Pocket Near Field Probe Boards (R5) – Now with 100% more layers!

Hello and welcome to Unit 3 Compliance.

We test your products for EMC and Electrical Safety, fix them if they don’t pass, and help you with all that boring standards and documentation stuff.

We also provide customised design for EMC training via Think EMC.

Hot off the press are the revision 5 of our Pocket Near Field Probe kits. Better than revision 4? “How is that possible?” I hear you ask…

New Features

  • Now on a 4 layer PCB (100% more layers!)
  • All sensing and signal traces are enclosed within ground plane sections on the outside of the PCB – preventing pickup from stray fields and reduces effects of fingers
  • Removed snap off sections
  • Better silkscreen markings
  • More formulae! (ok, just 3)

Download our Guide

But first things first – if you are new to Near Field Probing then you simply must check out our free eBook that has everything you needed to know (and probably a lot that you didn’t) about the art of near field probing to help solve EMC problems.

* Click here to download *

Assembly Instructions

Refer to the instructions in our Revision 4 guide. It’s exactly the same, only we’ve removed the snap off sections.

We hope you enjoy using it!


1% For The Planet Donations 2022

Every year we donate 1 percent of our turnover (sales) to environmental charities through our membership of One Percent for the Planet

Our chosen charities for donation from our 2022 financial year were:


Sumatran Orangutan Society logo

Creating Nature's Corridors logo

BCT logo


Happy birthday to us

Unit 3 Compliance is 5 Years Old!

Happy birthday to us

Five years ago I checked in my badge at SmarDTV, turning up the next day to start disassembling the EMC test laboratory I’d worked so closely with for the previous 9 years and purchased with my redundancy pay out.

I had no customers and no concrete plan, but a lot of friends and ex-colleagues who helped me get set up and gave me my first jobs. Thank you all.

Now the “me” is a “we” with Caroline, Lawrence, and Louise having joined Unit 3 Compliance. I’m very proud to work with such a great bunch of people and to do work that matters for customers who care about their products.

Looking ahead to the next 5 years, our plans are to become the best non-accredited EMC and safety testing consultancy and laboratory in the UK (and to have fun whilst doing so).

Hopefully we can keep growing steadily, improve our test facilities, invest in some new equipment, expand our range of services, and bring in some new members to the team. We’ve got so many ideas!

Thanks for being along for the ride, we really appreciate the relationships we have with our customers, peers, and suppliers.




New Team Member @ Unit 3 Compliance

Unit 3 Compliance has officially doubled in size with the employment of our first team member. Caroline Pearson has joined us bringing with her over 20 years of test engineering experience.

She is already getting quickly up to speed with our test setups and procedures. Her arrival will mean out capacity for solving our customers’ EMC problems will increase significantly.

Welcome Caroline!

1% For The Planet – Donations FY 2019

As part of our membership of 1% For The Planet we’ve made donations for the last financial year to the following environmental charities. These organisations are doing important work to preserve wildlife and habitats in the UK and around the world.

Rohde & Schwarz “Demystifying EMC” 2020 @ Silverstone, UK

It’s that time of year again when one of the things I look forward to the most comes around. No, not Christmas! Where have you been?

Every year, Rohde & Schwarz UK organise their “Demystifying EMC” event, organising technical training on a variety of topics as well as a compact but well formed trade show. 2020 is my third year in a row as an attendee. These last two years, Unit 3 Compliance has had an exhibition stand and I’ve been privileged to give a technical presentation as part of the training available on the day.

This year the Rohde & Schwarz team outdid themselves with record attendance causing them to have to close the registrations for the event early.

Not surprisingly the Unit 3 Compliance stand was as busy as ever with visitors from a wide range of companies and backgrounds, many new faces and some familiar ones from last year stopping by to say ‘hi’.

We also had a demonstration of the effects of poor PCB layout and it’s effect on EMC emissions being picked up by one of our near field probe kits (which flew off the table like hot cakes)

The highlight of my day was getting to deliver another technical talk – amazingly they had me back after last year! – on the subject of ground and grounding for EMC.

Rather than a list of “do this, don’t do this” I really put a lot of background work into this talk, creating images for each slide to try and illustrate clearly some of the concepts I was trying to illustrate.

I spy, with my little eye, something beginning with ‘G’

It seemed to go down really well and I had a lot of positive feedback on the day. Thank you for that, it’s sometimes hard to know if you’ve hit the mark or not. People coming up to me afterwards and saying “you’ve put into words what I’ve been struggling to say for years” and “I’ve really learned something new” makes the many hours spent on preparing this talk well worthwhile.

Whilst a “here’s-a-picture-talk-about-the-picture” makes for a great in person talk, it works very poorly as reference material after the event with just a picture and no text to go with it. So I decided to record the presentation again and push it out on YouTube. Powerpoint has a really nifty record presentation tool that can then export to a video.

So if you didn’t make it to the talk, or want to refer to the talk again, then here’s a link to the video.

Enjoy, and I’ll see you next year.


James Pawson presenting at R&S EMC 2019

Rohde & Schwarz Demysifying EMC 2019

A fantastic day at the Rohde and Schwarz Demystifying EMC 2019 show down at Silverstone. It provided a chance to reconnect with some familiar faces and meet a whole load of new ones. R&S always put on a good event with varied content and lots of interest.

I was presenting a talk entitled “From Design To Pre-Compliance: Pitfalls and Pro Tips” which received lots of positive feedback from the attendees.

The weather was glorious with bullet blue skies and The Wing venue in the centre of the circuit makes for a great location.

The Unit 3 Compliance stand was very popular throughout the day with a queue of people stopping by to say hello and talk about pre-compliance testing.

The Pocket EMC Debug Probes flew off the table too.

Busy, and a Birthday

It has been a very busy few months at Unit 3 Compliance; it feels like the chamber turntable hasn’t stopped spinning. There has been a wide range of products through the door from prosthetics to video wall controllers, from high spec IoT products to motion sensors, from lighting power supplies to RF amplifiers. I really love the variety of work!

I’ve also had some safety assessment work to carry out on which is always interesting. Disassembling mains transformers to measure the creepage distances inside is fascinating, getting out the angle grinder to hack the laminations apart just adds to the fun.

There have also been a fair amount of design reviews and general consulting work in between. To be able to work with customers right at the start of the project is invaluable as it sets them on the right path without having to find problems further down the line.

I’ve found lots of interesting nuggets of EMC information during this process that I’m looking forward to sharing with you in some future blog posts once I get time to sit down and write them up.

I managed to escape down to Lincoln to speak at the Open Source Hardware User Group oshcamp18 meetup on the subject of EMC testing. The delegates came up with lots of good questions at the end and the audience participation (see below slide) of the talk went down well. Higher! Lower!

play your compliance cards right!

Good to see reconnect with some old contacts and make some new ones. The other talks were very interesting also, lots of good work going on in the open source hardware field at the moment.

Lastly, and it snuck past without me spotting it, Unit 3 Compliance had it’s first birthday. It’s been a whole year since I got the keys to the unit. In that time, and with lots of help, it has gone from this:

the empty unit

Via this:

To this:

And finally this:


Here’s to the next 20 years of compliance, I hope to see you on the way.



log periodic christmas tree

Have an anechoic Christmas!

The office tree is up!

Wishing all the customers, suppliers and friends of Unit 3 Compliance a very happy Christmas and a prosperous New Year.

“Oh Christmas tree, oh Christmas tree

Your branches grow,

Log periodically…”

log periodic christmas tree

Antenna Miniaturisation

An article just published on Nature Communications covers some interesting and quite exciting developments in antenna miniaturisation.



Electrical antennae rely on being resonant or partly resonant with the electromagnetic wave at the frequency of interest. For a dipole, a length of lambda / 4 is ideal but antennae can be designed with electrical lengths down to lambda / 10. The technique of antenna construction shown in this research means that effective antennae can be constructed that work at electrical lengths of nearly lambda / 600.

If you take a 950MHz (mobile phone low band frequencies) full dipole it will have a length = c / (f * 2) = 16cm. With this new technology, this antenna length could come down to sub 1cm distances. This decrease by over a factor of 10 is highly significant and with the application to sub-resonant antenna designs, further decreases in size could reasonably be expected.



The technology itself is very clever, sandwiching a layer of piezoelectric material (voltage to mechanical movement) with a layer of ferromagnetic material to form what the paper refers to as a “ME heterostructure” (I prefer sandwich… mmmm… sandwich). The magnetic part of an incident EM wave causes the ferromagnetic layer to change shape in response. In turn, this makes the bonded piezoelectric layer change shape, creating a voltage on the output terminals. The process of reception is now mechanical rather than electronic with the tuning of the antenna primarily performed by selecting the materials based on their mechanical properties, thereby tuning the mechanical resonant frequency.

Similarly, applying a voltage to the piezoelectric material will change its shape, causing the shape of the

It’s worth taking a step back to point out that you can perform a similar trick with a conventional antenna by increasing the dielectric constant of the surrounding material. This changes the speed of light within this medium which is dictated by the Velocity Factor (VF) = 1 / sqrt [Er] (where Er is the dielectric constant or relative permittivity). This is why placing your antenna closely coupled to a plastic enclosure can change the effective frequency. Two downsides that make this approach less useful for antenna miniaturisation:

  1. The range of dielectric constants of insulating materials. FR4 PCB material is typically around 4, silicon and alumina can be in the 11-12 region. Higher values for liquids or more exotic materials do exist.
  2. The square root term around the dielectric constant causing the reduction in VF to become less significant with increasing Er

The mechanical “stiffness” of the new antenna (analogous to dielectric constant) is suitably high that the resonant wavelength is much smaller in the materials used leading the the significantly smaller antennae producible using this technique.


CMOS Process

What is even more exciting is that these new antennae are produced using a CMOS process (detailed in the supplementary material).

This means that integration of the antenna and receiver could be integrated onto the same silicon die in future. Not only would this make things ridiculously compact but it would also allow the receiver circuitry to be placed electrically right next to the antenna which could reduce coupling of noise and improve sensitivity.

It also gives the scope, as mentioned in the paper, of being able to print arrays of antennae on the same die. This could be used to make compact phased arrays, wideband arrays or just the key antennae for different frequencies required for a mobile communications device.

IoT (the favourite industry buzzword at present) solutions will get smaller, cheaper and easier to integrate, perhaps leading to a further connected-ness revolution. The potential impact is fascinating.


Magnetic Coupling and the Near Field

Because these antenna operate on the magnetic component of the EM wave, it should make them more efficient when operating in the near field.

Original image can be found here.

The near field is the distance between antenna and source when the ratio of distance to wavelength is below the ratio of 1 / 2*pi (see above chart). In this region, the impedances of the magnetic and electric fields are not related by the impedance of free space (approx 377 ohms). The field from a magnetic dipole decays with the cube of the distance (not the square) so being able to place a small magnetically sensitive resonant antenna closer to the magnetic field source provides a new method for sensing small currents right next to the source.



The decrease in size could lead to problems in the capacity to handle higher transmit powers or currents. Having said that, the thermal coupling of the antenna to a solid material should be good meaning the thermal resistance of the antenna to ambient could be both quite low and controllable.

Magnetic materials have other characteristics such as saturation and hysterisis so it will be interesting to see how it handles large DC or low frequency AC magnetic fields caused by electrical power wiring. I wonder if this will mean it gets classified as a magnetically sensitive component and starts to fall under the remit of IEC 61000-4-8 testing for such things.

Having worked on designs involving high voltage differential piezoelectric transformers below, I know that they require careful mechanical handling as they will chip, crack and break if treated roughly (although, probably just as much as ferrite of the same dimensions). Conventional metallic structure antennae are generally quite robust or can be made so. I believe the small mass and the encapsulation of these antennae in a plastic or ceramic package could well solve many of these issues.

This also presents the possibility of mechanical interference to an electrical signal. I don’t have a handle on what sort of high frequency mechanical vibrations might exist in the real world and I can imagine their energy would be quite low at the really high frequencies with elasticity of materials starting to take over. I can imagine trying to debug an RF sensitivity issue with a stethoscope for a change!

The technology website Futurism speculates that these could form the basis of a brain-computer interface. Needless to say, the EMC immunity applications of such a technology, especially in our increasingly “EM-dense” environment would be of massive concern. Perhaps we will be seeing the imminent return of the tin-foil hat as a genuine reason for keeping the government out of your brain!

You can read the full article here.

Header image taken from the original article.