Binary amplitude switch for photoacoustic transducer toward dynamic spatial acoustic field modulation.

Abstract

Photoacoustic (PA) transducers are an attractive method of producing high-amplitude, high-frequency, broad-bandwidth ultrasound signals with excellent immunity to electromagnetic interference, when compared with their traditional electroacoustic counterparts. However, the lack of effective control over the spatial sound field prohibits PA transducer technology from further widespread application. This paper presents the first, to the best of our knowledge, experimental study on the dynamic spatial ultrasound modulation strategy for the use of PA transducers, in which a novel PA transducer element is designed. This consists of a suspended compound PA conversion film, whose backing condition can be switched between air and glass through pneumatic actuation to create destructive and constructive acoustic wave interference, respectively. As a result, nearly an order of magnitude contrast in the output acoustic amplitude can be obtained by switching the device's backing condition given the same laser excitation, thus achieving a binary amplitude tuning. Furthermore, a linear PA transducer array consisting of three independently controllable elements is used for a proof-of-concept demonstration of the dynamic spatial sound field manipulation. To the best of the authors' knowledge, this is the first time that such a unique capability has been successfully applied to PA transducer technology.