부산대학교 도서관

The demand for compact secure wearable devices has motivated research into new biometrics that minimise the need for bulky additional hardware and computational resources. This work, for the first time, proposes and validates a new biometric utilising the physical layer characteristics of wireless devices to authenticate the user. To implement it, a compact wearable network is designed with a novel directional coupler to investigate properties of the human body through antenna characteristics. Machine learning techniques are applied to generate a biometric from antenna characteristics and identify a human through antenna-body interaction. This analysis led to a novel highly human sensitive antenna design with relatively good radiation efficiency to identify the human with a high classification accuracy yet can be used for communication at the same time. Biometric generation through antenna-body interaction combines a study of human body morphology with physical layer characteristics. The physical layer characteristics of close fitting wearable devices are shown to vary in a unique manner through electromagnetic interactions between the tissue morphology and the antenna. Experimental measurement results demonstrate the new biometric concept using return loss characteristics to identify individuals on multiple body parts. An optimized directional coupler design is implemented with the antenna to optimize the characteristic feature detection range for human identification. Experiments conducted on human subjects using a prototype standalone test-bed and sensing circuitry at 2.45 GHz show that classification accuracies of over 98% are achieved for stationary subjects and 93% for mobile subjects. The new physical layer biometric has the potential to be used for authentication and authorization by using return loss as an indicator for secure applications, using circuitry already implemented in wireless wearable communication systems. The antenna sensitivity towards the human body was investigated through numerical and experimental analysis, by measuring the variation of the return loss while interacting with multiple human bodies at 2.45 GHz. The study is focused on inducing current through the electric field generated by an antenna on most of the tissues of the human organ by placing the antenna in the close proximity to the human body. The human sensitive antenna’s radiation efficiency reduces because the power gets absorbed by the human body. A dual layered stacked patch design is introduced to overcome the radiation efficiency issue, which increases 27 % of the radiation efficiency from the previous design of the antenna and still maintains the sensitivity towards the human wrist.