Design, fabrication and characterization of Emfi-based ferroelectret air-coupled ultrasonic transducer

Air-coupled ultrasonic testing (ACUT) has many advantages over other non-destructive testing (NDT) methods, among which the most outstanding one is completely no contamination of the sample. Therefore, it can be applied in various conditions where liquid coupling media is not suitable. With the development of ACUT, it is found that mismatch between air and solid is one of the biggest difficulties confronting researchers, and electromechanical film (EMFi) with low acoustic impedance can be a promising solution when used as vibration element in air-coupled ultrasonic transducers. In this contribution, one planar and two spherically focused EMFi-based transducers were designed, fabricated, and their properties were characterized through frequency response test as well as focal length test. Then imaging experiments of PMMA samples were performed to demonstrate the possibility and feasibility of EMFi transducers in non-contact testing.