Concept and design of a 40 GHz differential sensor for the analysis of biomedical substances

This paper discusses a low cost coplanar differential sensor at 40 GHz suitable for the lab on chip integration. Its ability to resolve small permittivity differences with a high dynamic range was proved by analytical calculations and full-wave EM simulations and was finally validated with measurements. A sensitivity of τ = 2.5dB/%Δεr>eff was achieved for small permittivity differences. Thereby, a change of 100 % ethanol to 99 % ethanol mixed with 1 % DI water, results in a difference of ΔS21 = 5 dB. In order to further minimize the complexity e.g. for single use purposes, the influence of the absence of the termination resistors of the couplers was investigated.