In the present paper, guided four beam (G4B) piezoelectric transducers with enhanced sensitivities have been designed. Based on the suggested G4B structures, piezoelectric energy harvesters (PEHs) and acceleration transducers with higher voltages than their previously reported counterparts and with lower displacements than the single-cantilever PEHs (SC-PEHs) have been proposed. We have shown that it is possible to arrive at much more output voltages in comparison with the conventional PEHs by redesigning the structure of the cantilever beams. In 1 g acceleration, the maximum output voltage obtained from the proposed PEHs has been 13.49 V whereas the output voltage for the conventional G4B-PEH is 2.87 V. This paper for the first time proposes G4B-PEHs with smaller displacements and larger voltages compared to a SC-PEH. The same G4B framework has been studied as a piezoelectric acceleration transducer. The effect of piezoelectric length on the extracted voltage in both unimorph and bimorph cantilevers has been discussed and the optimized length has been calculated. An analytical method is developed to compute the resonance frequencies of different beam shapes whose results are in a good agreement with numerical simulations.

A high-sensitivity MEMS diaphragm hydrophone has been proposed. The designed hydrophone has a higher sensitivity in comparison with its previous counterparts. Readout electronics includes an integrated MOSFET and an external operational amplifier. An integrated ring MOSFET with a piezoelectric gate has been used as the strain to the electrical current transducer. The drain of the MOSFET has been connected to an operational amplifier that converts the transistor current to the voltage and also amplifies it. An analytical relation for the sensitivity has been derived which is in an outstanding agreement with the finite-element analysis. It has been proven that the changes in the channel length and mobility are negligible, and the transistor current is merely under the influence of the pressure-induced charges on the piezoelectric surface which directly produces the vertical electric field. It has been shown that the ring MOSFET transducer can help designing MEMS hydrophones with smaller dimensions while keeping the sensitivity as much as the larger structures.

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Piezoelectric nanotransducers may offer key advantages in comparison with conventional piezoelectrics, including more choices for types of mechanical input, positions of the contacts, dimensionalities and shapes. However, since piezo-semiconductive nanostructures are generally much easier to fabricate and integrate into functional systems than insulating materials, modeling becomes significantly more intricate and the effects of free charges have been considered only in a few studies. The available reports are complicated by the absence of proper nomenclature and figures of merit. Besides, some analyses are incomplete. For instance, the local piezopotential and free charges within axially strained conical piezo-semiconductive nanowires have only been systematically investigated for very low doping (1016 cm-3) and under compression. Here we give the definitions for the enhancement, depletion, base and tip piezopotentials, their characteristic lengths and both the tip-to-base and the depletion-to-enhancement piezopotential-ratios. As an example, we use these definitions for analyzing the local piezopotential and free charges in n-type ZnO truncated conical nanostructures with different doping levels (intrinsic, 1016 cm-3, 1017 cm-3) for both axial compression and traction. The definitions and concepts presented here may offer insight for designing high performance piezosemiconductive nanotransducers.