Surface acoustic wave (SAW) devices, as one-dimensional phononic crystals (PCs), have obtained much attention for many years in applications of resonators, filters and sensors. Much effort has been done to calculate the parameters such as reflection and velocity for designing SAW devices.

In recent years, two-dimensional (2D) piezoelectric PCs have obtained more attentions as they have richer properties of band gaps than one-dimensional PCs. However, most of the literatures focus on deriving transmission of piezoelectric PCs and electromechanical coupling coefficients of 2D piezoelectric PCs, while the important reflection and velocity parameters are not derived for PCs.

Researchers from the Institute of Acoustics, Chinese Academy of Sciences and the Huazhong University Science and Technology worked together and have proposed a model to extract the reflection and velocity parameters of 2D piezoelectric PCs with the finite element method for SAW.

The model built as shown in Fig.1 is composed of three-dimensional SAW delay lines with and without 2D piezoelectric PCs respectively. Perfect matching layer is used to absorb the reflective waves in the direction of wave propagation and a period boundary condition is used in the direction perpendicular to the wave propagation to reduce the time and memory cost of the model. Reflected and transmitted signals of piezoelectric PCs are obtained with a suitable windowing operation. Fig.2 displays the reflection and transmission of the PCs. It’s reasonable at the frequency of SAW delay line passband, while it’s inaccurate outside 120-170MHz due to big noise of the SAW delay line.

Experiments show that the velocity is smaller than the velocity of Rayleigh SAW on 128º-YXLiNbO3. It means that it can make delay line obtain longer delay time with PCs at the same size. Therefore, the result can put the 2D PCs applications into use of the delay line devices.

Fig.1 The model used in the calculation (Image by TIAN).

Fig.2 Reflection and transmission of Ni/128º-YXLiNbO3 piezoelectric PCs (Image by TIAN).

References:
TIAN Yahui, LI Honglang, KE Yabing, LUO Wei, HE Shitang. Extractions of Reflection and Velocity Parameters for Surface Acoustic Wave in Two-Dimensional Piezoelectric Phononic Crystals. 2014 IEEE International Ultrasonics Symposium Proceedings (pp. 2525-2528, September 2014, Chicago, IL). DOI: 10.1109/ULTSYM.2014.0630

Contact:
TIAN Yahui
Institute of Acoustics, Chinese Academy of Sciences, 100190 Beijing, China
E-mail: tianyahui@mail.ioa.ac.cn or yahuitian@yeah.net