Many measurements methods we use in the 21st century are highly dependent on the use of computer software. Software is used both to control automatic measurements and to relate measured quantities - the measurands - to parameters of interest. One example is network analyser measurements of dielectric properties of a specimen in a transmission line: the measurands are usually its scattering parameters (S-parameters), whereas the parameter of interest is generally its complex permittivity. The numerical modelling software that is applied to relate permittivity to the measured S-parameters in this case need not be too complex, but other measurement techniques require deeper analytical approaches to perform this task. NPL aspires to making all of its measurements traceable to international standards and in methods that rely upon modelling software, this entails the validation of this software to ensure that it does what it is intended to do. There are many methods for validating measurement software, they include checking against mathematically analytical cases, against previously validated software or against measurements on artefacts and specimens with known properties. Validation of this sort is essential if one is to have confidence in measurement results obtained with the aid of modelling software. NPL provides support for software validation through Software Support for Metrology.

CST Microwave Studio electric field model of Dielectric Waveguide Measurements 

More specifically, in the field of electromagnetic metrology and in particular in electromagnetic material measurement a wide range of validated software is needed at NPL to cover the equally wide range of measurement applications. There is an ongoing programme of software development to match our metrology R&D activities. Validated software is invaluable here because it is not only used in actual measurements, it can also be employed when designing instrumentation to perform sensitivity analysis for optimising performance and for estimating the effects of sources of uncertainty (e.g. from gaps around dielectric specimens in transmission lines). NPL’s expertise in validated software for RF and microwave metrology includes:

• Generic and flexible mode-matching software for a wide range of coaxial dielectric probes and resonator geometries, including TE-mode dielectric resonators and ‘split-post’ dielectric resonators for measuring complex permittivity on laminar specimens and thin films.
• Gaussian Beam analyses of fields in open resonators, which are used for millimetre-wave dielectric measurement.
• Monte Carlo modelling software for uncertainty analysis of dielectric measurements.
• Software for near-field scanning of antenna patterns.

In addition to these areas, which support measurement activities for NPL customers, forward looking research has been carried out at NPL on metamaterials. This has focused on numerical analysis of active and passive structured artificial dielectric surfaces.

Contact

Customer Service tel: +44 20 8943 8681
E-mail: materials_enquiries@npl.co.uk