Metamaterial Structure Featuring Multi-Mode Switchable Functionality

Objective Known as frequency-selective surfaces (FSSs), artificial electromagnetic metamaterials are periodic structures that selectively transmit or reflect electromagnetic waves. However, traditional passive FSSs with fixed electromagnetic filtering characteristics have limitations in complex modern environments. To this end, active frequency-selective surfaces (AFSSs) with switchable, reconfigurable, and tunable functionalities have caught attention for their flexible electromagnetic wave control capabilities. Although many researchers have devoted considerable efforts to developing AFSS structures with various advantageous features, limited attention has been paid to independent control of different polarizations. To satisfy the demand for polarization independent control in various applications, we propose a novel AFSS structure with four operating modes. The design allows independent modulation of transmission and reflection for TE or TM polarized wave at different frequency bands, providing dual-polarization transmission, TE or TM single-polarization transmission, and full-polarization shielding functionalities. Furthermore, the AFSS structure demonstrates excellent angular stability, ensuring almost consistent performance within an incidence range of 0 degrees-45 degrees for all operating modes. This characteristic is vital for practical applications that require stable functionality under varying incident angles. Finally, the presented polarization independent multi-mode AFSS structure exhibits promising potential in spatial filtering and radome applications that require specific polarization control. Methods We propose a novel multi-mode switchable AFSS structure with polarization independent control capability and excellent angular stability. The design involves a multi-layer filtering structure that enables the desired polarization independent control functionality. Specifically, we carefully design orthogonal top and bottom FSS structures to independently control TE and TM polarizations. Meanwhile, by integrating PIN diodes between adjacent unit cells in the top and bottom layers, we achieve the capability to switch among different operating modes. To enhance the understanding of the structure's working mechanism, we build TE and TM equivalent circuit models of the unit cell for analysis, with various polarized incident waves considered. Subsequently, we investigate the changes in the real and imaginary parts of the impedance for both transmission and shielding modes, providing valuable insights into transmission window generation. Furthermore, we present detailed TE and TM polarized transmission and reflection results for each operating mode at various incident angles. Additionally, we visualize the corresponding electric field distribution to effectively illustrate the working states. This comprehensive analysis highlights the versatility and adaptability of the proposed structure. Finally, to emphasize its advantages, we compare the proposed AFSS structure with some recent similar designs. The comparison demonstrates the unique strengths and benefits of our approach, making it a promising candidate for diverse applications requiring independent polarization control. Results and Discussions The proposed structure provides multi-mode switchability and polarization independent control, enabling four operating modes including dual-polarization transmission, TE polarization transmission and TM polarization reflection, TE polarization reflection and TM polarization transmission, and full-polarization shielding. In the transmission mode, the real parts of the TE and TM polarized input impedance of the structure closely match 377 Omega at 3. 6 GHz and 4. 6 GHz respectively, with their imaginary parts approaching zero. Both of them effectively match the air impedance, and consequently efficient transmission of both polarizations is achieved at these frequencies (Fig. 4). The structure achieves mode switching by adjusting the bias states of the top and bottom PIN diodes, ensuring that each mode exhibits highly stable performance independent of the others. Additionally, the structure demonstrates sound angular stability within an incidence range of 0 degrees-45 degrees (Fig. 5). Based on these functionalities, the proposed structure has great application prospect in spatial filtering, antenna enclosures, and other relevant fields. Conclusions We present a novel polarization independent control multi-mode switchable frequency-selective surface filter/shield. The structure is designed based on the equivalent circuit model with a multi-layer FSS architecture, where PIN diodes are loaded on the top and bottom layers to achieve independent control of TE and TM waves. By setting different bias voltages on the diodes, the structure can switch among the four operating modes, enabling transmission or reflection control of TE and TM waves. In the transmission mode, the structure forms low-insertion-loss transmission windows at center frequencies of 3. 6 GHz and 4. 6 GHz for TE and TM waves respectively. In the shielding mode, electromagnetic waves are prevented from penetrating the structure. Within the incident angle range of 0 degrees- 45 degrees, each mode exhibits stable performance, and the working states of different polarizations are not affected by other modes. In conclusion, the multi-mode reconfigurable AFSS design has promising application potential in wireless communication systems.