Data Acquisition Web

In the mid-1950s, scientists at Bell Labs discovered the piezo-resistive characteristics of germanium and silicon. Around 1970, the first silicon strain gages were developed for the automotive industry.

Although the substantial nonlinearity and temperature sensitivity, they had gage factors more than fifty times, and sensitivity more than a 100 times that of metallic wire or foil strain gages. Besides silicon is more elastic than metallic counterparts are. Semiconductor gages use the same epoxies used for foil gages, are much smaller and the cost is much lower. Disadvantages of semiconductor gages are temperature sensitivity, drift, and nonlinearity. With computer-controlled instrumentation, these limitations can be overcome through software compensation.

A further improvement of the metallic foil strain gage is the thin-film strain gage that eliminates the need for adhesive bonding. To produce the gage the procedure is first deposit an electrical insulation onto the stressed metal surface, and then deposit the strain gage onto this insulation layer. Vacuum deposition or sputtering techniques are used to bond the materials molecularly.

Inastomer is a flexible, conductive, elastomer-based composite. It shows excellent reliability, linearity and mechanical characteristics. The composite contains spherical carbon molecules which, when altered in proximity to each other by forces such as compression, torsions, elongation or bending, cause the conductivity of the material to increase in proportion to the magnitude of the applied force. Response of the sensor is almost instantaneous, and may be applied to curved or uneven surfaces.

A new smart force sensor is just a field effect transistor, contacted at both sides of its channel. Mechanical stress renders the transistor channel resistance anisotropic. Main features are high linearity, low hysteresis, cost-effective standard CMOS processing, and on-chip integration of analog and digital signal processing.