Understanding Smart Sensors - Nomads.usp

The Next Phase of Sensing Systems 31714.4 Not-So-Futuristic SystemsMany of the sensors that will be produced in the future will not surprise industrywatchers because researchers will have demonstrated them at early stages ofthe technology development. Table 9.1 listed MEMS technology that couldalso produce manufacturable products at some point in the future. Examples inthis section include a laboratory tool that can help researchers as well as technologiesthat may be used directly by a large number of consumers. The followingis a list of some of the more intriguing sensors that are in development:• “Nose-on-a-chip”;• Gas analysis system;• Camera-on-a-chip;• Atomic-force microscope;• Monolithic hearing aid;• Mass spectrometer;• Vehicle dynamics sensor;• Viscometer-on-a-chip;• Chemistry lab-on-a-chip;• DNA analyzer-on-a-chip;• ID verification-on-a-chip.14.4.1 Fabry-Perot InterferometerFabry-Perot interferometers (FPIs) are used in the laboratory to optically measurelengths or changes in length with a high degree of accuracy. Amicromachined version consists of two silicon wafers with deposited highlyreflective dielectric mirrors, as shown in Figure 14.1 [8]. This is already asecond-generation version of an earlier development. An FPI incorporates anumber of critical micromachined elements and semiconductor processes,including the controlled gap, movable silicon mesa corrugated support, siliconfusion bonding, capping wafer, control electrodes, and optical coating. MiniatureFPIs have applications in telephony systems to link large numbers ofcustomers to a central exchange. In addition, a small-gap FPI may have applicationsin sensors to measure small displacements and provide the feedback elementin a servo loop. Two visible-ultraviolet-range interferometers in series areexpected to give narrow-bandwidth selectivity for use as a spectrometer [9].