Characterization of interdigital capacitive strain gauges by direct write technology

Interdigitated capacitive strain gauges have several distinct advantages over resistive-based strain gauges, particularly for applications in harsh environments, such as high-temperature environments. In this work capacitive strain gauges have been fabricated using thermal spray technology. Gauges are fabricated using both a direct-write approach where the gauge is fabricated using a computer-controlled deposition system and by ultrafast laser micromachining in which blanket coatings sprayed onto a substrate are subsequently laser micromachined. Silver coatings were sprayed onto plastic, polymer, composites, fiberglass and alumina to form the strain gauges. An ultrafast laser machining technique was used to fabricate capacitive strain gauges on copper coated printed circuit boards as well as NiCr coatings on alumina substrate. The typical capacitance of strain gauge was in the range of 5-25 pF. Mechanical tests included gauge factor, linearity and zero shift. Temperature-based measurements include the temperature coefficient of capacitance (TCC) measurements and thermal cycling tests. The devices show promise for use in wireless strain monitoring applications.