UK Panel Commission A Representative
Dr Tian Hong Loh
National Physical Laboratory
Teddington TW11 0LW
E: tian.loh [at] npl.co.uk
Highlights of UK research relevant to Commission A
Time - The Greenwich Meridian Time (GMT) forms the basic reference of time, time zones and time differences across the world. The UK atomic time scale is held at the National Physical Laboratory and is based on an ensemble of hydrogen masers and caesium atomic clocks. These contribute to international atomic timescales and provide the reference for time and frequency dissemination and monitoring within the UK. Other activity has also developed a caesium fountain primary frequency standard to provide a top-level realisation of the second. Unique clock steering algorithms are being developed together with methods to evaluate clock and time transfer noise processes contributing to the development of the reference time scale for the European global satellite navigation system "Galileo". Since time and localisation are intimately connected, the accuracy of global positioning and tracking is governed by the accuracy of time and frequency standards.
Frequency - World-class research activity is underway in UK, together with parallel activity in US, Japan and Europe, in the development of a new generation of optical frequency standards, which are potentially more accurate than microwave standards. Optical frequency standards have many potential applications, ranging from improved satellite navigation systems to sensitive tests of fundamental physical theories. In future they could lead to the second being redefined in terms of an optical transition frequency.
Electromagnetics - Measurement of electromagnetic quantities and properties of materials in solid state from DC via RF and microwave up to terahertz frequencies and beyond is performed in a variety of specialist areas across the UK. Such measurements form the basis for international electromagnetic standards and for the traceability chain which ensures that all companies, institutions and research labs can have access to accurate reliable standards that are constantly updated to ensure their continued relevance. Some of the challenging areas in metrology of EM quantities are in the development of harmonics and flicker analysis techniques, the development of instrumentation for the operation of electrical quantum standards (Josephson effect voltage standard and Quantum Hall resistance standard), characterisation of dielectric, magnetic and magnet-electric materials and metamaterials, from radio- to optical frequencies, digital waveform measurement and measured performance of advanced wireless communications systems, exposure standards of field strength and specific absorption rate, etc. Of growing importance is the characterisation of complex propagation environments, calling for new measurement techniques, analysis methods and metrics for classification for application in ubiquitous boradband communication systems and wireless sensor networks.