The recent COVID-19 pandemic has shown that there is a substantial need for high-precision reliable diagnostic tests able to detect extremely low virus concentrations nearly instantaneously. Since conventional methods are fairly limited, there is a need for an alternative method such as THz spectroscopy with the utilization of THz metamaterials. This paper proposes a method for sensitivity characterization, which is demonstrated on two chosen multi-band THz metamaterial sensors and samples of three different subtypes of the influenza A virus. Sensor models have been simulated in WIPL-D software in order to analyze their sensitivity both graphically and numerically around all resonant peaks in the presence of virus samples. The sensor with a sandwiched structure is shown to be more suitable for detecting extremely thin virus layers. The distribution of the electric field for this sensor suggests a possibility of controlling the two resonant modes independently. The sensor with cross-shaped patches achieves significantly better Q-factors and refractive sensitivities for both resonant peaks. The reasoning can be found in the wave–sample interaction enhancement due to the better electromagnetic field confinement. A high Q-factor of around 400 at the second resonant frequency makes the sensor with cross-shaped patches a promising candidate for potential applications in THz sensing.

This paper presents the design of compact second-order bandpass filters based on dual-mode open-loop resonator. A filter design procedure is provided to facilitate the design process. The paper also describes the nature of the inherent transmission zero associated with the structure and presents a method of generating two additional zeros for improving stop-band performance. Finally, a filter design example is presented to validate the argument.