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Micromachines
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Acoustic Transducers and Their Applications
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Acoustic Transducers and Their Applications

A special issue of Micromachines (ISSN 2072-666X). This special issue belongs to the section "A：Physics".

Deadline for manuscript submissions: closed (10 April 2024) | Viewed by 25527

Special Issue Editors

Dr. Songsong Zhang

E-Mail Website
Guest Editor
School of Microelectronics, Shanghai University, Shanghai 200444, China
Interests: piezoelectric material; MEMS device process; piezoelectric transducer design; acoustic sensing model; acoustic device algorithm and system-level application
Special Issues, Collections and Topics in MDPI journals
Dr. Qiaozhen Zhang

E-Mail Website
Guest Editor
College of Information, Mechanical and Electrical Engineering, Shanghai Normal University, Shanghai 200234, China
Interests: intelligent sensing technology and system; RF micro-acoustic devices for mobile communication; modeling and simulation of piezoelectric thin-film micro-acoustic devices
Special Issues, Collections and Topics in MDPI journals
Dr. Xing Haw Marvin Tan

E-Mail Website
Guest Editor
Institute of High Performance Computing, A*STAR, Singapore 138632, Singapore
Interests: piezoelectric transducer design and simulation; piezoelectric material property extraction; bulk acoustic wave (BAW) devices; acoustic meta-surfaces (including meta-lens); beam steering
Special Issues, Collections and Topics in MDPI journals
Prof. Dr. Kenya Hashimoto

E-Mail Website
Guest Editor
School of Integrated Circuit Science and Engineering, University of Electronic Science and Technology of China, Chengdu 610056, China
Interests: surface and bulk acoustic wave devices
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear Colleagues,

Acoustics is one of the key forms of mechanical energy that is exerted everywhere in our world. It helps with sensing, actuating, and communicating, and even helps in medical or industrial matters. With a broad operating spectrum, it serves as the most pivotal tool in various implementations, ranging from airborne applications to studies through different media, especially for needs beyond the physical limitations of other mechanisms (e.g., optical or electromagnetic waves). Alongside the progression of advanced transducer technology, more acoustic device alternatives have been optimized for conventional applications. In addition, consistent research efforts in the field of frontier transducers enable rapid paradigm shifts in many emerging acoustic applications, which coherently accelerate the development of other peripheral technologies, such as thin-film materials used in acoustic transducers, circuits for acoustic devices, modules, algorithms, system integration, and even the integration of acoustic sensors into smart systems. In order to promote research efforts and advocate for continuous innovation in this field, in this Special Issue the current state of the art in the field of ‘acoustic transducers and their applications’ will be presented, covering a wide range of related topics, including, but not limited to, the following:

  • New piezoelectric materials: ceramics, thin films, single crystals, polymers, composites, 2D materials, etc.;
  • Acoustic transducers: acoustic sensors and actuators, circuits for acoustic devices, modules, algorithms, and integrated systems;
  • Piezoelectric devices/acoustic transducers: fabrication, testing, characterization, design, modeling, simulation, manufacturing, 3D printing, packaging, and system integration;
  • Acoustic transducer applications: nondestructive testing, acoustic arrays for holograms and beam steering, acoustic ranging, acoustic lenses, meta-materials and meta-surfaces, energy harvesting, medical imaging, wearable sensors, biomedical applications, virtual reality/augmented reality, and other emerging applications for the metaverse.

 

Dr. Songsong Zhang
Dr. Qiaozhen Zhang
Dr. Xing Haw Marvin Tan
Prof. Dr. Kenya Hashimoto
Guest Editors

Manuscript Submission Information

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Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Micromachines is an international peer-reviewed open access monthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 2600 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

  • Acoustic transducers and their design, simulation, testing, and characterization
  • Piezoelectric MEMS device
  • Thin-film piezoelectric materials and material properties
  • MEMS integration process
  • Acoustic modules, algorithms, circuits, and systems
  • Acoustic lenses and meta-surfaces
  • Acoustic transducer arrays and their applications
  • Implementation and usage of acoustic devices for various applications.

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Published Papers (15 papers)

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16 pages, 4921 KiB  
Article
Effect of Filling Material Properties on 1-3 Piezoelectric Composite Performance
by Yao Liu, Yang Zhou, Zhigang Zhao and Jinjie Zhou
Micromachines 2024, 15(7), 812; https://doi.org/10.3390/mi15070812 - 22 Jun 2024
Viewed by 720
Abstract
The 1-3 piezoelectric composite is the key component of the acoustic transducer, which is widely used in detection, due to the high energy conversion efficiency, cheap raw material, and low aging. To reveal the influence of epoxy mixture, used to connect the piezoelectric [...] Read more.
The 1-3 piezoelectric composite is the key component of the acoustic transducer, which is widely used in detection, due to the high energy conversion efficiency, cheap raw material, and low aging. To reveal the influence of epoxy mixture, used to connect the piezoelectric column, on the composite performance, a 1-3 piezoelectric composite model was built. The effects of mixture properties on the impedance curves, vibration mode, and deformation displacement of the composite were determined. Six 1-3 piezoelectric composites with different filling mixture properties, by changing the glass microspheres’ mass ratio in the epoxy, were prepared and measured to validate the model. The results showed that with the increase in the proportion of the glass microsphere in the epoxy mixture, the vibration coupling of the piezoelectric composites was gradually eliminated. The acoustic impedance was reduced by 12%. The electromechanical coupling coefficient and effective electromechanical coupling coefficient were increased by 5.4% and 8.3%, respectively. The density and Young’s modulus decrease in filling mixture can significantly improve piezoelectric composite performance. Full article
(This article belongs to the Special Issue Acoustic Transducers and Their Applications)
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16 pages, 5323 KiB  
Communication
An AlScN Piezoelectric Micromechanical Ultrasonic Transducer-Based Power-Harvesting Device for Wireless Power Transmission
by Junxiang Li, Yunfei Gao, Zhixin Zhou, Qiang Ping, Lei Qiu and Liang Lou
Micromachines 2024, 15(5), 624; https://doi.org/10.3390/mi15050624 - 6 May 2024
Cited by 2 | Viewed by 1434
Abstract
Ultrasonic wireless power transfer technology (UWPT) represents a key technology employed for energizing implantable medical devices (IMDs). In recent years, aluminum nitride (AlN) has gained significant attention due to its biocompatibility and compatibility with complementary metal-oxide-semiconductor (CMOS) technology. In the meantime, the integration [...] Read more.
Ultrasonic wireless power transfer technology (UWPT) represents a key technology employed for energizing implantable medical devices (IMDs). In recent years, aluminum nitride (AlN) has gained significant attention due to its biocompatibility and compatibility with complementary metal-oxide-semiconductor (CMOS) technology. In the meantime, the integration of scandium-doped aluminum nitride (Al90.4%Sc9.6%N) is an effective solution to address the sensitivity limitations of AlN material for both receiving and transmission capabilities. This study focuses on developing a miniaturized UWPT receiver device based on AlScN piezoelectric micro-electromechanical transducers (PMUTs). The proposed receiver features a PMUT array of 2.8 × 2.8 mm2 comprising 13 × 13 square elements. An acoustic matching gel is applied to address acoustic impedance mismatch when operating in liquid environments. Experimental evaluations in deionized water demonstrated that the power transfer efficiency (PTE) is up to 2.33%. The back-end signal processing circuitry includes voltage-doubling rectification, energy storage, and voltage regulation conversion sections, which effectively transform the generated AC signal into a stable 3.3 V DC voltage output and successfully light a commercial LED. This research extends the scope of wireless charging applications and paves the way for further device miniaturization by integrating all system components into a single chip in future implementations. Full article
(This article belongs to the Special Issue Acoustic Transducers and Their Applications)
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16 pages, 6766 KiB  
Article
Electromagnetic Acoustic Detection of Pipe Defects Hidden above T-Type Support Structures with Circumferential Shear Horizontal Guided Wave
by Xingjun Zhang, Jinjie Zhou, Yang Hu, Yao Liu and Xingquan Shen
Micromachines 2024, 15(4), 550; https://doi.org/10.3390/mi15040550 - 20 Apr 2024
Cited by 2 | Viewed by 1138
Abstract
When pipe defects are generated above the T-type support structure location, it is difficult to distinguish the reflection signals caused by the weld bead at the support structure from the reflection echoes of pipe defects. Therefore, in order to effectively detect pipe defects, [...] Read more.
When pipe defects are generated above the T-type support structure location, it is difficult to distinguish the reflection signals caused by the weld bead at the support structure from the reflection echoes of pipe defects. Therefore, in order to effectively detect pipe defects, a waveform subtraction method with a circumferential shear horizontal (CSH) guided wave is proposed, which is generated by an electromagnetic acoustic transducer (EMAT). First, a CSH0 guided wave mode with a center frequency of 500 kHz is selected to establish a three-dimensional model with and without pipe defects above the support structure. Following this, the influence of different widths of support structures on the echo signal is compared. Moreover, simulation and experimental results are used to compare the influence of different welding qualities on the detection results. Finally, the waveform subtraction method is used to process the simulation and experimental signals, and the influence of pipe defects with different lengths and depths is discussed. The results show that the non-through crack defect of 5 mm × 1 mm (length × depth) can be detected. The results show that this method can effectively detect the cracks by eliminating the influence of the weld echo, which provides a new concept for the detection of the defect above the support structure. Full article
(This article belongs to the Special Issue Acoustic Transducers and Their Applications)
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16 pages, 7169 KiB  
Article
Design and Characterization of Surface Acoustic Wave-Based Wireless and Passive Temperature Sensing System
by Zhixin Zhou, Hui Wang and Liang Lou
Micromachines 2024, 15(4), 544; https://doi.org/10.3390/mi15040544 - 18 Apr 2024
Viewed by 3339
Abstract
The surface acoustic wave (SAW) temperature sensor has received significant attention due to its wirelessly powered, battery-free, and chipless capabilities. This paper proposes a wireless sensing system comprising a one-port SAW resonator, helix antenna, and transceiver circuit. The SAW resonator used in this [...] Read more.
The surface acoustic wave (SAW) temperature sensor has received significant attention due to its wirelessly powered, battery-free, and chipless capabilities. This paper proposes a wireless sensing system comprising a one-port SAW resonator, helix antenna, and transceiver circuit. The SAW resonator used in this system is based on aluminum nitride (AlN) thin film, which exhibits high velocity and excellent piezoelectric properties. Simulations and experiments were conducted to investigate the performance of the designed SAW resonator. A helix antenna was also designed using finite element simulation to facilitate signal transmission between the SAW temperature sensor and the transceiver. An impedance-matching network was introduced between the helix antenna and the SAW resonator to optimize signal transmission. When the wireless SAW temperature sensor was placed within a certain distance of the mother antenna, the reflection peak of the SAW resonator was observed in the spectrum of the return signal. The frequency of the echo signal increased almost linearly as the temperature increased during the temperature tests. The fitted temperature coefficient of frequency (TCF) was −31.34 ppm/°C, indicating that the wireless temperature sensing system has high-temperature sensitivity. Full article
(This article belongs to the Special Issue Acoustic Transducers and Their Applications)
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12 pages, 9703 KiB  
Article
A Novel Nondestructive Testing Probe Using AlN-Based Piezoelectric Micromachined Ultrasonic Transducers (PMUTs)
by Jiawei Yin, Zhixin Zhou and Liang Lou
Micromachines 2024, 15(3), 306; https://doi.org/10.3390/mi15030306 - 23 Feb 2024
Cited by 1 | Viewed by 1711
Abstract
Ultrasonic nondestructive testing (NDT) usually utilizes conventional bulk piezoelectric transducers as transceivers. However, the complicated preparation and assembly process of bulk piezoelectric ceramics limits the development of NDT probes toward miniaturization and high frequency. In this paper, a 4.4 mm × 4.4 mm [...] Read more.
Ultrasonic nondestructive testing (NDT) usually utilizes conventional bulk piezoelectric transducers as transceivers. However, the complicated preparation and assembly process of bulk piezoelectric ceramics limits the development of NDT probes toward miniaturization and high frequency. In this paper, a 4.4 mm × 4.4 mm aluminum nitride (AlN) piezoelectric micromachined ultrasonic transducer (PMUT) array is designed, fabricated, characterized, and packaged for ultrasonic pulse–echo NDT of solids for the first time. The PMUT array is prepared based on the cavity silicon-on-insulator (CSOI) process and packaged using polyurethane (PU) material with acoustic properties similar to water. The fabricated PMUT array resonates at 2.183 MHz in air and at around 1.25 MHz after PU encapsulation. The bandwidth of the packaged PMUT receiver (244 kHz) is wider than that of a bulk piezoelectric transducer (179 kHz), which is good for axis resolution improvement. In this work, a hybrid ultrasonic NDT probe is designed using two packaged PMUT receivers and one 1.25 MHz bulk transmitter. The bulk transmitter radiates an ultrasonic wave into the sample, and the defect echo is received by two PMUT receivers. The 2D position of the defect could be figured out by time-of-flight (TOF) difference, and a 30 mm × 65 mm detection area is acquired. This work demonstrates the feasibility of applying AlN PMUTs to ultrasonic NDT of solids and paves the way toward a miniaturized NDT probe using AlN PMUT technology. Full article
(This article belongs to the Special Issue Acoustic Transducers and Their Applications)
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12 pages, 6110 KiB  
Article
Stepped-Tube Backside Cavity Piezoelectric Ultrasound Transducer Based on Sc0.2AI0.8N Thin Films
by Xiaobao Li, Haochen Lyu, Ahmad Safari and Songsong Zhang
Micromachines 2024, 15(1), 72; https://doi.org/10.3390/mi15010072 - 29 Dec 2023
Viewed by 1400
Abstract
This paper presents a novel piezoelectric micromachined ultrasonic transducer (PMUT) with theoretical simulation, fabrication, and testing. Conventional methods using a PCB or an external horn to adjust the PMUT acoustic field angle are limited by the need for transducer size. To address this [...] Read more.
This paper presents a novel piezoelectric micromachined ultrasonic transducer (PMUT) with theoretical simulation, fabrication, and testing. Conventional methods using a PCB or an external horn to adjust the PMUT acoustic field angle are limited by the need for transducer size. To address this limitation, the stepped-tube (expanded tube) backside cavity PMUT has been proposed. The stepped-tube PMUT and the tube PMUT devices have the same membrane structure, and the acoustic impedance matching of the PMUT is optimized by modifying the boundary conditions of the back cavity structure. The acoustic comparison experiments show that the average output sound pressure of the stepped-tube backside cavity PMUT has increased by 17%, the half-power-beam-width (θ-3db) has been reduced from 55° to 30° with a reduction of 45%, and the side lobe level signal is reduced from 147 mV to 66 mV. In addition, this work is fabricated on an eight-inch wafer. The process is compatible with standard complementary metal oxide semiconductor (CMOS), conditions are stable, and the cost is controllable, plus it facilitates the batch process. These conclusions suggest that the stepped-tube backside cavity PMUT will bring new, effective, and reliable solutions to ranging applications. Full article
(This article belongs to the Special Issue Acoustic Transducers and Their Applications)
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27 pages, 3788 KiB  
Article
Modeling a Fluid-Coupled Single Piezoelectric Micromachined Ultrasonic Transducer Using the Finite Difference Method
by Valentin Goepfert, Audren Boulmé, Franck Levassort, Tony Merrien, Rémi Rouffaud and Dominique Certon
Micromachines 2023, 14(11), 2089; https://doi.org/10.3390/mi14112089 - 12 Nov 2023
Cited by 1 | Viewed by 1207
Abstract
A complete model was developed to simulate the behavior of a circular clamped axisymmetric fluid-coupled Piezoelectric Micromachined Ultrasonic Transducer (PMUT). Combining Finite Difference and Boundary Element Matrix (FD-BEM), this model is based on the discretization of the partial differential equation used to translate [...] Read more.
A complete model was developed to simulate the behavior of a circular clamped axisymmetric fluid-coupled Piezoelectric Micromachined Ultrasonic Transducer (PMUT). Combining Finite Difference and Boundary Element Matrix (FD-BEM), this model is based on the discretization of the partial differential equation used to translate the mechanical behavior of a PMUT. In the model, both the axial and the transverse displacements are preserved in the equation of motion and used to properly define the neutral line position. To introduce fluid coupling, a Green’s function dedicated to axisymmetric circular radiating sources is employed. The resolution of the behavioral equations is used to establish the equivalent electroacoustic circuit of a PMUT that preserves the average particular velocity, the mechanical power, and the acoustic power. Particular consideration is given to verifying the validity of certain assumptions that are usually made across various steps of previously reported analytical models. In this framework, the advantages of the membrane discretization performed in the FD-BEM model are highlighted through accurate simulations of the first vibration mode and especially the cutoff frequency that many other models do not predict. This high cutoff frequency corresponds to cases where the spatial average velocity of the plate is null and is of great importance for PMUT design because it defines the upper limit above which the device is considered to be mechanically blocked. These modeling results are compared with electrical and dynamic membrane displacement measurements of AlN-based (500 nm thick) PMUTs in air and fluid. The first resonance frequency confrontation showed a maximum relative error of 1.13% between the FD model and Finite Element Method (FEM). Moreover, the model perfectly predicts displacement amplitudes when PMUT vibrates in a fluid, with less than 5% relative error. Displacement amplitudes of 16 nm and 20 nm were measured for PMUT with 340 µm and 275 µm diameters, respectively. This complete PMUT model using the FD-BEM approach is shown to be very efficient in terms of computation time and accuracy. Full article
(This article belongs to the Special Issue Acoustic Transducers and Their Applications)
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19 pages, 10163 KiB  
Article
Acoustic Characterization of Transmitted and Received Acoustic Properties of Air-Coupled Ultrasonic Transducers Based on Matching Layer of Organosilicon Hollow Glass Microsphere
by Xinhu Xu, Liang Zhang, Hulin Guo, Xiaojie Wang and Lingcai Kong
Micromachines 2023, 14(11), 2021; https://doi.org/10.3390/mi14112021 - 30 Oct 2023
Cited by 3 | Viewed by 1457
Abstract
An air-coupled transducer was developed in this study, utilizing hollow glass microsphere-organosilicon composites as an acoustically matching layer, which demonstrated outstanding acoustic performance. Firstly, a comparison and analysis of the properties and advantages of different substrates was carried out to determine the potential [...] Read more.
An air-coupled transducer was developed in this study, utilizing hollow glass microsphere-organosilicon composites as an acoustically matching layer, which demonstrated outstanding acoustic performance. Firstly, a comparison and analysis of the properties and advantages of different substrates was carried out to determine the potential application value of organosilicon substrates. Immediately after, the effect of hollow glass microspheres with different particle sizes and mass fractions on the acoustic properties of the matching layer was analyzed. It also evaluated the mechanical properties of the matching layer before and after optimization. The findings indicate that the optimized composite material attained a characteristic acoustic impedance of 1.04 MRayl and an acoustic attenuation of 0.43 dB/mm, displaying exceptional acoustic performance. After encapsulating the ultrasonic transducer using a 3D-printed shell, we analyzed and compared its emission and reception characteristics to the commercial transducer and found that its emission acoustic pressure amplitude and reception voltage amplitude were 34% and 26% higher, respectively. Finally, the transducer was installed onto a homemade ultrasonic flow meter for practical application verification, resulting in an accuracy rate of 97.4%. Full article
(This article belongs to the Special Issue Acoustic Transducers and Their Applications)
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15 pages, 2523 KiB  
Article
Quasi-3D Model for Lateral Resonances on Homogeneous BAW Resonators
by Carlos Udaondo, Carlos Collado and Jordi Mateu
Micromachines 2023, 14(11), 1980; https://doi.org/10.3390/mi14111980 - 25 Oct 2023
Cited by 1 | Viewed by 1153
Abstract
Lateral modes are responsible for the in-band spurious resonances that appear on BAW resonators, degrading the in-band filter response. In this work, a fast computational method based on the transmission line matrix (TLM) method is employed to model the lateral resonances of BAW [...] Read more.
Lateral modes are responsible for the in-band spurious resonances that appear on BAW resonators, degrading the in-band filter response. In this work, a fast computational method based on the transmission line matrix (TLM) method is employed to model the lateral resonances of BAW resonators. Using the precomputed dispersion curves of Lamb waves and an equivalent characteristic impedance for the TE1 mode, a network of transmission lines is used to calculate the magnitude of field distributions on the electrodes. These characteristics are specific to the stack layer configuration. The model’s implementation is based on nodal Y matrices, from which particle displacement profiles are coupled to the electric domain via piezoelectric constitutive relations. Consequently, the input impedance of the resonator is obtained. The model exhibits strong agreement with FEM simulations of FBARs and SMRs, and with measurements of several SMRs. The proposed model can provide accurate predictions of resonator input impedance, which is around 200 times faster than conventional FEM. Full article
(This article belongs to the Special Issue Acoustic Transducers and Their Applications)
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12 pages, 4964 KiB  
Article
Multiphysics Modeling and Analysis of Sc-Doped AlN Thin Film Based Piezoelectric Micromachined Ultrasonic Transducer by Finite Element Method
by Xiaonan Liu, Qiaozhen Zhang, Mingzhu Chen, Yaqi Liu, Jianqiu Zhu, Jiye Yang, Feifei Wang, Yanxue Tang and Xiangyong Zhao
Micromachines 2023, 14(10), 1942; https://doi.org/10.3390/mi14101942 - 18 Oct 2023
Cited by 3 | Viewed by 1690
Abstract
This paper presents a Piezoelectric micromechanical ultrasonic transducer (PMUT) based on a Pt/ScAlN/Mo/SiO2/Si/SiO2/Si multilayer structure with a circular suspension film of scandium doped aluminum nitride (ScAlN). Multiphysics modeling using the finite element method and analysis of the effect of [...] Read more.
This paper presents a Piezoelectric micromechanical ultrasonic transducer (PMUT) based on a Pt/ScAlN/Mo/SiO2/Si/SiO2/Si multilayer structure with a circular suspension film of scandium doped aluminum nitride (ScAlN). Multiphysics modeling using the finite element method and analysis of the effect of different Sc doping concentrations on the resonant frequency, the effective electromechanical coupling coefficient (keff2) and the station sensitivity of the PMUT cell are performed. The calculation results show that the resonant frequency of the ScAlN-based PMUT can be above 20 MHz and its keff2 monotonically rise with the increasing doping concentrations in ScAlN. In comparison to the pure AlN thin film-based PMUT, the static receiving sensitivity of the PMUT based on ScAlN thin film with 35% Sc doping concentration is up to 1.61 mV/kPa. Meanwhile, the static transmitting sensitivity of the PMUT is improved by 152.95 pm/V. Furthermore, the relative pulse-echo sensitivity level of the 2 × 2 PMUT array based on the Sc doping concentration of 35% AlN film is improved by 16 dB compared with that of the cell with the same Sc concentration. The investigation results demonstrate that the performance of PMUT on the proposed structure can be tunable and enhanced by a reasonable choice of the Sc doping concentration in ScAlN films and structure optimization, which provides important guidelines for the design of PMUT for practical applications. Full article
(This article belongs to the Special Issue Acoustic Transducers and Their Applications)
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12 pages, 9121 KiB  
Article
Partially Etched Piezoelectric Film Filled with SiO2 Structure Applied to A1 Mode Resonators for Transverse Modes Suppression
by Zhenyi Yu, Yu Guo, Sulei Fu, Baichuan Li, Peisen Liu, Shuai Zhang and Zongqin Sun
Micromachines 2023, 14(9), 1745; https://doi.org/10.3390/mi14091745 - 7 Sep 2023
Viewed by 1230
Abstract
With the arrival of the Fifth Generation (5G) communication era, there has been an urgent demand for acoustic filters with a high frequency and ultrawide bandwidth used in radio-frequency (RF) front-ends filtering and signal processing. First-order antisymmetric (A1) lamb mode resonators based on [...] Read more.
With the arrival of the Fifth Generation (5G) communication era, there has been an urgent demand for acoustic filters with a high frequency and ultrawide bandwidth used in radio-frequency (RF) front-ends filtering and signal processing. First-order antisymmetric (A1) lamb mode resonators based on LiNbO3 film have attracted wide attention due to their scalable, high operating frequency and large electromechanical coupling coefficients (K2), making them promising candidates for sub-6 GHz wideband filters. However, A1 mode resonators suffer from the occurrence of transverse modes, which should be addressed to make these devices suitable for applications. In this work, theoretical analysis is performed by finite element method (FEM), and the admittance characteristics of an A1 mode resonator and displacement of transverse modes near the resonant frequency (fr) are investigated. We propose a novel Dielectric-Embedded Piston Mode (DEPM) structure, achieved by partially etching a piezoelectric film filled with SiO2, which can almost suppress the transverse modes between the resonant frequency (fr) and anti-resonant frequency (fa) when applied on ZY-cut LiNbO3-based A1 mode resonators. This indicates that compared with Broadband Piston Mode (BPM), Filled-broadband Piston Mode (FPM) and standard structures, the DEPM structure is superior. Furthermore, the design parameters of the resonator are optimized by adjusting the width, depth and filled materials in the etched window of the DEPM structure to obtain a better suppression of transverse modes. The optimized A1 mode resonator using a DEPM structure exhibits a transverse-free response with a high fr of 3.22 GHz and a large K2 of ~30%, which promotes the application of A1 mode devices for use in 5G RF front-ends. Full article
(This article belongs to the Special Issue Acoustic Transducers and Their Applications)
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15 pages, 8629 KiB  
Article
Reem-Shape Phononic Crystal for Q Anchor Enhancement of Thin-Film-Piezoelectric-on-Si MEMS Resonator
by Mohammed Awad, Temesgen Bailie Workie, Jing-Fu Bao and Ken-ya Hashimoto
Micromachines 2023, 14(8), 1540; https://doi.org/10.3390/mi14081540 - 31 Jul 2023
Cited by 4 | Viewed by 1340
Abstract
This paper proposes a reem-shaped phononic crystal for the performance enhancement of TPoS resonators. The proposed phononic crystal offers an ultra-wide acoustic band gap that prevents energy leakage through the supporting substrate upon its placement at the anchoring boundary, resulting in significant improvements [...] Read more.
This paper proposes a reem-shaped phononic crystal for the performance enhancement of TPoS resonators. The proposed phononic crystal offers an ultra-wide acoustic band gap that prevents energy leakage through the supporting substrate upon its placement at the anchoring boundary, resulting in significant improvements in the resonator quality factor. Simulated results show reem-shape phononic crystals generate a band gap up to 175 MHz with a BG of 90% and enhance the anchor quality factor from 180,000 to 6,000,000 and the unloaded quality factor from 133,000 to 160,000, representing 33.3-fold and 1.2-fold improvements, respectively. Full article
(This article belongs to the Special Issue Acoustic Transducers and Their Applications)
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16 pages, 6358 KiB  
Article
A Compact Piezo-Inertia Actuator Utilizing the Double-Rocker Flexure Hinge Mechanism
by Pingping Sun, Chenglong Lei, Chuannan Ge, Yunjun Guo and Xingxing Zhu
Micromachines 2023, 14(6), 1117; https://doi.org/10.3390/mi14061117 - 26 May 2023
Cited by 2 | Viewed by 1535
Abstract
With a simple structure and control method, the piezo-inertia actuator is a preferred embodiment in the field of microprecision industry. However, most of the previously reported actuators are unable to achieve a high speed, high resolution, and low deviation between positive and reverse [...] Read more.
With a simple structure and control method, the piezo-inertia actuator is a preferred embodiment in the field of microprecision industry. However, most of the previously reported actuators are unable to achieve a high speed, high resolution, and low deviation between positive and reverse velocities at the same time. To achieve a high speed, high resolution, and low deviation, in this paper we present a compact piezo-inertia actuator with a double rocker-type flexure hinge mechanism. The structure and operating principle are discussed in detail. To study the load capacity, voltage characteristics, and frequency characteristics of the actuator, we made a prototype and conducted a series of experiment. The results indicate good linearity in both positive and negative output displacements. The maximum positive and negative velocities are about 10.63 mm/s and 10.12 mm/s, respectively, and the corresponding speed deviation is 4.9%. The positive and negative positioning resolutions are 42.5 nm and 52.5 nm, respectively. In addition, the maximum output force is 220 g. These results show that the designed actuator has a minor speed deviation and good output characteristics. Full article
(This article belongs to the Special Issue Acoustic Transducers and Their Applications)
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16 pages, 4990 KiB  
Article
A Real Time Method Based on Deep Learning for Reconstructing Holographic Acoustic Fields from Phased Transducer Arrays
by Shuai Wang, Xuewei Wang, Fucheng You, Yang Li and Han Xiao
Micromachines 2023, 14(6), 1108; https://doi.org/10.3390/mi14061108 - 24 May 2023
Viewed by 1533
Abstract
Phased transducer arrays (PTA) can control ultrasonic waves to produce a holographic acoustic field. However, obtaining the phase of the corresponding PTA from a given holographic acoustic field is an inverse propagation problem, which is a mathematically unsolvable nonlinear system. Most of the [...] Read more.
Phased transducer arrays (PTA) can control ultrasonic waves to produce a holographic acoustic field. However, obtaining the phase of the corresponding PTA from a given holographic acoustic field is an inverse propagation problem, which is a mathematically unsolvable nonlinear system. Most of the existing methods use iterative methods, which are complex and time-consuming. To better solve this problem, this paper proposed a novel method based on deep learning to reconstruct the holographic sound field from PTA. For the imbalance and randomness of the focal point distribution in the holographic acoustic field, we constructed a novel neural network structure incorporating attention mechanisms to focus on useful focal point information in the holographic sound field. The results showed that the transducer phase distribution obtained from the neural network fully supports the PTA to generate the corresponding holographic sound field, and the simulated holographic sound field can be reconstructed with high efficiency and quality. The method proposed in this paper has the advantage of real-time performance that is difficult to achieve by traditional iterative methods and has the advantage of higher accuracy compared with the novel AcousNet methods. Full article
(This article belongs to the Special Issue Acoustic Transducers and Their Applications)
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Review

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19 pages, 5149 KiB  
Review
Surface Acoustic Wave Humidity Sensor: A Review
by Maria Muzamil Memon, Qiong Liu, Ali Manthar, Tao Wang and Wanli Zhang
Micromachines 2023, 14(5), 945; https://doi.org/10.3390/mi14050945 - 27 Apr 2023
Cited by 13 | Viewed by 3136
Abstract
The Growing demands for humidity detection in commercial and industrial applications led to the rapid development of humidity sensors based on different techniques. Surface acoustic wave (SAW) technology is one of these methods that has been found to provide a powerful platform for [...] Read more.
The Growing demands for humidity detection in commercial and industrial applications led to the rapid development of humidity sensors based on different techniques. Surface acoustic wave (SAW) technology is one of these methods that has been found to provide a powerful platform for humidity sensing owing to its intrinsic features, including small size, high sensitivity, and simple operational mechanism. Similar to other techniques, the principle of humidity sensing in SAW devices is also realized by an overlaid sensitive film, which serves as the core element whose interaction with water molecules is responsible for overall performance. Therefore, most researchers are focused on exploring different sensing materials to achieve optimum performance characteristics. This article reviews sensing materials used to develop SAW humidity sensors and their responses based on theoretical aspects and experimental outcomes. Herein the influence of overlaid sensing film on the performance parameters of the SAW device, such as quality factor, signal amplitude, insertion loss, etc., is also highlighted. Lastly, a recommendation to minimize the significant change in device characteristics is presented, which we believe will be a good step for the future development of SAW humidity sensors. Full article
(This article belongs to the Special Issue Acoustic Transducers and Their Applications)
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