Development of 40 MHz Ultrasonic Transducers via Soft Mold Process

The present paper reports on 1-3 piezocomposites fabrication for ultrasonic transducers with operating frequencies up to 40 MHz based on recent developments of the soft mold technique. Compared to the established dice-and-fill technique, soft mold process allows for the manufacturing of 1-3 piezocomposites with higher variability of pillar design and distribution as well as smaller structural size. Consequently, spurious modes generated by the lateral composite layout can be pushed to higher frequencies, which allows for increased operating frequency. Different designs of circular piezoceramic pillars with decreasing spacings have been developed and characterized in order to shift spurious modes to frequencies approximately twice as the desired working frequency. Influence of pillar diameter and interpillar spacing on resonance modes are investigated by analyzing the produced transducers in respect of their electrical impedance spectra. Experimental results are explained in detail and compared to modelled data.