A spin out from the University of Oxford is developing sensors based on aerial near-field effects that could be used to identify plastics in recycling plants.

“We have a team of half a dozen and first round funding,” CEO of Oxford RF Sensors, Ross Walker, told Electronics Weekly. “The sensors are attracting quite a lot of interest from people who have sensing problems.”

Each sensor consists of an antenna, an oscillator and some signal conditioning. In either magnetic or electric form, the sensors measure the real and imaginary parts of magnetic susceptibility or electrical permittivity from materials.

There are two main ways of using the sensors: to analyse materials, or detect position or speed of known materials.

“Plastic identification is where we see a real strength,” said Walker. “It is quite important for the WEEE [electronic waste] Directive.”

The sensor in this case is capacitive, measuring permittivity. In some experiments with opaque plastics, which cannot be analysed by infra-red spectrometry, “we could quite easily distinguish ABS plastic with and without fire retardant”, said Walker. “The people in industry I have spoken to don’t have a solution for this.”

Water, particulates and oxidation in hydraulic oil, and bio-mass in water, are examples of liquids that can be analysed.

For speed sensing, but detecting teeth on a rotating cog, “you can look at almost any target material. We are not restricted to magnetic or metallic”, said Walker.

In this case, the imaginary part of permittivity, which equated to lossyness, said Walker, can be seen as amplitude modulation at the tooth passing frequency.

Sensing is near-field and, said Walker, as a rule of thumb, sensing range is roughly equal to the diameter of the aerial. And careful aerial design can eliminate the effects of sample size on results when the techniques are applied to material analysis.

“The optimum operating frequency of the RF sensor which may vary from a few kilohertz for large systems to tens of gigahertz for very small ones,” said the firm.

It is early days, but the company is starting to make links with industrial partners. “We are working with a number of companies, although there is no direct revenue yet,” said Walker.

IP2IPO provided the first round funding, investing £470,000 in return for a 35.9 per cent equity interest. It is the first spin-out from the Oxford’s physics department in which IP2IPO has invested.

www.oxfordrfsensors.com

See also: Electronics Weekly's roundup of content related to The WEEE Directive