Rational design of capacitive sensors with microstructured dielectrics for medical devices and robotics
Keywords: Chemical Engineering.

Pressure and proximity sensors are widely used in the healthcare and robotics industries. Among other applications, they are used for patient monitoring and robotic surgery, playing an integral role in improving health and safety. Currently, there is an increasing demand for highly specialized sensors within these industries, but the path of designing such sensors can be very circular, requiring multiple redesigns. To better address this challenge, the process must be linearized by enabling more targeted sensor design. To achieve targeted design of sensors for specialized applications, there are five major objectives: (1) better understanding of current sensor technologies, (2) more reliable and reproducible sensor fabrication methods, (3) simple models to predict sensor performance, (4) design rules based on computational and experimental results to inform targeted sensor design, and (5) proven efficacy of the targeted design for specific applications. This dissertation goes through this process specifically for capacitive pressure and proximity sensors. Micro-engineered pressure sensors are of particular interest because of their high sensitivity, fast response, and low limits of detection. The micro-engineering techniques include micropatterned structures, porous layers, multilayered packed structures, and combined approaches, and are compared in terms of ease of fabrication, active layer uniformity, shape and size versatility and tunability, and scalability. Understanding the current sensor technologies, advantages of different sensor types, and fabrication methods led to a focus on capacitive pressure sensors with micropatterned structures. The fabrication method for capacitive pressure sensors was improved for consistency and reliability by introducing a lamination layer to anchor the micropatterned structures—pyramids in this case—to the second electrode. A series of equations modeling the dielectric layer as both a spring and electrical circuit was developed to predict sensor response and was confirmed experimentally. This model was then used to predict how a variety of design parameters impacted the sensitivity and initial capacitance of the sensor. Further, the model was expanded to include alternative microstructure geometries and more performance parameters, enabling a more extensive comparison of microstructure design. Once the dielectric layer of capacitive pressure sensors was better understood, an analysis of the effects of electrode design was investigated, specifically for fringe-field capacitive sensors capable of both pressure and proximity sensing. Four novel electrode designs were compared to a traditional parallel plate design. All fringe-field designs had proximity sensing capabilities, distinguish between pressure and proximity regimes, and distinguish between conductive and insulating materials, however only one could recapitulate most of the pressure sensing capabilities of the parallel plate capacitive sensor. Finally, the newly obtained sensor performance trends were applied to targetedly design a sensor for early detection and prevention of diseases after surgical vascular bypass or plaque removal. This sensor was effective in vitro, in vivo, and in a human cadaver without the need to redesign, thus demonstrating the efficacy of using the design guidelines developed for linear, targeted sensor design