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Catheter-based intracardiac ultrasound offers the potential for improved guidance of interventional cardiac procedures. The objective of this research is the development of catheter-based mechanical sector scanners incorporating high frequency ultrasound transducers operating at frequencies up to 20 MHz. The authors' current transducer assembly consists of a single 1.75 mm by 1.75 mm, 20 MHz, PZT element mounted on a 2 mm by 2 mm square, 75 mum thick polyimide table that pivots on 3-mum thick gold plated polyimide hinges. The hinges also serve as the electrical connections to the transducer. This table-mounted transducer is tilted using a miniature linear actuator to produce a sector scan. This linear actuator is an integrated force array (IFA), which is an example of a micromachine, i.e., a microelectromechanical system (MEMS). The IFA is a thin (2.2 mum) polyimide membrane, which consists of a network of hundreds of thousands of micron scale deformable capacitors made from pairs of metallized polyimide plates. IFAs contract with an applied voltage of 30-120 V and have been shown to produce strains as large as 20% and forces of up to 8 dynes. The prototype transducer and actuator assembly was fabricated and interfaced with a GagePCI analog to digital conversion board digitizing 12 bit samples at a rate of 100 MSamples/second housed in a personal computer to create a single channel ultrasound scanner. The deflection of the table transducer in a low viscosity insulating fluid (HFE 7100, 3M) is up to +/-10 degrees at scan rates of 10-60 Hz. Software has been developed to produce real-time sector scans on the PC monitor.

Absfract-Integrated force arrays (IFA's) are a novel means of microelectromechanical actuation. They are membrances that consist of thousands of micron-scale deformable capacitors and are capable of contraction and force exertion in one dimension by application of an applied voltage. The theory and modeling of the static operation of a representative unit device and an array is presented. The electrostatic and elastic forces present in the system are considered and classical beam theory and superposition are applied to calculate the voltage-induced closure and force generation of the networks without the aid of finite element analysis. It is shown that contraction and force generation are expected at reasonable voltages for these modular structures: Ideal system contraction on the order of 40% is possible and minimum external forces of 4500 pN/mm2 are expected with the application of 50 V. [129]

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