Design and Optimization of the Dual-Mode Lamb Wave Resonator and Dual-Passband Filter

Radio frequency (RF) filters with multiple passbands can meet the needs of miniaturization and integration for 5G communications. This paper reports a dual-mode Lamb wave resonator (DLWR) and a dual-passband filter based on DLWRs. The DLWR consists of a piezoelectric film and two interdigital electrode (IDT) arrays with different thicknesses, which leads to the coexistence of two main modes in the resonator. The resonance frequencies of the two modes can be adjusted separately by changing the thicknesses of the IDTs, which greatly satisfies the requirements of the dual-passband filter. Four DLWRs with different electrode configurations are designed, and the influences of the periodic length and thicknesses of the IDTs on the performance of the DLWR are studied. When the thickness of the piezoelectric layer is 0.75 μm and the two thicknesses of the IDTs are 0.1 μm and 0.3 μm, the resonance frequency of the second main mode is 1.27 GHz higher than the resonance frequency of the first main mode in the DLWR. Furthermore, a dual-passband filter based on the proposed DLWRs is demonstrated with an insertion loss less than 1 dB and a band rejection of about 15 dB. Moreover, two passbands at 2.45 GHz and 3.88 GHz with bandwidths of 66 MHz and 112 MHz, respectively, are achieved. The presented DLWR shows a potential application that can be used to obtain RF filters with adjustable dual passbands.

Dimensional Effects of Polymer Piezoelectric Films for Wind Energy Harvesting

Arrays of flexible polymer piezoelectric film cantilevers that mimic grass or leaves is a prospective idea for harvesting wind energy in urban areas, where the use of traditional technologies is problematic due to low wind velocities. Conversion of this idea into an economically attractive technology depends on various factors including the shape and dimensions of individual films to maximize generated power and to minimize associated costs of production, operation, and maintenance. The latter requirement can be satisfied with rectangular films undergoing flutter in ambient air. Flexible piezoelectric films that displace due to low forces and can convert mechanical energy into electrical energy are ideal for this application. The goal of the presented study is to determine the key dimensions of the piezoelectric film to enhance generated power within the wind range characteristic for urban areas from 1.3 to 7.6 m/s. For this purpose, experiments were conducted in a wind tunnel using piezoelectric polymer films of polyvinylidine fluoride with the length, width, and thickness varying in the ranges of 32 - 150 mm, 16 - 22 mm, and 40 - 64 µm, respectively. Voltage and power outputs for individual samples were measured at wind speeds ranging from 0.5 to 16.5 m/s. Results demonstrated that a single film could produce up to 0.74 nW and that the optimal film dimensions are 63 mm × 22 mm × 40 µm (from considered samples) for the wind energy harvesting in urban areas. Further improvement in power production can be expected when using films with reduced thickness, low elastic modulus, and increased length, and by assembling films in arrays.

Enhanced Coupling Coefficient in Dual-Mode ZnO/SiC Surface Acoustic Wave Devices with Partially Etched Piezoelectric Layer

Surface acoustic wave (SAW) devices based on multi-layer structures have been widely used in filters and sensors. The electromechanical coupling factor (K2), which reflects energy-conversion efficiency, directly determines the bandwidth of the filter and the sensitivity of sensor. In this work, a new configuration of dual-mode (quasi-Rayleigh and quasi-Sezawa) SAW devices on a ZnO/SiC layered structure exhibiting significantly enhanced K2 was studied using the finite element method (FEM), which features in the partial etching of the piezoelectric film between the adjacent interdigitated electrodes (IDTs). The influences of piezoelectric film thickness, etching ratio, top electrodes, bottom electrodes, and the metallization ratio on the K2 were systematically investigated. The optimum K2 for the quasi-Rayleigh mode and quasi-Sezawa mode can exceed 12% and 8%, respectively, which increases by nearly 12 times and 2 times that of the conventional ZnO/SiC structure. Such significantly promoted K2 is of great benefit for better comprehensive performance of SAW devices. More specifically, a quasi-Rayleigh mode with relatively low acoustic velocity (Vp) can be applied into the miniaturization of SAW devices, while a quasi-Sezawa mode exhibiting a Vp value higher than 5000 m/s is suitable for fabricating SAW devices requiring high frequency and large bandwidth. This novel structure has proposed a viable route for fabricating SAW devices with excellent overall performance.