A topology optimization mathematical model for periodic heat transfer structure with anisotropic multi-material is established based on the element-free Galerkin method (EFGM) and alternative active-phase algorithm. The multi-material relative densities of EFGM nodes and thermal compliance are selected as the design variables and optimization objective, respectively. The multi-material relative densities of EFGM nodes in the design sub- domains are adjusted by periodic constraint. The effects of the number of the multi-material categories and design subdomains, and the thermal conductivity factors on the optimal anisotropic multi-material topology of periodic heat transfer structure are investigated. The heat transfer performance analysis of periodic topological structure with anisotropic multi-material is carried out and the optimal topological structures with three types of materials are 3D printed. The results indicate that the profiles of the optimal multi-material topological structures are smooth and the advantages of the proposed model are verified further. The number of multi-material categories and design subdomains are recommended to be 3-4 and 3-5 respectively, and the thermal conductivity factors is suggested to be within the range of 2-4.

In this paper, a hybrid coding method for chipless radio-frequency identification (RFID) tag with angular orientation is proposed. Frequency-shift coding is achieved by controlling the size of three complementary split single ring resonators (CSSRR). And on the basis, we add a dimension of polarisation coding, which is achieved through changes in the radar cross-section (RCS) response caused by the rotation of CSSRR. Three angular-orientation structures are designed to identify the polarised rotating angle of each CSSRR by their changes in the RCS response. The simulated and measured results show that the hybrid frequency-polarisation coding can generate 884736 coded IDs (19.75 bits), which is 216 times more than the number of IDs generated by the frequency coding only.

To address the limitation of conventional UHF RFID near-field reader antennas with narrow area coverage, this paper presents a wide-area near-field frequency-scanning reader antenna based on substrate integrated waveguide (SIW). By reducing the equivalent width of the SIW, the frequency sensitivity of the phase constant is enhanced, which effectively extends the scanning range even within a narrow bandwidth. Furthermore, an odd-symmetry slot structure and a dual-port differential feeding network are designed to synthesize bidirectional beams, compensating for field-strength blind spots inherent in single-port configurations. Leveraging the reader's Frequency-Hopping Spread Spectrum (FHSS) mode and the SIW's frequency-scanning characteristics, dynamic frequency switching enables controllable near-field energy distribution scanning. Simulation results demonstrate that the antenna achieves wide-area coverage through near-field electromagnetic energy superposition and reconstruction, improving the effective reading rate by 36.26% relatively.

In this paper, a Substrate Integrated Waveguide (SIW) resonant slot array antenna suitable for UHF band (902-928 MHz) RFID system is designed. The beam scanning is realized by using the Frequency-Hopping Spread Spectrum (FHSS) mode of RFID reader and the characteristics of SIW frequency scanning antenna. The simulated and measured results, based on the FR4 dielectric substrate, show that the antenna operates within the bandwidth of 902-928 MHz, with a beam scanning angle of 3 degrees. The design can improve the reliability and stability of RFID system by switching the beam with small amplitude.

In this paper, the method of hybrid frequency-polarization coding is proposed for chipless tag coding. The encoding is achieved by the change of polarization angle and frequency shift coding technology. The structure consists of two CSRRs and three angular-orientation structures with no dielectric substrate. The angular-orientation structure is used to recognize the polarization angle. The results show that the hybrid frequency-polarization coding can reach 9216 coded IDs, which is 36 times more than the number of IDs reached by the single frequency coding.

This study introduces a novel phase compensation-based, asymmetric frequency selective surface (FSS). Aimed at enhancing angular stability, the phase compensation method utilizes the reflected phase gradient changes generated by two FSSs at large grazing angles. The ultimate improvement in angular stability comes from unit amalgamation to achieve phase complementarity, effectively dealing with the phase shift of incident waves caused by large grazing angles. Based on this principle, the asymmetric FSS structure is built with 3 components: a Minkowski fractal cell, a bent-line square-loop cell, and a thin square-loop parasitic cell. Simulation results show the structure demonstrates a 0 relative shift of resonant frequency within an incidence range of 0-80° under transverse electric (TE) polarization. However, it exhibits a maximum relative shift of 5.12% in resonant frequency at an 80° incidence under transverse magnetic (TM) polarization. Compared with E 1 and E 2 units, this structure significantly reduces frequency deviation—by 100% at 80° incidence under TE polarization and by 80.12% and 83.26% compared with E 1 and E 2 units under TM polarization. Finally, the proposed FSS model was fabricated and processed, with measured data basically aligning with the simulated results.

In this article, the near-field Radio Frequency Identification Devices (RFID), reader antenna is designed. In the study of near field reader antenna, it is mainly divided into induction near field reader antenna and radiation near field reader antenna. Firstly, an antenna array element is designed in this paper. The antenna realizes circular polarization. The near-field focusing method is adopted to realize the control of the identification area in the near field. On this basis, the identification performance is further optimized by the design of unequal spoke feed, which can effectively reduce the error rate outside the identification area. The area of high electric field intensity remains ${120}\text{mm}^{{*}}{120}\text{mm}^{{*}}{200}\text{mm}$ and the electric field intensity outside the region is effectively reduced

A novel 2.5-D miniaturized multifunctional active frequency selective surface (2.5-D MAFSS) is proposed in this article. The structure uses two sets of the same gradual bending patches on the upper and lower surfaces respectively, and is connected with adjacent units. In addition, a PIN diode is loaded on the horizontal direction of the upper surface and the vertical direction of the bottom surface of the unit.By changing the ON-OFF state of the PIN diode, four independent working states can be achieved.At the same time, compared with the existing structure, the structure can achieve better miniaturization performance, the size of each unit is only 0.05λ 0 × 0.05λ 0 , where λ 0 is the wavelength of the free-space.

Radiation source localization is very important in electromagnetic environmental monitoring activities. Most current positioning methods can only obtain source position estimates at the center of fixed grids, and these methods usually require prior knowledge of the monitoring environment. In this paper, a new variational Bayesian-based radiation source positioning method is proposed, which dose not need the prior knowledge of the environment. We modify dictionary parameters at multiple stages, and thus, the estimated locations can be at any positions in the grids. In addition, we select the self-information of different observation data and eliminate relevant interferences. As a result, the computational complexity can be reduced while guaranteeing the localization accuracy. Simulation results show that the proposed method can improve the localization accuracy effectively compared with the state of the art.

This paper proposes a via-based novel metamaterial absorber (MA) for achieving stable energy absorption at/under oblique incidence of large angle. The TMV s of the absorber are located in the center of the patches to connect the two metal patches from different sides to achieve the miniaturization effect. This method reduces the center frequency of MA by introducing a vertical TMV s to play an important role in angle stability and polarization insensitivity. A set of closed-form equations were applied to effectively calculate the circuit inductances and capacitances, and the changes caused by the addition of vias can be seen more visually. Meanwhile, according to the vector transmission line equations, the impedance characteristics of transmission line at large angular oblique incidence can be obtained, and the design of the absorber can be simplified by matching the impedance with that of the free space. Finally, a MA with angle stability and polarization insensitivity characteristic is designed. The simulation results show that when the oblique incident angle is in the range of 60 to 70 degrees, the bandwidth is 2GHz (from 11.98GHz to 13.11GHz) with a high absorptivity (≥ 90%) for both TE- and TM- mode.

In this letter, a metamaterial absorber (MA) with air cavity loaded with four lumped resistors is proposed and realized for ultra-broadband absorption of transverse electric (TE) polarization mode at large angle of oblique incidence. In order to realize the steady absorption at the large angle range from 50° to 70°, the optimal optimized angle is 62° through the impedance matching formula, and the parameters of the metamaterial absorber are optimized at this angle. The simulation results indicate that all absorption bands of TE mode over 90% in the angle of 50° to 70° are maintained above 9 to 15 GHz and the relative bandwidths are more than 60%, where the maximum and the minimum values are 69.07% and 61.65%, respectively.

This article presents an angularly stable bandstop frequency selective surface(FSS) based on lumped inductors. The proposed FSS uses a modified square-loop structure as the basic unit cell and is loaded with passive lumped elements to further improve angular stability. Loaded lumped elements allow for lower resonant frequency and thus enable miniaturization compared to the modified square-loop FSS without lumped inductors. The simulation results exhibit great angularly stable performance with incident angles varying from 0° to 80° for both TE and TM polarizations. Furthermore, changing the slit width between unit cells will change the resonant frequency, but still, maintain great angular and polarization stability. Therefore, the proposed FSS can meet the needs of different frequency bands in practical applications and has high application value.

In this letter, a hybrid ground designed for antennas operating at 7.6 GHz is proposed, which can absorb the incident wave in the band and realize phase cancellation out of the band. To realize phase cancellation, two kinds of absorber elements with effective phase difference outside the absorbing frequency point are designed. And the proposed absorber is used to replace part of the antenna floor, so as to further reduce the energy by absorbing. Compared to the same size metal ground, the hybrid ground can achieve RCS reduction at around 7GHz, 7.6GHz and 8.5GHz. The design method of hybrid ground is feasible.

On the basis of combining the two concepts of digital coding metasurface and metasurface antenna, low radar cross-section (RCS) coding metasurface antenna array with dynamic scattering performances is presented in this paper. Extending scattering factor theory to coding metasurface antenna, by controlling the states of PIN diodes randomly, the scattering performances of coding metasurface antenna array can be tuned dynamically without degrading its radiation property. Based on phase cancellation principle, a 8 × 8 antenna array was finally simulated and fabricated. By comparing several different layouts, taking checkerboard layout, new chessboard layout, and “0101” square ring nested layout as examples, both monostatic and bistatic RCS of the antenna mentioned above can be reduced 10 dB or more in the frequency range of 9–10.5 GHz under the illumination of x-polarized incident wave. The measured data are consistent with the simulation data, which proves the effectiveness of the proposed method.

In this article, a miniaturized design of multi beam antenna system based on strongly coupled antenna is proposed. By opening the connection part of the cross junction of the multi-beam feed network, all couplers are closed-loop connected in turn. The space in the open cross junction ring is used to set the antenna array, and the purpose of miniaturization is achieved. Subsequently, the problem of coupling between antennas is faced. In this paper, the decoupling structure using the concept of phase shift of antenna array is used. According to this structure, the simulation of four antennas is carried out and on this basis. In the last part, the multi beam antenna system is simulated and analyzed after adding Butler matrix. The system has good performance and good miniaturization effect.

This communication describes a miniaturized $4\times 4$ Butler Matrix Using Distributed capacitors in the Quasi-Arbitrary Phase-Difference Hybrid Coupler. First, A traditional branch-line coupler with any phase difference can be calculated by the impedance and phase of each short side. next, a transmission line can be replaced by a high impedance transmission line and parallel capacitors. To miniaturize the circuit, all distributed capacitances are placed inside the branch coupler. On the basis of the compact branch coupler configuration, the compact Butler matrix needs to eliminate the independent phase shifter and frequency divider. A distributed capacitive branch coupler with arbitrary phase difference is proposed to replace the traditional branch coupler. Through the miniaturized design of branch couplers and the elimination of phase shifters and crossover junctions, the design of the butler matrix is 66% smaller than the traditional butler matrix design proceedings.

In this paper, to realize stable absorption under large angle oblique incidence, a metamaterial absorber (MA) with air cavity embedded with lumped resistors is proposed by optimizing its input impedance to match the oblique incident interface wave impedance at transverse electric (TE) polarization mode. According to the vector transmission line equations, the characteristic impedance of transmission line for oblique incidence can be derived. As a result, the absorption band over 90% at the angle from 60° to 70° is improved to 7.9 - 12.3GHz since the impedance is well matched through adjusting the absorber's plane structure.

In this letter, a polarization conversion metasurface antenna (PCMA) array for stealth design method is proposed. The array is composed of polarization conversion metasurface (PCM) subarray and their mirror subarray, which simultaneously plays the role of antenna element and PCM. So that, a certain phase cancellation can be produced between subarray and mirror one. The backward scattering is canceled while the radiation performance is maintained. This method has the characteristics of simplicity, low profile and easy to be implemented. Average area occupied by each antenna element can be reduced to 0.15 lambda 02. Simulation and measured results show that the maximum reduction of monostatic RCS of aforementioned PCMA is 16.3 dB in 8.2-13.6 GHz band, and the relative bandwidth of effective RCS reduction (more than 10 dB) reaches 34%, which verifies the effectiveness of the polarization cancellation design method based on the integration of array elements and PCM.

This paper presents a 2.5-dimensional switchable frequency selective surface based on the active device reed switch. This structure uses reed switches instead of PIN diodes to connect the upper and bottom metal patches on the basis of 2.5 dimensions. The structure can control the connection and disconnection of the reed inside the reed switch by controlling whether the external magnetic field is applied or not, thereby controlling the switching of the structural performance. When the external magnetic field is not applied, the internal reed remains disconnected. At this time, the structure has a pass band of 0-3GHz; when a certain strength of the external magnetic field is applied to connect the internal reeds, there will be a stop band ranging from 1.90 GHz to 2.12 GHz, and the center of the stop band is 2.028 GHz. In addition, the structure has good miniaturization performance, and the unit size is only 0.08 λ× 0.08 λ.

In this letter, a switchable frequency selective surface (FSS) based on the rotatable magnet is first proposed for polarization selector. The unit cell of the switchable FSS is composed of a rotatable cuboid-magnet and a F4B substrate. The cuboid-magnet is inserted into the substrate which controlled by the orthogonal dual-U-shaped electromagnetic control system. The FSS has a characteristic of polarization selectivity at 8.66 GHz by rotating the cuboid-magnet. To confirm the simulation results, a prototype of the proposed FSS is fabricated and measured. The measured result shows that the switchable FSS can selective the passband in transverse-electric polarization or transverse-magnetic polarization.