Understanding Smart Sensors - Nomads.usp

The Next Phase of Sensing Systems 319COHCAccelerometerTemperatureBarometricPLoadcontrolNOMisc.gasNoisedetectionSignalconditioningLow∆PADCLonworksneuroncontrolchipNetworkLoadcontrolFigure 14.2 A highly integrated sensor concept for automated building control.An example of how micromachining is extending the types of measurementsand improving the performance compared to previous approaches is aMEMS-based chemical sensor. For those devices, a thin-film metal oxide technologyis combined with an embedded microheater on a thin, micromachinedsilicon diaphragm. The small sample area of a micromachined sensor can morereadily be raised to the higher operating temperature required for detecting thepresence and actual value of specific chemicals. The polysilicon heaters in thechemical sensor operate at temperatures that can reach 450°C. The ability tochange the temperature in a short period of time is used to minimize the effectsof humidity and also to reduce power consumption [11]. Sensitivity from 10:1to 100:1 for a specific gas and a response time of 2 minutes or less are commonfor these devices. These products are aimed at industrial and consumer applications,but ongoing development should provide units for automotive and otherextremely cost-sensitive applications in the future.14.4.3 Speech Recognition and MicromicrophonesCombinations of technologies will provide future products. One possibility isthe combination of speech recognition algorithms, complex computing capability,and micromachined microphones. Neural networks are being investigatedfor intelligent sensors in speaker-independent speech-recognition systems[12]. Such research has resulted in an acoustic preprocessing chip that offloads