Understanding Smart Sensors - Nomads.usp

Transceivers, Transponders, and Telemetry 195effort from nurses and doctors. In addition, the onset of problems can bedetected quickly and appropriate action taken sooner.RF telemetry has also been investigated for microminiature transducersfor biomedical applications. Transferring data and power into and out of thebody to implanted transducers is a critical area because of the reliability of thecomponent and, more important, the restrictions and potential of infection tothe patient. A microstimulator has been developed that measures only 1.8 mm 3by 1.8 mm 3 by9mm 3 using RF telemetry operating at 1 MHz for power andcontrol [31]. The assembly includes a micromachined silicon substrate that hasthe stimulating electrodes, CMOS, and bipolar power regulation circuitry; acustom-made glass capsule electrostatically bonded onto the silicon carrier toprovide a hermetically sealed package; hybrid chip capacitors; and the receivingantenna coil. The application of microtelemetry will be more practical withimprovements in integrated micromachining and reduction in the receivingantenna size.8.5 RF MEMSMEMS technology is being used to develop RF components that demonstratesuperior high-frequency performance relative to conventional (usually semiconductor)devices. These new devices provide potential for new system capabilities[32]. Darpa has investigated MEMS technology for radio front ends,capacitor banks, and time-delay networks for quasi-optical beam steering andreconfigurable antennas.A recently issued patent describes a monolithically integrated switchedcapacitor bank using MEMS technology that is capable of handling gigahertzsignalfrequencies in both the RF and millimeter bands [33]. In addition, thetechnique maintains precise digital selection of capacitor levels over a wide tuningrange. Each MEMS switch includes a cantilever arm suspended above thesubstrate that extends over a ground line and a gapped signal line with a set ofcontacts on the arm and the substrate. The MEMS switch is actuated by a voltageapplied to the top electrode that produces an electrostatic force and attractsthe control capacitor structure toward the ground line, causing the electricalcontact to close the gap. The integrated MEMS switch-capacitor pairs have alarge range between their on-state and off-state impedance and exhibit superiorisolation and insertion loss characteristics.Antennas, transmission lines, and other RF components are being builtusing micromachining techniques [34]. The new micromachined chips areless expensive than previous silicon versions. Figure 8.13 shows a 40-GHz