Flexible Polymer-Ceramic Composite Materials for High Sensitive Pressure Sensing Applications in Harsh Environments

Flexible Polymer-Ceramic Composite Materials for High Sensitive Pressure Sensing Applications in Harsh Environments Kavin Sivaneri Varadharajan Idhaiam Robotics aligned with completing physical activities in the space environments will require a new suit of solid-state sensors that are versatile and robust, and will provide precise information about contact events with various space assets. One of the vital sensing mechanisms is the “feelof-touch” or “tactile/haptic” feedback to the robotic system. Current robotics tactile/force sensor use mechanical switches for the feedback to determine whether the end-effector is in contact, which does not provide sufficient information regarding the local force and point-of-contact for the robotic end-effector. To tackle these challenges, the current work focusses on the development of flexible tactile sensor arrays that conform to the geometry of the end-effector and provide information about contact location, force magnitude, and force type. The sensor arrays were also composed of robust materials sufficient for the desired space application; the sensor system was designed to withstand the harsh environment, temperature fluctuations, and desired sensitivity. In this research, tactile sensor arrays were fabricated and tested, which were flexible, thick film, capacitive sensors that are composed of a 2:2 laminar polymer-ceramic composite. The composite was composed of four distinct layers, which consist of a polyimide support (Kapton film), patterned Pt electrodes, a compliant elastomer layer, and a ceramic dielectric layer (HfO2). Three different capacitive sensor architectures were developed to study the influence of the dielectric HfO2 layer on the sensitivity of the sensor. The baseline architecture was composed the compliant elastomer layer (Arathane 5753 A/B) sandwiched between the Pt electrodes. A bi-layer architecture was also fabricated with an additional HfO2 thin film deposited onto the elastomer in order to magnify the capacitive response of the sensor structure. In a tri-layer architecture, the HfO2 layer was sandwiched between elastomer layers to understand the influence of the additional elastomer layer on the sensitivity and pressure distribution across the sensor structure. These materials were tested over a wide temperature range from -60 to 120 C. The fabricated sensor showed good sensitivity and cycle stability between 0 and 360 kPa. The influence of temperature variations on the capacitive and mechanical properties of the composites was also studied in detail. Thermomechanical loading cycles were performed with an in situ electrical acquisition to characterize the sensor. Chemical and structural characterization of the HfO2 layer deposited on the flexible substrate was evaluated by a combination of conductive atomic force microscopy (c-AFM), raman spectroscopy, and x-ray photoelectron spectroscopy (XPS), and the optical properties were analyzed by ultra-violet visible spectrophotometer (UV-Vis). Embedding strategies were proposed and developed to shield the sensors against the direct exposure to cosmic rays, atomic oxygen, ultraviolet rays, and damages caused by direct contact with other objects in space. The sensors were embedded in a 3D printed prototype which mimics the actual geometry of the gripper tool, a silicone layer was used to provide the mechanical compliance and to support the top plate holding the sensor. The embedded prototype was tested in a mechanical analyzer to study the capacitive response and analyze the influence of the residual capacitance from the silicone layer and the top plate. The final prototype was built and demonstrated with the customized electronics and a software program to directly read-out the pressure/force signal from the sensor.