C.J. Stevens

Metamaterial endoscope for magnetic field transfer: near field imaging with magnetic wires

We report on the development and use of a highly anisotropic magnetic metamaterial for near-field imaging. The material consists of an array of Swiss Roll structures, resonant near 21.3 MHz, with a peak value of relative permeability ~35. At this peak, the material transfers an input magnetic field pattern to the output face without loss of intensity and with a spatial resolution equal to the roll diameter. It behaves as a near-field imaging device consisting of a bundle of magnetic wires.

Enhanced detection of buried assets

This paper reports the design of a new resonator system to enhance the identification of buried underground assets. Results from theoretical calculation, simulation, laboratory measurement, and field test are presented and practical considerations are highlighted. The proposed system has the potential to benefit future civil engineering installations.

A simple tuning method for high temperature superconducting microstrip filters

In this paper we report a simple tuning methodology of high temperature superconducting (HTS) microstrip filters. In order to establish this new tuning approach a 5 pole lumped element HTS bandpass filter, centre frequency 800 MHz, narrowband (bandwidth, 7.6 MHz), is designed and fabricated on a 2 inch (diameter) YBa2Cu3O6.94 thin film of thickness 700 nm and lanthanum aluminate (LaAlO3) substrate of 0.5 mm thickness. The filter was etched using conventional photolithography and a wet chemical etching process. The 5 pole lumped element filter is tested in an integrated RF-cryocooler measurement system at 65 K and also in liquid nitrogen (77 K). We demonstrate a 19.3 MHz downward shift of the centre frequency of the 5 pole filter response. This is achieved by overlaying two layers of thin dielectric tape (PTFE) (50.0 µ mt hickness, permittivity 3.2) ove rt he conducting patterned part of the filter surface. A full wave electromagnetic analysis of the dielectric environment of this tuning arrangement matches the measured response closely. To improve the passband response, the filter is tuned in liquid nitrogen, placing pieces of sapphire rods over the resonators of the filter layout.

Synthetic aperture analysis of multipath propagation in the ultra-wideband communications channel

We discuss synthetic aperture techniques for radio imaging and direction-of-arrival (DoA) analysis in an indoor ultra-wideband (UWB) environment. A wavefront reconstruction technique is used for visual representation of time-evolutionary wave traversal, and optical diffraction theory is used to transform complex channel data from a rectilinear synthetic aperture into its angular spectrum. Using this analysis with measured channel data, the DoA properties of UWB propagation are investigated. It is demonstrated that the channel experiences strong angular clustering in general. Initial evidence of frequency selective scattering is also reported. The significance of these results for beam-forming, diversity and MIMO systems is highlighted.

Increasing MIMO capacity in ultra-wideband communications through orthogonal polarizations

This paper assesses the performance of polarization MIMO in an indoor ultra-wideband communications system using measured channel data. The orthogonality of the polarization subchannels is established through correlation analysis and eigenvalue decomposition. The performance advantage is quantified in terms of the gain in Shannon capacity and is compared with narrowband and unipolar systems. It is shown that the fading correlation of the polarized subchannels is lower than 0.3, and the system can achieve spectral efficiencies as high as 17.5 b/s/Hz, providing a channel capacity of over 130 Gbps on a full-band dual-polar UWB system.

A compact, higher order, high temperature superconductor microstrip bandpass filter on a two-inch lanthanum aluminate substrate for personal communication service applications

A practical design methodology for a compact parallel-coupled microstrip bandpass filter structure with steep attenuation is introduced using a computer-aided full wave electromagnetic simulation based on the method of moments. The structure consists of an array of fully aligned half-wavelength spiral meander line resonators. Aimed at application in the front-end receiver of digital cellular communication service, a 12-pole high temperature superconductor filter with 2.27% fractional bandwidth at 883.0 MHz was designed. The filter is fabricated using thallium–barium–calcium–copper oxide (TBCCO) thin films on a two-inch lanthanum aluminate (LaAlO3) wafer. The S-parameter measurements show a good agreement with the simulated results. At 70 K, the 12-pole filter shows less than 0.4 dB insertion loss, 0.3 dB passband ripple, better than 12 dB return loss. The out of band rejection at 3 MHz below the passband edges is more than 60.0 dB. In order to estimate the power handling capability of the filter, the third-order intermodulation distortion was measured. A sensitivity analysis for the observed frequency shift in the filter is reported. Also from this analysis an approach for using the same design in 0.5% FBW applications is discussed.

A Split Ring Resonator Dielectric Probe for Near-Field Dielectric Imaging

A single split-ring resonator (SRR) probe for 2D surface mapping and imaging of relative dielectric permittivity for the characterisation of composite materials has been developed. The imaging principle, the analysis and the sensitivity of the SRR surface dielectric probe data is described. The surface dielectric properties of composite materials in the frequency range 1–3u2009GHz have been measured based on the magnetic resonance frequency of the transmission loss of the SRR dielectric probe when in contact with the surface. The SRR probe performance was analysed analytically and using full-wave simulation, and predictions showed close agreement with experiment for composite materials with spatially varying dielectric permittivity manufactured by 3D printing. The spatial and permittivity resolution of the SRR dielectric probe were controlled by the geometrical parameters of the SRR which provided flexibility to tune the SRR probe. The best accuracy of the dielectric permittivity measurements was within 5%.

Discretely-sampled partial aperture receiver for orbital angular momentum modes

Spatial modes, such as orbital angular momentum (OAM) modes, are of interest for creating high spectral-efficiency line-of-sight wireless links in propagation environments with limited diversity gain. Four-element receive arrays have been designed using a Monte-Carlo method so as to enable the simultaneous reception of four different OAM modes. A test-bed operating in the 5GHz band has been developed to validate the principle experimentally. The test beds transmitter is an eight-element uniform circular array, which allows the generation of OAM modes with mode numbers l = ∊ {±3, ±2, ±1,0}. The receiver is a four element array, and all elements in the transmit and receive arrays have a dedicated programmable phase shifter to facilitate rapid adjustment between modes.

Comparison of simulation and measurement for 1-D metamaterial devices

We have conducted numerical and experimental studies of a simple metamaterial structure formed from C shaped copper rings. Our study focuses on the investigation of the individual resonant elements by surface current and Q factor. We have also analysed wavelike signal propagation along these structures axes recently predicted theoretically - so called magneto-inductive waves (MIWs). Computer based finite difference electromagnetic methods have been employed to both visualize the surface currents and investigate the effects of varying coupling within the structures. Experimental work has closely followed the theoretical work with measurements carried out using a Vector Network Analyzer to determine the frequency dependent scattering parameters. Applications of these structures are also considered in our work and the aim is to develop a robust, reliable design tool that enables rapid determination of the appropriate dimensions to enable operation of a magneto-inductive waveguide at a desired frequency. The simulation work demonstrates the possibilities for wave propagation in curved guides formed from stacks and rows of elements. And these may form the basis for a new class of microwave filter offering tunability and flexibility and requiring no direct connections to the driving circuits.

Small-scale delay-domain statistics of the frequency-selective indoor wireless channel

In this paper, electromagnetic signal propagation in the frequency-selective indoor wireless channel is investigated with the help of ultra-wideband channel measurements. Delay-domain statistics used to characterise the multipath delay spread are evaluated numerically. The spatial variation of these parameters over a short range is studied, and their statistical behaviour is analysed. It is demonstrated that the mean and rms delay spread exhibit spatially distributed alternating zones of high and low spread over a short range corresponding to electromagnetic interference fringes. Furthermore, they are approximated with Gaussian random variables. A theoretical explanation is provided for this small-scale behaviour.