Lili Yuan

Effects of viscous liquid on SH-SAW in layered magnetoelectric structures

We investigate analytically shear horizontal surface acoustic wave (SH-SAW) propagation in layered magnetoelectric structures loaded with viscous liquid, which involves a thin piezomagnetic layer bonded perfectly to an unbounded piezoelectric substrate. The dispersive relations are obtained and the effects of liquid viscosity on the phase velocity and attenuation of the waves are analyzed and discussed. From the results we can find that the effects of the liquid viscosity on the properties of SH-SAW are remarkable. The phase velocity decreases with increase of the viscous coefficient, or with increase of the frequency, and the attenuation increases with the frequency of the waves and the liquid viscosity, respectively. The relationship between attenuation and frequency or viscosity is nonlinear, but the former is a concave curve, whereas the latter is a convex curve. The attenuation decreases with the piezomagnetic coefficient, and increases obviously with the thickness of the layer. The analytical method and the results are useful for the design of acoustic wave devices based on magnetoelectric materials for liquid phase application, which could be resonated by either magnetic or electric fields.

Lateral-field-excited bulk acoustic wave sensors on langasite working on different operational modes

Lateral-field-excited (LFE) bulk acoustic wave sensors on langasite working on different operational modes are investigated and compared. Langasite LFE sensors on pure-LFE mode and pseudo-LFE mode are designed and fabricated. The sensitivities of the devices to changes in liquid electrical properties (e.g., conductivity or permittivity) and micro-mass changes on their surfaces were tested and compared. The experimental results show that compared with langasite pure-LFE devices, langasite pseudo-LFE devices have superior sensitivities to both liquid conductivity and liquid permittivity changes. For the micro-mass changes, the pure-LFE devices showed high sensitivity, whereas the pseudo-LFE devices do not, because they cannot resonate in air. On this basis, the physical interpretation of these results is discussed.

Effect of the Ferroelectric Inversion Layer on Resonance Modes of LiNbO3 Thickness-Shear Mode Resonators

The effect of the ferroelectric inversion layer on resonance modes of LiNbO3 thickness-shear mode resonators was investigated. It is found that with the ferroelectric inversion layer, the spurious modes of the LiNbO3 resonators can be suppressed significantly. Moreover, mechanisms of the effect are discussed. This discovery is important to investigate high-sensitivity bulk acoustic wave sensors using LiNbO3 thickness-shear mode resonators.

Propagation behavior of Rayleigh waves in a phononicmagnetoelectric layered structure

In this paper, we investigate the characteristics of the Rayleigh surface acoustic waves in one-dimensional layered structures which consisting of a thin isotropic layer bonded perfectly to piezomagnetic/ piezoelectric periodic substrate. The explicit formulations of Rayleigh wave dispersion relations in such layered structure with consideration of magnetoelectrically open and shorted cases are derived based on the plane wave expansion method. The band gaps are calculated taking magneto-electro-elastic coupling into account. The influences of material and the filling fraction are discussed in detail. From the result, we can find the width of the open band gap is wider than the shorted case. The analytical method and the results can be useful for the design of the filters and transducers.

Investigation of quasi lateral-field-excitation on (yxl)-17° LiNbO3 single crystal

Quasi lateral-field-excitation (LFE) on LiNbO3 crystal is investigated both theoretically and experimentally. It is found that when the driving electric field direction is parallel to the crystallographic X-axis of the piezoelectric substrate, (yxl)-17° LiNbO3 LFE bulk acoustic wave devices work on quasi-LFE mode. The experimental results agreed with the theoretical prediction well. The results provide the cut of LiNbO3 crystal for quasi-LFE bulk acoustic wave devices, which is important for designing high performance LFE sensors on LiNbO3 substrates.

A novel thickness-shear mode resonator using a LiNbO 3 plate with an inversion layer

The previous investigations showed that a local domain inversion takes place when bare LiNbO3 plates undergo heat treatment at temperatures higher than 1070°C. The LiNbO3 plates with an inversion layer have been used to fabricate piezoelectric bulk acoustic wave devices. The researches on the application of inversion layer piezoelectric devices mainly focused on high frequency ultrasonic transducers working on the thickness extensional mode. The research on inversion layer devices working on the thickness shear mode has not been reported. In this work, several experiments were done to investigate the characteristics of the inversion layer device working on the thickness shear mode. It is found that when the device works on the 2nd harmonic of the thickness shear mode under the role of the inversion layer, spurious modes decrease obviously. The mechanism of suppressing spurious modes through the inversion layer was analyzed. Therefore, bulk acoustic wave devices with an inversion layer working on the thickness shear mode have a good prospect in sensors and resonators.

Thickness-shear and thickness-twist vibrations of rectangular quartz crystal plates with nonuniform thickness

ABSTRACT An analysis was performed on the vibration of a rectangular contoured quartz plate resonator. The surface of the resonator has different curvatures in the two in-plane directions. The analysis was based on the equation by Tiersten and Smythe, which has variable coefficients. The power series method was used. Thickness-shear and thickness-twist vibration frequencies and modes were obtained. The effects of the curvatures of the resonator surface were examined. Two types of boundary conditions were considered from which the proper size of the resonator was determined. The results are useful in the understanding of these resonators and their design.

Propagation of SH-SAWS in a layered magnetoelectric phononic crystal structure

We analyze the propagation behavior of SH-SAWs in one-dimensional layered periodic magnetoelectric structures which consisting of a thin periodic piezomagnetic/ piezoelectric layer bonded perfectly to the isotropic substrate. The explicit formulations of SH-SAWs dispersion relations in such layered structure with consideration of magnetoelectrically open and shorted cases are derived based on the plane wave expansion method. The band gaps are calculated taking magneto-electro-elastic coupling into account. The influences of material and the filling fraction are discussed. From the result, we can find the width of the open band gap is wider than the shorted case. The analytical method and the results can be useful for the design of the filters and transducers.

Analysis of coupled fast-shear and extensional vibrations of a LiTaO3 crystal plate with a ferroelectric inversion layer

The resonance vibrations of LiTaO3 fast-shear overtone mode resonators with a ferroelectric inversion layer are analyzed. In addition to the fast-shear mode, the coupled extensional mode is considered. Different from most of the LiTaO3 resonators studied in the literature that are based on the slow-shear mode, the resonator in this paper operates with the fast-shear overtone mode. Results show that the capacitance ratio assumes maxima at two resonances, which are identified to be the second overtone modes of fast-shear and extension, respectively. It is found that the thickness of the inversion layer has obvious influences on the capacitance ratio of fast-shear and extensional modes. This condition may provide a simple method to adjust capacitance ratios of piezoelectric resonators. The influence mechanisms are also discussed. Besides, the effect of the cut angle of the crystal on the mode shape of vibrations is also investigated. The results can be used as important basis of parameters designs of LiTaO3 resonators operating on the fast-shear overtone mode.

Power delivery to a piezoelectric transducer embedded in an elastic body by acoustic waves

ABSTRACT We studied the transmission of power to a piezoelectric transducer embedded in an elastic body by acoustic waves. A four-layer mechanics model was constructed. A theoretical analysis was performed using the equations of linear piezoelectricity and elasticity. The input admittance, the output voltage and the efficiency of the power transmission structure were calculated. It was shown that significant energy transmission can be produced at a few resonant frequencies. The effects of various physical and geometric parameters were examined. The performance of the structure is sensitive to these parameters and design optimization is necessary for effective power transmission. It was found that the location of the piezoelectric transducer inside the elastic body does not matter much. As long as the strain in the transducer is large and does not change its sign along the transducer thickness, a significant output can be received.