Design, Fabrication and Characterization of Multi-Frequency MEMS Transducer for Photoacoustic Imaging

TL;DR

This paper introduces a new MEMS transducer design that enables multi-frequency operation for improved photoacoustic imaging performance.

Contribution

The novel integration of multiple resonant geometries in a single MEMS transducer expands the bandwidth for photoacoustic imaging.

Findings

The cantilever array design achieved the highest modal density with a broad frequency range from 275 kHz to 7.5 MHz.

Complex MEMS geometries like the floated cross and cantilever arrays significantly outperformed traditional designs in bandwidth.

The integration of diverse MEMS structures enables broadband sensitivity without sacrificing miniaturization.

Abstract

This work presents the design, fabrication, and experimental characterization of microelectromechanical system (MEMS) ultrasonic transducers engineered for multi-frequency operation in photoacoustic imaging (PAI). The proposed devices integrate multiple resonant geometries, including circular diaphragms, floated crosses, anchored cross membranes, and cantilever arrays, within compact footprints to overcome the inherently narrow frequency response of conventional MEMS transducers. All devices were fabricated using the PiezoMUMPs commercial microfabrication process, with finite element simulations guiding modal optimization and laser Doppler vibrometry used for experimental validation in air. The circular diaphragm exhibited a narrowband response with a dominant resonance at 1.69 MHz and a quality factor (Q) of 268, confirming the bandwidth limitations of traditional geometries. In contrast, complex designs such as the floated cross and cantilever arrays achieved significantly broader spectral responses, with resonances spanning from 275 kHz to beyond 7.5 MHz. The cantilever array, with systematically varied arm lengths, achieved the highest modal density through asynchronous activation across the spectrum. Results demonstrate that structurally diverse MEMS devices can overcome the bandwidth constraints of traditional piezoelectric transducers. The integration of heterogeneous MEMS geometries offers a viable approach for broadband sensitivity in PAI, enabling improved spatial resolution and depth selectivity without compromising miniaturization or manufacturability.

Figures