School of Physics - Microwave Division

Here is a brief list of the projects presently being undertaken in the Microwave Division of the Frequency Standards and Metrology Group. For further details on each project, please click on the title of the project

1. Testing the Fundamentals of Physics using Cryogenic Microwave Oscillators

Collaborators
SYRTE (Paris Observatory France)

Funding
ARC DP0343391, LX0453861, BNM (France)

Contact: Professor Michael Tobar. News Release

Nature Review Article

New experiments are now being developed at UWA and Paris to test the fundamentals of physics. Experiments that measure the isotropy of the speed of light (Mordern Michelson Morley experiment) and the time independence of the Fine Structure Constant using cryogenic sapphire oscillators are under development at UWA. Also, we have transported a liquid helium cooled sapphire oscillator to Paris, who have built a Cesium fountain clock with the world's best long term stability. The SYRTE Cesium fountain has already put the best laboratory limit on the time independence of the fine structure constant. By combining the sapphire oscillator with the French atomic clocks further tests of fundamental physics are possible. Recently we tested the constancy of the speed of light more acurately than before. The same data re-analysed in a different way will be able to test the Standard Model of Physics in the photon sector, which is based on the theoretical work of the Standard Model Extension by V. Alan Kostelecky and co-workers at Indiana University.

2. Cryogenic Liquid Helium Cooled Sapphire Microwave Oscillators to Pulse Atomic Clocks

Collaborators
SYRTE (Paris, Observatory France)
ENS (Paris, France)
CNES (Toulouse, French Space Agency)

Funding
ARC DP0343391, LX0453861, CNES (France)

Contact: Professor Michael Tobar.

Cryogenic liquid helium cooled sapphire oscillators provide the most pure signals at microwave frequencies for timing intervals between one second to one day. The construction of such oscillators has a long history at UWA. Research began in 1982 and has gone through three generations of upgraded design. The latest third generation design is more mature and robust and maybe transported to other sights with minimum of fuss. During 2003 a third generation oscillator was transported to the French Space Agency in Toulouse. The oscillator now provides the 'fly wheel' pulsed signal for ground tests of the PHARAO atomic clock. Second and first generation oscillators also exist at the Paris Observatory and the National Measurement Laboratory respectively. These oscillators are routinely used to pulse atomic clocks. The excellent performance of the sapphire oscillator at the frequency of the pulse enabled the first realisation of a quantum limited atomic clock.

3. Solid Nitrogen Cooled Sapphire Oscillators

Collaborators
LPMO (Besancon, France)
IRCOM (Limoges, France)

Funding
ARC DP0343391, LX0453861

Contact: Professor Michael Tobar.

We are developing suitable "fly-wheel" oscillators for quantum limited atomic frequency standards based on temperature stabilized sapphire resonators. For space and some terestrial applications, liquid helium cooled systems are large and expensive. Also, it is possible to radiatively cooled near 40-50 K in space. Promising new designs based on a novel resonator configurations cooled to solid nitrogen temperature (50 K) are under investigation. We have shown that this type of oscillator could achieve a frequency stability better than 10^-14. The design of this type of resonator is only possible with advanced software from IRCOM. Also, there are now many terrestrial atomic fountains under construction world-wide that will require such a highly stable oscillator, which only this technology can provide.

4. Ideal Signal Sources and Measurement Systems

Collaborators
PSI (Fremantle Australia)

Funding
ARC LP0214171, PSI

Contact: A/Prof. Eugene Ivanov.

This project is a colloboration between Industry (PSI Pty. Ltd.) and the University of Western Australia. The research is focused on building signal sources that give an output which comes as close as possible to an ideal "sine wave" output. Such signal sources play an important role in commercial applications such as communication, radar and navigation systems, as well as fundamental physical experiments. Also, the research involves building noise measurement systems only limited by thermal noise. Recently a measurement below the Standard Thermal Noise Limit was built based on the recycling technique.

5. Measurement of Electronic and Magnetic Properties of Materials

Collaborators
LPMO
IRCOM
Warsaw University of Technology
JCU

Funding
ARC LX0453861, LX0242351

Contact: Dr. John Hartnett

We have co-developed the most accurate technique to measure the complex permittivity and magnetic susceptibility of low-loss anisotropic dielectric materials. The technique was sensitive enough to discover for the first time anisotropy in the dielectric loss tangent (imaginary permittivity),and has provided important characterisation of materials necessary for the construction of high-Q temperature stabilised resonators. The new technique was used to create a new database for complex permittivity of low-loss materials and subsequently won the best paper prize in the Institute of Physics Journal, "Measurement Science and Technology".More recently we undertook further work on this topic at the University of Limoges, funded by the French National Centre for Scientific Research (CNRS) and the Australian Research Council, we discovered a new type of mode in highly anisotropic dielectric resonators,which was implemented to measure the complex permittivity. Recently we invented the Dual-Mode Frequency-Locked technique. This is a new method to measure the Temperature Coefficient of Prmittivity (TCP) very accurately and has allowed the design of new frequency standards based on the Dual-Mode oscillator.

6. Novel High-Q Microwave and Millimeterwave Resonators

Collaborators
Warsaw University of Technology
IRCOM
PSI (Fremantle Australia)

Funding
ARC LP0214171, LX0453861, LX0242351, PSI

Contact: Professor Michael Tobar.

We have studied the properties of low-loss crystalline dielectric resonators. This work has led to the invention of the thermoelectric stabilised Sapphire Loaded Cavity, which has a quality factor of 2x10⁵ and an absolute centre frequency designed to 1 part in 10⁷. This invention and method of design has been patented internationally and is commercially available from PSI. The resonator has an order of magnitude higher quality factor than any other cavity resonator and has been sub-licensed overseas to major aviation and defence companies. Current research in this area includes:

New techniques to temperature stabilise the resonant frequency at liquid nitrogen temperature and room temperature.
The invention of a new class of resonators based on the Bragg reflection effect.
Investigation of modes in spherical resonators.