Inherent silicone based sensor elements for actively deformable, fluidically actuated medical devices
Microsystems
Final Report Abstract
The project aim was the fundamental research of conductive silicone-based compliant sensors and the determination of their limits and possibilities in application for medical instruments. The investigations showed that inherent silicone-based capacitive sensors can be built for the quantitative evaluation of compressive forces. These can be used to extend the functionality of compliant silicone-based systems. Currently, electrical circuits limit the evaluation of changes in sensor capacity in the double-digit picofarad range (authors recommendation). Due to the size of electrode carrier for cochlear impbants, it is currently impossible to use these sensors in medical instruments. Compared to the current stage of research, the project’s contributions are: - Development of a methodical flow chart for determining material properties for the quantitative property determination of compliant silicone-based systems, - Introduction of two new parameters for assessing the consideration of the Mullin effect: volume-related mean strain and volume-related mean stress softening, - Development of a method to determine the three Mullin parameters, r, m and ß, for the modified Ogden-Roxburgh model from experimental data, - Development of a manufacturing process for planar capacitive silicone-based sensors with dielectric thicknesses of 20 micrometers, - Development of electronics for the incremental, quantitative acquisition of compressive forces, - Development of an FE-based method for comparing sensor arrangements, - Development of two FE models to simulate the insertion process of straight and pre-curved actuatable electrode carriers, - Extension of the insertion test bench for the automated insertion of initially straight actuatable electrode carriers, - Performing automated insertions of 3:1 scale actuatable electrode carriers, - Validation of the functionality of both actuator forms [Zen17, Zen19a], - Proof of reduction of insertion forces (factor 8.5) and increased insertion angle (factor 1.9) for insertions of straight, actuatable electrode carriers (3:1 scale) and - Design of two functional models: I) sensorized surface as a 4x4 sensor array for quantitative compressive force detection and display; II) sensor module for the incremental quantitative detection and display of compressive forces. Furthermore, a need for research arises with regard to manufacturing technologies for the production of silicone based capacitive sensors. The focus should be on increasing the capacity and reducing the overall installation space through: - Reducing the dielectric thickness of non-electrically conductive, silicone-based precision films to 1 micrometer (thickness used: 20 micrometers, commercially available: 10 micrometers, Q3/2020), - Reducing the required electrode thickness from electrically conductive silicone to 0.1 mm (thickness used: 0.4 mm) and - Production of 3D capacitor shapes (e.g. wound capacitors) and on an automated, not manual production.
