| Background, Motivation and Objective High frequency dense array transducers are required for higher resolution in medical ultrasonic diagnosis. However, conventional fabrication methods for array transducer based on the machining of piezoelectric ceramics and PVDF films are encountering the limitation in miniaturization. We have proposed to utilize polyurea film as ultrasonic transducers, and investigated the fundamental characteristics in transmitting/receiving high frequency ultrasonic waves up to 100 MHz. The polyurea film of 0.1 µm to 5 µm is prepared through vapor deposition with high controllability in thickness. Miniature array electrodes can be fabricated using lithographic technique since the polyurea has chemical resistance. Taking advantage of the features of polyurea film, a 32-element linear array working at 100 MHz is prototyped in this study. Statement of Contribution/Methods Two types of different configurations are tested in prototyping array transducers using polyurea film. In the first configuration, the bottom electrode deposited on a polyimide substrate is etched into 32 elements before the deposition of the polyurea layer and top electrode. In the second configuration, the top electrode made on the surface of the polyurea film is etched into 32 sections. The width of each element is 10 µm, and the spacing between the elements is 20 µm. Results We observed the resonances at around 30, 65 and 100 MHz for each element of 32 through the electrical admittance measurements. The effective electromechanical coupling coefficient for the resonance of 100 MHz was 0.132. We carried out beam steering experiments being based on phased array method for receiving ultrasonic pulses launched from the angle of 0.4°, 2.3° and 2.7°. The angles were successfully recognized with the beam width of around 7°. Pulse/echo operation was also tested. Discussion and Conclusions Through the beam steering experiments and the pulse/echo tests, the feasibility of polyurea-based array transducers for high frequency operation has been successfully confirmed. The polyurea layer survived the chemical etching process of the array electrodes. This means that the polyurea is one of the most promising materials for making high frequency dense array transducer with the use of lithographic techniques. |