NPL offers coaxial probes with 7 mm and 44 mm diameters (measured at the bead), for measuring dielectric properties of liquids (10 MHz to 10 GHz), the coaxial probes are used in conjunction with vector network analysers (VNA) to measure the complex permittivity of liquids and compressible materials, such as the phantoms used for SAR measurements.

The 44 mm diameter probe is optimal for measurements over the frequency range 10 MHz to 500 MHz and employs a cylindrical sample reservoir to reduce the volume of liquid required.  The 7 mm probe extends the frequency range up to approximately 10 GHz.

NPL software controls the calibration and measurement sequence and calculates the permittivity from the measured S₁₁ using a modal analysis. Calibration is by means of measurement on air, on a reference liquid (such as ethanol or methanol) and on a short-circuit.

A least squares algorithm is employed which shows the residual errors for the calibration and allows individual calibration measurements to be repeated. An additional script using a Monte-Carlo algorithm determines the uncertainties in the measured complex permittivity values.

Measurement range approx.
10 MHz to 500 MHz    (44 mm probe)
100 MHz to 10 GHz       (7 mm probe)

Probe connector type:

N-type  (44mm probe)
APC7     (7 mm probe)

Software operating system requirements:
Windows XP

VNA Compatibility:
Agilent 8753 series analysers or
Rhode & Schwarz ZVB analysers

On-site installation and staff training for these systems is also available.

RF & Microwave