The electrical response of thick-film resistors to hydrostatic pressure and uniaxial stress between 77 and 535 K

The longitudinal gauge factor for a thick-film resistor material (Heraeus 8 241) printed on an alumina substrate is found to be 12.6 at 295 K. The piez oresistive coefficient G, the unit change in resistivity per unit change in strain is 19.5, with a negative temperature coefficient of - 0.00335 K-1, measured between 77 and 535 K. Thick-film resistors of different geometry w ere subject to hydrostatic pressure, and by the use of the piezoresistive e quation based on elastic theory, and elastic modulus data for Heraeus 8241, G was calculated and found to be 19.7 at 295 K, thus validating the piezor esistive equations and the elastic modulus value for Heraeus 8241. Hydrosta tic pressure tests at elevated temperature were believed to be subject to s ome error, 10% at 500 K, due to adiabatic heating effects. However, it is a pparent that resistance change can be predicted with a knowledge of strain in the x, y and z axes. This will prove useful for thick-film strain sensor design, where the thick-film resistor is simultaneously stressed in more t han one direction. (C) 1999 Elsevier Science S.A. All rights reserved.