This letter reports a phononic crystal (PnC) cavity resonance device to realize an enhanced directional acoustic sensing. The acoustic cavity in the PnC device is designed with a line defect produced by replacing a line array from a perfect PnC. The line-defect PnC will make a defect band related to the cavity resonance within the perfect PnC band gap range. The design enhances the input sound wave at the resonance frequency of the acoustic cavity under the normal incidence, which produces an enhanced direction-sensitive response. The proposed device shows desirable directional acoustic sensing property, and the sensing frequency can be decreased by enlarging the effective refractive index of the acoustic cavity. The PnC cavity resonance devices present broad application prospects in weak signal detection and sound source localization.
A Timoshenko beam model combined with piezoelectric constitutive equations and an electrical model was proposed to describe the energy harvesting performances of multilayered d 15 mode PZT-51 piezoelectric bimorphs in series and parallel connections. The effect of different clamped conditions was considered for non-piezoelectric and piezoelectric layers in the theoretical model. The frequency dependences of output peak voltage and power at different load resistances and excitation voltages were studied theoretically, and the results were verified by finite element modeling (FEM) simulation and experimental measurements. Results show that the theoretical model considering different clamped conditions for non-piezoelectric and piezoelectric layers could make a reliable prediction for the energy harvesting performances of multilayered d 15 mode piezoelectric bimorphs. The multilayered d 15 mode piezoelectric bimorph in a series connection exhibits a higher output peak voltage and power than that of a parallel connection at a load resistance of 1 MΩ. A criterion for choosing a series or parallel connection for a multilayered d 15 mode piezoelectric bimorph is dependent on the comparison of applied load resistance with the critical resistance of about 55 kΩ. The proposed model may provide some useful guidelines for the design and performance optimization of d 15 mode piezoelectric energy harvesters.
This letter reports a dual-directionally tunable acoustic metamaterial comprising a matrix and two spiral beams with an embedded permanent magnet. Two types of vibration modes associated with band gaps can be excited under out-of-plane and in-plane excitations. The out-of-plane and in-plane transmissions of the metamaterial move toward two directions because of their modal characteristics when external magnets are introduced to tune the magnetic force monotonically. The mechanism of the dual-directional tunability is theoretically clarified. A composite dual-directionally tunable metamaterial prototype achieves the flexible tuning of the metamaterial band gap. Such effect provides broad application prospects for low-frequency vibration isolation in practical environments.
Vibrations carry a wealth of useful physical information in various fields. Identifying the multi-source vibration information generally requires a large number of sensors and complex hardware. Compressive sensing has been shown to be able to bypass the traditional sensing requirements by encoding spatial physical fields, but how to encode vibration information remains unexplored. Here we propose a randomized resonant metamaterial with randomly coupled local resonators for single-sensor compressed identification of elastic vibrations. The disordered effective masses of local resonators lead to highly uncorrelated vibration transmissions, and the spatial vibration information can thus be physically encoded. We demonstrate that the spatial vibration information can be reconstructed via a compressive sensing framework, and this metamaterial can be reconfigured while maintaining desirable performance. This randomized resonant metamaterial presents a new perspective for single-sensor vibration sensing via vibration transmission encoding, and potentially offers an approach to simpler sensing devices for many other physical information.
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