Ultrasound and optical scanners using micromachine technology

Numerous applications benefit from both high frequency ultrasound imaging and optical imaging techniques. High frequency ultrasound imaging is used in intracardiac and intravascular imaging as well as imaging the skin, eye, and small animals for genetic studies. Potential uses of optical scanners range from bar code scanners and laser printers in industry to corneal resurfacing and optical coherence tomography in medicine. A major issue in developing these systems is steering the acoustic and optical beams. This work describes the design, fabrication and testing of new types of ultrasound and optical beam scanning devices.; These devices are fabricated from polyimide films using photolithography and use a linear polyimide MEMS actuator to mechanically scan the beams. This actuator, the integrated force array (IFA), is a network of hundreds of thousands of micron scale deformable capacitors that electrostatically contract with an applied voltage. Forward viewing tables pivoting on cantilever hinges and side scanning structures tilting on torsion hinges were fabricated on polyimide substrates with tables 1.125 mm and 2.25 mm wide. These structures were modeled using one dimensional beam theory and ANSYS finite element analysis prior to fabrication.; For the ultrasound probes, PZT transducers were fabricated on these tables that operate at 20 MHz and 30 MHz and yielded insertion losses of 20–26 dB with fractional bandwidths of 34–49%. The transducer assemblies driven by MEMS actuators produced sector scans of 20–45° in air at resonant frequencies of 32 Hz to 90 Hz and sector scans in fluid of 6–8°. Both forward viewing and side scanning devices were then used in conjunction with a single channel high frequency ultrasound system to make real time images of wire phantoms.; The optical scanning devices had gold-coated silicon mirrors mounted on the table in place of the PZT transducers. Only side scanning devices were developed for optical applications. For environmental protection, the devices were conformally coated with 500 angstroms of parylene. These devices demonstrated optical scan angles up to 146° for applied voltages up to ±50 volts. These devices were also used to steer a laser beam in a prototype bar code scanner to demonstrate functionality.