Responsive temperature and pressure sensor design for in-situ prosthesis monitoring applications based on the piezoelectric and pyroelectric effects in lead zirconate titanate

Student thesis: Doctoral Thesis

Abstract

This thesis presents the development of a sensor based on the pyroelectric and piezoelectric effects that can be used to measure both temperature and/or axial stress for specific use within a prosthetic socket, and more generally as a responsive temperature sensor capable of detecting high frequency skin temperature oscillations in medical diagnostic applications. Knowledge of an amputees’ residual limb skin temperature is considered to be of particular importance as an indicator of tissue health. With this in mind, a prototype wearable sensor for real-time temperature measurement at the skin/prosthetic socket/liner interface was developed and measurements that provide a proof of concept are presented. The sensor exploits the large pyroelectric effect present in ferroelectric lead zirconate titanate PbZrx(Ti(1-x)03) (PZT) and has several inherent advantages over other methods of temperature sensing. The sensor element chosen is a low cost commercially available diaphragm PZT-5H element with a brass substrate. While the development of the sensor concentrates on the specific application of surface temperature measurement, the mathematical models developed also describe the sensor response to an applied axial stress that can be used as a measure of the pressure applied to the residual limb by the confinement of a prosthetic socket. Using the mathematical models, substrate clamping was found to significantly increase the effective pyroelectric coefficient. A subsequent experimentally obtained value for the effective pyroelectric coefficient was found to be very close to the value predicted by the mathematical models, confirming the effect of substrate clamping. Immittance models are developed to investigate the temperature dependence of the sensor element immittance, mechanical and constant strain electrical capacitances over the temperature range 20°C to 40°C.Both capacitances were found to be significantly temperature dependent and therefore charge-mode signal conditioning was chosen to mitigate temperature effects on the signal-conditioning response. Subsequent response measurements were found to yield a linear response over the temperature range of interest. Bipolar and unipolar charge amplifier designs are developed and built to provide signal-conditioning for use in sensor response measurements. The unipolar type is a single supply 5V prototype with low power consumption and is also designed for use with an e-Health platform in a wearable sensor configuration. In addition, a single supply enhanced open loop gain design that mitigates the effect of reduced dielectric resistance in the sensor element is presented.Using the developed mathematical models, the sensor is predicted to be capable of measuring frequencies from DC up to 6.8rads−1 with a rise time to the 98% peak of 0.12s and 0.18s for a DC and 6.8rads−1 step, respectively. However, the use of a polymer liner between the sensor element and measurement surface is found to severely limit the usable frequency response of the sensor due to severe amplitude and phase distortion, precluding direct use of the sensor to measure skin surface temperature. Being relevant to the safety of remote e-Health monitoring, the challenges ICT networks must face to maintain quality of service are discussed and it is shown that an increasing amount of traffic, increasing power consumption and electronic bottlenecks are three main challenges that require a solution. The ability of ICT networks to satisfy the growing global demand for data is under threat due to the speed limitations of current CMOS based electronic technologies, leading to electronic bottlenecks and threats to the sustainability of the quality of service critically required for e-Health monitoring.
Date of Award14 May 2020
Original languageEnglish
Awarding Institution
  • University Of Strathclyde
SponsorsUniversity of Strathclyde
SupervisorIvan Glesk (Supervisor) & Arjan Buis (Supervisor)

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