Key Takeaways & Executive Findings
- •• The proposed CFSR achieves a wide −1 dB transmission band (8.79–10.41 GHz) with low insertion loss (0.44 dB at 9.59 GHz) and two high absorption bands (>90%) with wide-angle stability up to 60°. • The design integrates three metasurfaces and a 3D-printed metastructure, simplifying the transmission band design while enhancing absorption performance. • Equivalent circuit model (ECM) and impedance characterization elucidate the physical mechanisms, providing a systematic design methodology for high-performance Rasorbers. • Experimental results confirm the simulated performance, demonstrating the practical viability of 3D-printing technology in advanced electromagnetic structures.
Abstract
The present investigation introduces a composite frequency selective Rasorber (CFSR) that demonstrates a wide −1 dB transmission band, two high absorption bands with absorptivity higher than 90%, and large oblique incidence angles up to 60°. The CFSR consists of four functional layers separated by three dielectric slabs, which includes lossless metasurface-Ⅰ (MS-Ⅰ), loss metasurface-Ⅱ (MS-Ⅱ), loss metasurface-Ⅲ (MS-Ⅲ), and a three-dimensional metastructure (3D-MS). MS-Ⅰ functions as a reflector for two absorption bands with a minimal insertion loss transmission window. MS-Ⅱ is designed for high-frequency absorption. MS-Ⅲ serves as a low-frequency absorption layer for CFSR and an impedance matching layer for MS-Ⅱ. The design methodologies for the transmission window in MS-III and the introduction of 3D-MS are key to achieving high-performance CFSR. The physical mechanisms of CFSR are explained through equivalent circuit model (ECM) analysis and impedance characterization. Finally, measurement results confirm that the proposed CFSR exhibits a −1 dB transmission band ranging from 8.79 to 10.41 GHz with a minimum insertion loss of 0.44 dB at 9.59 GHz; furthermore, the frequency range where reflection coefficient remains below −10 dB is measured to be between 3.33 and 18.00 GHz, aligning well with simulation outcomes.
1. Introduction
In recent decades, the frequency selective Rasorber (FSR) has garnered significant attention due to its efficient transmission of electromagnetic (EM) energy within the operating band while effectively absorbing out-of-band EM energy [1]. Leveraging these properties, FSR can be utilized for radar cross section (RCS) reduction, enhanced electromagnetic compatibility, and more [2, 3]. Unlike FSRs with only one transmission band and one absorption band, the A-T-A type FSR exhibits a transmission band sandwiched between two absorption bands, thereby expanding the potential application scenarios of FSRs further [4−12].
Generally, the ideal FSRs should possess wide −1 dB transmission windows and 90% absorption bands simultaneously [13, 14]. To accomplish this objective, three different designs incorporating representative deficiencies are proposed. For instance, WANG et al [15] designed an FSR with 80% absorption bands ranging from 3.68 to 7.26 GHz and 12.3 to 14.2 GHz, as well as a −1 dB transmission band spanning from 8.12 to 11.00 GHz. JIA et al [16] proposed an FSR with 90% absorption bands ranging from 3.19 to 9.00 GHz and 11.85 to 21.18 GHz, along with a transmission window at 10.00 GHz with a minimum insertion loss of 0.26 dB. WAN et al [17] also demonstrated an FSR with 90% absorption bands ranging from 1.50 to 3.60 GHz and 15.20 to 21.80 GHz, as well as a −2 dB transmission band spanning from 8.00 to 12.50 GHz. The aforementioned studies have their own limitations. Although the transmission window in Ref. [15] exhibits a wide range with minimal insertion loss, its 90% absorptivity bandwidth is narrow. On the other hand, Ref. [16] demonstrated higher absorptivity exceeding 90%, but at the cost of a narrow transmission bandwidth. Lastly, while Ref. [17] boasted both absorptivity above 90% and a wide transmission window bandwidth, it suffers from high insertion loss. Additionally, the transmission band of A-T-A type FSRs is typically achieved by incorporating various parallel resonant elements, such as meandered cross dipoles, interdigital capacitors, and rectangular spiral resonators [18−20]. Our team believes that the integration of these structures may introduce additional complexity to the model design during simulation process.
To overcome above limitations and simplify design process of transmission band, this study proposes a new A-T-A FSR that demonstrates a wide −1 dB transmission band with low insertion loss, two high absorption bands with absorptivity higher than 90%, and large oblique incidence angles up to 60°. The working mechanism of the composite frequency selective Rasorber (CFSR) is illustrated in Figure 1. In details, the CFSR consists of four functional layers separated by three dielectric slabs, which include lossless metasurface-Ⅰ (MS-Ⅰ), loss metasurface-Ⅱ (MS-Ⅱ), loss metasurface-Ⅲ (MS-Ⅲ), and a three-dimensional printing metastructure (3D-MS). MS-Ⅰ functions as a reflector for two absorption bands while maintaining a minimal insertion loss transmission window.
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LIU Yan-qiong, MA Zhe-yi-pei, JIANG Chao (2025). Strong absorption and high transmission Rasorber with wide-angle enabled by 3D-printing metastructure and three metasurfaces. Journal of Central South University. https://doi.org/10.1007/s11771-025-6047-7
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Frequently Asked Questions
What is a frequency selective Rasorber (FSR)?
A frequency selective Rasorber (FSR) is an electromagnetic structure that allows transmission of signals within a certain frequency band while absorbing out-of-band electromagnetic energy, thereby reducing radar cross section and improving electromagnetic compatibility.
What are the key performance features of the proposed CFSR?
The proposed composite frequency selective Rasorber (CFSR) exhibits a wide −1 dB transmission band from 8.79 to 10.41 GHz with a minimum insertion loss of 0.44 dB, two absorption bands with absorptivity above 90%, and stable performance for oblique incidence angles up to 60°.
How does the 3D-printing metastructure contribute to the design?
The 3D-printing metastructure (3D-MS) is a key component that enables the high-performance CFSR by providing additional design flexibility and simplifying the transmission band design, while also contributing to the wide-angle stability and absorption performance.
What is the significance of the equivalent circuit model (ECM) analysis?
The equivalent circuit model (ECM) analysis provides a systematic understanding of the physical mechanisms behind the CFSR's performance, allowing for efficient design optimization and prediction of the structure's electromagnetic behavior.
What are the potential applications of this CFSR?
The CFSR can be used for radar cross section (RCS) reduction, electromagnetic compatibility enhancement, and other applications requiring simultaneous transmission and absorption of electromagnetic waves, such as in stealth technology and communication systems.
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