Development of a human presence detection system using a novel electrostatically-enhanced displacement current sensing technique

Over the last few years, increasing attention has been paid to the research field of remote detection of human electrophysiological and other bio-activity related signals. Such an interest is mainly due to a growing need to develop new devices able to contactlessly record human vital parameters for clinical and healthcare purposes. At the same time, military and humanitarian activities have renewed the desire of having human presence identification systems based on biological parameters, both for security and rescue activities. The aim of this research is to provide a potential solution to those needs by investigating the deployment of a new electrostatically enhanced displacement current sensing technique for detection human bio-activity related signals. The investigation started with identification and analysis of the problems with currently available techniques, and the potential solutions provided by other research groups as described in the literature. Once the signals to be detected were identified, notably electrophysiological signals related to human’s heart and muscles activities, as well as other body-movement linked electric variations, an exhaustive analysis and characterization of such signals were performed. This was followed by system specifications, design and development of our new displacement current sensor started. This thesis describes a newly developed low-cost displacement current sensor for non-contact, non-invasive detection of electrophysiological and other bio-activity related signals, well suited for applications requiring remote and portable means for detection of human presence. The sensor consists of an input electrode forming the sensor head or antenna, an amplification stage employing a simple improvised trans-impedance amplifier, and a filtering stage. It operates by detecting the displacement current induced between the human body and the sensor’s antenna, by heart and muscle movement related signals of the subject, and further enhanced by the presence of an electrostatically charged dielectric layer at the front of the sensor’s electrode. Reported results, obtained in normal unshielded environment, demonstrate the sensor’s remarkable capability in recording heart related bio-activity signals at off-body distance up to 0.4 m, and skeletal muscle movement related bio-activity signals within 10m off-body distance with no obstacle in between, and 5m off-body distance with a non-metallic concrete wall in between. These positive and encouraging performance figures stimulated our interest in further developing the sensor into a prototype for a human presence detection system that is able to provide a 2D image reconstruction of the subject shape, by utilizing an array of 25 identical units of the same sensor. Experimental results for testing the performance of this sensor array have demonstrated the suitability of electrostatic enhanced displacement current sensors for the detection of human bioactivity related electric signals and, as a consequence, human presence detection itself.