Design and development of bilayer sensor systems for biomedical and automotive applications

This investigation concerned the design and development of a novel measurement system that incorporates bilayer sensors for monitoring applications in the biomedical and automotive industry. The bilayer sensors are made primarily from a configuration of soft magnetic material on a non magnetic substrate that is used to enhance the changes in the relative permeability of the material, caused by tensile or compressive stresses. Three modulation techniques were examined as a method for convening the sensor signal information this is the first use of the phase (PM) and frequency (FM) modulation methods in conjunction with bilayer sensors. The measurement system incorporated, in software code, a range of mathematical concepts used for extracting and processing the sensor information signal. The use of simulated and acquired modulation signals allowed the comparison of the modulation techniques. Optimisation of the bilayer sensor was considered by studying the effects of the bilayer sensor physical dimensions and parameters on its performance. Also the thermal stability of the bilayer sensor and FM system was examined. Physiological measurements for the detection and monitoring of cardio respiratory activities were conducted. A bilayer sensor measurement system was used for the first time not only to detect but also to map the normal heartbeat rate through the hemo-dynamics of the carotid artery. The system was used to monitor a range of respiratory activities such as normal respiration, deep inhalation/exhalation and apnoea. The application of the sensor is a non-invasive and a non-disturbing method for monitoring biomedical activities related to skin curvature changes. The bilayer sensor measurement system was used for monitoring of airflow in turbulent conditions. Measurements were conducted for a variety of airflows and at a range of distances from the centre of the tube, were the flow is at maximum. Furthermore the effect of substrate thickness and material choice was investigated on the performance of the sensor. This investigation led to the design and construction of a novel measurement system than can successfully detect and quantify displacements in the micron range. The application of this system to biomedical and automotive applications showed the universality and adaptability of the bilayer sensors and its measurement method

Applications of the bi-layer thin film sensor system for registering cardio-respiratory activity

A novel bi-layer thin film sensor system was used for accurately registering physiological parameters associated with body movements, such as cardiac and respiratory activities. The bi-layer curvature sensor system can provide additional medical information about the cardiac activity of the patient by mapping the five characteristic waves of the normal heartbeat rate (P, Q, R, S and T wave). This system was also used for registering physiological parameters such as the monitoring of lung ventilation which can give a range of information about the patients health (normal respiration patterns, deep inhalation/exhalation and apnoea), easily distinguishable in the output signal. The bi-layer thin films used consist of a magnetic layer and a non-magnetic counter layer that is utilized to enhance the changes in the relative permeability of the material caused by tensile or compressive stresses during bending. The measuring system is based on a personal computer in conjunction with the LabVIEW® graphical programming package. The nature of this configuration provides the necessary features for sensor signal acquisition, analysis and data presentation. The results from the sensor application on patients demonstrate that this system can provide a robust, cost effective solution to monitoring cardio-respiratory activity with minimum inconvenience to the patient, which is necessary for prolonged, undisturbed monitoring

Thermal stability of bi-layer thin film displacement sensors systems

The bi-layer thin film measurement system uses the principle of frequency modulation for the detection of displacement. The measuring system utilizes a personal computer based system using the LabVIEW® graphical programming package that provides the features necessary for acquiring the sensor signal, analyzing it and displaying the results. The results from the acquisition were compared with previously developed amplitude and phase modulation based systems to show that the frequency modulation technique provides a robust and accurate solution to evaluate magnetostrictive materials and their application in magnetic sensors. The performance of the bi-layer thin film sensor was examined and its thermal stability, over the temperature range of up to 180 ◦C, was tested in an environmental chamber. The temperature rise does cause inductance change, but the sensor signal remains unaffected due to the nature of the frequency modulation method. Thus, having two materials, with different thermal coefficients of expansion in a bi-layer thin film sensor does not adversely influence the sensor signals. This creates a temperature independent sensor that is needed for applications where there are temperature variations