Fabrication and Testing of a PZT Strain Sensor for Soil Applications

Development of economical and compact strain sensors is crucial for efficient and precise dynamic measurement of strain magnitudes in soils. This paper deals with the design and fabrication of a lead zirconate titanate (PZT) strain sensor for soil mechanics applications. Initially, the sensor design parameters such as the diameter (1.35 cm) and thickness (300 μm) of the PZT diaphragm were designed using finite-element modeling and analysis. The theoretically obtained finite-element solutions for voltage and displacement of the PZT diaphragm were confirmed empirically. The fabrication process for the strain sensor is discussed in detail along with the design for specific test benches to test the electrical and mechanical characteristics at different stages of fabrication of the strain sensors. Maximum displacement achieved by the diaphragm was found to be 250 μm, yielding a voltage magnitude of 7.3 mV. The magnitude of voltage produced for a diaphragm displacement of 250 μm was empirically determined and was found to be 6.6 mV. The sensor was then packaged in polydimethylsiloxane and calibrated against unpackaged sensor, for the voltage generated for corresponding load forces (89-539 kPa) applied to the sensor. Finally, the packaged strain sensor was tested in three different soil substrates and the voltage magnitudes produced for corresponding load forces applied on top of the substrate were compared.