Opto-Acoustic Transducers for Potentially Sensitive Ultrasonic Imaging

Abstract

The most inherently sensitive type of ultrasonic system for real-time imaging is one that operates in a manner similar to that of a scanning electron-beam microscope. In the acoustic system, an ultrasonic beam is focused at a plane within an object. The focal spot is rapidly scanned in a raster pattern over this plane and the transmitted (or scattered) sound energy is collected by a piezo-electric receiver. The receiver output is displayed on a synchronously-scanned television monitor, yielding a visual image of the spatial pattern of acoustic opacity (or reflectivity) in the object plane. This paper describes an embodiment of this type of system for operation at megahertz frequencies in which the key element is an opto-acoustic transducer (OAT) whose function is to convert an impinging optical intensity pattern into a corresponding spatial pattern of generated acoustic amplitude. An incident optical pattern can be formed and scanned by optical equipment, which will generate, scan and focus a corresponding acoustic beam. This approach does not require the use of high-density transducer arrays with individualized electronics or acoustic lenses and therefore, inherently possesses the potential advan-tages of simplicity and versatility over existing or other proposed scanning-focused beam systems.