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In this monograph, the authors report the current advancement in high

frequency piezoelectric crystal micromachined ultrasound transducers

and arrays and their biomedical applications.

Piezoelectric ultrasound transducers operating at high frequencies

(>20 MHz) are of increasing demand in recent years for medical imaging

and biological particle manipulation involved therapy. The performances

of transducers greatly rely on the properties of the piezoelectric

materials and transduction structures, including piezoelectric coefficient

(d), electromechanical coupling coefficient (k), dielectric permittivity

(e) and acoustic impedance (Z). Piezo-composite structures are

preferred because of their relatively high electromechanical coupling

coefficient and low acoustic impedance. A number of piezo-composite

techniques 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 to

achieve fine features or not suitable for manufacturing of high frequency

ultrasound transducers (>20 MHz). The piezo-composite micromachined

ultrasound transducers (PC -MUT) technique discovered over

the last 10 years or so has demonstrated high performance high frequency

piezo-composite ultrasound transducers.

In this monograph, piezoelectric materials used for high frequency

transducers is introduced first. Next, the benefits and theory of piezo

composites is presented, followed by the design criteria and fabrication

methods. Biomedical applications using PC -MUT and arrays

will also be reported, in comparison with other ultrasound transducer

techniques. The final part of this monograph describes challenges and

future perspectives of this technique for biomedical applications.