"> Tangle Tamers Electrical Engineers Ltd

Magnetic Fields and Shielding

"Thanks to the hard work of Rupert and his team, our cages once again well exceed specification, and we would heartily recommend him to anyone needing work, especially with power or signal faults, on their MRI systems and installations."

Dr William Hallet
Head of Clinical Development Imaging Physics
GlaxoSmithKline Clinical Imaging Centre

We offer:

-Low frequency and DC magnetic field surveys below 10 kHz

-On site surveys and investigation of magnetic field issues

-Specification, design and validation services for magnetic screening and shielding

-Identification and resolution of earthing and bonding problems affecting the performance of Faraday cages

-Testing and evaluation of LF and DC magnetic screens, shields and Faraday cages

Locations include:

-Medical Imaging

-Neuroscience facilities

-Research labs and production environments

-Electron microscopes, spectroscopes and lithography systems

- Complex buildings for media

- Sensitive instrumentation and measurement

Measurement and screening of magnetic field sources:

-Cables and switchgear



-Large magnets

-Geomagnetic field swing from moving steel 

-Electric transportation such as trams and trains

We work with leading electromagnetic shielding manufacturers to develop methods and materials for screening specialist equipment.

We have developed techniques for generation and measurement of DC and low frequency magnetic fields enabling us to de-bug and validate screened rooms rapidly.

Our capabilities allow us to measure in the lab, in the field and adapt to all of our clients needs.

University of Cambridge
Materials Science and Metallurgy (MSM)
New building for materials research group

Tangle Tamers carried out initial field surveys to establish background levels of DC and low frequency magnetic fields, combined with earthing and bonding checks on the building design.

We found that various cables and the UPS systems caused high fields at some intended electron microscope column centres. These had to be reduced by fitting screening at the sources. Design recommendations also included replacing all the BMS power supplies in the microscopy suites with toroidal transformers.

Field attenuation was measured at many points in the screened room for the FEI Titan, validating the room's effectiveness.  

We carried out a field quietness survey for all the microscope rooms. This used load bank networks to create worst case real and reactive electrical loading conditions, simulating the predicted future maximum loads expected once the building became operational.

Global EMC
Low Frequency Magnetic Field Measurements
400kV National Grid cables and substation

A low frequency magnetic field survey for Global EMC on a set of National Grid underground 400kV cables and a 400kV substation. These measurements formed the basis for designs of screening a  property development against "electro-smog".  

GlaxoSmithKline (GSK)
Clinical Imaging Centre
Faraday cage earth faults

GSK had problems with multiple earth paths on the Faraday cages of 2 MRI rooms. They were getting poor image quality from the scanner installed in one of the rooms.  The other unoccupied MRI room had been half dismantled to try to find fortuitous earth paths.

We injected test currents into the cages and scanner earthing systems and tracked these currents around the cages using their fields. We were able to find fortuitous earth points to within ~20cm non-invasively. Small easily-repaired holes in the stud walls allowed the shorts to be removed and remedied.

Various barrier joints in the services and quench pipes had been badly insulated. Using large custom made current clamps we were easily able to identify and remedy these faulty insulated joints.  

Global EMC 
Attenuation Performance Measurements
Faraday cages made from a range of materials

Global EMC had become concerned about an "urban myth" indicating that Aluminium could be a better material for building LF and DC Faraday cages. Global built prototype screened boxes from a variety of materials and we carried out a range of attenuation measurements on these prototypes. 

The detailed results belong to Global, but we can say without a doubt that, at low frequencies and DC, the plain Aluminium prototype performed worst out of all materials tested.