Optically Transparent Tri-Wideband Mosaic Frequency Selective Surface with Low Cross-Polarisation

Acquiring an optically transparent feature on the wideband frequency selective surface (FSS), particularly for smart city applications (building window and transportation services) and vehicle windows, is a challenging task. Hence, this study assessed the performance of optically transparent mosaic frequency selective surfaces (MFSS) with a conductive metallic element unit cell that integrated Koch fractal and double hexagonal loop fabricated on a polycarbonate substrate. The opaque and transparent features of the MFSS were studied. While the study on opaque MFSS revealed the advantage of having wideband responses, the study on transparent MFSS was performed to determine the optical transparency application with wideband feature. To comprehend the MFSS design, the evolutionary influence of the unit cell on the performance of MFSS was investigated and discussed thoroughly in this paper. Both the opaque and transparent MFSS yielded wideband bandstop and bandpass responses with low cross-polarisation (−37 dB), whereas the angular stability was limited to only 25°. The transparent MFSS displayed high-level transparency exceeding 70%. Both the simulated and measured performance comparison exhibited good correlation for both opaque and transparent MFSS. The proposed transparent MFSS with wideband frequency response and low cross-polarisation features signified a promising filtering potential in multiple applications.

Study on frequency selective/absorption/reflection multilayer composite flexible electromagnetic interference shielding fabric

Three kinds of electromagnetic functional materials, frequency selective surface, carbonyl iron coated absorbing fabric and conductive woven fabric, were laminated to filter, absorb and reflect electromagnetic waves. Through equivalent circuit analysis, the frequency selection characteristics and the correlation between the shape and size of the periodic structure of cross-shaped and Jerusalem-shaped frequency selective surfaces were studied. It is found that frequency selective surfaces can reduce the transmission coefficient of carbonyl iron coated fabric at the resonance point, so that the working frequency band of the composite shielding material can be controlled and adjusted. The stacking order has no effect on the frequency selective surface/frequency selective surface double-layer materials, but influence the transmission coefficient of composite materials with frequency selective surface superimposed carbonyl iron coated fabric and/or conductive woven fabric. Among all samples, the transmission coefficient of Jerusalem-shaped/carbonyl iron coated fabric-3/conductive woven fabric has the most strong shielding effect, which is up to −51.72 dB at 10.48 GHz. It is proved that using flexible fabric as the matrix and compounding materials with different electromagnetic functions is an effective method to realize high efficiency and adjustable electromagnetic shielding ability.

Bandwidth Control of Loop Type Frequency Selective Surfaces Using Dual Elements in Various Arrangements

Frequency-selective surfaces (FSSs) have applications across multiple disciplines due to their unique electromagnetic properties. This paper investigates the use of both rounded square loops (RSLs), and simple loop type dual elements arranged in unique patterns, to control the transmission and reflection bandwidth and resonant frequencies over KU and K frequency bands supported by equivalent circuit models (ECMs). The FSSs were fabricated using laser engraving to create conductive loop type elements on a thin, flexible and optically transparent Mylar substrate (relative permittivity of 2.7 and thickness of 65m). The frequency response of the surfaces are controlled through the element self-inductance and capacitive coupling with neighbouring elements. This work shows that different arrangements result in the formation of multiple distinct resonances. The theoretical and experimental results were in good agreement where rounded squares and dual element arrays were employed to create broadband and multiband band-stop FSSs. A polarization sensitive surface exhibited stop-bands at 12GHz and 16GHz in transverse electric polarization and a stop-band at 14.4GHz in transverse magnetic polarization. This technique can be applied to any periodic array through careful selection of the individual elements in the array, as well as their arrangement.

Cascaded PT-Symmetric Artificial Sheets: Multimodal Manipulation of Self-Dual Emitter-Absorber Singularities, and Unidirectional and Bidirectional Reflectionless Transparencies

We herein introduce cascaded parity-time (PT)-symmetric artificial sheets (e.g., metasurfaces or frequency selective surfaces) that may exhibit multiple higher-order laser-absorber modes and bidirectional reflectionless transmission resonances within the PT-broken phase, as well as a unidirectional reflectionless transmission resonance associated with the exceptional point (EP). We derive the explicit expressions of the gain-loss parameter required for obtaining these modes and their intriguing physical properties. By exploiting the cascaded PT structures, the gain-loss threshold for the self-dual laser-absorber operation can be remarkably lowered, while the EP remains unaltered. We further study interferometric sensing based on such a multimodal laser-absorber and demonstrate that its sensitivity could be unprecedentedly high and proportional to the number of metasurfaces along the light propagation direction.