Response Analyses of Micro-Ultrasonic Sensor Devices for Underwater Robotic Applications

The vastness of the ocean offers great challenges for various underwater exploratory and communication related applications using multiple robotic platforms such as remotely operated vehicle (ROV), underwater glider, vertical profiler and autonomous surface vessel (ASV). Small in size, higher sensitivities and lower power consumptions of micro-ultrasonic devices make it a perfect match for those robotic platforms. This paper proposed two micro-ultrasonic transducer (MUT) designs for underwater applications. Two sensing mechanisms were utilized namely, piezoelectric (pMUT) and capacitive (cMUT). The objective is not meant for comparison, but it is rather a work carried to investigate on the option available to cater different underwater applications. Responses of those micro-devices were identified using finite element method (FEM). Three different materials were suggested for each design; which was ZnO, PZT and quartz for pMUT and Si₃N₄, Teflon and PDMS for cMUT. Analyses conducted including mechanical, piezoelectric and frequency. PZT were found to be the most responsive material for pMUT with voltage response at 1.3×10^-3 μm/V and 2750.2 pC/V of charge response but carried the lowest resonant frequency at 85.9 kHz. For cMUT design, PDMS had the highest detection sensitivity, which is equal to 1.6 μm/Pa. This occurred at the resonance of 515.9 kHz. However, in terms of static deflection analysis, PDMS showed the weakest performance. This suggests the need for delicate design considerations and tradeoffs. Final specification of both designs was summarized at the end of the report as a guideline to underwater robotic engineers in determining the best applications within the specified performance.