Fabrication, Characterization and Application of PZT-Silane Nano-Composite Thin-Film Sensors and Actuators
Structural health monitoring (SHM) plays a very important role in improving structural safety, preventing catastrophic failures and lowering maintenance costs. Current sensing methods have some limitations, such as being bulky, heavy, or brittle, making them unsuitable for SHM of composite structures. In response to the need for a flexible, printable sensor with low curing temperature, a nano-composite thin-film with additive manufacturing capability that consists of numerous lead-zirconate-titanate (PZT) nanoparticles embedded in a silane matrix is proposed and studied in this dissertation. This dissertation includes fabrication, characterization, and applications of proposed thin-films with rigid or flexible substrates and parallel-plate or interdigitated electrodes as piezoelectric actuators and sensors. Fabrication includes the following steps: First, PZT nanoparticles with size distribution ranging from 300 to 800 nanometers, are fabricated via hydrothermal synthesis.The PZT nanoparticles are then suspended in a silane-based fluid to form a PZT ink that can be printed, sprayed, or drop-cast onto a substrate. The deposited PZT ink is subsequently cured at low temperature (e.g., 120 ◦C) to form the PZT-silane thin- film sensor. A similar ink and thin-film sensor using crushed bulk PZT is also fabricated for comparison. The aerosol-jet printed results for both inks are provided and compared. Characterizing the material properties of the PZT-silane thin films includes two parts: dielectric and piezoelectric characterization. The dielectric constant and loss are measured through an impedance analyzer. Piezoelectric properties are estimated by applying a calibrated force directly onto the film while an accurate, double-end charge amplifier isolates and records the tiny induced charge from background electrical noise. A finite element model is created to simulate the experimental setup in order to estimate the piezoelectric coefficient d33 from the measurements. A PZT-silane nano-composite thin film with parallel-plate electrodes, drop-cast near the fixed edge of a thin flexible cantilever beam made of kapton, has been successfully demonstrated as an actuator. Velocity measurements at the free end are found to be in synchronization with actuation signals when driving the PZT-silane thin film actuator near natural frequencies of the beam. To demonstrate its validity as a vibration sensor, a PZT-silane thin film is attached to a square aluminum plate supported by four pillars. The frequency response of the charge measured from the PZT thin-film sensor is in close agreement with the vibration measurements from a laser Doppler vibrometer. PZT ink is drop-cast on a flexible substrate in two electrode formats for evaluation: parallel-plate and interdigitated electrodes (IDEs). The parallel-plate electrode format is difficult to implement, because silver electrodes cannot be properly printed onto the PZT film with high conductivity and dimension accuracy. In contrast, IDEs inkjet-printed onto a polyethylene terephthalate (PET) film demonstrate excellent resolution and conductivity. Sinusoidal voltage applied over the IDEs drives PZT thin-film with IDEs device into resonance serving as a resonator. PZT thin films with printed IDEs are demonstrated as vibration and strain sensors. Vibration tests are carried out on wing and beam structures with small angle oscillations. PZT thin-film with IDEs are attached on one side of these test structures and commercially acquired foil strain gauges on the other side for comparison and characterization. Strain and charge frequency domain measurements are recorded and amplitude peaks correlate to structural vibration frequencies. PZT-IDE sensor outputs at wing/beam oscillation frequency are found to increase with vibration amplitude and charge responses are approximately proportional to strain gauge outputs. This validates PZT-silane thin films with printed IDEs as strain sensors. The directional dependence of their sensing capability is demonstrated in theory, finite element analysis and experimentation. Two PZT-silane thin film devices with printed IDEs oriented 90 degrees apart show different sensitivities towards single-axis strain and experimentation proves PZT thin films with IDEs can distinguish strains in two dimensions.
- Mechanical engineering