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Baum T.C.,RMIT University | Ghorbani K.,DST Group | Nicholson K.J.,DST Group
European Microwave Week 2016: "Microwaves Everywhere", EuMW 2016 - Conference Proceedings; 46th European Microwave Conference, EuMC 2016 | Year: 2016

High impedance surfaces (HIS) have attracted a significant amount of attention in recent years, as they allow for the manipulation of surface currents on ground planes for antennas. These same structures, along with various similar resonant elements have been exploited to design near perfect narrow band absorbers. This class of absorbers has also been used to develop multi-resonant and broadband responses using lossy, high dielectric mediums (i.e. graphite, carbon, etc.). This paper investigates a high resolution, coherent Doppler tomographic (CDT) image of a simple lossy mushroom HIS structure, designed from structural composite materials. The resonating elements are investigated for their surface wave scattering properties and are shown to create complex scattering interactions within the HIS absorber. The HIS structure resonated at 6.2 GHz with a -10.48 dB reflection coefficient. A wideband analysis indicates that the overall scattering is reduced. © 2016 EuMA.

Stepanov D.Y.,DST Group
Optics InfoBase Conference Papers | Year: 2016

A pair of wavelength-matched Bragg gratings in a polarization maintaining fiber comprises a reflective tunable waveplate. Polarization of the reflected laser light is continuously tuned by tuning the laser wavelength or by straining the device. © OSA 2016.

Krieg B.,DST Group | Forrester C.,DST Group
5th Asian-Australian Rotorcraft Forum, ARF 2016 | Year: 2016

It is common practice to truncate aircraft load spectra by removing small cycles on the assumption that they are responsible for only a small proportion of total fatigue damage. As helicopter spectra have significantly greater small cycle content than their fixed wing counterparts, DST Group has undertaken a coupon test program to experimentally investigate the fatigue effects of removing small loads from helicopter spectra. Four truncation levels were tested on two coupon designs made from AL7075-T7351 Aluminum and the effect on crack growth and total life was experimentally investigated. It was found that removing small cycle content from a helicopter load spectrum produced a less damaging test spectrum, resulting in non-conservative life estimations and crack growth rate estimations. It was determined that small cycles, with expected stress-lives far beyond published values, are responsible for a significant proportion of fatigue damage in helicopter spectra. Copyright © 2016 by the American Helicopter Society International, Inc. All rights reserved.

Francis D.B.,DST Group | Cervera M.A.,DST Group | Frazer G.J.,DST Group
2017 IEEE Radar Conference, RadarConf 2017 | Year: 2017

We introduce a radar network design methodology to address the challenge of designing a network of skywave overt-he-horizon radar (OTHR). The approach can be used to optimise the number of radars, the location of each radar, the sensitivity of each radar, and the total network system cost, based on the chosen mission objectives. The approach postulates these parameters and evaluates radar performance based on ionospheric propagation and noise models and a model of the radar detection and tracking sensitivity. We demonstrate the method with a stylised example of a three radar network directed at the eastern region of Australia from radars located in New Zealand, Norfolk Island and New Caledonia. The network is evaluated for performance with respect to commercial aircraft flights operating between several major Australian cities and Sydney. © 2017 IEEE.

Duk V.,University of Adelaide | Rosenberg L.,DST Group | Ng B.W.-H.,University of Adelaide
IEEE Transactions on Aerospace and Electronic Systems | Year: 2017

Small target detection in the maritime environment remains a challenging problem. Maritime radars traditionally use non-coherent processing methods due to the time-varying and range-varying nature of the Doppler spectra. However, the radar backscatter may contain sea-spikes, which can last for seconds and resemble targets. This paper presents an application of stationary wavelet transforms (SWT) to improve target detection in medium grazing angle X-band sea-clutter. Since different components (sub-bands) of the SWT decomposition reveal different spectral characteristics of the returned signal, a method of selecting the appropriate sub-band is presented using an entropy-based metric. A Monte Carlo simulation using a cell averaging constant false alarm rate detector is then used to demonstrate the improvement of the SWT scheme against unfiltered data. © 1965-2011 IEEE.

News Article | October 27, 2016
Site: phys.org

The Cryogenic Sapphire Oscillator, or Sapphire Clock, has been enhanced by researchers from the University of Adelaide in South Australia to achieve near attosecond capability. The oscillator is 10-1000 times more stable than competing technology and allows users to take ultra-high precision measurements to improve the performance of electronic systems. Increased time precision is an integral part of radar technology and quantum computing, which have previously relied on the stability of quartz oscillators as well as atomic clocks such as the Hydrogen Maser. Atomic clocks are the gold-standard in time keeping for long-term stability over months and years. However, electronic systems need short-term stability over a second to control today's devices. The new Sapphire Clock has a short-term stability of better than 1x10-15, which is equivalent to only losing or gaining one second every 40 million years, 100 times better than commercial atomic clocks over a second. The original Sapphire Clock was developed by Professor Andre Luiten in 1989 in Western Australia before the team moved to South Australia to continue developing the device at the University of Adelaide. Lead researcher Martin O'Connor said the development group was in the process of modifying the device to meet the needs of various industries including defence, quantum computing and radio astronomy. The 100cm x 40cm x 40cm clock uses the natural resonance frequency of a synthetic sapphire crystal to maintain a steady oscillator signal. Associate Professor O'Connor said the machine could be reduced to 60 per cent of its size without losing much of its capability. "Our technology is so far ahead of the game, it is now the time to transfer it into a commercial product," he said. "We can now tailor the oscillator to the application of our customers by reducing its size, weight and power consumption but it is still beyond current electronic systems." The Sapphire Clock, also known as a microwave oscillator, has a 5 cm cylinder-shaped crystal that is cooled to -269C. Microwave radiation is constantly propagating around the crystal with a natural resonance. The concept was first discovered by Lord Rayleigh in 1878 when he could hear someone whispering far away on the other side of the church dome at St Paul's Cathedral. The clock then uses small probes to pick up the faint resonance and amplifies it back to produce a pure frequency with near attosecond performance. "An atomic clock uses an electronic transition between two energy levels of an atom as a frequency standard," Associate Professor O'Connor said. "The atomic clock is what is commonly used in GPS satellites and in other quantum computing and astronomy applications but our clock is set to disrupt these current applications." The lab-based version already has an existing customer in the Defence Science and Technology Group (DST Group) in Adelaide, but Associate Professor O'Connor said the research group was also looking for more clients and was in discussion with a number of different industry groups. The research group is taking part in the Commonwealth Scientific and Industrial Research Organisation's (CSIRO's) On Prime pre-accelerator program, which helps teams identify customer segments and build business plans. Commercial versions of the Sapphire Clock will be made available in 2017. Explore further: A new EU project on ultra-precise atomic clocks

Xu S.,University of South Australia | Dogancay K.,University of South Australia | Hmam H.,DST Group
ICASSP, IEEE International Conference on Acoustics, Speech and Signal Processing - Proceedings | Year: 2016

This paper is concerned with unmanned aerial vehicle (UAV) path optimization for AOA target localization via distributed processing. A distributed UAV path optimization algorithm based on gradient descent method is developed using the diffusion extended Kalman filter (DEKF). With this algorithm, a group of UAVs can realize self-adaptive path optimization in order to improve estimation performance. The presented distributed path optimization strategy aims to minimize the estimation mean squared error (MSE) by minimizing the trace of the error covariance matrix. The UAV dynamic communication topology caused by communication range constraint is analyzed. Furthermore, the UAV 6-degree-of-freedom (DOF) dynamic modeling is taken into consideration to generate realistic UAV trajectories. The properties and effectiveness of the proposed algorithm are discussed and verified with simulation examples. © 2016 IEEE.

Xu S.,University of South Australia | Dogancay K.,University of South Australia | Hmam H.,DST Group
ICASSP, IEEE International Conference on Acoustics, Speech and Signal Processing - Proceedings | Year: 2016

This paper investigates the problem of how to optimize the path of a single moving own-ship for angle-of-arrival (AOA) target tracking in three-dimensional (3D) space. First, a novel 3D pseudolinear Kalman filter (PLKF) is proposed to reduce computational complexity and to improve stability of an extended Kalman filter solution. This filter consists of an xy-PLKF and a z-PLKF, transforming the nonlinear azimuth and elevation angle measurements into pseudolinear models. We show that when the own-ship and target are at the same height, the z-PLKF will be unbiased. Next, a gradient-descent path optimization algorithm is developed for the xy-PLKF aiming at minimizing the trace of the covariance matrix. Then, a grid search path optimization method is designed for the z-PLKF. Simulation examples verify the effectiveness of the proposed path optimization algorithm. © 2016 IEEE.

Ristic B.,RMIT University | Gunatilaka A.,DST Group | Gailis R.,DST Group
Atmospheric Environment | Year: 2016

The problem is to estimate the parameters of a source continuously releasing hazardous material into the atmosphere. The concentration measurements are collected at a number of known locations by a moving binary sensor, characterised by an unknown threshold. The paper formulated a solution in the Bayesian framework, using a dispersion model of Poisson distributed particle encounters in a turbulent flow and assuming the environmental parameters (wind velocity, diffusivity, particle lifetime) are known. The method is implemented using an importance sampling technique and successfully validated with three experimental datasets under different wind conditions. In this context, the estimates of the source release rate are not of practical use, being scaled with an unknown constant related to the binary threshold. © 2016

Dykas B.,DST Group | Becker A.,DST Group
IEEE Aerospace Conference Proceedings | Year: 2016

An initial feasibility study is conducted through subscale testing in order to assess several sensing techniques for their ability to detect corrosion damage and lubrication failure in propulsion ball bearings. Conventional vibroacoustic methods are compared and a thermography technique is examined in brief. Initial results indicate that for small, distributed corrosion pitting damage, PZT acoustic emission (AE) sensors mounted to the bearing supports provide the highest signal to noise ratio and most robust indication of bearing damage among the methods attempted. Conventional accelerometers responded to damage as expected, but an ultrasonic microphone showed significant promise for a noncontact method that would be easiest to implement during routine maintenance checks. Degraded lubrication conditions as well as interactions of rolling elements with corrosion pitting can be diagnosed by comparing spectral content within the acoustic signal, and enveloping techniques conventionally applied to vibration signals can be effectively applied to the acoustic signal. © 2016 IEEE.

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