Excitation of thick-film resonant sensor structures

Thick-film technology is attractive in sensor applications because of its cheapness and robustness. The main problem is the relative difficulty of controlling the dimensions and properties of the films without adding expensive trimming processes. Resonant sensors, on the other hand, have a number of advantages, including a relative insensitivity to variations in the added films. Combining the two technologies could therefore be advantageous. Two methods of exciting mechanical resonance in a simple cantilever beam are investigated. The first is based on periodic Joule heating in a conventional thick-film resistor and the second on piezoelectric deformation of a specially formulated ink. In each case, a strain sensor is added to provide for sustained oscillation by electronic positive feedback. Open-loop measurements show that in each case a Q factor of the order of 200 is achievable