Terahertz (THz) waves, which fall between microwaves and infrared bands, possess intriguing electromagnetic properties of non-ionizing radiation, low photon energy, being highly sensitive to weak resonances, and non-polar material penetrability. Therefore, THz waves are extremely suitable for sensing and detecting chemical, pharmaceutical, and biological molecules. However, the relatively long wavelength of THz waves (30~3000 μm) compared to the size of analytes (1~100 nm for biomolecules, <10 μm for microorganisms) constrains the development of THz-based sensors. To circumvent this problem, metasurface technology, by engineering subwavelength periodic resonators, has gained a great deal of attention to enhance the resonance response of THz waves. Those metasurface-based THz sensors exhibit high sensitivity for label-free sensing, making them appealing for a variety of applications in security, medical applications, and detection. The performance of metasurface-based THz sensors is controlled by geometric structure and material parameters. The operating mechanism is divided into two main categories, passive and active. To have a profound understanding of these metasurface-assisted THz sensing technologies, we review and categorize those THz sensors, based on their operating mechanisms, including resonators for frequency shift sensing, nanogaps for enhanced field confinement, chirality for handedness detection, and active elements (such as graphene and MEMS) for advanced tunable sensing. This comprehensive review can serve as a guideline for future metasurfaces design to assist THz sensing and detection.

The ability to transmit wireless signals into the body is important for medical communication, sensing, and powering technologies. However, the efficiency of signal transmission is limited by the large reflection encountered at the interface between air and biological tissue. Here, we demonstrate an approach to overcome this reflection using cascaded metasurfaces (MSs) with deeply subwavelength thickness to transform the wave impedance at the air–tissue interface. We develop a procedure to systematically synthesize these MSs using a multilayer tissue model that can account for different body compositions. Using this procedure, we design a three-layer MS operating at 2.45 GHz with $\lambda /24.5$ thickness. Full-wave simulations in a computational human body model show that the MS provides transmission equivalent to replacing the background with a tissue-matched medium, while experimental measurements demonstrate 12.1 dB enhancement of transmission into a multilayer tissue phantom.

Conventional chiral metasurfaces are constrained by predetermined functionalities and have limited versatility. To address these constraints, we propose a novel chirality-switchable terahertz (THz) metasurface with integrated heating control circuits tailored for spin-selective anomalous reflection, leveraging the phase-change material vanadium dioxide (VO₂). The reversible and abrupt insulator-to-metal phase transition feature of VO₂ is exploited to facilitate a chiral meta-atom with spin-selectivity capabilities. By employing the Pancharatnam–Berry phase principle, complete 2$\pi$ reflection phase coverage is achieved by adjusting the orientation of the chiral structure. At the resonant frequency of 0.137 THz, the designed metasurface achieves selective absorption of a circularly polarized wave corresponding to the state of the VO₂ patches. Concurrently, it reflects the circularly polarized wave of the opposite chirality anomalously at an angle of 28.4° while maintaining its handedness. This chirality-switchable THz metasurface exhibits promising potential across various applications, including wireless communication data capacity enlargement, polarization modulation, and chirality detection.

Intelligent reflecting surfaces (IRSs) have emerged as a cost-effective technology for terahertz (THz) communications by enabling programmable control of the wireless environment. This paper provides a comprehensive overview of IRSs-aided THz communications, covering hardware designs, advanced signal processing techniques, and practical deployment strategies. It first examines key THz reconfigurable metasurface architectures, including electronic, optical, phase-change material, and micro-electromechanical systems (MEMS)-based implementations, highlighting their reconfiguration mechanisms and challenges. Then, fundamental effects including near field and beam squint in wideband THz systems are analyzed, along with their impacts on system performance. The paper further explores conventional and beam-squint-assisted channel estimation methods, innovative beam management strategies, and deployment considerations across large- and small-scale scenarios. Practical experiments at 220 gigahertz (GHz) validate the effectiveness of IRS in improving signal strength and communication reliability for both single-user and multi-user setups.

An upconversion biocompatible implant is the first step of translating decades‐old near‐infrared nanotransducer research into wireless phototherapeutic devices that can be implanted underneath the skin. The use of a hydrogel and cladding results in an upconversion optical fiber that is able to upconvert in a flexible manner and even transmit NIR at maximal bending is described by Kah‐Leong Lim, Yong Zhang, Brian K. Kennedy, and co‐workers in article number 2001459. This concept is applicable to various needs of wireless phototherapeutics. With better designs in the future, upconversion implants will be able to be translated from the bench to the bedside.

This paper presents a novel three-layer cascaded bianisotropic metasurface for enhancing wireless power and data transmission across the air-tissue interface in implantable bioelectronic systems. The proposed metasurface simultaneously addresses two fundamental challenges in electromagnetic wave regulation for bioelectronics: (1) mitigating reflection losses due to impedance mismatch at the air-tissue boundary and (2) reducing polarization sensitivity of implanted devices to incoming linearly polarized signals. Experimental validation using porcine tissue at 28 GHz demonstrates a significant transmission enhancement of 6.07 dB and an axial ratio below 3 dB across the 27.2-28.6 GHz band, ensuring consistent and robust circular polarization performance over a wide spectrum. These results represent a significant advancement in implantable device interfaces, offering dual functionality of polarization conversion and impedance matching in a single compact platform.