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as a joint project with Rochester General Hospital. Other research areas under way include: design improvement for titanium dental root implants, in-situ testing of bioceramic materials for short-and longterm biocompatibility, microstructural evaluation of bioceramic interfaces for bone-ceramic joining and dental decay correction, piezoelectric ceramics for signal detectors and diagnostic and healing biosystems, and carbon-carbon and other composites for bone implants that encourage tissue growth. Institute director Fischman, a specialist in structural ceramics, was primarily responsible for forming the High Performance Ceramics Laboratory at the College, where his group developed a zirconia femoral endo head for total hip replacements.
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High-Performance Microwave Circuits Built on Soft Substrates New methods for making state-of-theart, high-performance microwave circuits on a soft, flexible substrate could be used by makers of radar systems, avionics electronics, and other systems where large, high-precision hybrid circuits are needed. Using the techniques, researchers at Sandia National Laboratories accurately patterned and etched circuit conductors, achieving 1/4 mil tolerances and linewidths as narrow as two mils. Features can be machined into the soft substrate with one-mil accuracies. Precision features were needed in the circuits because of the highfrequency requirements of the synthetic aperture radar (SAR) system for which they were developed. In developing the higher frequency SAR, Sandia researchers needed a substrate with a lower dielectric constant to reduce potential losses of the radio frequency signal. They also needed a more mechanically forgiving material than commonly used ceramics to allow them to build larger circuits without the substrate cracking. These circuits, u p to three times larger than normal hybrid circuits, were needed to accommodate a greater number of functions than found in other SAR systems. The hybrid circuits used in the SAR system are assembled with a combination of silicon circuits and surface-mounted capacitors and resistors, making them similar to a miniature printed circuit board. While previous radars had five to six smaller micro-
circuits, the new SAR uses 18. The researchers chose a commercially available laminate substrate called Duroid, a composite ma
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