• Titanium Dioxide Engineered for Near-dispersionless High Terahertz Permittivity and Ultra-low-loss

      Chuying, Yu; Zeng, Yang; Yang, Bin; Donnan, Robert S.; Huang, Jinbao; Xiong, Zhaoxian; Mahajan, Amit; Shi, Baogui; Ye, Haitao; Binions, Russell; et al. (Nature Publishing Group, 2017-07-26)
      Realising engineering ceramics to serve as substrate materials in high-performance terahertz(THz) that are low-cost, have low dielectric loss and near-dispersionless broadband, high permittivity, is exceedingly demanding. Such substrates are deployed in, for example, integrated circuits for synthesizing and converting nonplanar and 3D structures into planar forms. The Rutile form of titanium dioxide (TiO2) has been widely accepted as commercially economical candidate substrate that meets demands for both low-loss and high permittivities at sub-THz bands. However, the relationship between its mechanisms of dielectric response to the microstructure have never been systematically investigated in order to engineer ultra-low dielectric-loss and high value, dispersionless permittivities. Here we show TiO2 THz dielectrics with high permittivity (ca. 102.30) and ultra-low loss (ca. 0.0042). These were prepared by insight gleaned from a broad use of materials characterisation methods to successfully engineer porosities, second phase, crystallography shear-planes and oxygen vacancies during sintering. The dielectric loss achieved here is not only with negligible dispersion over 0.2 - 0.8 THz, but also has the lowest value measured for known high-permittivity dielectrics. We expect the insight afforded by this study will underpin the development of subwavelength-scale, planar integrated circuits, compact high Q-resonators and broadband, slow-light devices in the THz band.
    • Ultrafast Electric Field-induced Phase Transition in Bulk Bi0.5Na0.5TiO3 under High Intensity Terahertz Irradiation

      Yang, Bin; Zhang, Man; McKinnon, Ruth A.; Viola, Giuseppe; Zhang, Dou; Reece, Michael J.; Abrahams, Isaac; Yan, Haixue; University of Chester; Queen Mary University of London; Central South University
      Ultrafast polarization switching is being considered for the next generation of ferroelectric based devices. Recently, the dynamics of the field-induced transitions associated with this switching have been difficult to explore, due to technological limitations. The advent of terahertz (THz) technology has now allowed for the study of these dynamic processes on the picosecond (ps) scale. In this paper, intense terahertz (THz) pulses were used as a high-frequency electric field to investigate ultrafast switching in the relaxor ferroelectric, Bi0.5Na0.5TiO3. Transient atomic-scale responses, which were evident as changes in reflectivity, were captured by THz probing. The high energy THz pulses induce an increase in reflectivity, associated with an ultrafast field-induced phase transition from a weakly polar phase (Cc) to a strongly polar phase (R3c) within 20 ps at 200 K. This phase transition was confirmed using X-ray powder diffraction and by electrical measurements which showed a decrease in the frequency dispersion of relative permittivity at low frequencies.
    • Verification of calculation code THERM in accordance with BS EN ISO 10077-2

      Nammi, Sathish K.; Shirvani, Hassan; Shirvani, Ayoub; Edwards, Gerard; Whitty, Justin P. M.; Anglia Ruskin University, Anglia Ruskin University, Anglia Ruskin University, University of Chester, University of Central Lancashire (Anglia Ruskin Research Online, 2014)
      Calculation codes are useful in predicting the heat transfer features in the fenestration industry. THERM is a finite element analysis based code, which can be used to compute thermal transmittance of windows, doors and shutters. It is important to verify results of THERM as per BS EN ISO 10077-2 to meet the compliance requirements. In this report, two-dimensional thermal conductance parameters were computed. Three versions of THERM, 5.2, 6.3 and 7.1, were used at two successive finite element mesh densities to assess their comparability. The results were all compliant with the aforementioned British Standard.
    • Visual-Inertial 2D Feature Tracking based on an Affine Photometric Model

      Aufderheide, Dominik; Edwards, Gerard; Krybus, Werner; South Westphalia University of Applied Sciences, University of Chester, South Westphalia University of Applied Sciences (Springer, 2015-04-08)
      The robust tracking of point features throughout an image sequence is one fundamental stage in many different computer vision algorithms (e.g. visual modelling, object tracking, etc.). In most cases, this tracking is realised by means of a feature detection step and then a subsequent re-identification of the same feature point, based on some variant of a template matching algorithm. Without any auxiliary knowledge about the movement of the camera, actual tracking techniques are only robust for relatively moderate frame-to-frame feature displacements. This paper presents a framework for a visual-inertial feature tracking scheme, where images and measurements of an inertial measurement unit (IMU) are fused in order to allow a wider range of camera movements. The inertial measurements are used to estimate the visual appearance of a feature’s local neighbourhood based on a affine photometric warping model.
    • Volatile Liquid Detection by Terahertz Technologies

      Baxter, Harry W.; Worrall, Adam A.; Pang, Jie; Chen, Riqing; Yang, Bin; University of Chester; Fujian Agriculture and Forestry University (Frontiers Media, 2021-04-08)
      The prospect of being able to move through security without the inconvenience of separating liquids from bags is an exciting one for passengers, and there are important operational benefits for airports as well. Here, two terahertz (THz) systems, 100 GHz sub-THz line scanner and attenuation total reflection-based THz time domain spectroscopy (TDS), have been used to demonstrate the capability of identifying different liquid samples. Liquid samples’ THz complex permittivities are measured and their differences have contributed to the variation of 100 GHz 2D images of volatile liquids with different volumes inside of cannister bottles. The acquired attenuation images at 100 GHz can easily be used to distinguish highly absorbed liquids (Water, Ethanol, Fuel Treatment Chemicals) and low loss liquids (Petrol, Diesel, Kerosene and Universal Bottle Cleaner). The results give a promising feasibility for mm-wave imager and THz spectroscopy to efficiently identify different volatile liquids.