Ya-hui Tian

Analysis of rayleigh surface acoustic waves propagation on piezoelectric phononic crystal with 3-D finite element model

In this paper, two surface acoustic wave (SAW) delay line structures respectively with and without phononic crystals (PCs) were applied to analyze the propagation of Rayleigh SAW in the 2D piezoelectric PCs in theory. Three-dimensional (3D) finite element method (FEM) was adopted to analyze the model using the commercial software COMSOL MULTIPHYSICS. Experiments were also designed to verify the theoretical results, which show good consistency with the theoretical results. Thus this model can be used to analyze more other structures of 2D piezoelectric PCs, which can be applied to improve the performance of SAW devices.

Extractions of reflection and velocity parameters for surface acoustic wave in two-dimensional piezoelectric phononic crystals

Two-dimensional (2D) piezoelectric phononic crystals (PnCs) have richer properties of band gaps than 1D PnCs but not enough study on the calculation of designing parameters such as reflection and velocity. This paper proposed a model to calculate these parameters of 2D piezoelectric PnCs with finite element method (FEM). In the model, by comparing two SAW delay line structures respectively with/without PnCs and using time domain window to wipe out triple reflection, reflection and velocity can be achieved. Through an example of 2D Nickel/128°YXLiNbO3, it shows that the transmission and reflection of 2D piezoelectric PnCs change rapidly in the frequency band, which is different from the 1D IDTs, and the velocity of the SAW in the 2D PnCs is slower than in the free surface of the piezoelectric substrate.

P-Matrix Analysis of Surface Acoustic Waves in Piezoelectric Phononic Crystals

Large time/memory costs have constituted a significant obstacle for accurately analyzing surface acoustic waves (SAWs) in large-sized two-dimensional (2-D) piezoelectric phononic crystals (PnCs). To overcome this obstacle, this study introduces the unit P-matrix and its associated cascading. To obtain an accurate unit P-matrix, the Y parameters of the SAW delay lines were derived using a three-dimensional (3-D) finite-element model (FEM) with and without 2-D piezoelectric PnCs, respectively, on the transmitting path. A time window function was adopted to extract the desired signals from the P-matrix analysis. Then, unit P-matrix cascading was used to obtain SAW propagation parameters for the large-sized piezoelectric PnCs. Using this method, the SAW in aluminum (Al) /128°-YXLiNbO3 PnCs was analyzed over 150 periods. Experiments were also conducted. To choose the appropriate size of the unit P-matrix, the variance between experimental results and theoretical results, and time/memory cost were compared for different periods. The results indicate that cascading by unit P-matrix of 25 PnCs periods can be appropriately adopted to accurately derive the SAW propagation parameters over 150 periods. This indicates the accuracy of the unit P-matrix derived by 3-D FEM and the effectiveness of P-matrix analysis.

Influence of filling fraction on the band gaps of two-dimensional piezoelectric phononic crystals in radio frequency

This paper has studied the influence of filling fraction on the band gaps of two-dimensional (2-D) piezoelectric phononic crystals (PnCs) in radio frequency (RF). The 2-D piezoelectric PnCs consists of tungsten (W) stubs on the finite slab of 128°YXLiNbO3 substrate. With Bloch periodic theorem, the single cell model was built using the three-dimensional (3-D) finite element method (FEM). Based on the 3-D FEM model, band structures of the 2-D piezoelectric PnCs were calculated with different filling fractions. Results show that with the increase of the filling fraction, amount of the band gaps increase from one to two, the width of the first band gap becomes narrower and the second band gap become wider firstly and then become narrower, but all these widths become convergent. These results are useful for the applications of the 2-D piezoelectric PnCs in the RF devices as broadband filters and multi-channels filters.

Analysis of the relationship between the properties of line defect waveguide and the distribution of displacement vector within band gaps of the phononic crystal

This paper has analyzed the relationship between the distribution of displacement vectors and the properties of corresponding line defect waveguide within the band gaps of PCs. In order to obtain the band gaps of PCs, a delay line model was built. Through simulating this model by finite element method, the displacement vectors in PCs also can be obtained. To analyze the properties of corresponding line defect waveguide, the model of line defect waveguide has been built and calculated. With this method, a PCs consisting of 128°YX lithium niobate matrix with cylindrical hole from a square lattice is analyzed. The results show that the SAW displacement vector in the propagation direction decrease slowly and the SAW displacement vector in the transverse direction is large relatively, it will have a good property of line defect waveguide.

A weighted waveguide for surface acoustic waves based on two-dimensional pizoelectric phononic crystals

This paper has proposed a weighted waveguide for surface acoustic waves (SAW) based on two-dimensional piezoelectric phononic crystals (PnCs). In order to analyze the transmission of the weighted waveguide based on PnCs, SAW delay line model was built. In the model, period boundary condition was adopted to reduce the time and memory of model cost and perfect matching layer was adopted to absorb the reflection of the waves. Three-dimensional finite element method (FEM) was used to calculate the transmission coefficients and analyze the acoustic field distribution. Results showed that the band gaps and band passes are separated in the x and y direction. Thus the weighted waveguide can prohibit the waves in one direction while permit the waves in another direction. This property of weighted waveguide can be used in the SAW devices in the future study.

An approach to calculate reflectivity of the 2-D phononic crystals reflecting gratings in two directions

As a new structure, reflecting gratings based on two-dimensional (2-D) piezoelectric phononic crystals (PCs) have been studied for several years. This paper has proposed an approach to analyze the reflectivity of this reflecting grating in two directions. In the method, resonant modal was firstly analyzed with three-dimensional (3-D) finite element method (FEM) using the commercial software COMSOL Multiphysics, which was accurate and be suitable for 2-D PCs structures. With the resonant modal analysis, reflectivity can be obtained. The results show that the reflectivity of the 2-D reflecting grating is 2.2 times higher than 1-D reflecting grating in the x direction and 5.6 times in the y direction. These results demonstrate that the 2-D PCs reflecting grating can be used in SAW resonators to improve their performances. More researches are to be done to apply the 2-D PCs on the SAW resonators.

Resonant modal analysis of the two-dimensional phononic crysals transducers

A three-dimensional (3D) finite element method (FEM) model was proposed to analyze the resonant modal of the transducers based on two-dimensional (2D) phononic crystals (PnCs). Using this model two modals existed with symmetric modal and anti-symmetric modal can be extracted, and then reflectivity of the transducers was derived. An example of transducer based on 2D PnCs composed of IDTs of aluminum strips and tungsten stubs on top of IDTs was analyzed. The calculated reflectivity with different thickness of the stubs shows that a optimal thickness of tungsten stubs exists for a specified IDTs. This modal analysis offer a useful tool for the optimal designing 2D PnCs on the surface acoustic waves devices.