Stephen M. Hanham

Lattice resonances in antenna arrays for liquid sensing in the terahertz regime

Terahertz antenna arrays supporting narrow lattice resonances are proposed as an alternative sensor-on-chip approach to liquid sensing. An array of metallic rectangular antennas fabricated on a polyethylene naphthalate (PEN) substrate is used to demonstrate the sensing of a number of fluids. Good agreement is shown between experiment and simulation with Q-factors of around 20 and a figure-of-merit (FOM) of 3.80 being achieved. Liquid sensing with antenna arrays is simple both in terms of fabrication and setup. The working frequency can be tuned with a suitable choice of substrates and array parameters. The nature of the lattice resonance means that the whole sample is used to provide the conditions required for resonance occurrence, eliminating the need to preferentially locate the sample in small areas of high field concentration. The antenna arrays could also potentially be coupled with a microfluidic system for in situ sensing or used in a reflection setup.

Microwave Debye relaxation analysis of dissolved proteins: Towards free-solution biosensing

Aqueous solutions of a variety of proteins at different concentrations are examined through microwave spectroscopy and compared to sodium chloride and polystyrene nanospheres. The complex permittivity is analysed in terms of the Debye model and the Stokes-Einstein-Debye relation in conjunction with the Maxwell-Garnett equation. According to Einstein’s classical theory of viscosity with Brenner’s adaptation [H. Brenner, Chem. Eng. Sci. 27, 1069 (1972)] for arbitrary solute shapes, the ratio of the alterations of static permittivity and relaxation time of low concentration solutions is found to be independent of concentration and determined by the molecular shape. Our results represent a route towards free-solution identification through molecular finger-printing.

Terahertz imaging at 77 K

Terahertz (THz) technology is receiving increasing attention around the world due to its important potential in many application areas. Novel compact solid-state sources and detectors are being sought for?THz radiation and detection. We report the realization of a?THz imager based on a high- Tc superconducting (HTS) Josephson detector working above liquid nitrogen temperature (77?K). The detector, made of a YBa2Cu3O7?x (YBCO) step-edge Josephson junction, is coupled to a thin-film ring-slot antenna and a hemispheric silicon lens. Images of high visual quality are obtained which demonstrate unique properties of?THz radiation such as the sensitivity to water content and the ability to penetrate packaging materials. The results should stimulate further research leading to the development of a HTS superconducting?THz imaging system.

Terahertz imaging using a high-Tc superconducting Josephson junction detector

A high-Tc superconducting (HTS) detector based on a YBa2Cu3O7−x (YBCO) step-edge Josephson junction has been developed and applied to terahertz (THz) detection. The detector was coupled to a ring-slot antenna designed for operation at 600 GHz, and used for THz imaging. The results suggest that the characteristic voltage and frequency of our HTS step-edge junctions can be readily optimized for the chosen THz frequency range at easily achievable temperatures. The images also clearly demonstrate some of the unique properties of THz radiation, including the sensitivity to water content and the ability to penetrate packaging materials. (Some figures in this article are in colour only in the electronic version)

Broadband terahertz plasmonic response of touching InSb disks.

The spectral characteristics of localized surface plasmons (LSPs) depend strongly on the geometry of the metal nanostructure sustaining them. [ 1 , 2 ] This fact makes the tuning of their lightharvesting and focusing abilities across the whole visible and infra-red regimes possible. Lately, the tailoring of the spectral width of LSP resonances through design has attracted much attention due to its many potential applications in technological areas as diverse as sensing, imaging and photovoltaics. [ 3 , 4 ] The excitation of Fano-like resonances in composite nanoparticles has been shown to be useful for controlling their optical properties within an extremely narrow frequency window. [ 5 ] In contrast, transformation optics (TO) has recently been proposed as a route to transfer the broad bandwidth behavior of plasmonic waveguides to nanoantennas using geometric singularities. [ 6 , 7 ]

High Efficiency Excitation of Dielectric Rods Using a Magnetic Ring Current

We describe a theoretical analysis of the excitation of the fundamental surface wave mode on an infinite dielectric rod by a magnetic ring current that is interior to the rod. Earlier work has provided results for an external ring source. Results obtained by us show that for an interior source excitation efficiencies close to 100% are possible for high permittivity dielectrics and launching efficiencies greater than 90% can be achieved over bandwidths greater than 20%. This is a higher efficiency than is possible with an exterior source. Simulation results verifying the theoretical analysis are presented for the practical case of a coaxial waveguide exciting the dielectric rod.

Evolved-Profile Dielectric Rod Antennas

A systematic approach is presented for the design of profiled dielectric rod antennas that satisfy specified radiation pattern objectives. The approach uses a body of revolution method of moments technique to rapidly analyze arbitrarily profiled dielectric rods while a genetic algorithm is used to achieve the design objectives. As examples we present dielectric rod designs optimized for maximum gain and low sidelobes. These designs are compared with a conventional linear profile design. Measured results are presented and these are shown to agree well with the calculated radiation patterns. We show that improved gain and sidelobe performance is achieved using a non-linear rod profile compared to a standard linear profile. The generality of the approach is demonstrated with a shaped beam antenna design that has a cosecant-squared pattern.

Development of a Terahertz Imaging System

This paper introduces work being conducted by the authors towards developing terahertz (THz) imaging technologies. Specifically this paper addresses two topics: the development and implementation of a THz imaging system, and design of a THz detector. The THz imaging system has been implemented to allow exploration across a broad range of applications. An overview and design of this system are presented, along with early images acquired with the system. A high temperature superconducting device capable of detection at THz frequencies is being designed. As development of this detector is at an early stage simulated detector performance results are given; however, it is expected that detector results will be presented at the conference.

A ring slot excited dielectric rod antenna for terahertz imaging

Terahertz radiation has many unique properties that lends itself to applications not possible elsewhere in the electromagnetic spectrum. The radiation passes through many materials that are opaque in the visible spectrum and can be used to form sub-millimeter resolution images. Potential applications for terahertz imaging technology range from skin cancer detection to concealed weapon detection. Current terahertz imaging systems are limited to acquiring one or a few pixels simultaneously leading to impractically long image acquisition times. Large terahertz imaging arrays are required to realize practical systems and real-time imaging frame rates. Improved performance of existing imaging systems and better fabrication methods are also desired. To address these needs we are investigating an integrated focal plane array of terahertz antennas. We present the theory and simulation results for terahertz dielectric rod antennas excited by a ring slot source, as well as some early fabrication results.

Contact-free sheet resistance determination of large area graphene layers by an open dielectric loaded microwave cavity

A method for contact-free determination of the sheet resistance of large-area and arbitrary shaped wafers or sheets coated with graphene and other (semi) conducting ultrathin layers is described, which is based on an open dielectric loaded microwave cavity. The sample under test is exposed to the evanescent resonant field outside the cavity. A comparison with a closed cavity configuration revealed that radiation losses have no significant influence of the experimental results. Moreover, the microwave sheet resistance results show good agreement with the dc conductivity determined by four-probe van der Pauw measurements on a set of CVD samples transferred on quartz. As an example of a practical application, correlations between the sheet resistance and deposition conditions for CVD graphene transferred on quartz wafers are described. Our method has a high potential as measurement standard for contact-free sheet resistance measurement and mapping of large area graphene samples.