Recognising people using smart phone antennas: A fuzzy biometric

Many calls are made to mobile phones by machines and for nuisance avoidance it would be useful to know if the caller was human or not. Also for convenience it would also be useful to know if the person using a mobile was the same as the one normally using it and if that person was an adult or a child. A wrong result could be used to trigger a request for a key code. Using the hand and four mobile frequency band antennas this paper has investigated the effects of different people on the input impedance of mobile phone antennas with the aim of establishing whether the effect is distinct enough to allow a fuzzy biometric to be achieved. Hands were placed at a range of distances from the antenna, using a test rig designed specifically for this experiment. The frequencies of operation were 900 MHz, 1800 MHz, 1900 MHz and 2.4 GHz. Results showed that the effect of each volunteer on the antenna's input impedance varied significantly when their hand was 30 mm or less from the antenna and that below 10mm they were distinct between volunteers.