With recent developments, terahertz (THz) technology has attracted great interest in many different fields of research and application. In particular, biosensors that detect a thin film of captured pathogens are in high demand for rapid diagnosis. Based on the interaction between analytes under test and electromagnetic (EM) field, THz resonators are sensitive to changes in the permittivity of the analyte and have the potential to become sensitive thin-film sensors. However, conventional metamaterial methods have low Q factors, leading to small amplitude variations and ambiguous detection. Here, we present a photonic crystal (PhC)–based resonator with a high Q factor that is sensitive to a monolayer of beads in the µm size range. The PhC resonator made of high resistivity silicon (HRSi) shows a Q factor of 750, which is much higher compared to metamaterial-based methods. Its resonance shift is linearly related to the coverage of the micron-sized beads on its surface. Moreover, simulation results with a thin film model of a single layer of the beads showed agreement with the experimental results. Although the achieved sensitivity needs to be improved by enhancing the field concentration on the analyte, our results suggest that THz PhC resonators with high Q factor are promising for biosensing applications. We anticipate our work to be a starting point for biochips with improved sensing capabilities and more functionality.

Monitoring pathogens has become a major challenge for society and research in recent years. Of great interest are refractive index sensors, which are based on the interaction between analytes and electromagnetic waves and allow label-free and fast detection. In addition, the electromagnetic waves can be exploited for wireless communication. However, current refractive index biosensors can only be read from a few centimeters. Here, we demonstrate an innovative concept of a passive wireless sensor based on a sub-terahertz photonic crystal resonator. The fabricated sensors have a reading range of up to 0.9 m and elevation and azimuth acceptance angles of around 90°. We demonstrate the stand-off detection of sub-µm thin-film proteins as test analytes. The proposed wireless sensor opens the door to a non-electronic, compact, and low-cost solution and can be extended to a wireless sensor network monitoring airborne pathogen, which may provide a pre-infection detection to prevent their spread efficiently.

In this paper, we propose a Photonic Crystal (PhC) resonator based corner reflector for sensing the Angle-of-Arrival (AoA) of the incident wave from an interrogator. The sensor is constructed of joining a flat metal plate with a one-dimensional PhC resonator at an angle of 90∘. The PhC resonator is designed by inserting a defect layer between two quarter-wave Bragg mirrors in order to create a deep notch in the backscattering. While the PhC resonator provides unique spectral signatures in the “specular direction” related to AoA (i.e. by shifting the notch position), the corner configuration allows the back-scattering of these signatures to the direction of the interrogator. As a proof of concept, EM simulation and measurement are performed in W-band on a 40-mm squared PhC resonator perpendicularly joined with a same size metal plate. Based on signatures, a resolution of less than 6∘ can be achieved in the angular range -35∘ to 35∘. Due to the corner configuration that allows a high Radar Cross Section (RCS), the proposed sensor shows the potential of sensing the AoA at long reading ranges.

In recent years terahertz (THz) technology has attracted great interest in biosensing applications. Due to the interaction between analyte and electromagnetic (EM) field, a THz resonator is sensitive to changes in the refractive index of the analyte and can be used as a thin-film sensor for rapid pathogen diagnosis. To achieve high sensitivity and reliability, the sensor should have a high Q factor, a high field concentration at the site of the analyte, and the ability to compensate for temperature effects. However, conventional metamaterial methods have a low Q factor, which may lead to ambiguous detection and no attention has been paid to address the temperature effects. Here, we present a photonic crystal (PhC) based chip consisting of a reference channel and a sensing channel with two identical PhC slot resonators. The resonance difference between the resonators is temperature invariant and can be used for analyte detection. The dual-channel PhC chip has a Q factor of 5063 and a figure of merit of 3.1 /RIU/ $\mu \text{m}$ (RIU is refractive index unit), which are higher than that of metamaterial sensors. The chip is designed and simulated for the W band by 3D field simulations and is verified by measurements. Our results suggest that THz PhC resonators can provide high sensitivity and high resistance to environmental effects. We anticipate our work to be a starting point for future biosensing applications.