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We present the design and numerical investigation of a reconfigurable and miniature locally resonant surface acoustic wave demultiplexer based on a ZnO pillar phononic crystal, for the first time. Hollow cylinder line defects are used as waveguides, due to their good structural controllability over the local resonant waveguiding frequency and bandwidth. Two local resonant surface acoustic waveguides are designed and simulated as the output channels of the demultiplexer, and the shear-horizontal wave transmission spectra are calculated for each channel individually. The designed radio frequency demultiplexing output channels support frequencies of 4.14 GHz and 4.28 GHz, with respective bandwidths of 40 MHz and 60 MHz, while their spatial separation is just about 800 nm. In order to achieve a reconfigurable output characteristic, the effect of acoustoelectric interaction in piezoelectric semiconductors is numerically simulated in this study. The acoustoelectric interaction causes an additional stiffness in ZnO that can be released by adding extra charge carriers, i.e., increasing conductivity, thus changing the effective elasticity of the ZnO structures and the guiding frequencies of the output channels. Two output frequencies show red shifts of about 100 MHz and 150 MHz by extremely increasing the conductivity of ZnO structures from 0.01 S/m to 100 S/m. [ABSTRACT FROM AUTHOR]

Here, we introduce a tailorable coupled resonator surface acoustic waveguide (CRSAW), based on a linear defect of elliptical cylinders inside a phononic crystal of ZnO pillars on a Si substrate. The designed elliptical resonators allow the emergence of a minimally dispersive, monomode shear-guiding band inside the local resonance bandgap, owing to their partially broken structural symmetry in comparison with their previously reported counterparts such as pillars and hollow cylinders. Moreover, by introducing reconfigurable waveguide behavior, we benefit from the acoustoelectric-induced elasticity modulation of ZnO, which is a semiconducting piezoelectric material. Switching the conductivity of ZnO structures between two limiting low and high values (0.01 S m−1 and 100 S m−1), a considerable waveguide modulation at full width at half maximum (FWHM) (ΔFWHM = −21%) and guiding frequency (Δfd = −2.81%) are achieved for the designed optimized elliptical cylinder CRSAW while maintaining an acceptable loss value. Benefiting from the proposed ZnO-based elliptical CRSAW, we have achieved simultaneous monomode and low-bandwidth surface acoustic waveguide behaviors, without involving significant fabrication complications. The designed structures open up new horizons toward the realization of promising building blocks for designing reconfigurable and miniaturized SAW RF-filters, demultiplexers, and Mach–Zehnder devices for wireless communications applications. [ABSTRACT FROM AUTHOR]

Highlights • We designed tunable acoustic resonators, based on piezoelectric defect sites in phononic crystals. • We have optimized the defect size, structure and electrically stimulated strain configuration. • We have achieved a maximum frequency shift of 1140 Hz, versus exerting 1% strain to the defect rods. • The proposed electrical tunable acoustic resonator is promising for emerging new reconfigurable devices. Abstract Reconfigurable phononic crystals (PnCs) and related devices are highly attractive because of their flexibility for different applications. We present the design procedure for a tunable acoustic resonator based on a 2D PnC, consisting of a periodic array of piezoelectric rods of radii 175 μm as inclusions arranged in air background. A single point defect devised by a rod of radius 161 μm, replacing one of the inclusions, plays the role of the acoustic resonator, leading to a defect frequency in the phononic band gap (f d ≈ 432 kHz). Applying a ∼1% strain to the defect rod, via an external voltage, tunes the defect resonant frequency within the phononic band gap. It is shown that the maximum tunability and the frequency shift depends on the defect size, and is achieved about Δ f d = 440 Hz for the defect with the expense of descending quality factor. Considering the pattern of the localized pressure field, we introduce a multi-defect structure with five symmetric defect rods, corresponding to the maxima of field distribution. It is shown that maximum frequency shift of the dominant defect frequency is achieved about Δ f d = 1.14 kHz for defect radius of 161 μm, when all five defect rods are strained. The proposed tunable filter based on multi-defect structure results in an enhancement of about 2.6 times in the maximum frequency shift, in comparison with the single defect structure, and introduces a promising approach for realizing tunable acoustic devices. [ABSTRACT FROM AUTHOR]

Triboelectric nanogenerators have been emerged as the most promising mechanical energy harvesters, during last few years. Here, a sonic triboelectric nanogenerator with 7-fold enhanced output power is reported, in which carbon nanotubes are utilized to increase the electrode's effective surface area. To improve the efficiency we have taken advantage of acoustic wave localization in a sonic array. For this purpose, first we have studied an array of periodic acoustic scatterers by simulation. Then, we have designed a 1-D phononic crystal consisting of five steel slabs standing in air medium, which leads to resonance of incident acoustic wave at f = 4.34 kHz. We implemented the design, but replaced the middle scatterer by triboelectric nanogenerator. An enhancement factor of about 4 has been measured for the output voltage of the sonic nanogenerator at f = 4.24 kHz, when it is embedded in the sonic array. Also, power enhancement factor of 7-fold has been achieved (P out ≈4 μW/m 2 ), benefiting from the applied sonic cavity. The measured resonance frequency and enhancement factor are in acceptable agreement with the simulation results. The presented enhanced energy harvesting configuration proposes a compact and low cost structure, which allows parallel energy harvesting, and seems promising for realizing sonic harvesters. [ABSTRACT FROM AUTHOR]