A Fluidics-Based Double Flexural Membrane Piezoelectric Micromachined Ultrasonic Transducer (PMUT) for Wide-Bandwidth Underwater Acoustic Applications.

Khairul Azman Ahmad,Muhammad Naim Haron,Khairu Anuar Mohamed Zain,Asrulnizam Abd Manaf,Mohamad Faizal Abd Rahman

doi:10.3390/s21165582

Khairul Azman Ahmad, Muhammad Naim Haron + Show 3 more

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https://doi.org/10.3390/s21165582

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Abstract

In acoustic receiver design, the receiving sensitivity and bandwidth are two primary parameters that determine the performance of a device. The trade-off between sensitivity and bandwidth makes the design very challenging, meaning it needs to be fine-tuned to suit specific applications. The ability to design a PMUT with high receiving sensitivity and a wide bandwidth is crucial to allow a wide spectrum of transmitted frequencies to be efficiently received. This paper presents a novel structure involving a double flexural membrane with a fluidic backing layer based on an in-plane polarization mode to optimize both the receiving sensitivity and frequency bandwidth for medium-range underwater acoustic applications. In this structure, the membrane material and electrode configuration are optimized to produce good receiving sensitivity. Simultaneously, a fluidic backing layer is introduced into the double flexural membrane to increase the bandwidth. Several piezoelectric membrane materials and various electrode dimensions were simulated using finite element analysis (FEA) techniques to study the receiving performance of the proposed structure. The final structure was then fabricated based on the findings from the simulation work. The pulse–echo experimental method was used to characterize and verify the performance of the proposed device. The proposed structure was found to have an improved bandwidth of 56.6% with a receiving sensitivity of −1.8864 dB rel 1 V µPa. For the proposed device, the resonance frequency and center frequency were 600 and 662.5 kHz, respectively, indicating its suitability for the targeted frequency range.

Highlights

Introduction iationsFor underwater applications, PMUTs are widely used in different areas, including for control, communication, and imaging
The thickness of the air cavity is not influenced by the increase in stress that occurs in the PZT5H membrane
The results showed that the Throughout this study, a novel structure involving dual flexural membranes with a backing layer was successfully fabricated and tested

Summary

Introduction

Introduction iationsFor underwater applications, PMUTs are widely used in different areas, including for control, communication, and imaging. PMUT studies are often based on the polarization of piezoelectric films, which generate the electric charge required to induce an electrical signal in response to the amount of acoustic energy hitting the membrane [2]. This consists of a double membrane and double cavities, aiming to provide both good sensitivity and a wide bandwidth for the targeted application. The first layer of the flexural structure consists of an acoustic matching layer (PDMS), first flexural membrane (PZT5H), air cavity, and electrodes. In theory, when an ultrasonic wave hits the PMUT, the first flexural membrane bends and induces a charge at the positive electrode.

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