A fabrication procedure for airborne ultrasonic phased arrays based on cellular electromechanical film

In this work, a novel procedure that considerably simplifies the fabrication process of ferro electret-based multi-element array transducers is proposed and evaluated. Also, the potential of ferro electrets as active material for air-coupled ultrasonic transducer design is demonstrated. The new construction method of multi-element transducers introduces two distinctive improvements, first, the active ferro electret material is not discretized into elements and, second, the need of structuring upper and lower electrodes in advance of the permanent polarization of the film is removed. In order to validate the procedure, two linear array prototypes of 32 elements were built and evaluated. A low crosstalk among elements, below -30 dB, was measured by interferometry. Likewise, a homogeneous response of the array elements, with a maximum deviation of plusmn1.8 dB, was obtained. Acoustic beam steering measurements were accomplished at different deflection angles using a calibrated microphone. The ultrasonic beam parameters, namely lateral resolution, side lobes level, grating lobes and focus depth, were congruent with theory. The proposed procedure simplifies the manufacturing of multi-dimensional arrays with arbitrary shape elements and not uniformly distributed. Furthermore, this concept can be extended to non-flat arrays as long as the transducer substrate conforms to a developable surface.