Access Control System Based on Ring Resonator’s Sensitive Properties

The paper is dedicated to the development of a new type of electromagnetic (EM) devices to achieve unique output signal patterns for their potential applications in secure systems. The proposed device involves modification of a microstrip transmission line modification by ring resonators. The ring resonator is an EM component that is characterized by high sensitivity, impedance of which can be easily adjusted by its shape changing. It was performed with the ring resonator’s microstrip lines lengthening from 1 to 13.5 mm that allows the resonance frequency changing from 1 to 1.6 GHz, demonstrating the tunability of the device. The modification of a microstrip transmission line with one or a few of such ring resonators by their strong near-field coupling leads to a deep minimum/minima appearance in the transmission line transfer function (S21-parameters spectrum). This minimum can disappear under direct touching of the ring resonator by a human finger – changing of the total capacitance of the ring resonator. It means that the consequence touching/untouching of the ring resonator leads to a modulation of the input transmission line signal and producing unique output signal patterns. As the number of ring resonators increases, the complexity of these patterns also increases. The variety of the patterns can be unique and secure; thus, the output signals can serve as a key for creation of password for systems of access control. To ensure that the security level provided by the device meets the necessary standards, the keyspace – the total number of possible unique patterns – was estimated for various combinations of the developed ring resonators. The analysis revealed that with 14 available ring resonators, the keyspace can exceed 1015, indicating a vast number of possible combinations and, therefore, a very high level of security.