| Love wave is the shear wave that its energy is mainly concentrated in waveguide layer, and it’s not easily coupled with surface medium. And the Love wave device is widely used in the sensors, the biochip and many other fields because it has the advantages of high sensitivity, high precision, miniaturization and etc. However, the Love acoustic wave is not easily observed and measured. So far, the two-dimensional finite element model or without using interdigital transducer were used in the Love wave device modeling. Thus the Love wave propagation characteristics cannot be represented visually. At the same time, in the measurement of Love wave device, there is a mismatch between the impedance of Love wave device and the characteristic impedance of transmission line. And there is no any mature matching setup and matching method. In order to solve the above problems, the modeling simulation and the impedance matching of Love wave device are studied systematically in this paper.In order to characterize accurately the particle displacement and the dispersion relationship of the Love wave device, a three-dimensional modeling scheme of Love wave device is proposed. In the scheme, a limited number of units are applied to approximate the real physical structure and the actual load conditions such as interdigital transducer and waveguide layer. By means of the Love wave device with the 128°YX-LiNbO3 piezoelectric substrate, the Al metal interdigital transducer, and the ZnO thin film waveguide layer material, the three-dimensional model scheme of the Love wave device can be verified. The experimental results show that the frequencies of Love modal wave are 49.072 MHz, 49.295 MHz, 49.607 MHz, 50.062 MHz in the frequency range from 49 MHz to51MHz. At these frequencies, the Love waves only have the particle displacement along the X direction, and the particle displacements along the Y direction and Z direction are zero. Furthermore, the dispersion relationship is that the velocities of Love wave will decrease vary with the angular frequency increasing.In order to solve the mismatch problem between the impedance of the Love wave device and the characteristic impedance of transmission line, the Smith impedance chart is designed to analyze the impedance matching system. Through the analysis of the Smith impedance matching method, the matching network structure is summarized, which provides a theoretical basis for the design of impedance matching circuit of the Love wave device. Meanwhile, a load impedance matching setup and matching method is proposed. According to the regulation of the switch state in the device, the mismatch channel and the matching channel corresponding to the Love wave device to be tested are separately formed, and different passive load impedance matching networks are designed for two ports. Thus the Love wave device under test completes the load impedance matching step by step. By testing the impedance matching circuit of the fabricated Love wave device, the port one and the port two can not only achieve the impedance matching center, but also at the center frequency point, the reflection loss of the port one is changed from-4.3710 dB to-28.010 dB and the reflection loss of the port two is changed from-9.1856 dB to-38.133 dB by matching, which indicates that the two port matching performance has been improved. |
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