Compact Broadband Multi-Frequency PMUT Arrays for Photoacoustic Vascular Sensing

Abstract

Continuous cuffless blood-pressure (BP) monitoring requires compact sensors capable of tracking arterial diameter with high repeatability. Time-resolved photoacoustic (PA) sensing is attractive because vessel diameter is directly encoded in the temporal separation between the anterior- and posterior-wall arrivals in the PA A-line signal, eliminating the need for beamforming and image reconstruction. Here, we present a compact (2.5 mm $\times\,\, 5$ mm) multi-frequency piezoelectric micromachined ultrasonic transducer (PMUT) receiver fabricated by a cavity silicon-on-insulator (CSOI) process. The high-fill-factor design provides three receive bands centered at approximately 3.5, 5.5, and 11 MHz, with PA −6 dB fractional bandwidths of 126%, 103%, and 110%, respectively. Owing to the large effective acoustic aperture and low-noise front-end readout, the low-frequency array achieves a noise-equivalent pressure (NEP) of $2.9~\boldsymbol {mPa}/\sqrt { \boldsymbol {Hz}}$ at 3.5 MHz. Using a compact 532 nm pulsed laser delivering $\sim 5~\mu $ J/pulse, the system resolved vessel phantoms with inner diameters down to 1.0 mm at a depth of 5 mm in an optically clear medium, detected PA signals up to 40 mm in clear media, and maintained vessel detection up to 6 mm in a scattering tissue-mimicking medium. These results demonstrate that complementary low-, mid-, and high-frequency PMUT arrays can jointly provide penetration depth and diameter resolution within a compact footprint, supporting the development of wearable PA sensors for cuffless vascular monitoring. [2026-0042]