An ultra-thin broadband active frequency selective surface absorber for ultrahigh-frequency applications

Abstract

At frequencies below 2 GHz, conventional microwave absorbers are limited in application by their thickness or narrow absorption bandwidth. In this paper, we propose and fabricate an ultra-thin broadband active frequency selective surface (AFSS) absorber with a stretching transformation (ST) pattern for use in the ultrahigh-frequency (UHF) band. This absorber is loaded with resistors and varactors to produce its tunability. To expand the tunable bandwidth, we applied the ST with various coefficients x and y to the unit cell pattern. With ST coefficients of x = y = 1, the tunability and strong absorption are concisely demonstrated, based on a discussion of impedance matching. On analyzing the patterns with various ST coefficients, we found that a small x/y effectively expands the tunable bandwidth. After this analysis, we fabricated an AFSS absorber with ST coefficients of x = 0.7 and y = 1. Its measured reflectivity covered a broad band of 0.7–1.9 GHz below −10 dB at bias voltages of 10–48 V. The total thickness of this absorber, 7.8 mm, was only ∼λ/54 of the lower limit frequency, ∼λ/29 of the center frequency, and ∼λ/20 of the higher limit frequency. Our measurements and simulated results indicate that this AFSS absorber can be thin and achieve a broad bandwidth simultaneously.

Metamaterial absorber integrated microfluidic terahertz sensors

“…As well known, by tuning the structure parameters of the MDM metamaterial, a resonant perfect absorption can be observed with the incident wave fully trapped in the spacer between the two metal layers, resulting in a named metamaterial perfect absorber (MPA) . It is very similar to frequency selective surface absorber in microwave , where the periodic subwavelength structures are used to manipulate the electromagnetic response. Particularly, the MPA is deep sub‐wavelength and angle‐independent.…”

The Optimization of Switching Scheme in Multi-Layer Phase-Modulated Surface and Its Influence on Scattering Properties

“…(12). Figure 5 shows the angular scattering pattern at the fundamental frequency f 0 when the number of AFSS layers L = 0, 1 and 2.…”

“…The multi-active-layer PMS studied here successfully reduces this energy to a lower level and helps avoid being detected by radar as a result; ii) Enlarging the size of PMS directly is a method to reduce the fundamental scattering energy of PMS; however, we obtain this reduction by optimizing the switching scheme of PMS, and the differential evolution (DE) algorithm is used for the optimization. Results indicate that the method proposed in this paper has a better performance in improving the absorbing performance than enlarging the size of PMS under the same construction complexity; iii) An expanded absorbing bandwidth is obtained in papers [10][11][12]. However, we do not expand the absorbing bandwidth of PMS in infrequency domain but reduce the spatial coverage of scattering echo energy, which actually expands the absorbing "bandwidth" at spatial angle; iv) By studying PMS with different numbers of active layers, we summarize the variation tendency of the fundamental scattering energy of PMS and find that the floor effect appears during the variation process, which means that the number of layers in PMS should be confined; therefore, the research in this paper is beneficial for finding a balance point in improving the absorbing performance of PMS and reducing its construction complexity at the same time.…”

“…In [10,11], an 'array' polynomial approach was conducted to predict the positions of the reflectivity nulls for PMS, and the results indicated that the range of reflectivity null was expanded by regulating the switching scheme of PMS. In [12], the authors designed an ultra-thin broadband AFSS absorber with a stretching transformation (ST) pattern for use in the ultrahigh-frequency (UHF) band. Results indicated that the absorbing bandwidth of absorber was expanded by adjusting the unit cell pattern of AFSS.…”

An Ultra-Thin Low-Frequency Tunable Metamaterial Absorber Based on Lumped Element

“…Additionally, the fractal metal structures [10] and the multilayer [11][12][13] were realized to design wideband absorber. As a remarkable method, loading with lumped element was utilized to achieve broadband absorption [14][15][16]. Although many efforts towards the improvement of the performance about MAs are flourishing, the low-frequency and broadband absorber are not easily realized without lumped elements or increasing material thickness.…”