B.D. Zaitsev - Dr. Sc. (Phys.-Math.), Professor, Head of Laboratory of Physical Acoustics, Saratov branch of Kotel\'nikov IRE of RAS. E-mail: zai-boris@yandex.ru I.A. Borodina - Ph. D. (Phys.-Math.), Senior Research Scientist, Laboratory of Physical Acoustics, Saratov branch of Kotel\'nikov IRE of RAS. E-mail: borodinaia@yandex.ru A.A. Teplykh - Ph. D. (Phys.-Math.), Senior Research Scientist, Laboratory of Physical Acoustics, Saratov branch of Kotel\'nikov IRE of RAS. E-mail: teplykhaa@mail.ru I.E. Kuznetsova - Dr. Sc. (Phys.-Math.), Associate Professor, Leading Research Scientist, Laboratory of Electronic Processes in Semiconductor Devices, Kotel\'nikov IRE of RAS (Moscow). E-mail: kuziren@yandex.ru

As it is well known acoustic waves in piezoelectric plate have a series of advantages in comparison with other types of acoustic waves propagating in piezoelectric materials. They possess wide spectrum of dispersive characteristics, are more piezoactive and sensitive to the change in electrical boundary conditions compared to surface acoustic waves (SAW). These peculiarities point on the possibility of development of various chemical and biological sensors and also devices for processing signals on basis of these waves, operating at frequencies < 10-15 MHz at achievable minimal values of plate thickness of ~100 µm. Numerous studies have shown that results of calculations of devices on the plate waves often do not coincide with experimental data. By analogy with surface acoustic waves this is connected with so called effects of the second order. These effects change pulse characteristics, amplitude-frequency and phase-frequency characteristics, level of attenuation and other parameters. Analysis has shown that at development of devices on the plate acoustic waves operating in frequency range of 1-10 MHz the most significant effects of the second order are the reflections of acoustic waves from interdigital transducers (IDTs) leading to the appearance of the signals of multiple rereflections (triple, fivefold and so on). These signals cause the ripples on the frequency dependence of insertion loss in continuous regime. For suppression of these signals there exist the following methods. At first, one should increase the efficiency of excitation and reception of acoustic waves and use enough matching with outside electric circuit. The electromechanical coefficient of the wave must be high enough. Secondly one often uses the IDT with split fingers. In this case the distribution of HF electric field has twice as much period as compared with spatial period of mass loading and period of distribution of electrical boundary conditions. So the efficiency of reflections from IDTs significantly decreases. The influence of reflections of acoustic waves from IDTs was demonstrated on two samples of delay line. Each delay line represented two IDTs with split fingers which were placed on the plate of Y−X lithium niobate. Each transducer contained 5 pairs of split fingers with aperture of 8 mm. The period of each transducer was equal 1.3 mm. These transducers excited and received shear-horizontal acoustic wave of zero order (SH0), which propagated along X axis. The frequency range of these lines was equal 2.9-4 MHz. In the first delay line the plate thickness and electromechanical coupling coefficient were equal h = 0.5 mm and К2 = 22%, respectively. In the second line h = 0.2 mm and К2 = 32%. Experiments which were carried out in pulse regime showed that the ratios of the power of the main signal and signal of the triple passing turned out to be 27 and 12 dB for the first and second delay lines, respectively. At that the ratios of the power of the main signal and signal of fivefold passing are equal 20 and 31 dB. The measurements performed in continuous regime by means of meter of S parameters have shown that ripples on frequency dependencies of insertion loss for first and second delay lines are equal 4-5 dB and 1 dB, respectively, that quite correlated with data of pulse regime. We also measured the frequency dependencies of the phase of output signals. It has been found that for second line this dependency is close to linear whereas the frequency dependence of phase for the first delay line has significant deviation from linear law. It is obvious that this fact is connected with powerful signals of triple and fivefold passing. Therefore it has been experimentally shown that increase in efficiency of transformation of electrical signal into acoustical one and vice versa leads to significant decreasing the signals of triple and fivefold passing and decreasing the amplitude of ripples on the amplitude-frequency and phase-frequency characteristics of delay lines on acoustic waves in piezoelectric plate even without compensation of IDT capacities and without matching transformers. The delay line under study may be used for development of various chemical and biological sensors and sensors of different physical parameters.

 

1. Toda K. Frequency characteristics of an interdigital transducer for Lamb wave excitation // J. Appl. Phys. 1974. V. 45. P. 5136.
2. Toda K. Lamb wave in a thin piezoelectric ceramic plate under the influence of static tensile stress // J. Appl. Phys. 1975. V. 46. P. 5114.
3. Jin Y., Joshi S.G. Characteristics of ultrasonic Lamb waves in 128° rotated Y‑cut litium niobate // IEEE Trans. on Utras., Ferroel. and Freq. Contr. 1994. V. 41. № 2. P. 279.
4. Borodina I.A., Dzhoshi S.G., Zajjcev B.D., Kuznecova I.E. Akusticheskie volny v tonkikh plastinakh niobata litija // Akusticheskijj zhurnal. 2000. T. 46. № 1. S. 42−46.
5. Kuznetsova I.E., Zaitsev B.D., Joshi S.G., Borodina I.A. Investigation of acoustic waves in thin plates of lithium niobate and lithium tantalite // IEEE Trans. on Ultras., Ferroel. and Freq. Contr. 2001. V. 48. № 1. P. 322.
6. Dmitriev V.V., Akpambetov V.B., Bronnikova E.G., Demidov V.P., Karpeev D.V., Larionov I.M. Integralnye pezoehlektricheskie ustrojjstva filtracii i obrabotki signalov. M.: Radio i svjaz. 1985. 176 s.
7. Rechickijj V.I. Akustoehlektronnye radiokomponenty. M.: Radio i svjaz. 1987. 193 s.
8. Morgan D. Ustrojjstva obrabotki signalov na poverkhnostnykh akusticheskikh volnakh. M.: Radio i svjaz. 1990. 415 c.
9. Zaitsev B.D., Joshi S.G., Kuznetsova I.E. Investigation of quasi-shear-horizontal acoustic waves in thin plates of lithium niobate // Smart Material & Structures. 1997. V. 6. P. 739.
10. Zaitsev B.D., Joshi S.G., Kuznetsova I.E. Efficient Reflectors for Ultrasonic Lamb Waves // Proc. of SPIE. SmartStructuresandDevices. 2000. V. 4235. P. 228.
11. Joshi S.G., Zaitsev B.D., Kuznetsova I.E. Reflection of plate acoustic waves produced by an array with periodically distributed mechanical load // IEEE Trans. on Ultras., Ferroel. and Freq. Contr. 2002. V. 49. № 12. P. 1730.
12. CHajjkovskijj D.S. Osobennosti preobrazovanija i rasprostranenija poverkhnostnykh akusticheskikh voln v sloistojj volnovodnojj strukture na poverkhnosti pezokristallov. Dis. - kand. fiz.-mat. nauk. Saratov. 2007. 109 s.