In this paper, a hybrid full-wave analysis of surface acoustic wave (SAW) devices is proposed to achieve accurate and fast simulation. The partial differential equation (PDE) models of the physical system in question and graphics processing unit (GPU)-assisted hierarchical cascading technology (HCT) are used to calculate acoustic-electric characteristics of a SAW filter. The practical solid model of the radio frequency (RF) filter package is constructed in High Frequency Structure Simulator (HFSS) software and the parasitic electromagnetics of the entire package is considered in the design process. The PDE-based models of the two-dimensional finite element method (2D-FEM) are derived in detail and solved by the PDE module embedded in COMSOL Multiphysics. Due to the advantages of PDE-based 2D-FEM, it is universal, efficient and not restricted to handling arbitrary materials and crystal cuts, electrode shapes, and multi-layered substrate. Combining COMSOL Multiphysics with a user-friendly interface, a flexible way of modeling and mesh generation, it can greatly reduce the complicated process of modeling and physical properties definition. Based on a hybrid full-wave analysis, we present an example application of this approach on a TC-SAW ladder filter with 5° YX-cut LiNbO₃ substrate. Numerical results and measurements were calculated for comparison, and the accuracy and efficiency of the proposed method were verified.

Radio-frequency (RF) surface acoustic wave (SAW) resonators used as filters and duplexers are mass-produced and widely used in current mobile phones. With the numerous emergences of the diverse device structure, a universal method used for the accurate and fast simulation of the SAW resonator calls for urgent demand. However, there are too many instances where the behavior of the entire acoustic resonator cannot be characterized rapidly and efficiently due to limitations in the current computer memory and speed. This is especially true for SAW resonators configured with long arrays of inter-digital transducers (IDTs), and we have to resort to a periodic analysis. In this paper, the previously reported generalized partial differential equations (PDE) based on the two-dimensional finite element method (2D-FEM) model is extended to analysis for the periodic structure of the SAW resonator. We present model order reduction (MOR) techniques based on FEM and periodic boundary conditions to achieve a dimensionally reduced PDE model without decreasing the accuracy of computations. Examples of different SAW devices, including the regular SAW, IHP-SAW and TC-SAW resonators, are provided which shows the results of the periodic analysis compared with the experimental results of the actual resonators. The investigation results demonstrate the properties of the proposed methodology and prove its effectiveness and accuracy.

This paper presents the results of a numerical simulation and experimental test of a multi-element focused air-coupled transducer. The experimental structure of each transducer element comprises 1-3 connectivity piezo-composite stacking with two matching layers to overcome the enormous impedance mismatch between the piezo-composite disc and air. The numerical simulation is carried out using the circular-piston radiation model, and the experimental results for the acoustic field agree well with the simulation results. Furthermore, surface microcracks are detected successfully using a C-scan system involving the designed multi-element focused air-coupled transducer. The results show that the designed multi-element focused air-coupled transducer offers excellent focusing ability and is beneficial for detecting surface microcracks.

This work presents a low insertion loss air-coupled ultrasonic transducer with a parallel laminated piezoelectric structure. The relevant parameters of this structure are theoretically analyzed. For overcoming the enormous acoustic impedance mismatch between the piezoelectric material and air, a 1–3 connectivity piezoelectric composite, and a stack of two low acoustic impedance matching layers are adopted. The experimental results show that the insertion loss of −17.5 dB is obtained under the pitch-catch mode with the length of the air column of 50 mm by selecting a suitable air-coupled ultrasonic transducer combination. The insertion loss improvement is 3.8 dB compared with a monolayer piezoelectric structure with an identical active area.

Surface acoustic wave (SAW)-based sensors have become highly valued for their use as nanosensors in industrial applications. Accurate prediction of the thermal stability is a key problem for sensor design. In this work, a numerical tool based on the finite element method combined with piezoelectric Lagrangian equations has been developed to accurately predict the thermal sensitivity characteristics of surface acoustic wave devices. Theoretical analysis for the geometric nonlinearity contributing to the frequency–temperature characteristic and material constants’ dependency on temperature were taken into consideration. The thermomechanical equilibrium equation built on the three-dimensional finite element method (3D-FEM) mesh node took mesh movement into account because thermal expansion was employed. The frequency–temperature characteristics of different SAW modes, including Rayleigh waves and leaky waves excited on a piezoelectric substrate of quartz or lithium tantalate, respectively, were calculated. The theoretical accuracy of the proposed numerical tool was verified by experiments.

SignificanceA multiplexed fiber laser sensing system for cell temperature is proposed. To the best of the authors’ knowledge, this is the first multilongitudinal mode (MLM) optical fiber laser sensor array designed for cell temperature sensing.AimA two-channel cell temperature sensing system with high sensitivity and real-time sensing capability is achieved. The temperature change of human hepatoellular carcinomas (HepG2) cells under the influence of exogenous chemical aflatoxin B1 (AFB1) can be monitored in real time.ApproachA fiber laser cavity consists of a pair of fiber Bragg gratings (FBGs) with matched central wavelengths and a piece of erbium-doped fiber (EDF). The static FBG is utilized for design of fiber laser cavity and laser modes selection. In comparison, the sensing FBG is used for cell temperature sensing. The sensing FBG has a length of 10 mm and a diameter of 200 μm. Beat frequency signals (BFS) are generated by MLM lasers after optical-to-electrical conversion at a photodetector. Frequency change of a BFS is closely related to the reflected wavelength change of the sensing FBG. Through frequency division multiplexing, two fiber laser cavities are designed in the sensing system for two-channel temperature sensing. Frequency shift of a BFS that represents temperature change of cells can be automatically recorded in seconds.ResultsA two-channel cell temperature sensing system is designed with high sensitivities of 101.62 and 119.82 kHz / ° C, respectively. The temperature change of HepG2 cells under the influence of exogenous chemical AFB1 is monitored in real time.ConclusionsThe proposed system has the advantages of simple structure, high sensitivity, and two-channel sensing capability. Our study provides a simple and effective method to design a fiber laser sensor system without complex demodulation techniques and expensive optical components.