Electromagnetic interference is something we all experience from time to time.  

From a hiss on the phone to the fuzzy lines on an analogue TV during a thunderstorm, EMI (as it is known) gets everywhere.  

When it comes to the sensitive electrical components on military jets, this interference - which is created by the electromagnetic signals manmade or from naturally occurring sources - can be more than just annoying.  

“Modern aircraft use sensors that send signals to the control systems that are vital to the safety and functionality of the aircraft," says Mark Johnson, EMI business lead at Oxley Group, in Ulverston. 

"These signals from the sensors are protected by the filtering diverting away high frequency interference, ensuring the data is clear and accurate. The effect of not having adequate filtering varies from a poor display in the cockpit, right down to some systems shutting down. It can be quite serious. 

"It's very important that some of these sensors are not just working but they're working perfectly all the time. No-one wants a malfunction when they’re travelling at 600 miles an hour. 

“Typical applications are the radio, the radar, the guidance, the missile release. Anywhere where you press a button and you want something to happen. You have to make sure the signal from pressing the button gets right to the device without any interference.” 

Oxley has been manufacturing and developing EMI filters since it was first founded in 1942 by Freddy Oxley, who made the components for the RAF during World War Two. 

Today, as well as military and commercial aircraft - including the Airbus A320, the world’s highest selling airliner - Oxley’s EMI filters are in use on everything from oil platforms to trains, rifles and land-based vehicles. 

“Wherever there’s a signal that needs to be protected they can be put to use,” says Mark. 

In many cases Oxley will have to make customised parts for specific applications, meeting demanding space, weight and shock constraints, working with high power requirements or developing a bespoke connector or interface. 

The process of designing and making an EMI filter is complex. Around 20 stages are involved in the manufacturing process. They are then subjected to rigorous testing to ensure they meet the necessary standards.  

Oxley manages all of this end to end from the Ulverston site. Manufacturing takes place by hand, as well as with automation where machine precision is required.  

“Some operations are automated but there are also some skills which you just cannot automate,” says Mark.  

Precision technical ceramics play a key part in filtering out interference and Oxley has a dedicated inhouse ceramics facility.  

The team design and manufacture ceramic planar arrays which form part of the filter, working to exacting tolerances required by customers. 

"When you put the ceramic in the furnace it loses about 44 per cent of its volume, it shrinks differently in each direction. We have to take all that into account,” says Mark. 

“Some of our processes are toleranced to microns. You can’t see the tolerances we're working to by eye. 

"The assembly process has lots of variants but for the ceramic we have one process to which we rigidly adhere to ensure that we get consistency and reliability. It’s very specialist, skillful work.” 

"The whole process is all about making sure that the parts come out perfectly," says Jayne Moorby, head of marketing at Oxley. 

"It's about managing the manufacture and handling of the ceramics to make sure that we're not getting cracks and chips in them and we check every single individual product at numerous stages.” 

The challenges of producing EMI filters have seen many manufacturers outsource production overseas and Oxley is one of the few remaining companies which makes them in the UK.  

Around 25 people work on producing them at Oxley, each specialising in different parts of the process.  

“When Freddy founded the business in the 40s, one of the things he believed in was that if you had a full end to end provision yourself, you could be the master of your own destiny," says Jayne.  

"We do everything end to end here from design, prototype, metalwork, assembly, the ceramic manufacture and all of the testing. There are only a very few ancillary services that we can't do in-house, which enables us to have excellent quality control and traceability for all our products. 

“EMI filters play such a vital role and they really are everywhere, but most people don’t even appreciate they exist and that so many of them are made here in Cumbria.”