A reflective metasurface for broadband OAM vortex wave generation

Abstract

In this paper, we proposed a reflective metasurface which controls the phase delay of the electromagnetic (EM) wave through geometric phase manipulation. By coding the metasurface unit cells in different orientation angles, an orbital angular momentum (OAM) wave can be obtained through the metasurface reflection. A broadband reflective OAM wave with mode l = −1 was demonstrated which was experimentally observed from 8.3 GHz to 11.6 GHz. The mode spectrum of OAM wave was analyzed and the spectrum weight was about 0.82 through numerical calculation and about 0.47 through experimental measurement for the mode l = −1. The realization of this broadband OAM wave has the potential application to improve the OAM wave based communication capacity.

Generation of Millimeter-Wave High-purity OAM Beam Using Hexagonal P-B Phase Meta-atom Metasurface

“…To further analyze the quality of the OAM beam generated on the metasurface, the OAM spectrum has been analyzed using the Fourier transform. The calculation formula is as follows [8]:…”

“…Currently, the main methods for generating vortex beams are spiral phase plates (SPP) [3], antenna arrays [4], and metasurfaces [5][6][7][8][9]. Spiral phase plates require complex machining processes to introduce phase factors and are thicker, which is not conducive to machining and integration.…”

“…However, achieving broadband and high mode purity with such a resonant meta-atom is difficult. Yang et al [7] achieved a broadband meta-atom phase using the geometric (P-B) phase, which was achieved by varying the azimuth angle of the square ring structure to produce a broadband OAM metasurface with a mode purity of up to 0.7.Zhang et al [8] achieved a broadband OAM metasurface with a mode purity of 0.8 using a z-structured P-B phase meta-atom. These broadband metasurfaces are designed based on ideal planar waves, but in practice, the feed antennas are spherical or quasi-spherical, which can affect the purity of the OAM beam.…”

A Metamaterial Energy Power Detector Based on Electromagnetic Energy Harvesting Technology

“…Fortunately, the emergence of the EM metamaterial harvester provides an ideal solution for this . Based on the unique transmission, − reflection, − and absorption − properties of metamaterial for EM waves, the metamaterial harvester is capable of absorbing EM energy almost perfectly into the device at a wide range of angles of incidence and multiple states of polarization and transfers it to the load at the highest efficiency for utilization. − When the load is a resistor, the incident EM energy will be converted into heat on the resistor, according to the law of conservation of energy, and the power intensity of the EM wave emitted to the surface of the device will be reflected by this part of the heat, combined with the infrared thermal imager, which can be realized on the power of the incidence of EM waves to visualize the detection. In addition, benefiting from the characteristic that the metamaterial array can be extended and spliced at will, the detector based on the metamaterial harvester can detect the power intensity of EM waves in an arbitrary area range and visualize the distribution of the power intensity in that area as an output.…”

Terahertz Metamaterials for Biosensing Applications: A Review

“…As a result, various novel properties of the EM wave, including negative refraction [20,21], perfect absorption [22,23], strong optical activity [24][25][26] and extraordinary transmission [27][28][29], can be realized, which provide a fascinating platform to realize broad applications such as invisible cloaking [30][31][32], superlenses [33][34][35] and polarization conversion [36][37][38]. In addition, two-dimensional metamaterials, or metasurfaces, have received intensive research attention recently, which control the wavefront of the EM wave and realize functions including flat-lens focusing [39,40], beam shaping [41] and imaging [42][43][44], etc. The resonance of metamaterials is also affected by the environmental property surrounding the metamaterials.…”