Understanding Smart Sensors - Nomads.usp

4 Understanding Smart Sensorssmart sensors and accelerate development and commercialization of smartsensors.1.2 Mechanical-Electronic Transitions in SensingAn early indication of the transition from strictly mechanical sensing to electronictechniques is demonstrated in the area of temperature and positionmeasurements. Thermistors and semiconductor temperature sensors that werelower in cost, smaller in size, and easier to interface to other circuit elementsreplaced thermocouples and expansion thermometers. In position measurements,variable-reluctance sensors with magnetic pickups have been replacedby Hall-effect, optical, and magnetoresistive (MR) sensing elements. All thosetechniques make use of a previous problem that detracted from the ideal performanceof a transistor or an IC. The sensitivity of transistors to temperature,light, magnetic fields, stress, and other physical variables is exploited in manyexisting semiconductor sensors.The expanding range of parameters that can be sensed using semiconductortechnology is part of the increasing interest in smart sensing. Withmicromachining, or chemical etching techniques, mechanical structures havebeen produced in silicon that have greatly expanded the number and types ofmeasurements that can be made. For example, a rubber diaphragm connectedto a potentiometer can be replaced by a silicon diaphragm and piezoresistiveelements for measuring pressure. That approach has been used in productionsensors for over two decades. More recently, cantilever beams and otherTable 1.2Sensing TechniquesTechniquePiezoresistiveCapacitivePiezoelectricOptoelectronicMagneticRadarLaser infrared radar (lidar)UltrasonicStatus in Silicon SensorPressure, accelerationPressure, acceleration, positionPressure, acceleration, vibrationPosition, velocityPosition, velocity, magnetic fieldLimited productionProduction/research/developmentProduction