Pressure propagation in encapsulated pressure sensor systems

Medical technology has been developing at a rapid pace, using new microsystem technologies to develop implantable monitoring devices. A key issue is the need for biocompatible materials which serve as protection both for the human body and the vulnerable electric components. Given the great relevance of hypertension in cardiovascular medicine, a reliable way to monitor blood pressure over long periods of time via an implantable pressure sensor could be beneficial to the treatment of many patients. The aims of this thesis were to investigate the influence of a protective silicone covering on the signal received by the pressure sensor and to apply the findings to the development of an implant for long-term monitoring of arterial blood pressure. As a first step, the influence of the encapsulation’s shape and material parameters on pressure propagation was examined. Due to little or no available literature on this topic, preliminary tests using each component were conducted. Consecutevely, mathematical models predicting silicone influence on pressure propagation were developed. The calculated results were verified by empirical testing. For all models used, the correlation between the amplitude reduction and the aspect ratio of the silicone height to the silicone width was determined, showing that all damping due to the silicone has the characteristic of a low pass filter. A mathematical model was then used to simulate the effects of various system designs for the implantable blood pressure sensing unit of the Hyper-IMS system. The Hyper-IMS has shown promising results regarding pressure and temperature monitoring in a vascular model as well as first in-vivo experiments with sheep, but further testing and development will be needed to allow it to reach widespread clinical use