Milestones:Active Shielding of Superconducting Magnets, 1984-1989


Date Dedicated
Dedication #
Eynsham, Oxfordshire, United Kingdom
IEEE Regions
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United Kingdom and Ireland
Achievement date range


Active Shielding of Superconducting Magnets for MRI, 1984-1989


At this site, the first actively shielded superconducting magnets for diagnostic Magnetic Resonance Imaging (MRI) use were conceived, designed, and produced. Active shielding reduced the size, weight, and installed cost of MRI systems, allowing them to be more easily transported and advantageously located, thereby benefiting advanced medical diagnosis worldwide.

Street address(es) and GPS coordinates of the Milestone Plaque Sites

Siemens Magnet Technology, Wharf Road, Eynsham, Oxfordshire, United Kingdom. OX29 4BP.GPS coordinates: 51.777878, -1.363863, Siemens Magnet Technology, Wharf Road, Eynsham, Oxfordshire, United Kingdom. OX29 4BP.GPS coordinates: 51.777878, -1.363863

Details of the physical location of the plaque

It is intended to mount the plaque in the ground floor entrance hall of the site or on an external wall adjacent to the entrance.

How the plaque site is protected/secured

The site is a significant design and manufacturing location and is staffed on a 24/7 basis throughout the year. The site is in a semi-rural location so visiting will generally be by arrangement although the plaque will be seen by the significant number of industry and student visitors who come and go to the site on most days. Current contact is Simon Calvert the company's Head of Product Definition and Innovation and Chief Technology Officer; if the milestone is approved it is likely Siemens will appoint an administrator/coordinator for any visits specifically to see the Plaque.

Historical significance of the work

This proposed milestone concerns the development of practically realisable actively shielded superconducting magnets. This work has had huge significance by enabling the much more widespread adoption of MRI (Magnetic Resonance Imaging) by lowering overall system costs and allowing the installation of such machines without requiring hospitals to be built or re-built around them. This has significantly contributed to MRI becoming the imaging method preferred by clinicians and patients alike. MRI has revolutionised diagnosis and monitoring of many conditions and been of immense benefit to humanity (and even to the treatment of animals in certain cases). For a detailed description of MRI see:

The company now known as Siemens Magnet Technology has been a pioneer of the magnet technology that underpins MRI machines. The invention of the superconducting magnet (1961) and the development of a superconducting magnet large enough to allow a human body to be placed inside it (1980) were in themselves key enablers of this truly game changing medical technology. Whilst MR imaging is possible with a resistive magnet the resolution of the images is insufficient to be really useful. 1.5 and 3 Tesla magnets are now common and Siemens Magnet Systems have recently developed a 7T magnet which was runner up for the prestigious UK Royal Academy of Engineering MacRobert Award in 2016. An MRI machine based on a magnet of that size would be extremely difficult to transport, and costly and difficult to site without active shielding for the reasons set out in the section below. The original key developments have been recognised and commemorated in several ways including with a 'blue plaque' (although not an IEEE milestone plaque) at the site where they were carried out (the former Oxford Instruments site in Oxford UK); unfortunately this site now has no connection with the business and no engineering activity so a milestone plaque at that site would not get useful exposure.

A subsidiary (Oxford Magnet Technology) was formed in 1982 and a new site was built at Eynsham, Oxfordshire in 1984, Siemens was a key client and acquired first a 51% share and bought the remaining 49% of the JV in 2003 and the business became Siemens Magnet Technology. Active Shielding was developed at that site and this is considered to be the best location of a Milestone Plaque as it will not only commemorate this game changing technology but will also get exposure to engineers working in the field and students visiting the site giving maximum visibility both to the achievement and to the IEEE.

At the time of the development of Active Shielding the Company was known as Oxford Magnet Technology, this later became Siemens Magnet Systems. The patents are in the name 'Oxford Advanced Technology Ltd' which was the name of the OMT legal entity at that time.

MRI is now one of the fundamental diagnostic tools on which modern medicine depends. Active Shielding was a key enabler to MRI becoming so widespread and important, with annual sales/installations of such machines increasing from a few units a year to over a 1000 units a year from the Eynsham site today. Truly a technology that has benefited all mankind.

The key people involved in the development were:

· John Woodgate (OMT Managing Director) – deceased · David Hawksworth (OMT Engineering Director and later Managing Director) – deceased · John Bird (Magnet Engineer responsible) · Frank Davis (Technical Director)

Siemens Magnet Technology is believed to still be in contact with Frank Davis

Features that set this work apart from similar achievements

Early Superconducting magnets used heavy and expensive iron shielding to reduce the level of stray fields which have undesirable effects on other equipment (e.g. pacemakers) as detailed above.

Whilst there was some prior art in active shielding which is cited in the patents the earlier work did not produce techniques suitable for the high field strengths needed for NMR/MRI nor would it readily accommodate changes to the bore field strength which are sometimes required. The Oxford Advanced Technology work led to techniques which could be realised in production volumes and led to stable outcomes through the ranges required. As has been said this led to machines which were lighter, cheaper, easier to transport and more flexible in terms of possible location making MRI much more widely available, benefiting huge numbers of people.

Significant references

The US and European Patents are attached: US4587504, filed Nov 7th 1984, granted 6th May 1986 Media:US4587504.pdf and EP144171B, Filed 9th Nov 1984, granted 31 Jan 1990 Media:EP144171B1.pdf Patents are public documents.

Other supporting documents are: 00133510, IEEE TRANSACTIONS ON MAGNETICS, VOL. 27, NO. 2, MARCH 1991; A 2-TESLA ACTIVE SHIELD MAGNET FOR WHOLE BODY IMAGING AND SPECTROSCOPY 01065051, IEEE TRANSACTIONS ON MAGNETICS, VOL. MAG-23, NO. 2, MARCH 1987; CONSIDERATIONS IN THE DESIGN OF MRI MAGNETS WITH REDUCED STRAY FIELDS 01063856, IEEE TRANSACTIONS ON MAGNETICS, VOL. MAG-21, NO. 2, MARCH 1985; PRESENT STATUS OF MRI MAGNETS at OXFORD - useful in its description of earlier shields using Iron weighing 20T for a 1Tesla magnet 00402514, IEEE TRANSACTIONS ON APPLIED SUPERCONDUCTIVITY, VOL. 5, NO. 2, JUNE 1995: Trials and triumphs of superconductivity: The making of Oxford Instruments - useful background on the overall contribution of the Oxford Instruments/Siemens team up to that date. The copyright in all of these lies with the IEEE and they are normally subject to a charge - they will therefore be submitted by email.

Contemporary brochure on actively shielded magnets issues by Oxford in the mid 1980's Media:20180724192657.pdf

Slides from Siemens Magnet systems showing the position of Active Shielding within the timeline of Superconducting MRI Magnet developments and the growth in delivered volumes. The mid 1990's dip was a US market issue affecting all manufacturers Media:OMT developments and sales growth.pdf


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