A Microstrip Probe Based on Electromagnetic Energy Tunneling for Extremely Small and Arbitrarily Shaped Dielectric Samples

An energy-tunneling sensor is fabricated by joining two air-suspended short-circuited microstrip cavities with a common ground interconnected by a half-wavelength wire. Due to tunneling, highly concentrated fields are created at the tip of the wire. In this letter, we propose to exploit these concentrated fields to detect the presence of extremely small and arbitrary shaped samples and their dielectric properties. The simulation and measurement results show respective frequency shifts of 60 and 80 MHz in the tunneling frequency when 2 ×2 ×1.6 mm³ samples of FR4 and Rogers 6006 materials are placed on the wire tip. This kind of energy tunneling probe can bring a special advantage in the area of biomedical and forensic analysis where, usually the samples are small in size with no defined shape.