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Lei, Hong. (Michigan State University) “Modeling and fabrication of ionic polymer-metal composite (IPMC) sensors”, (2015), Advisor: Tan, Xiaobao
Ionic polymer-metal composites (IPMCs) are an important class of electroactive polymers (EAPs) with built-in actuation and sensing capabilities. They have received tremendous interest for their potential in various sensor applications. In this dissertation, a physics-based dynamic model is proposed for cantilevered IPMC sensors that are excited at the base, and the humidity dependence of IPMC sensing dynamics is discussed based on this model. To ensure the sensing consistency, thick parylene encapsulation is proposed for IPMC sensors, and the performance of encapsulated IPMC sensors is evaluated. Fabrication and modeling of two novel IPMC sensors and micro-fabrication of IPMC-based artificial lateral line system are also presented. These contributions are further elaborated below.
The proposed dynamic model is physics-based, and it combines the vibration dynamics of a flexible beam under base excitation and the ion transport dynamics within an IPMC. In addition, it incorporates the effect of a tip mass. The model is further reduced to finite dimensional one, based on which an inverse compensation scheme is proposed to reconstruct the base excitation signal given the sensor output. Both simulation and experiments are conducted to validate the model and the inverse compensation scheme. The humidity-dependence of IPMC sensing dynamics is also studied based on the latter model, where the humidity-dependence of five physical parameters is captured with polynomial functions, which are then plugged into the model to predict the IPMC sensing output.
Encapsulated IPMC sensors based on thick parylene coating are presented to ensure sensing consistency. The proposed fabrication process comprises major steps of parylene deposition and water drive-in. The physical properties of coated IPMCs are tested and their sensing performances are evaluated under different media along with the comparison with the typical naked IPMC sensors. Experimental results show that the proposed thick parylene coating can effectively maintain the sensing consistency, which allows IPMC sensors to be used in practical applications.
Two novel IPMC sensors capable of omnidirectional sensing are proposed. One is fabricated by plating two pairs of electrodes on orthogonal surfaces of a Nafion square column, and the other uses Nafion tubing as the raw materials to fabricate a tubular IPMC. The sensing responses of both fabricated IPMC sensors are characterized to evaluate their omnidirectional sensing capabilities and the coupling issue is discussed for both cases. An empirical model and a physical model are further developed for the proposed square column IPMC sensor and tubular IPMC sensor, respectively.
Inspired by the lateral line system, a micro-fabrication process is presented to realize flow sensor arrays based on IPMCs. Several challenges are addressed in the proposed recipe including the non-planar process, soft material, and selective formation of electrodes. A new approach of double-subtraction is developed and the first prototype is presented.
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