Comparison of Bulk Piezoelectric and Opto-Mechanical Micromachined Detectors for Optoacoustic and Ultrasound Sensing

Abstract

Optical detection of sound, using optomechanical micromachined ultrasound sensors (OMUS), is a promising detection technology for optoacoustic (OptA) imaging because it achieves a small active detection area, in the few tens of micrometers size, without loss of sensitivity as a function of area size. It also has potential to be produced as array configurations at low cost. However, while OMUS sensitivity has been reported in terms of noise equivalent pressure density (NEPD), there has been no comparison to conventional piezoelectric transducers under identical conditions. We differentially compared a highly sensitive ring-resonator-based OMUS and a single element focused piezoelectric ultrasound transducer (FPUT), under the same experimental conditions. The comparison considered the detectors’ signal-to-noise ratio (SNR), impulse response, axial point-spread-function and their spatial sensitivity. Our results show that OMUS attained lower SNR to FPUT, when operating at the same working distance, but similar performance when placed close to the sample interrogated, for example, as it relates to OptA microscopy. Advantageously, OMUS uniquely offers the spatial behavior of a point-like acoustic detector which reduces the sensitivity to ultrasound interference effects occurring on the large detection area of FPUTs. We discuss the implications of the two detection approaches in the design of OptA systems.