UA71213A - Surface-acoustic-wave device for measuring pressure - Google Patents

Abstract

The proposed surface-acoustic-wave device for measuring pressure contains a membrane, piezoelectric acoustic waveguide with interdigital surface-acoustic-wave transducers, which are arranged on the waveguide surface, and an electric oscillation amplifier. The outputs of the transducers are coupled with the input of the amplifier. The membrane is installed at a distance from the surface of the acoustic waveguide that is commensurable with the surface acoustic wave length.

Description

Description of the invention

The invention relates to acoustoelectronics devices and can be used in measuring technology. 2 A known surface acoustic wave (SAW) device for pressure measurement |1) containing a piezoelectric sound pipe, on one face of which two counter-pin PAH transducers are placed, connected to an amplifier of electric oscillations, and on the opposite face a cylindrical a depression that forms a flat, circular membrane that is sensitive to pressure.

The disadvantage of such sensors is a narrow range of measured pressure, due to the fact that in a round rigidly pinched membrane (with a low pinch coefficient) there are regions with deformations of the opposite sign, which leads to compensation of the reaction of the membrane to external influences, as well as low reliability due to possible the destruction of the membrane due to the fragility of the piezoelectric sound pipe during overloads and the difficulty of manufacturing the membrane.

The closest thing to the invention is a PAH device for measuring pressure, which contains a piezoelectric 12 sound pipe, on one face of which there are two counter-pin PAH transducers connected to an amplifier of electric vibrations, and on the other face, a recess with a cross section in the form triangle, the depth of which is constant across the aperture of the acoustic channel and changes monotonously in the direction perpendicular to the electrodes of the counter-pin PAH transducers, decreasing from the central region of the recess to its periphery (21. 20 The disadvantage of the device is low reliability due to the possible destruction of the plate during overloads due to the fragility of of the isoelectric sound pipe, as well as the complexity of the membrane.

The task of the invention is to increase reliability and manufacturability.

The solution to the given problem is achieved by the fact that the PAH device for measuring pressure, which contains a membrane and a piezoelectric sound pipe, on the surface of which there are counter-pin transducers 29 PAHs, connected to an amplifier of electric vibrations. What is new is that the membrane is located above the surface of the piezoelectric sound pipe at a distance commensurate with the length of the surface acoustic wave.

Figure 1 shows a pressure sensor on PAH; Fig. 2 is a section A-A of Fig. 1.

The device for measuring pressure on the PAH (Fig. 1) contains a piezoelectric sound pipe 1, on the surface of which there are absorbers of surface acoustic waves 2 and 3, counter-pin transducers of PAH 4 and 5, at 30 connected to an amplifier of electric vibrations b, the output of which is connected to the coaxial connector 7. All these "-elements form an autogenerator with a frequency-setting element made in the form of a piezoelectric sound pipe with counter-pin transducers, and are located in a housing 8, which is hermetically sealed with a membrane 9, which made of elastic material (for example, bronze, steel, etc.) and located above the surface of the piezoelectric sound pipe at a distance commensurate with the length of the surface acoustic wave. That's it

The location of the membrane is due to the fact that for its effective influence on the parameters of the wave propagating through the sound pipe, it is necessary to ensure the movement of the membrane in the PAH electric field, the electric potential of which decreases with distance from the surface of the sound pipe according to the exponential law.

The PAH device for measuring pressure works as follows. "

The generation of electric oscillations in the autogenerator on the PAH is possible when two conditions are met: 50 balance of amplitudes and balance of phases |Z). Taking into account the task - measuring the pressure acting on the membrane, the above conditions can be presented in the form:

From» The condition of the balance of the amplitudes of the eye, 0 45 where D. - total losses in the autogenerator circuit, which must be compensated by amplifying the signal in the amplifier - 6; ko Kk, - the gain coefficient of the amplifier. -k 70 Phase balance condition c» Fo ru u u - opo (2) de tsu - complete phase shift in the autogenerator circuit; z» Fu total phase shift in the amplifier circuit, counter-pin converters and matching elements;

Тр - phase shift in the sound pipe in the absence of external influences, which is equal to Йо - глид / Мо - sk 8)

Ho de m, vo, »- phase speed, length of characteristic curve and frequency of generated oscillations in the absence of external influences; because G is the distance between counter-pin converters;

Ж, - additional phase shift in the sound pipe, caused by the dispersion of the phase speed of the PAH in the section of the sound pipe | due to the location of the membrane 9 in the electric field of the surface acoustic wave at a distance X from the surface of the sound pipe, which can be given by the formula: - the steepness of the dispersion characteristic;

With -

Ua vah "IkhR)| - the phase velocity of the PAH when the membrane is located in the electric field of the wave at a distance X(P) from the surface of the piezoelectric sound pipe, which changes under the influence of the pressure of the surrounding medium P; 75 M -17Zhod - the number of lengths of surface acoustic waves on the excited section of the sound pipe |, which is equal to the active length of the membrane; 2- an integer that determines the mode of oscillations, as a rule, n -150...250.

It follows from relations (2) and (3) that the frequency of generated oscillations is determined by the relation: 20

Fu eye cape)

Т-(пп--- A KV uh ikh or zv As a rule, in autogenerators on PAH, the phase slope in the sound line a(Zho i Zhai) is much greater than the phase slope ach ha for other components.

In this case, сх» р (роу« 2 ) and the phase attack in the sound pipe prevails, that is, it will control the stability and frequency of the autogenerator, which can be presented in the form с 30 геп Яку ма «- 2 1 сх

The increase in the frequency of the autogenerator, taking into account ratios (4) and (6), is determined by the ratio: - 35 and - x x (7)

We are 2 Ma g--- Y Vch --2- Gb

Х, Пп х, « 20 It can be seen from relation (7) that the increase in the frequency of the autogenerator is determined by the dispersion of the phase speed with the PAH, which is caused by the deflection of the membrane under the influence of pressure. Therefore, measuring the frequency of the autogenerator allows you to determine both the absolute value and the pressure drop acting on the membrane. :z" Experimental studies conducted by the authors showed that the effective influence of the membrane on the phase velocity of the PAH occurs when the value of the relative gap between the membrane and the surface of the sound pipe is 5015, in this section the dispersion characteristic is close to linear, and its steepness is (for example, for a sound pipe made of lithium niobate) a value of the order of 55.0. 100 Ulym Fr. It should be noted that the steepness of the characteristic is determined experimentally for a specific design, since it is a complex function of the design parameters of the sound pipe, membrane and the size of the gap xX!7,. As a rule, in measuring transducers, the PAH is -10...10Ωm, which corresponds to the frequency of Х - З00..30М ГИ, therefore, for the - linearity of the output characteristic of the device, the deflection of the membrane should be from хи-о0 to шу» хххх З 015АдД -195..15MmMKkmM.

The dependence of membrane deflection X on pressure P is determined by the type of membrane and its design parameters.

For quantitative calculations, consider a membrane with a rigid center (Fig. 1, 2), the deflection of which depends on

P pressure is determined by the ratio |4): k-K.R (8) 60 where dovi 9) k--V

E-Z b5 z.a-rnau st-1- aso

Ar -E---- 5 5-2 2 2535 5 5 53 5 - l tya 16 sii s Kt; Vi kyu - the working radius of the membrane and the radius of its rigid center;

KE - Poisson's ratio and modulus of elasticity of the membrane material;

P - pressure difference; 70 p - thickness of the membrane (for small deflections X/p--1).

Then the relation (7) can also be presented in the form

Shk: ot: (t r- Mo Pet - Mo Ve

Hn p

R. in where 8-1 M sq. cha ZR

Ri in kik ; Ra ka Kk.

The sensitivity of the device is determined by the ratio: in ZE OO Momozero Moyu er (2) т «

We accept the following design parameters: - phase velocity of PAK mu - 3488 m/s (for a sound pipe made of lithium niobate U72 - section); со - the length of the undisturbed wave xu -85.107m (7-59, iBM Hz); "- - the distance between counter-pin converters I-PO5 m; - The number of PAHs in the undisturbed area is M-200; cm - working radius of the membrane KE -0P2m; - - the radius of the rigid center of the membrane h U OLY m; - - the thickness of the membrane n -0001th; - membrane material - steel; « - modulus of elasticity of the membrane material is 22.10 NIme; - Poisson's ratio i - 028; - s We determine: и ' -2 . » k-t lot Mr. A LOT y 1

Nick

Se2Y;hueRINO; ХУ Ххх У TB 10. this. From the relation (8), we determine the limit value of the measured pressure on the linear section of the dispersion characteristic of the Vila 7 JAC. 244 1ObNIME ZOM t. Art. -sho 70 The maximum increase in the frequency of the autogenerator (in relation (11) we assume a steepness of 5" - sope on the c" linear section of the dispersion characteristic)

In the same way - Im Y ro - M. Ma KO. would Riyak -

Ha G -2 with 00. 3409 30, 107100. 244107

R» po15 and sh 34837 HC 34, VAK.

The sensitivity of pressure measurement with such a device is equal to 190 Hz.

YAR Bdyako 244.10 Nim" mm Hg.

At the resolution of industrial frequency meters (for example Ch3-54) and-10G4, the potential resolution of the device is

AT 10 2 bo AR ----- - 2 PObemMMm of mercury. - 6.9 N/m with 190 "shchi"

A change in the design parameters of the sound pipe, counter-pin converters, the membrane of the use of a differential switching scheme, in which the signals of two autogenerators are subtracted on

PAH allows you to control the sensitivity of the device, the range of the measured pressure, reduce the influence of destabilizing actors depending on the required tactical and technical characteristics of the measuring devices.

Kk . . . Kk .

Thus, the device, unlike the prototype, allows for increased reliability, since the membrane can be made of a strong material, and a higher manufacturing processability will lead to a higher percentage of yield of suitable products during mass production.

An additional advantage of the proposed device for pressure measurement is the possibility of unification with 7/0 devices for different dynamic ranges, since only a change in the design of the primary transducer is required, while the secondary transducer (sound pipe with counter-pin transducers and amplifier) remains unchanged.

Sources of information: 1. Rechytsky V.I. Acoustoelectronic radio component. - M.: Soviet Radio, 1980. - P. 216-218. 2. Author's certificate of the USSR Mo1131024 NOZNO/OO // 5011 11/00, 1984. 3. Rechitsky V.Y. Acoustoelectronic radio component. - M.: Soviet Radio, 1980. - P. 199-218. 4. Ponomarev S.D., Andreyeva L.E. Calculation of elastic elements of machines and devices. - M.: Mashinostroenie, 1980. -6b.242. 9 ri and ? went 0-2

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Claims (1)

The formula of the invention A device on surface acoustic waves for measuring pressure, containing a membrane and a piezoelectric sound channel, on the surface of which there are counter-pin transducers of surface acoustic waves, connected to an amplifier of electric oscillations, which is characterized by the fact that the membrane is located above the surface p' of the isoelectric sound pipe at a distance commensurate with the length of the surface acoustic wave. r Official bulletin "Industrial Property". Book 1 "Inventions, useful models, topographies of integrated microcircuits", 2004, M 11, 11/15/2004. State Department of Intellectual Property of the Ministry of Education and Science of Ukraine. 60 b5