Dielectric Measurement Services
NPL's capability here covers low loss, medium and high loss materials and both solid and liquid dielectrics. Services we can offer for suitable materials include:
- Dielectric measurements (complex permittivity), 1 kHz to 110 GHz
- Measurement of complex permeability, 100 MHz to 18 GHz
- Provision of reference materials and traceability
- Research collaborations on the electromagnetic properties of materials
Measurement Techniques
NPL specialises in the methods listed below. In a number of cases the methods mentioned were initiated or largely developed at NPL. Some of these techniques are used for fully traceable measurements for sustomers; others are used for research investigations. Many of the techniques listed can be used for both solids and liquids. NPL is always willing to develop new methods which are appropriate to your needs, so do please contact us if you need help with electromagnetic materials measurements.
Liquid immersion cell for accurate, traceable ‘static’ permittivity measurements on solid dielectrics (typically operated at 1 MHz).
Admittance cells for medium loss (loss tangent 0.001 to 0.03) to high loss materials, relative permittivities in the range 1 to 30. Frequencies 1 kHz to 1 GHz (most cells operate up to 10 MHz) - planar specimens, or coaxial cells are used for liquids and particulate dielectrics.
Measurement of tissue equivalent liquids 300 MHz to 6 GHz, particularly those used in SAR (Specific Absorption Rate) measurements.
High temperature cells for e.g. foodstuffs (up to 90 °C, 2.45 GHz), ceramics (up to 400 °C, 1 MHz) and reference liquids (from 10 °C to 50 °C, 10 kHz to 1 MHz).
Coaxial line and waveguide transmission line measurements 100 MHz to 18 GHz for medium to high loss dielectrics and for relative permittivities up to 100. Both 14 mm and 7 mm, and related reflection cells, are in use.
Coaxial and waveguide transmission line measurements 100 MHz to 18 GHz for magnetic materials (e.g. ferrite RAM, ferroelectric composites).
Coaxial and waveguide probes for minimally invasive measurements, ideally on malleable solids and liquids of medium to high loss, 50 MHz to 18 GHz (NPL-developed, with NPL numerical software, e.g. for layered and circular specimens).
Dielectric resonator evaluation, 100 MHz to 18 GHz in Courtney Resonator or Cavity specimen holders.
Resonators for low loss microwave measurements: re-entrant (70 MHz to 700 MHz), split-post (1.8 GHz to 10 GHz), TM02 (approx. 500 MHz), TE01: (8 GHz to 12 GHz).
Millimetre-wave open resonators for low loss materials, typically at 32 GHz to 110 GHz, also 8 GHz to 12 GHz.
Microwave Quasi-Optical Methods: including Gaussian Beam reflectometry and free-space reflectometry, with fields measured by an optically modulated scatterer (OMS) for measuring dielectric sheet and RAM reflections and surface waves.
Measurements on thin film and laminar dielectrics, typically 10 to 300 μm in thickness, in the frequency range 1 kHz to 110 GHz, by a number of techniques given above.
Terahertz: quasi-optical measurements on materials properties are carried out a THz frequencies by using THz Pulse Imaging (TPI) methods.
Good Practice Guide
Many of the lessons learnt from RF and Microwave dielectric measurements over many years at NPL have been compiled into a good practice guide concerned with practical measurement and how to improve their accuracy.
A Guide to Characterisation of Dielectric Materials at RF and Microwave Frequencies, R N Clarke (ed.), published by the Institute of Measurement and Control and NPL, 2003.
Workshops and Measurement Clubs
NPL also runs workshops and club meetings to allow scientists, engineers and metrologists to present their work and share experiences. Please see the Events section for upcoming meetings.
Contact
Customer Service tel: +44 20 8943 8681
E-mail: materials_enquiries@npl.co.uk