Novel method to reduce the transverse sensitivity of granular thin film strain gauges by modification of strain transfer

Abstract

Strain gauges based on polyimide carrier foils and piezoresistive granular thin films are highly sensitive to strain. Unlike conventional metal foil, granular film strain gauges also have a pronounced sensitivity to strain acting in the transverse direction. A novel method that allows for the modification of the strain transfer is proposed and proven experimentally. The method is based on the creation of stand-alone polyimide paths, on top of which the piezoresistive thin film is located. In this way, the granular film hardly receives any transverse strain; hence, the transverse sensitivity is drastically reduced. A picosecond laser system can be used for both patterning of the thin film and for controlled ablation of polyimide in order to generate well-defined high path structures. The working principle of the method is demonstrated by simulation, followed by an experimental verification using measurements of the transverse gauge factor. Furthermore, the output signal of force transducers may be increased using granular thin film strain gauges of reduced transverse sensitivity.