The usefulness of waveguide circuits at frequencies as high as 3THz has now been demonstrated culminating in the realisation of a 2.5THz waveguide mixer implementing Schottky diodes. For waveguide devices to be optimised at these frequencies it has been necessary to modify the design of the waveguide mount paying particular consideration to areas such as ease of assembly, simplification of machining, reliability and fast adjustment of the RF circuit. This paper discusses the detailed design and associated RF performance of a new 2.5THz waveguide mixer mount that makes use of the following: an ultrasonically bonded RF circuit, a non-contacting backshort and part fabricated waveguide. All of these features are aimed at determining the optimum impedance required by the Schottky diode used and thus provide a more ideal circuit in which to place it.

From a commercial point of view the terahertz region from 100GHz to 10THz remains largely unexplored. The main reason for this has been the lack of readily available, rugged solid state detection technology that has sufficient sensitivity for applications such as passive imaging. This is particularly true when arrays of such detectors are considered. Until recently the main technology driver has been ground based Radio Astronomy. Here the drive for absolute noise performance has focused effort towards the development of cryogenically cooled detection techniques, primarily utilising liquid Helium cooled superconducting devices. Commercially, the use of such cryogens will usually rule out most potential high volume applications largely for practical reasons such as running cost, convenience and health and safety issues. In order to kick-start the commercial exploitation of the terahertz region an alternative detection technology is required. The detector technology reported here has its origins in remote sensing applications where the low noise performance requirements are not quite so stringent. Here, reliability, low power operation, low mass and volume are combined with rugged design. These so happen to be the main prerequisites for any commercial solution. For space borne technology, however, cost is not usually an issue and correspondingly until the application of manufacturing methodology the technology has been prohibitively expensive to adopt. This paper reports on the current state of the art in solid state detector array technology aimed at exploiting commercial applications in the terahertz region. An overview of the technology background is provided combined with a forward look outlining the areas where rapid technology advancement can be expected. The utilisation of this detector technology in the application of real time passive terahertz imaging will be shown.

Advances in micro-fabrication techniques combined with accurate simulation tools has provided the means for the realisation of complex terahertz circuitry. Silicon micro-machining provides the way forward to fabricate accurate rugged structures. Multi-level deep reactive ion etching can be used to replace traditional machining methods achieving smaller feature size, improved surface finish and greater freedom in circuit layout. Photonic Bandgap waveguides enable three dimensional arrangements of active devices antennae and filters, and removes the requirement for metallisation of adjoining surfaces. This paper describes some of the state of the art terahertz circuit design and realisation using these techniques.

This paper presents a rapid, versatile, and practical technique for the manufacture of layer-by-layer photonic crystals in the millimeter- and submillimeter-wave regions. Mechanical machining is used to derive a rugged layer-by-layer structure from high-resistivity silicon wafers. Unlike traditional anisotropic etching techniques, this method does not rely on any particular crystal orientation of the substrate and allows greater flexibility in the photonic crystal design. Automatic alignment of alternating layers is achieved via careful placement of the separation cuts. Using this ability, two configurations of photonic crystals are realized and their RF characteristics are measured and presented. Firstly, a symmetrical photonic crystal is studied as an initial demonstration of the technique. This is followed by an asymmetrical example, where a different frequency response is observed for the two orthogonal polarizations of the incident radiation. Two measurement techniques are used to characterize the photonic crystals and the merits of each are discussed. Theoretical predictions are seen to agree well with the measured behavior.

The Terahertz (THz) regime represents the last significantly unexplored part of the electromagnetic spectrum. There are simple physical reasons why it is difficult to produce a compact, efficient solid-state fundamental source of radiation. In this contribution, we review the potential of miniaturized vacuum technologies as an alternative route to the development of low-cost sources of THz radiation for a variety of practical applications.

Initial measurements are presented of a dipole antenna mounted on top of a photonic crystal structure at terahertz frequencies. The configuration and test setup are described. The dipole on top of the photonic crystal has higher directivity in contrast to a single dipole element. The ability of this technology to suppress surface waves is noted.

We report on a novel diode geometry, with reduced thermal resistance, for Heterostructure Barrier Varactor, HBV, diodes. The pillar geometry presented here involves the complete removal of the substrate, electrical contact is made by the forward and reverse side processing of metallic pillars. We propose that there is a limit to the maximum number of barriers that can be used to increase the power capability of a HBV. An analytical model has been developed to study these effects. In considering the case of a perfect thermal heat sink the limit is found to be fourteen, in applying this model to the new pillar structure this is reduced to six.

AIMS:This study compared the antimicrobial activity of Melaleuca alternifolia (tea tree) oil with that of some of its components, both individually and in two-component combinations. METHODS AND RESULTS:Minimum inhibitory concentration and time-kill assays revealed that terpinen-4-ol, the principal active component of tea tree oil, was more active on its own than when present in tea tree oil. Combinations of terpinen-4-ol and either gamma-terpinene or p-cymene produced similar activities to tea tree oil. Concentration-dependent reductions in terpinen-4-ol activity and solubility also occurred in the presence of gamma-terpinene. CONCLUSION:Non-oxygenated terpenes in tea tree oil appear to reduce terpinen-4-ol efficacy by lowering its aqueous solubility. SIGNIFICANCE AND IMPACT OF THE STUDY:These findings explain why tea tree oil can be less active in vitro than terpinen-4-ol alone and further suggest that the presence of a non-aqueous phase in tea tree oil formulations may limit the microbial availability of its active components.

A technique has been developed which allows the fabrication of channels within the body of multiple layers of negative, resist. Previously this was only possible in the positive resist system but with the transfer to negative resist, higher and more clearly defined channels are now possible. Thick negative resists are also easier to process than their positive counterparts, allowing multiple crossing channels. The physical structure of a full height W-band waveguide with an integrated E-plane filter has been fabricated with this technique. The fabrication procedure presented in this paper is quick, reproducible and easily implemented using standard photolithography equipment.

Research into the mode of action of the essential oil of Melaleuca alternifolia (Tea tree oil) is briefly reviewed. Its mode of action is interpreted in terms of the membrane-toxicity of its monoterpenoid components and different approaches for determining cell membrane damage are discussed.