Processing of miniature hollow sphere transducers

During the past two decades, we have designed and fabricated a large family of composite ferroelectrics for use as sensors, actuators, and transducers. These devices employ stress and strain amplification mechanisms and provide superior acoustic matching to seawater and the human body. Recently we have concentrated on flat-panel arrays thinner than 3 mm constructed from miniature flextensional transducers (Cymbals) or small hollow sphere transducers (BBs) embedded in polymers. This paper focuses on fabrication of BB hollow spheres. Millimeter size hollow spheres are produced using a coaxial nozzle slurry process or sacrificial core coating from 1-10 mm diameter with 10-200 μm wall-thickness. The principal resonance modes are the breathing mode (ranging from 100 kHz at 15 mm diameter to 1.5 MHz at 1 mm diameter) and the wall thickness vibration (10-100 MHz). We also discuss a method for providing the BBs with internal electrodes, a process which allows for even smaller diameters in the sub-millimeter range.