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.

Digital potentiometers are substantial components for the design of many mixed-signal electronic circuits and systems. Their capability to program resistance value almost instantly provides hardware designers an additional level of freedom. Unfortunately, this feature is limited to DC and lower frequencies, due to parasitic effects. Nowadays, memristors as continuously tunable resistors are becoming candidates for potentiometer successors. Memristors are two-terminal non-volatile devices which have less significant parasitic effects and a wide resistance range. The memristance value can be changed on the fly. Using nanotechnology, memristor implementation has a nanoscale footprint with nanosecond transition between resistive states. In this paper, we present a comparison between the frequency characteristics of digital potentiometers and the only commercially available memristors. Memristor parasitic effects dominate at higher frequencies which extends the bandwidth. In order to present the advantages of memristive circuits, we have analyzed and implemented tunable circuits such as a voltage divider, an inverting amplifier, a high-pass filter, and a phase shifter. A commercially available memristor by KnowM Inc. is used for this purpose. Experimental results obtained by the measurements verify that a memristor has equal or better characteristics than a digital potentiometer. Memristive realizations of voltage dividers and inverting amplifiers have a wider bandwidth, while filters and phase shifters with a memristor have almost identical frequency characteristics as the corresponding realizations with a digital potentiometer.

When the memristor was fabricated for the first time, it launched an entirely new field of research. Many of the published papers regarding memristors are primarily theoretical and are based on computer simulations. Some recent papers analyze the memristor’s programming circuits, but to the best of the authors’ knowledge, no memristor has been embedded into a commercial analog circuit. This paper is practically oriented and it is based on the experimental results obtained by measurements on the circuit prototype. We present a solution for automated programming of a commercially available memristor and its implementation in tunable active bandpass filter design. The novelty of this paper is that the active bandpass filter’s central frequency could be programmed during the filter operation, so a pause for memristor state-switching is not required. The experimental results are promising, and open up possibilities for the memristor’s application in analog systems.