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To address the challenges of low-quality and single-mode generation of Bessel beams produced by metasurfaces, a full-space metasurface (FS-MS) has been proposed. Based on the polarization and spatial multiplexing principles, the designed unit consists of a polarized reflective grid in the upper layer and a polarization converter in the lower layers. The FS-MS independently controls the phase of co-polarized electromagnetic (EM) waves in reflection mode and both the amplitude and phase of cross-polarized EM waves in transmission mode. Therefore, switching between transmission and reflection modes can be achieved by altering the polarization of incident radiation. The phase distribution of FS-MS is determined based on theories of diffraction-free Bessel beam generation and field superposition. The results indicate that at 12 GHz, in reflection mode, two controllable-power zeroth-order Bessel beams are generated. The diffraction-free ranges of the equal power double beam are 551 mm and 608 mm, respectively, and full widths at half-maximum (FWHM) are 46.44 mm and 52.97 mm. In transmission mode, a Bessel beam with mode l =  +2 is produced. The simulation results agree well with the measured results, and the multifunctional FS-MS facilitates the application of Bessel beams in near-field wireless communication and wireless power transmission. [ABSTRACT FROM AUTHOR]

A reconfigurable reflective metasurface design is proposed in this letter, allowing for beam scanning capabilities. This paper integrates a tunable capacitor into the metasurface unit. This paper integrates a tunable capacitor into the metasurface unit. The resonant characteristics of the metasurface unit are controlled by the tunable capacitor, which can be adjusted by changing the rotation angle of the metal plate on the tunable capacitor. By rotating the metal plate of the capacitor, it achieves state 1 at maximum capacitance and state 0 at minimum capacitance, resulting in a phase difference of 180° ± 20° between the states, thereby enabling 1-bit phase control. Leveraging the principle of phase compensation, the phase distribution of the array is designed to exhibit directional radiation characteristics. A reflective metasurface composed of a 20 × 20-element array is designed and simulated with these characteristics. The simulation results indicate that the scanning angle of the array-reflected beam can reach ± 50°, with a peak gain exceeding 14.6 dBi, an average gain of 13.8 dBi, and a gain loss of 1.5 dB. The beam's 3 dB beamwidth exceeds 15°, enabling broader coverage. Joint simulations in typical indoor scenarios confirm the improved signal strength, highlighting the array's versatility. This design allows the reflective array to function as a passive reflector relay, effectively improving signal coverage in indoor NLOS. [ABSTRACT FROM AUTHOR]

In this paper, a bifunctional full-space metasurface (FS-MS) with dual-band is proposed. Two metal layers are located on each side of the unit dielectric substrate, independently regulating the phase in the transmission and reflection. The metasurface can reflect x-polarized waves at 28 GHz and transmit y-polarized waves at 35 GHz. Based on the anisotropy and Huygens theories, the reflected and transmitted beams can be tuned flexibly. The metasurface design is carried out as an illustration of the reflected Bessel beams and the transmitted focusing or OAM beam. The results show that the metasurfaces can realize double zero-order Bessel beams, bifocals with a focusing efficiency of 22.27%, and an OAM beam with a mode purity of 74.12%. The proposed FS-MS, devoid of multilayer stacking and metal perforations, exhibits a simple structure, low profile, and ease of processing, all of which make them a promising candidate for applications in intelligent housing systems. [ABSTRACT FROM AUTHOR]

A broad-beam planar reflective metasurface design for indoor signal coverage is presented in this letter. The proposed metasurface unit is designed as a multi-resonant structure using an additional branch on the double ring, which achieves a reflection phase shift covering 360° and a reflection magnitude remaining above 0.8 by varying the length of the square ring. To simplify the array configuration, the unit incorporates 2-bit phase quantization. In order to broaden the reflection beam of metasurface, the phase distribution of the array is determined by the aperture field superposition method. The angles of the different electromagnetic (EM) waves within the single aperture are adjusted to be moderately distinct. The co-simulation and measurement of the horn antenna and the reflective metasurface are carried out. The results show that the metasurface can generate a broad beam at 4.8 GHz with a 3 dB beamwidth of 21°, achieving a beam gain of 18dBi. The broad beam can maintain a 3 dB beamwidth greater than 19° in the 4.2–5.6 GHz band. The reflective metasurface can be used as a passive repeater to optimize signal quality and enhance wireless communication coverage in indoor non-line-of-sight (NLOS) paths. [ABSTRACT FROM AUTHOR]

A simple and sensitive photothermal technique--photothermal detuning, in which the spectral shift of an optical coating caused by absorption-induced temperature rise is used to measure the photothermal signal--and its application for the absorption measurement of coated optical components are developed theoretically and experimentally in detail for the first time to the best of our knowledge. The theoretical description of the photothermal detuning signal with a continuous-wave modulated laser beam excitation is presented. Experiments are conducted with a highly reflective coating used at 532 nm to measure the photothermal detuning signal and to evaluate the absorption at 532 nm by detecting the spectral shift with a probe beam at a wavelength of 632.8 nm. By optimizing the incident angle of the probe beam, the amplitude of the photothermal detuning signal is maximized. Good agreement is obtained between the experimental results and the theoretical predictions. OCIS codes: 350.5340, 300.1030, 310.1620.

A transmissive metasurface polarization beam splitter (MPBS) with three-layer dielectric substrate was designed to meet the application requirements of polarization beam splitting devices. The microstructure unit cell was composed of an elliptical patch and a square resonant ring, and the phase and amplitude responses to the x- and y-polarized incident waves were independent. Here 16 transmissive unit cells designed with a 90° phase difference and more than 0.8 transmission coefficient could be used to realize different functions by pre-designing distribution of "00", "01", "10", "11" encoding particles in x- and y-direction. We experimentally demonstrated a 2-bit encoding MPBS that separated x- and y-polarization incident waves into two different directions at 15 GHz respectively using specially designed encoding unit cells. The work may alleviate the shortage of advanced multifunctional devices and provide important application prospect in imaging, MIMO system, etc. [ABSTRACT FROM AUTHOR]