 37.86 °, Θ, where Θ is measured from the X axis) with a thickness of h = 500 μm and 12 IDT pairs forming 12 acoustic channels. The orientation of the IDT pairs relative to the edge of the substrate (crystallographic axis X) is: Θ ₁ = 0 °, Θ ₂ = 30 °, Θ ₃ = 60 ° and Θ ₄ = 90 °. The periods of IDT equidistant from the common center 61 are the same. The periods of IDT, remote from this center 61 in different ways, are different. So, IDT 10.1, 11.1, 12.1 and 13.1, located on the periphery of the plate, have a period of λ ₁ = 500 μm. IDT 10.2 ... 13.2, located closer to the center 61, λ ₂ = 300 microns. Finally, for IDT 10.3 ... 13.3 located closest to center 61, λ ₃ = 200 μm.

As an example, FIGS. 9-12 show the amplitude-frequency characteristics of acoustic plate modes excited in a multisensor array using IDT with λ ₁ = 500 μm (IDT 10.1, 11.1, 12.1 and 13.1). The number of modes excited by these IDTs is about 40. The total number of sensors (excited modes) in the entire lattice is approximately 120.

It should be noted that the applicability of the patented design for both gases and liquids is based on the low absorption of most acoustic plate modes upon contact of the piezoelectric plate with both gas and liquid (in contrast to the complete disappearance of surfactants in the presence of liquids).

To increase the sensitivity of all acoustic sensors, a special adsorption film can be placed in the sample zone. The film can be applied both on the working 71 and on the back 72 of the plate, and in the second case - even on the entire back side.

The operation of the device is illustrated by the example of the structure shown in Fig. 8. Initially, in the absence of a sample, the phases (as shown in Fig. 7), amplitudes and frequencies (as shown in Figs. 9-12) of all acoustic plate modes excited in the array are measured. Then the test sample (gas, liquid) is applied to the zone around the conditional center 61 and repeated measurements of the phase, amplitude and frequency of the same modes are carried out. The magnitude of the changes in these measured parameters either directly serve as a characteristic of the sample, or can be subjected to special mathematical processing, which allows you to calculate this characteristic of the sample [H.T. Nagle, R. Gutierrez-Osuns, S.S. Schiffman // IEEE Spectrum, v. 35, no.9, p.22, 1998; W. Gopel. Sensors and Actuators, v. B52, p. 125, 1998; U. Ewimar, W. Gopel. Sensors and Actuators, v. B52, p. 143, 1998].

Thus, the given examples of the implementation of the patented design for the electronic nose (gas analysis) and electronic language (fluid analysis) systems substantiate the achievement of the technical result, namely, increased selectivity due to a significant (more than an order of magnitude) increase in the number of sensors and applicability both for gases and for liquids.

Claims (8)

1. A multisensor acoustic array containing a plane-parallel plate of a piezoelectric crystal having a crystallographic axis lying in the plane of the plate and passing through the conditional center of the plate having a working and back sides, electroacoustic interdigital transducers (IDTs) placed symmetrically in pairs on the working side of the plate with the formation of a set of acoustic channels, the directions of propagation of acoustic waves in which intersect at the conditional center of the plate, and the zone around g conditional center in the form of a circle for the sample,
characterized in that
the acoustic channels are capable of exciting in the plate a family of plate-like modes of oscillation with a wavelength less than or equal to the thickness of the plate, while IDTs in different acoustic channels have different values of the period of the pins and / or angles between the crystallographic axis of the plate and the mentioned directions of propagation of acoustic waves. 2. The lattice according to claim 1, characterized in that the plate-like modes of vibration include linearly polarized acoustic modes of quasi-longitudinal and quasi-vertical polarization. 3. The lattice according to claim 1, characterized in that the number of pairs of IDT pins in a single acoustic channel satisfies the condition of frequency resolution of neighboring modes of oscillations with close speeds:
(v _{n + 1} -v _n ): v _{n is} less than or equal to 0.01,
where v _n ; v _{n + 1} are the propagation velocities of vibration modes of n and n + 1 orders of magnitude, respectively. 4. The lattice according to claim 1, characterized in that in the center of the working side of the plate in the area around the conditional center there is a film of a substance sensitive to the composition of the gas sample. 5. The lattice according to claim 1, characterized in that in the center of the back of the plate in the area around the conditional center is a film of a substance that is sensitive to the composition of a gas and / or liquid sample. 6. The lattice according to claim 1, characterized in that the plate is made of ST-quartz crystal and has a thickness of 500 μm. 7. The lattice according to claim 1, characterized in that the plate is made of 128 ° Y-LiNbO ₃ crystal and has a thickness of 500 μm. 8. The lattice according to claim 1, characterized in that the plate is made of a 128 ° Y-LiNbO ₃ crystal in the form of a disk 500 μm thick, IDTs are located around the conditional center of the disk on three concentric circles at angles Θ ₁ = 0 °, Θ ₂ = 30 °, Θ ₃ = 60 ° and Θ ₄ = 90 ° to the crystallographic axis X of the mentioned crystal, and the IDT periods from the periphery to the center decrease and amount to 500 μm, 300 μm and 200 μm.

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