Abstract
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.
Highlights
Foil strain gauges are used for sensor applications, such as load cells or torque transducers, and for the stress analysis of mechanical components
The transverse gauge factor of highly sensitive strain gauges based on a piezoresistive, granular thin film and a polyimide carrier can be dramatically reduced by modifying the strain transfer
This can be achieved by means of a picosecond laser which allows for the reproducible production of strain gauges consisting of a stand-alone polyimide path with the thin film on top
Summary
Foil strain gauges are used for sensor applications, such as load cells or torque transducers, and for the stress analysis of mechanical components. M. Mathis et al.: Novel method to reduce the transverse sensitivity of granular thin film strain gauges foil SGs show different properties compared with conventional metal foil SGs, especially concerning the gauge factor values (Vollberg et al, 2015). Sensitive SGs can reach longitudinal gauge factors up to 30 (Schultes et al, 2018), allowing for the measurement of very small strains, which can be advantageous for stress analysis and sensor applications. A strain perpendicular to the current direction and parallel to the surface plane of the thin film only results in a comparatively small resistance change in the SG This principle was first examined by means of finite element analysis (FEA), and it was verified via measurements of the transverse gauge factor. The resultant low kT of the strain gauges was utilized for tension/compression force transducers with the benefit of a higher sensitivity
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