In this paper, a flexible and frequency-reconfigurable band-stop Frequency Selective Surface (FSS) is studied theoretically and experimentally. The flexible FSS is fabricated through screen printing, a low-cost, high-efficiency additive manufacturing methodology. With the load of bias voltage controllable varactor, resonance frequency tuning from 3.51GHz to 6.02 GHz has been measured to prove the frequency reconfigurability of the FSS under bias of 0-20V. Outstanding wide angular stability under oblique incidence has also been examined both in theory and measurement. The FSS resonance frequency is completely fixed under incidence from 0°-60°, and the angular stability maintains under different bias voltages. The mechanical flexibility, frequency-reconfigurability and angular stability makes it meaningful in applications of flexible/conformal coverage for aiming objects, including electromagnetic scattering control, EMC (Electromagnetic Compatibility), etc.

Metal mesh films have been shown to be a promising strategy to effectively mitigate the growing issue of electromagnetic interference (EMI) in optoelectronic systems. To achieve superior shielding effectiveness, it is common to increase the thickness of the mesh film. However, mesh-based shielding materials have frequency-dependent shielding effectiveness that decreases as the frequency increases. Simply increasing the thickness of the mesh cannot effectively enhance the EMI shielding effectiveness at high frequencies. This will further lead to challenges such as increased processing difficulties and higher costs. In this paper, we present an infrared transparent electromagnetic shielding window based on metal mesh with irregular patterns and proper thickness. The mesh coating is fabricated on a sapphire substrate using ultraviolet photolithography technology and exhibits an efficient electromagnetic shielding effectiveness of more than 20 dB over the wide frequency range of 1.7–18 GHz while maintaining high infrared optical transparency. More importantly, there is no distinct variation in shielding effectiveness between low and high frequency ranges, demonstrating a balanced shielding characteristic across a broad frequency band. This work could be crucial in designing cost-effective and efficient EMI shielding windows for optoelectronic systems.

This article introduces an innovative methodology for the design of energy selective surfaces (ESS) using machine learning. The methodology differs from traditional ESS design approaches that rely on equivalent circuit models. Instead, it involves the training of a forward prediction neural network for the electromagnetic performance of ESS and utilizing an optimization algorithm to achieve the optimal ESS structure. The optimization objective is to align the transmission pole in the transmitted state and transmission zero in the protection state with the target frequency point, achieving a minimal insertion loss (IL) and a maximal shielding efficiency (SE) at the same time. The designed ESS structure consists of a metal frame, a nonlinear induction region, and a resonant region formed by a randomly distributed 0/1 matrix, whose electromagnetic performance varies with the distribution of the 0/1 matrix. Through multiple simulations, 6,000 sets of training data are obtained and used to train a fully connected neural network. Subsequently, the particle swarm optimization algorithm is employed to optimize the objective function. Following these procedures, several ESS structures are successfully obtained. After prototype fabrication and testing, all samples demonstrate consistency with expected results by achieving a low IL and a high SE near the target frequencies.

To satisfy the demands of wireless communication systems for tunable shielding materials, in this work, a graphene/ion gel/graphene sandwich structure is proposed, based on graphene and a solid ionic material ion gel. After modelling, preparing and testing, it was found that the structure could achieve more than 10 dB shielding effectiveness tuning in GHz and THz bands. Meanwhile, the adjusting speed of the structure was also studied, displaying effective dynamic tuning in the second order. Furthermore, the fabricated samples have the advantages of a low profile, easily conformable, and convenient processing, which are of great potential in emerging electronic devices.

This paper proposes a graphene-based flexible printed attenuator consisting of printed microwave transmission line and graphene/ion-gel tunable structure, which can realize the transmission of microwave signals with tunable attenuation and have flexible conformal characteristics. According to the adjustable resistivity of graphene in microwave band, we utilize ion-gel to produce electric double layer (EDL) effect to adjust the conductivity of graphene at a low bias voltage. The coplanar waveguide (CPW) transmission line is prepared on a flexible substrate by screen printing process. The implementation of this flexible printed attenuator relies on the integration of printed CPW and graphene/ion-gel functional components. The flexible attenuator has an obvious attenuation characteristic at a lower applied bias voltage (1.3V), and the adjustable range of attenuation is greater than 15 dB in the frequency range of 500 MHz - 4.8 GHz. This work demonstrates a proof-of-concept tunable attenuator with the characteristics of dynamically adjustable attenuation, low working voltage, facile fabrication and flexibility, and will provide some references for the future development of planar tunable attenuators.