Mohd Ikhwan Hadi Yaacob

Modeling of circular piezoelectric micro ultrasonic transducer using CuAl10Ni5Fe4 on ZnO film for sonar applications

Modeling and theoretical characterization of piezoelectric micro ultrasonic transducer (pMUT) using ZnO film sandwiched between nickel aluminum bronze (CuAl10Ni5Fe4) electrodes was reported in this paper. The transducer is targeted to be utilized in sonar applications. Analyses on the model were carried out using finite element method. Model’s dimensional parameters were optimized for desired performance. Simplified technique was proposed to determine transmit and receive sensitivities of the model. As the result, micro ultrasonic transducer model with resonance frequency of 40 kHz was proposed with estimated receive and transmit sensitivities of −93 dB re 1 V/μPa and 137 dB re 1 μPa/V, respectively. Further model validations require actual device fabrication and this will be included in our future works.

Modelling of a novel design of microfluidic based acoustic sensor

This paper reports the initial investigation on a novel acoustic sensor design based on micro fluidic technology. The report includes the proposed design structure and the simulation of key structure materials that affect the performance of such sensor. Simulation works included the analysis of acoustic response of the membrane and the damping effect when the cavity gap is filled with liquid or electrolyte material. For membrane analysis three different materials, silicon nitride (Si3N4), Teflon and Polydimethylsiloxane (PDMS) are simulated to obtain the most responsive material with respect to acoustic pressure signal. PDMS was found to be the most responsive material with the deflection sensitivity of 1.6 μm/Pa. Both Si3N4 and Teflon yielded a sensitivity of 0.034 μm/Pa and 0.67 μm/Pa respectively. In damping analysis, Propylene Carbonate electrolyte was used as a backing layer that filled the cavity gap. With the PDMS was selected as the membrane structure, harmonic analysis was performed to investigat the damping effect caused by electrolyte material on resonance frequency and deflection sensitivity. Result showed that with the proposed design structure and electrolyte backing layer, the harmonic frequency was shifted to a lower value with the maximum deflection was reduced by about 50%. The result also suggests the needs for selecting the right gap material for micro fluidic application that can compromise the damping and the response of the membrane.

Flow analysis of microfluidic-based acoustic sensor

This work studied the behaviour of two different material candidates to be used as liquid for a microfluidic-based acoustic sensor. These liquid will be used as an electrolyte where the capacitive sensing mechanism is adopted. ANSYS was used to simulate the laminar flow of these materials inside the device. From the simulation, flow characteristics such as pressure distribution, velocity profile and flow response were obtained. Pressure distribution plot exposed the maximum pressure region where the flow was also maximum. The region was found to occur just at the starting point of the microchannel. Velocity profile indicated the velocity contour plot and flow direction based on the difference in pressure (represent the acoustic pressure) between the sensing membrane and the microchannel end. Finally, from the flow response, the performance of two different liquids was obtained and analysed. In terms of performance response to the applied pressure, Methanol showed a better response with approximately 18 times higher than Propylene Carbonate.

Design of Polyimide based Piezoelectric Micromachined Ultrasonic Transducer for Underwater Imaging Application

Micromachined ultrasonic transducer has been used in many application for example non-destructive test, medical diagnostic and underwater application. One of the underwater application is underwater acoustic imaging system. Underwater acoustic imaging system needs a transducer with wide bandwidth to perform high resolution image. In previous paper, Capacitance Micromachined Ultrasonic Transducer (CMUT) and Piezoelectric Micromachined Ultrasonic Transducer (PMUT) was studied in acoustic imaging. In this paper, PMUT was designed and studied their receiving sensitivity. The target operating frequency is in between 300 kHz to 700 kHz for underwater acoustic imaging. Simulation using Comsol 5.0 was used to determine the PVDF thickness, pitch element and substrates material, Polyimide and Silicon for desired frequency and high receiving sensitivity. In this paper, Polyimide was used as substrate rather than previous paper was used Silicon as substrate. The positive and ground electrode with lateral structure was fabricated onto Polyimide substrate. The polyvinylidene difluoride, (PVDF) used as sensing element was placed on top of electrodes to obtain polarization and with lateral structure of electrodes, PMUT will induced the d33 mode polarization. The Pulse-echo method was used in experiments to determine the receiving sensitivity. PMUT was obtained receiving sensitivity at -80.84 dB rev 1V/uPa with resonance frequency, 525 kHz. Low frequency for PMUT was obtained at 450 kHz and high frequency for PMUT was obtained at 650 kHz. Bandwidth for PMUT is 38.1%.

200 kHz pMUT using PZT on PDMS membrane for sonar applications

An effort to enhance receiving response of piezoelectric micromachined ultrasonic transducer (pMUT) at low frequency is reported. PMUT is fabricated on the glass substrate with the vibrating membrane formed by a layer of polydimethylsiloxane (PDMS) polymer. Lead zirconate titanate, Pb(Zr, Ti)O3 (PZT) is utilized as the piezo-active layer and nickel as electrodes. Spin coating and low temperature wafer bonding are proposed as part of the key fabrication methods. Fabricated transducer is characterized in the compact acoustic tank setup using 500 kHz and 1.25 MHz reference projectors. Analyses reveal the resonance frequency of pMUT is at 200 kHz where maximum receiving response at −36.6 dB re 1V at 10 λ and 20 V peak to peak of drive voltage on reference projector. Finally, response spectrum of the transducer is plotted against two commercial hydrophones at equivalent frequency band for validation and comparison.

Vibration analysis of pMUT with polymer adhesion layer

Wafer bonding using polymer adhesive layer has gained many attentions for various MEMS applications. Numerous techniques and processes that utilize polymer adhesive have been established recently, mainly for wafer bonding and device packaging. However, adhesive layer contribution in vibrating micro structure such as micro ultrasonic transducer requires further investigations. This paper reports performance difference of piezoelectric micro ultrasonic transducer (pMUT) with polymer adhesion layer of PDMS, Cytop and Polyimide. Finite element analysis was utilized to analyze structure behavior during vibration. Frequency analysis revealed 41 kHz shift in devices resonant frequency when different type of polymers employed as adhesive layer. Further investigations through piezoelectric analysis found that PDMS has contributed in 40% decrease of voltage response than other two polymers at only 6×10−5 μm/V, but carry the highest stress response at 2×10−5 μm/Pa in both transmit and receive modes in mechanical analysis. Finally, same analysis cycle was conducted on pMUT structure with polymer adhesive layer being replaced by polysilicon at the same thickness.

Modeling and theoretical characterization of circular pMUT for immersion applications

This paper reported modeling and theoretical characterization of circular piezoelectric micromachined ultrasonic transducer (pMUT) for immersion applications. Zinc oxide (ZnO) was employed as piezo active material and nickel aluminum bronze alloy UNS C63000 (CuAl10Ni5Fe4) also known as “sea bronze”, was introduced as electrodes. First, virtual fabrication process was carried out within software environment to form a pMUT model. Then, resonance frequency of the model was finalized and fine tuned by manipulating its structural parameters which are diaphragm diameter and piezo active layer thickness. Next, receiving and transmitting responses were estimated using finite element approach through the combination of piezoelectric analysis and modal analysis. From these analyses, the pMUT model having a resonance frequency of 40.82 kHz was successfully modeled. Transmitting response was estimated at 137 dB (re 1 µPa/V) at 41 kHz on the surface of the transducer while the receiving response was estimated at − 93 dB (re 1 V/µPa) at 38 kHz of frequency. Virtual fabrication process and finite element analysis for model performances estimation have proved to reduce the development time. From the comparison made, the usage of sea bronze and ZnO film replacing conventional gold, platinum and lead zirconate titanate (PZT) were proven to deliver exceptional performances with better durability. However, device fabrication is essential in order to validate the findings and this will be included in our future works. Furthermore, the model needs to be extended so that the value of acoustic impedance within the device can be estimated.