Force sensitive resistors

Polliack et al. recently compared the accuracy, hysteresis, drift, and effect of curvature on sensor performance for these commercial prosthetic systems (force sensitive resistors F-Socket Measurement System, Tekscan, Inc., Boston, Mass. and Socket Fitting System, Rincoe, Golden, Colo prototype capacitive sensor. Novel Electronic, Minneapolis, Minn.). These authors concluded that the current systems were more appropriate for static use because the hysteresis, drift, and large standard deviations become more problematic during dynamic and long-term loading. 

Scanning thermal microscopy (SThM) is a contact AFM technique that allows spatial mapping of temperature or thermal conductivity across a sample surface in addition to topography. Most thermal probes utilize a temperature-sensitive resistor placed on the end of the tip. These resistor probes can be fabricated from a V-shaped Wollaston wire made of a platinum inner core and outer sheath of silver, in which the silver sheath is etched away at the V-shaped tip. Eigure 19 shows a Wollaston wire probe. In passive mode, the tip is scanned across a heated sample under constant-force feedback (contact mode) and a small current is passed through the probe to sense the tip resistance. The resistance value at any point is a measure of the local temperature, and thus a temperature map and topographic image may be produced simultaneously. 

High sensitivity, selectivity, and ability to operate in turbid solutions are advantages of electrochemical biosensors. Amperometric detection is based on measuring the oxidation or reduction of an electroactive compound at a working electrode (sensor). A potentiostat is used to apply a constant potential to the working electrode with respect to a second electrode (reference electrode). A potentiostat is a simple electronic circuit that can be constructed using a battery, two operational amplifiers, and several resistors. The applied potential is an electrochemical driving force that causes the oxidation or reduction reaction. 

Static force measurements (in which there is no apparent motion) usually rely on measurement of strain due to the applied force. Figure 18.6(c) illustrates the typical construction of a common force transducer called a load cell. The applied force produces a proportional strain in the S-shaped structural member, which is measured with a sensitive displacement transducer, usually a strain gauge resistor or a piezoelectric crystal. 

The resistive-type sensors measure strain-related mechanical properties such as strain, force, acceleration, and pressure-utilizing piezoresistive properties of sensitive film resistors [2,14,38,39]. These sensors are also incorporated as biosensors for detecting biomolecules. The electrode configuration is the same as in electrochemical transducers, but it measures the change of resistance when biomolecules interact with the biologically sensitive elements [2]. The piezoresistive microcantilever sensors are also extensively studied for biosensing. The piezoresistive sensors. 

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