Jinwook Kim / Li Sibo / Xiaoning Jiang
In this monograph, the authors report the current advancement in highfrequency piezoelectric crystal micromachined ultrasound transducersand arrays and their biomedical applications.Piezoelectric ultrasound transducers operating at high frequencies(>20 MHz) are of increasing demand in recent years for medical imagingand biological particle manipulation involved therapy. The performancesof transducers greatly rely on the properties of the piezoelectricmaterials and transduction structures, including piezoelectric coefficient(d), electromechanical coupling coefficient (k), dielectric permittivity(e) and acoustic impedance (Z). Piezo-composite structures arepreferred because of their relatively high electromechanical couplingcoefficient and low acoustic impedance. A number of piezo-compositetechniques have been developed, namely “dice and fill”, “tape-casting”,“stack and bond”, “interdigital phase bonding”, “laser micromachining”and “micro-molding”. However, these techniques are either difficult toachieve fine features or not suitable for manufacturing of high frequencyultrasound transducers (>20 MHz). The piezo-composite micromachinedultrasound transducers (PC -MUT) technique discovered overthe last 10 years or so has demonstrated high performance high frequencypiezo-composite ultrasound transducers.In this monograph, piezoelectric materials used for high frequencytransducers is introduced first. Next, the benefits and theory of piezocomposites is presented, followed by the design criteria and fabricationmethods. Biomedical applications using PC -MUT and arrayswill also be reported, in comparison with other ultrasound transducertechniques. The final part of this monograph describes challenges andfuture perspectives of this technique for biomedical applications. 3