Transferred electron oscillators at MM wave frequencies and their characterisation using quasi-optical techniques

A study of high frequency millimetre wave oscillators is performed operating at W- band and above, using test bench equipment designed and constructed in St. Andrews. Octave tuneable oscillators have been designed, constructed, and used to characterise developmental Gunn devices, as well as to provide ideal oscillators for test bench measurement systems. These oscillators have been sold to many millimetre-wave laboratories throughout Britain. The operation, optimisation and characterisation of these oscillators is described in detail, and various non-linear effects are explained and modelled successfully. The wideband tuneability and matching has also allowed evaluation of new developmental Gunn devices to accurately determine the optimum operating frequency range of the devices. This was part of a developmental program by GEC Hirst and MEDL which has now produced state of the art GaAs Gunn oscillators at 94GHz. Much of the characterisation of the oscillators is performed using novel quasi-optical techniques, which has allowed low loss accurate performance at these very high frequencies. Several quasi-optical techniques are described and the design, manufacture and evaluation of many optical components are given. In particular, the frequency and harmonic content of the oscillators was determined using a Martin-Puplett Interferometer which utilised a frequency counting technique. This enabled easy wideband measurements to be performed with much greater accuracy than traditional cavity wavemeters. In addition, a state of the art noise bench has been designed and constructed for operation at W -band and above, that utilises a novel open resonator to effect a very high Q suppression filter. The system has been shown to make noise measurements at much lower power levels and with greater sensitivity than comparable systems

Large cross-effect dynamic nuclear polarisation enhancements with kilowatt inverting chirped pulses at 94 GHz

This work was supported by UK Research Council EPSRC research grant EP/R13705/1 and Wellcome Trust 099149/Z/12/Z.Dynamic nuclear polarisation (DNP) is a process that transfers electron spin polarisation to nuclei by applying resonant microwave radiation, and has been widely used to improve the sensitivity of nuclear magnetic resonance (NMR). Here we demonstrate new levels of performance for static cross-effect proton DNP using high peak power chirped inversion pulses at 94 GHz to create a strong polarisation gradient across the inhomogeneously broadened line of the mono-radical 4-amino TEMPO. Enhancements of up to 340 are achieved at an average power of a few hundred mW, with fast build-up times (3 s). Experiments are performed using a home-built wideband kW pulsed electron paramagnetic resonance (EPR) spectrometer operating at 94 GHz, integrated with an NMR detection system. Simultaneous DNP and EPR characterisation of other mono-radicals and biradicals, as a function of temperature, leads to additional insights into limiting relaxation mechanisms and give further motivation for the development of wideband pulsed amplifiers for DNP at higher frequencies.Publisher PDFPeer reviewe

Compact corrugated feedhorns with high Gaussian coupling efficiency and -60 dB sidelobes

We demonstrate that very high performance, extremely compact, scalar corrugated feedhorns can be designed and constructed by optimizing the excitation and phasing of the HE11, HE12 and HE13 modes near the throat of the horn whilst limiting excitation of higher order modes. We present the design and measurement of two families of dual-profiled horn, both with a directivity of 20 dBi that couple with very high efficiency to a fundamental Gaussian mode. The first was optimized for sidelobe performance and features sidelobes approaching -60 dB for a horn length of only 15.6λ. The second was designed to minimize horn length and achieves sidelobe levels below -35 dB for a horn which is only 4.8λ long. The horns exhibit excellent coupling to the fundamental free-space Gaussian mode, with LG00 power coupling of 99.92% and 99.75% respectively. We demonstrate excellent agreement between simulation and experiment at 94 GHz and simulate the performance over a 20% bandwidth. High performance compact scalar horns are of interest because they reduce manufacturing risk at high frequencies, and reduce size and weight at lower frequencies, which can be important in horn arrays and space applications, where horn arrays often have serious weight and size restrictions.PostprintPeer reviewe

Shape dependent conformable holographic metasurfaces

Funding: European Research Council - 819346; Engineering and Physical Sciences Research Council - EP/V029975/1; Royal Society - URF\R\211033.In this paper, the design, fabrication, and experimental demonstration of conformable holographic metasurfaces are reported. Here, it is shown that the produced holographic image changes as the metasurface is applied to targets with different shapes. The demonstration is based on a reflective type metasurface, where the reflected polarization is perpendicular to that of the incident light. In addition, how the parameters of the metasurface determine the quality of the images produced and the ability to produce independent images are discussed critically.Publisher PDFPeer reviewe

An output coupler for a W-band high power wideband gyro-amplifier

This work was supported by the Engineering and Physical Sciences Research Council (EPSRC) U.K. under Research Grant EP/K029746/1, and Science and Technology Facilities Council (STFC) U.K. under Research Grants ST/K006673/1 & ST/K006703/1, ST/N002326/1 & ST/N002318/1.An output coupler for a W-band high power wideband gyro-amplifier has been designed, manufactured and experimentally measured. It consists of a high performance sin2-parallel corrugated horn integrated with a broadband multi-layer window. The major design requirements are that the horn/window combination must have an input return loss lower than -30 dB over a 10 GHz bandwidth, provide a high quality output beam pattern, and operate under ultra-high vacuum conditions. The coupler converts a circular wave guide TE11 mode into the free space Laguerre Gaussian LG00 mode over the frequency band of 90–100 GHz with a measured return loss of between -30 and -40 dB and a simulated Gaussian coupling efficiency of over 99% at 94 GHz.PostprintPeer reviewe

Meaningful engagement: computer-based interactive media art in public space.

Interactive technologies, including electronic devices are increasingly being utilized as a medium for artistic expression and have been placed in freely accessible public environments with mixed results. When audiences encounter computer-based interactive media arts in a public space they are drawn by various interactivities, to play and experiment with them. However, whether the audience is able to gain a meaningful experience through those physical interactivities has remained an issue of both theoretical and practical debate. This paper will focus on these aspects, most specifically through the study of interactive art in freely accessible public space. The author proposes four new conceptual/analytical tools for examining the subject. It is anticipated that this paper will provide possible alternative strategies for both artists and art researchers in this field with a purpose to enhance intellectual engagement with their audiences, so as to succeed in leading interactors to obtain meaningful experience and rewards

Psychosocial determinants of quit motivation in older smokers from deprived backgrounds: a cross-sectional survey

Objectives To identify psychosocial determinants of quit motivation in older deprived smokers. The evidence may be used to optimise smoking cessation interventions for the target population.Design Cross-sectional survey using online recruitment methods including Facebook-targeted advertising.Setting UK, 2019.Participants Current smokers aged 50 years or older and from a socioeconomically deprived background.Main outcome measures Measures included motivation to stop smoking, smoking history, perceived social support, self-efficacy for quitting, self-exempting beliefs and lung cancer risk perception. Multivariable regression was used to analyse factors associated with quit motivation.Results Of a total 578 individuals who consented to take part, 278 (48.1%) did not meet the inclusion criteria. Of the 300 eligible participants, most were recruited using Facebook (94.0%), were aged 50–64 years (83.7%) and women (85.7%). Most participants were renting from a housing association (72.0%) and had low education (61.0%). Higher motivation to quit was statistically significantly associated with a higher intensity of previous quit attempts (p=0.03), higher quit confidence (p=0.01), higher smoking self-efficacy (p=0.01), a lower risk-minimising beliefs score (p=0.01) and using traditional nicotine replacement therapy (NRT) when trying to stop smoking or cut down (p≤0.001).Conclusion Older smokers from deprived backgrounds face complex barriers to quitting smoking. Interventions are needed to increase self-efficacy for quitting, modify risk-minimising beliefs and target elements of previous quit attempts (ie, the use of NRT) that are associated with motivation to stop smoking

Orientation selection in high-field RIDME and PELDOR experiments involving low-spin CoII ions

AG and CLM were supported by postgraduate fellowships by the EPSRC-funded doctoral training centre ‘integrated magnetic resonance’. This work was supported by the European Union Seventh Framework Programme (PCIG12-GA-2012-334496). The W-band instrument was developed under the U.K. Research Councils Basic Technology Program (grant EP/F039034/1) and the Q-band equipment is supported by the Wellcome Trust (099149/Z/12/Z).Orientation selective (OS) RIDME and PELDOR were conducted on a low-spin CoII complex coordinated by two nitroxide (NO) labelled 2,2':6',2''-terpyridine ligands. Co-NO RIDME at W- and Q-band gave insight into the relative orientation between the Co-NO interspin vector (rCo-NO) and the NO moiety. This was further supported by W-band Co-NO PELDOR that also allowed elucidating the relative orientation of the CoII and NO g-tensors. Differences to earlier predictions were confirmed by DFT calculations. Finally, NO-NO PELDOR allowed retrieving the mutual orientations between the NO-NO interspin vector (rNO-NO) and the NO moieties. The results demonstrate that OS-RIDME and -PELDOR can provide geometric and electronic structure information on a system containing a CoII ion and two nitroxides. Especially, the high sensitivity and ease of interpretation of RIDME at W-band opens avenues for new applications of CoII as orthogonal spin label.PostprintPeer reviewe

Active Steps Evaluation: Full Report

Background: Active Steps is a remote behaviour change service supporting inactive adults with a lung condition to become physically active. Aim: To determine the efficacy of Active Steps in improving physical activity and quality life