Evaluating surface impedance models for terahertz frequencies at room temperature

Published versio

Benchmarking a commercial (Sub-)THz focal plane array against a custom-built millimeter-wave single-pixel camera

For the first time, the characteristics of an evolving commercial camera technology that can operate at millimeter-wave frequencies has been independently investigated. In this work, we benchmark the TeraSense camera against a custom-built single-pixel camera at W-band, for image quality and aperture reflectance. It is found that the Tera-1024 TeraSense camera exhibits limited image resolution and fidelity, with significant levels of systematic spatial noise. In a poor signal-to-noise ratio scenario, the addition of random noise exacerbates these problems. Possible causes of both beam and image distortion have been identified in quasi-optical applications, which gives important insight into the best use of (sub-)THz cameras and interpretation of their images. Inherent standing waves caused by the significant power reflectance of the camera aperture is investigated in detail. A simple W-band one-port quasi-optical scalar network analyzer is developed, to determine the levels of reflectance for both cameras, with its bespoke calibration routine derived from first principles - providing a low-cost solution for many non-destructive testing applications. It is found that the TeraSense camera (with additional RAM) and single-pixel camera (having default RAM) have measured reflectance values of 27% and 3%, respectively, over a corresponding aperture area ratio of approximately 714:1. While our single-pixel camera provides excellent image resolution and fidelity, it inherently suffers from very slow raster-scanning speeds and operational bandwidth limitations. For this reason, the TeraSense camera technology is excellent for performing qualitative measurements in real time, with the caveats outlined in this paper

Secure thermal infrared communications using engineered blackbody radiation

The thermal (emitted) infrared frequency bands, from 20–40 THz and 60–100 THz, are best known for applications in thermography. This underused and unregulated part of the spectral range offers opportunities for the development of secure communications. The ‘THz Torch' concept was recently presented by the authors. This technology fundamentally exploits engineered blackbody radiation, by partitioning thermally-generated spectral noise power into pre-defined frequency channels; the energy in each channel is then independently pulsed modulated and multiplexing schemes are introduced to create a robust form of short-range secure communications in the far/mid infrared. To date, octave bandwidth (25–50 THz) single-channel links have been demonstrated with 380 bps speeds. Multi-channel ‘THz Torch' frequency division multiplexing (FDM) and frequency-hopping spread-spectrum (FHSS) schemes have been proposed, but only a slow 40 bps FDM scheme has been demonstrated experimentally. Here, we report a much faster 1,280 bps FDM implementation. In addition, an experimental proof-of-concept FHSS scheme is demonstrated for the first time, having a 320 bps data rate. With both 4-channel multiplexing schemes, measured bit error rates (BERs) of < 10(−6) are achieved over a distance of 2.5 cm. Our approach represents a new paradigm in the way niche secure communications can be established over short links

Properties of purely reactive Foster and non-Foster passive networks

The mathematical concept of strongly real functions of positive and negative types is introduced to network theory for the first time. In this letter we show that the driving point reactance/susceptance of a pure Foster network, made up of only ideal positive inductance and capacitance element, is a strongly real function of real frequency of positive type. As a corollary, for a pure non-Foster network made up of only ideal negative inductance and capacitance elements, we show that the driving point reactance/susceptance is a strongly real function of real frequency of negative type. It is shown that a condition for a purely reactive passive network to exhibit a positive or negative reactance/susceptance-frequency gradient is that the driving point immittance should have alternating poles and zeros lying on the real frequency axis. Finally, it is shown that either purely Foster or non-Foster networks can be constructed by combining ideal Foster and non-Foster reactive elements

3-D printing of microwave components for 21st century applications

Additive manufacturing using 3-D printing is an emerging technology for the production of high performance microwave and terahertz components. Traditionally, these components are made by (micro-)machining. However, recent advances in rapid prototyping technology have led to its use in creating high performance and low weight RF components. In this review paper ten state-of-the-art exemplars are described, covering a wide variety of applications (absorbers, waveguides, antennas and lenses) operating over a broad range of frequencies, from 8 to 330 GHz

CHARACTERISING ROOM TEMPERATURE THz METAL SHIELDING USING THE ENGINEERING APPROACH

Published versio

Advances in Front-end Enabling Technologies for Thermal Infrared ‘THz Torch’ Wireless Communications

The thermal (emitted) infrared frequency bands (typically 20-40 THz and 60-100 THz) are best known for remote sensing applications that include temperature measurement (e.g., noncontacting thermometers and thermography), night vision and surveillance (e.g., ubiquitous motion sensing and target acquisition). This unregulated part of the electromagnetic spectrum also offers commercial opportunities for the development of short-range secure communications. The ‘THz Torch’ concept, which fundamentally exploits engineered blackbody radiation by partitioning thermally-generated spectral radiance into pre-defined frequency channels, was recently demonstrated by the authors. The thermal radiation within each channel can be independently pulsemodulated, transmitted and detected, to create a robust form of short-range secure communications within the thermal infrared. In this paper, recent progress in the front-end enabling technologies associated with the ‘THz Torch’ concept is reported. Fundamental limitations of this technology are discussed; possible engineering solutions for further improving the performance of such thermalbased wireless links are proposed and verified either experimentally or through numerical simulations. By exploring a raft of enabling technologies, significant enhancements to both data rate and transmission range can be expected. With good engineering solutions, the ‘THz Torch’ concept can exploit 19th century physics with 20th century multiplexing schemes for low-cost 21st century ubiquitous applications in security and defence

Ultra-low Cost THz Short-range Wireless Link

This paper demonstrates an ultra-low cost THz system for implementing a short-range wireless communications link in the far/mid-infrared parts of the electromagnetic spectrum. The basic prototype front-end hardware is deliberately kept very simple; based around miniature incandescent light bulbs, THz filters and pyroelectric infrared sensors. While only a low data rate has been experimentally demonstrated so far, this does not represent a fundamental limitation, as a number of technological enhancements are possible. It is believed that this “THz torch” technology has its niche in ubiquitous security applications that do not require high data rates or large distance operation (e.g. secure RFID, smart key fobs and remote controls).Accepted versio