This paper presents a wearable metasurface multiple-input multiple-output (MIMO) antenna for biomedical applications in a 5 GHz wireless body area network (WBAN) with broadband, circular polarization (CP), and high gain. The physical properties of the MIMO antenna element and the principles of polarization conversion are analyzed in-depth using characteristic mode analysis. For the proposed MIMO antenna, the measured −10 dB impedance bandwidth is 34.87% (4.76–6.77 GHz), and the 3 dB axial ratio bandwidth is 22.94% (4.9–6.17 GHz). By adding an isolation strip, the measured isolation of the two antenna elements is greater than 19.85 dB. The overall size of the MIMO antenna is 1.67λ₀ × 0.81λ₀ × 0.07λ₀ at 5.6 GHz, and the maximum gain is 7.95 dBic. The envelope correlation coefficient (ECC) is less than 0.007, with the maximum diversity gain greater than 9.98 dB, and the channel capacity loss is less than 0.29 b/s/Hz. The specific absorption rate (SAR) of the wearable MIMO antenna is simulated by the human tissue model, which proves that the proposed antenna conforms to international standards and is harmless to humans. The proposed wearable metasurface MIMO antenna has CP, broadband, high gain, low ECC, and low SAR, which can be used in wearable devices for biomedical applications.

In this paper, a dual-band pixel terahertz (THz) metamaterial absorber sensor has been designed based on an Improved Binary Ant Colony Optimization (IBACO) algorithm incorporating competitive learning and teaching learning mechanisms, which enables transcend the constraints of metamaterial absorber sensor methods that rely on a priori knowledge and design experience, leading to significant consumption of time and computational resources. Equivalent circuit model theory and impedance matching theory, as well as further discussion of current and field distributions, are undertaken to elucidate the underlying physical mechanisms. Notably, the sensor demonstrates exceptional frequency selectivity and polarization independence, achieving absorption rates exceeding 97% at 0.6598 THz and 0.9443 THz, and sensitivities of 69.6 GHz/RIU and 146.4 GHz/RIU, respectively, corresponding to figures of merit (FOM) of 8.81 and 31.15, which positions the sensor as a viable candidate for applications in RF stealth and detection sensing. Compared to conventional design approaches, the proposed method facilitates the rapid development of sensors tailored to specific design objectives, thereby heralding new possibilities for designing high-performance terahertz and other electromagnetic devices.

This letter presents a flexible, wearable, broadband circularly polarized antenna. A novel polarized conversion metasurface is loaded onto the flexible antenna, greatly expanding impedance and axial ratio bandwidths with the size of 52.6 mm × 49.6 mm × 6.325 mm (0.91 λ₀ × 0.86 λ₀ × 0.11 λ₀, λ₀ = 5.2 GHz). Besides, Characteristic Mode Analysis is applied to reveal the working mechanism of the antenna. Experimental results indicate that an impedance bandwidth of 4.48-8.39 GHz (60.8%) and a 3 dB axial ratio bandwidth of 4.43-6.52 GHz (38.2%) could be achieved. Additionally, when the human tissue is 10 g, the peak specific absorption rate (SAR) is 0.3800 W/kg, which is far below the limits of 2.0 W/kg under the 10 g average. The conducted robustness analysis demonstrates the antenna's exceptional stability under various operational conditions, making it a promising candidate for integration into wearable sensor systems.

Ground-based metal targets are highly visible in passive microwave remote sensing (PMRS) due to their low brightness temperature (BT), making them easily detectable. However, existing passive jamming techniques face limitations such as low effectiveness and technical complexity, highlighting the need for more efficient solutions. This article proposes a passive radiation jamming principle based on metamaterial absorber, elucidating the feasibility of passive radiation jamming against PMRS. A cross square ring staggered rectangular absorber (CSRSRA) with a fourfold symmetric multilayer composite structure is designed to achieve high absorptivity and broadband absorption. Theoretical analysis and simulations demonstrate that the CSRSRA effectively absorbs radiation from ground-based metal targets, ensuring that the detected BT closely matches that of the surrounding environment. This consistency effectively jams the target’s visibility in PMRS. The experimental results confirm the high absorption performance of the CSRSRA, while field experiments further validate its feasibility in jamming the BT of ground-based targets. The results demonstrate that the CSRSRA provides an efficient and practical approach for passive radiation jamming against PMRS, enhancing target concealment while significantly reducing technical complexity.