Abstract-A 90°-Inclined Linearly Polarized Probe for Terahertz Mueller Imaging

Xuexuan Ruan,  Kung Bo Ng, Huan Yi, Shi-Wei Qu, Chi Hou Chan, 

https://ieeexplore.ieee.org/document/8740178

A novel terahertz (THz) probe, consisting of a 90°-inclined linearly polarized (LP) component incorporated with a pyramidal-shaped TE 10 mode rectangular open-ended waveguide (OEWG), is introduced in this paper. The pyramidal feed, located beneath the substrate, is made of brass plated with gold. The radiation component, placed on tip of the OEWG, is achieved by standard printed-circuit and plated-through-hole techniques. Measurement results demonstrate that the proposed probe possesses an impedance bandwidth (VSWR ≤ 2) of better than 18.5% from lower than 270 to higher than 325 GHz. In the impedance bandwidth, the measured gain is from 7.2 to 8.2 dBi and all radiation patterns are relatively symmetric with relatively small back radiation and cross-polarization levels. The proposed probe is a potential component for Mueller imaging at THz frequencies.

Abstract-3-D Printed Circularly Polarized Modified Fresnel Lens Operating at Terahertz Frequencies

Chi Hou Chan, Geng-Bo Wu, Ka Fai Chan, Shi-Wei Qu, Yuan-Song Zeng, 

https://ieeexplore.ieee.org/document/8676352

In this paper, a novel 3-dimensional (3-D) printed circularly polarized (CP) modified Fresnel lens antenna operating at 300GHz is introduced. By virtue of the superior geometric flexibility of the 3-D printing technique, a modified Fresnel lens consisting of subwavelength discrete dielectric posts in the odd-numbered Fresnel zones is proposed. It is further demonstrated that by integrating dielectric anisotropic metamaterial, the modified Fresnel lens can realize CP radiation fed by a simple linearly polarized (LP) open-ended waveguide (OEWG). The 3-D printing approach is also investigated to push the performance envelops of the 3-D printer for realization of the THz CP lens. The measured results show that the axial ratios (AR) of the fabricated antenna prototype are smaller than 3dB from 265 to 320GHz. Moreover, the modified Fresnel lens has a maximum gain of 27.4dBic, which is 0.9dB lager than that of the conventional Fresnel zone plane antenna (FZPA). These validate the concept, the design, and the fabricated prototype.

Abstract-Terahertz Wavefront Control on Both Sides of the Cascaded Metasurfaces

Huan Yi,  Shi-Wei Qu, Kung-Bo Ng,  Chun Kit Wong, Chi Hou Chan

http://ieeexplore.ieee.org/document/8103003/

In this paper, two kinds of cascaded metasurfaces are proposed for the simultaneous control of the reflected and transmitted wavefronts in the terahertz (THz) frequency band. First, an array of arrow-shaped elements backed by a strip grating is investigated. When the polarization of the incidence field is parallel to the orientation of the strip grating, the reflected and transmitted waves with approximately equal amplitude will be generated and there is a constant phase difference between them when the element dimensions are varied. Proved by the simulation and measured results, the metasurface based on the proposed element can simultaneously deflect the transmitted and reflected wavefronts but only by the same angle. Second, independent control of both amplitudes and phases of the transmitting and reflecting waves is achieved by cascading four metallic layers in order, i.e., a y-oriented strip layer, a y-directed grating layer, the arrow-shaped element, and an x-directed grating, with respect to different polarizations of the incident field. The simulation and measured results show that the y-polarized incident waves can be reflected by the four-layered metasurface into a designed reflection angle, while the x-polarized incident waves can be focused on the other side of the metasurface in a transmitting manner. Compared with the reported THz metasurfaces, the proposed elements can provide more advanced wavefront-control ability and they also feature the advantages of compact size, low cost, and lightweight. Therefore, the proposed metasurfaces can be applied as beam splitters for low-cost and compact THz imaging and detection systems.

Abstract-Flat Terahertz Reflective Focusing Metasurface with Scanning Ability

Huan Yi, Shi-Wei Qu, Bao-Jie Chen, Xue Bai, Kung Bo Ng,  Chi Hou Chan

https://www.nature.com/articles/s41598-017-03752-3

The ability to manipulate the propagation properties of electromagnetic waves, e.g., divergence, focusing, holography or deflection, is very significant in terahertz applications. Metasurfaces with flat structures are attractive for achieving such manipulations in terahertz band, as they feature low profile, lightweight, and ease of design and installation. Several types of terahertz reflective or transmitting metasurfaces with focusing function have been implemented recently, but none of them can provide scanning ability with controllable focus. Here, a flat reflective metasurface featuring controllable focal shift is proposed and experimentally demonstrated. Furthermore, the principle of designing a focus scanning reflective metasurface is presented and the focusing characteristics are discussed, including focus scanning along a line parallel or orthogonal to the metasurface with a large bandwidth. These interesting properties indicate that this flat reflective metasurface could play a key role in many terahertz imaging and detection systems.

Abstract-Low-cost two-layer terahertz transmit array

 Huan Yi ;  Shi-Wei Qu ;  Chi Hou Chan

http://ieeexplore.ieee.org/document/7940131/

In this Letter, a flat terahertz (THz) transmit array with a two-layer element is investigated. The proposed element can provide 360° phase coverage with a transmission coefficient better than −3.52 dB at 250 GHz. Then a transmit array based on the element is designed with a low focal-to-diameter ratio of 0.3. Simulation results reveal that the transmit array has large backward radiation. A WR-03 open-ended waveguide with a thick wall is used to feed the transmit array, thus the backward radiation is further reflected to the forward direction and the gain is increased by 1.7 dB at 250 GHz. Then the transmit array is fabricated using standard, low-cost PCB technology, and the measured results show that a peak gain of 28.8 dBi with an aperture efficiency of 32% is achieved. In general, the proposed transmit array has simple structures and can be fabricated by standard PCB technologies which are suitable for applications in low-cost THz systems.

Abstract-Terahertz Reflecting and Transmitting Metasurfaces

Shi-Wei Qu,  Huan Yi,  Bao Jie Chen,  Kung Bo Ng, Chi Hou Chan,

http://ieeexplore.ieee.org/document/7918550/

Bridging the terahertz gap requires synergism between the microwave and photonic communities. Advances in each of these two communities are often complementary but sometimes overlooked. One example is the manipulation of waves, known as anomalous diffraction via the use of metamaterials. This is achieved by controlling the surface impedance of each pixel at the interface of two different materials or alternately the phase and magnitude of the wave diffracted off the pixel. In this paper, a review of developments in wave manipulation from microwave to optical frequencies is presented, together with our new results in the terahertz regime. Generation of phase curves for pixel design requires a priori information on material properties at terahertz frequencies. Fabrication of terahertz devices entails micromachining in the clean room while their experimental validation demands both amplitude and phase information. Through judicial selection of practices in microwave and photonic communities, we can further the exploration of wave phenomena at terahertz frequencies.

Abstract-Controlling Dispersion Characteristics of Terahertz Metasurface

• • 
    
• • 
    
  • 
    
  • 
    
  • 
    
  • 
    
  Shi-Wei Qu,
• Wei-Wei Wu,
• Bao-Jie Chen,
• Huan Yi,
• Xue Bai,
• Kung Bo Ng
• & Chi Hou Chan

• Affiliations
• Contributions
• Corresponding author

Scientific Reports

 

http://www.nature.com/srep/2015/150323/srep09367/full/srep09367.html

Terahertz (THz) metasurfaces have been explored recently due to their properties such as low material loss and ease of fabrication compared to three-dimensional (3D) metamaterials. Although the dispersion properties of the reflection/transmission-type THz metasurface were observed in some published literature, the method to control them at will has been scarcely reported to the best of our knowledge. In this context, flexible dispersion control of the THz metasurface will lead to great opportunities toward unprecedented THz devices. As an example, a THz metasurface with controllable dispersion characteristics has been successfully demonstrated in this article, and the incident waves at different frequencies from a source in front of the metasurface can be projected into different desired anomalous angular positions. Furthermore, this work provides a potential approach to other kinds of novel THz devices that need controllable metasurface dispersion properties.

Subject terms:

• Electrical and electronic engineering
• Metamaterials
• Surfaces, interfaces and thin films
• Terahertz optics

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Abstract-Applications of spoof planar plasmonic waveguide to frequency-scanning circularly polarized patch array

Xue Bai, Shi-Wei Qu and Huan Yi

shiweiqu@uestc.edu.cn

School of Electronic Engineering, University of Electronic Science and Technology of China (UESTC), Chengdu 611731, People's Republic of China 

http://iopscience.iop.org/0022-3727/47/32/325101

Spoof planar plasmonic waveguides (SPPWs) show potential applications in many microwave and terahertz systems, e.g. imaging, communication and sensing, due to their capability of highly confining spoof surface plasmon polaritons (SPPs) and relatively low propagation loss. Meanwhile, efficient electromagnetic emission from the SPPWs is one of the dominant factors in the practical applications. In this article, we demonstrate a beam-scanning circularly polarized (CP) antenna based on the SPPW of blind-hole array, which can efficiently convert spoof SPPs propagating in the SPPW into free-space emissions. Several centre-inclined rectangular patches are adopted to achieve the CP emission. The antenna array was designed and fabricated in the microwave frequency band, and the measured results validate the good emission performance of the proposed array, e.g. high gain and wide-scan angle. Finally, the proposed idea can be further extended into the terahertz frequency band.