Biographical Memoirs of Fellows of the Royal Society
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Peter John Lawrenson. 12 March 1933—27 October 2017

Michael J. Turner

Michael J. Turner

Active Transducer Research Ltd, Units 1–3, Rabbit Hill Business Park, Great North Road, Arkendale, North Yorkshire, HG5 0FF, UK

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    Born in Prescot, Lancashire, Peter Lawrenson rose from relatively humble origins to become a leading figure in the world of electrical motors and generators—first as an academic and latterly as a businessman. Noteworthy research throughout the 1960s quickly earned him a personal chair at the University of Leeds, and for a number of years he was head of department at the university's School of Electrical & Electronic Engineering. He is particularly remembered for pioneering the application of numerical methods to electromagnetic field problems, and for promoting and commercializing the switched reluctance motor, which—via the business, Switched Reluctance Drives Ltd, that he co-founded with research colleagues—was transformed from a laboratory curiosity to a commercially viable and highly efficient alternative to conventional electrical machines. A leading figure in the Institution of Electrical Engineers (IEE, latterly the IET), he also served with distinction as IEE president in 1992.

    Birth and early years

    Peter John Lawrenson was born in Prescot, a small town close to Liverpool but at the time within the county of Lancashire, England. His father, John Lawrenson, had done well at school and, perhaps as a result, did not follow his forefathers into the local coal mining industry, but instead became a mechanical engineering draughtsman at the town's then main employer, British Insulated Cables (BI). BI was later to merge with Callender's Cable & Construction Company to form the famous British Insulated Callender's Cables company (BICC).

    Peter's mother, Emily (née Houghton), met John Lawrenson at BI while working as a tracer in the drawing office. They married in 1922 and moved to Manchester for a short period when John took an engineering position with wire manufacturer and metal goods supplier Richard Johnson, Clapham & Morris Ltd (Anon. 2015, 2021). Emily returned to her parents’ home to have her first and only child, and Peter was born in Prescot on 12 March 1933 (figure 1).

    John Lawrenson returned to BI soon afterwards as assistant to the works engineer, and the family moved to a house of their own in Eccleston Park. Soon after returning to Prescot, however, John's health began to decline, and he died in 1949 from complications of asthma when Peter was only 16.

    One of seven children, Peter's mother Emily came from a large and close-knit family, and as a result Peter benefitted from many doting aunts and uncles. He formed close bonds with this extended family that were to last throughout his life, perhaps unsurprising given the early death of his father.

    Houghton family life centred around Emily's parents’ shop, which not only sold sweets and other sundry items, but also housed a small library. A frequent customer was the young (later well-known) comedian Ken Dodd, who lived in the nearby Liverpool suburb of Knotty Ash. Some 30 years later (as Peter's wife Shirley recalls), Peter's aunt attended one of Dodd's shows and he recognized her, remarking: ‘Hey, missus—I used to buy my sweets from you!’


    Peter studied at Prescot Grammar School, where he quickly shone academically, winning the end-of-year prize at least once and eventually becoming head boy. He also found time for diverse extracurricular activities and, remarkably, as a teenager (after his father's death) he even designed a house for his mother, which was later built in Warrington Road, Prescot.

    His first scientific pursuits outside the classroom were in the field of chemistry, and although Peter never shared with his children the full extent of his exploits as a junior rocket scientist (and would later shake his head in dismay at what he had done), he hinted at loud explosions, scorched hedges, singed grass and broken paving stones—including, on at least one occasion, near the local police station!

    Figure 1.

    Figure 1. Emily and John Lawrenson with young Peter (ca 1935).

    Peter also enjoyed sports, and from a young age played cricket; he fondly remembered his father arriving by bicycle to watch. He later represented his school in both cricket and athletics. Both he and his father were ardent fans of Everton Football Club, and would watch them play whenever they could.

    Peter made several life-long friends while at school, including Geoffrey Worrall and Gordon Lloyd, and together they became regular players on the grass courts of the Prescot Tennis Club at Parkside. One of Peter's notable traits, evident even in these early days, was the depth to which he engaged in any new activity or interest. ‘If a job is worth doing, it is worth doing well’, he would say. Tennis soon became the sport that dominated the boys’ summers, and in the early 1950s Peter and Geoff reached the semi-finals of the Lancashire Boys Doubles Tournament, only to be roundly beaten by a duo who subsequently played at Junior Wimbledon.

    Meanwhile, above the Houghton family sweetshop, card games became a further pastime, with contract bridge attracting competitive hands and heated debate. These early passions for bridge and tennis were retained by Peter throughout his adult life, and he continued to play both with skill and enthusiasm long into his retirement years.

    An able scholar, Peter excelled in mathematics but also shone in many other subjects, so that as his schooldays drew to a close in 1951, he still had no idea of what to pursue as a career. One of the school governors, an electrical engineer, suggested he apply for the Institution of Electrical Engineers (IEE) Duddell Scholarship, aimed at students from low-income families whose fathers were members. Peter did not strictly meet the latter criterion, but despite feeling intimidated—and incidentally smelling of fish from his Uncle Leslie's delivery van after the journey from Prescot to the IEE's London headquarters in Savoy Place—he was able to sway (as he later recalled) ‘the enormously important and serious looking individuals seated around a huge table’, winning a stipend of £150 per annum (Anon. 1951).

    So it was that Peter left Prescot in 1951 to study electrical engineering at the University of Manchester, once again being driven there by his proud Uncle Leslie (figure 2) in the fish van.

    Figure 2.

    Figure 2. From left: Uncle Leslie, Aunt Flo, Emily Lawrenson and Peter (ca 1950).

    University of Manchester—undergraduate studies, postgraduate research and engagement

    As at high school, university life provided plenty of scope for extracurricular fun, including cycling—Peter would later recall the hazards of riding a tandem without brakes—tennis and, of course, girls. It was through his tennis playing that he met his future wife, fellow Manchester student Shirley Hannah Foster, who was studying music. They drew each other as partners in a mixed doubles tournament, won the tournament and went out to celebrate; they never looked back.

    Shirley was the third child of Albert and Mildred Foster, who ran a business (Stenmor Ltd) in Macclesfield supplying offices with paper and stationery products. After graduation, Shirley went on to teach English and music at Manchester Central High School.

    After receiving his bachelor's degree, Peter remained at the University of Manchester and joined Professor Eric Laithwaite's research group, which was investigating linear induction motors. The textile industry—specifically cotton—was still of great commercial importance in Manchester, and for his master's degree Peter was tasked with developing a self-oscillating linear motor to propel a shuttle across a weaving loom. Characteristically, he rose to the challenge (1, 2)* but, although his linear motor was technically successful, he was frustrated to discover that it could not compete commercially with the incumbent mechanical drive system. Given the importance he would later ascribe to the commercial as well as technical viability of his work, it is clear that this early experience was not lost on Peter, as he later recalled in an interview published by the IEE in 1992, following his appointment as president (Dettmer 1992):

    Technically the project was successful, and we established a stable oscillation that was capable of maintaining a shuttle in motion. However, the shuttle drive mechanism used in commercial looms at that time weighed virtually nothing and cost a mere 17 shillings and sixpence, and I rapidly came to the conclusion that a linear motor could never compete with that. My experience with the shuttle drive was an early exposure to the need to assess both technical and commercial criteria.

    With help and encouragement from Shirley, Peter did, however, utilize material from his MSc thesis to win the 1956 Royal Society of Arts/Sunday Times Science in Industry essay competition (Anon. 1956). He used his prize money to buy Shirley an engagement ring, and they were married in April 1958 at the Parish Church of St Peter in Prestbury (figure 3).

    Figure 3.

    Figure 3. Peter and Shirley Lawrenson on their wedding day, 5 April 1958.

    Initially, Peter and Shirley lived in Didsbury before buying their own house in Sale Moor, where their first child, Mark, was born in December 1958. They continued to play tennis and would push Mark in his pram down to Brooklands Tennis club while they played. After Mark's arrival, Shirley taught English in evening classes at nearby Stretford Technical College.

    First employment—Metropolitan-Vickers

    Following the completion of his MSc in 1956, Peter joined Metropolitan-Vickers (a subsidiary of Associated Electrical Industries, AEI) in Trafford Park, Manchester (Anon. 2022), as an engineer in the Electrical Machines section, headed at the time by Willis Jackson FRS (later Sir Willis Jackson). Shirley recalls Peter cycling to work each day, covering a distance of about six miles each way between Sale Moor and Trafford Park. At ‘Met Vicks’ (as it was informally known) Peter was tasked with researching the so-called ‘stray losses’ of large electrical machines, that is, the energy losses (wasted as heat) not accounted for by basic calculations. It was at this point that his interest in electromagnetism really took hold. From the IEE's 1992 presidential interview, it is clear that his research at Metropolitan-Vickers was a key source of inspiration and motivation for his seminal book on the numerical solution of electromagnetic field problems (Dettmer 1992):

    One of the problems I was concerned with at the time was the short-circuit behaviour of the end windings of turbo-generators. Despite being some 6 inches by 1.5 inches cross-section, during a short circuit the windings would wave about like bits of string until finally they would fail. Clearly, we needed to know more about the forces acting on the windings, and I set about establishing a method that, pretty reliably, would allow these forces to be calculated.

    At this time this was viewed as a very difficult three-dimensional analytical problem. I took a numerical approach. I replaced the windings with an equivalent set of many straight elements as small or as large as was necessary to ensure accuracy, and then wrote down the general three-dimensional fields for each. That was really very easy. The application of numerical methods to general field problems was thought rather radical at this time and I came in for a fair amount of abuse. I remember important people at Savoy Place saying they wanted equations. My response was, what would you rather have; [sic] equations or the answer?

    Despite this mild controversy, the work was published in 1961 (5), and Peter's pragmatic numerical approach anticipated by many years the use of so-called ‘finite element’ methods, now universally employed for the computer solution of complex electromagnetic field (and many other mechanical, acoustical and thermal) engineering problems. The work was also the genesis of his seminal textbook, Analysis and computation of electric and magnetic field problems (6), co-authored with his colleague and friend Professor Ken Binns of the University of Liverpool. Although Peter was characteristically fastidious about the written word, throughout his career he nevertheless relied heavily on Shirley's skills in written English, and she recalls long nights spent proofreading the book. Completion of the manuscript was not, however, the end of their worries. Having finally sent the text to Pergamon Press in East Germany, the course of history took a turn: the Berlin Wall was erected, and the book was feared lost forever. Nothing was heard from the publishers for eight long months, after which time—to the authors’ immense relief—‘an immaculately type-set proof was returned’ (Dettmer 1992).

    Return to academia—the University of Leeds

    By the start of the 1960s, the future at Metropolitan-Vickers/AEI was looking increasingly uncertain, and Peter had already embarked on some part-time teaching, lecturing in field theory at Manchester College of Science and Technology. Having rather enjoyed this he decided to seek a permanent position in academia, and sent applications to the universities of Bristol, Manchester and Leeds. Impressed by Peter's work on field calculations and linear machines (15), and possibly also having seen a draft of his forthcoming book, Geoffrey Carter—then head of the Department of Electrical Engineering at Leeds—was instrumental in Peter's appointment as lecturer in 1961 (figure 4).

    Figure 4.

    Figure 4. Peter Lawrenson at work in the basement Machines Laboratory, University of Leeds. Photograph from the Lawrenson family collection; copyright unknown.

    The Department of Electrical Engineering at Leeds at that time had a young and enthusiastic team of researchers, as Peter Clarricoats (FRS 1990)—who joined the staff in 1963—later recalled (personal communication to Shirley Lawrenson, November 2017):

    Research on motors by Peter Lawrenson proceeded with great enthusiasm at a time when many research workers like myself [sic] concentrated their energies on topics stimulated by WW2. That Peter chose to work in this area that others in the engineering profession thought of as no practical significance demonstrates his determined and innovative mind.

    Although the 1960s was a decade of much hard work and further academic achievement, this did not stop Peter from living a full life outside the university, not least with the birth of three daughters, Ruth (b. 1960), Rachel (b. 1963) and Isobel (b. 1965). Showing his love of innovation and excellence (and a life-long interest in music), despite being short of money he purchased a pair of Lowther TP-1 loudspeakers, which were to adorn his living room for more than 50 years. He also continued to play tennis, was introduced to squash, and his love of sports cars was born. With some informal help from the University's Mechanical Engineering Workshop, he constructed a Lotus Elan from a kit, a car he kept for many years. Several more sports cars were to follow in later years, including a Ford Sierra Cosworth, a Spectre R42 and an Aston Martin. Night classes in jewellery and silversmithing—which Peter attended along with colleague Peter Child—provided still another diversion. As ever, Peter engaged in this with zeal, at one point even considering jewellery-making as an alternative to his academic career. One surviving example of his craft, still treasured by the Lawrenson family, is striking in that its design was clearly inspired by the contour map of an electrical or magnetic field.

    Reluctance motors

    Throughout the 1960s and early 1970s, Peter's publications show a growing interest in alternative forms of electric motor, specifically the ‘reluctance’ machine. These were already in limited use, notably in textile machinery where independently driven shafts needed to be synchronized not only in respect of speed but also their mechanical angle of rotation. This benefit aside, conventional wisdom was that reluctance motors were inherently inferior to conventional machines. Peter's own words from the 1992 IEE interview (Dettmer 1992) are again illuminating:

    At the time I moved to Leeds, it was widely held that the prospects for major innovation in electric drives were remote. Most electrical machines have a magnetic field produced in one part […] and electric currents in the other part. It's the magnetic field acting on the electric currents that makes the thing go round, and it had been obvious to everybody that you couldn't do better than that. But I had the belief from a field viewpoint that you could do better, not by exploiting forces on the currents, but by using the forces created on the iron, just as is done in a solenoid. I'd first been drawn to this idea from work on the linear motor, where two distinct forces are in operation: the action of the field on the current producing the propulsive motion, and the attractive force due to the action of the field on the secondary iron. The force on the iron [the so-called ‘reluctance force’] is about ten times greater than the force on the current, and this suggested to me there was a great potential in machines based on magnetic principles, leading directly to my work on reluctance motors.

    This inspiration—combined with Peter's willingness to challenge established beliefs—led to a considerable body of research work and the publication of many academic papers throughout the 1960s, initially focusing on alternating current synchronous reluctance motors.

    Peter's research was rewarded by rapid promotion at Leeds—to reader in 1965 and two years later to a personal chair, allowing him to adopt the title of professor at the remarkably young age of 33. His inaugural lecture (7), delivered in February 1969, unsurprisingly centred around his new form of alternating current reluctance motor—though not yet the switched reluctance machine, for which he would ultimately be most celebrated.

    Academic leadership and management

    Thanks in no small part to Peter's input, Leeds became a notable centre of expertise in electrical machines, especially reluctance motors and the closely related stepping motor. Numerous further publications throughout the 1970s thus bore Peter's name, although—as his primary role gradually changed to one of academic management—more of the ‘hands-on’ research was necessarily carried out by colleagues Michael Stephenson and Austin Hughes, together with research students including Paul Acarnley, Philip Blenkinsop and Jasmin Corda.

    A significant block of papers—co-authored with, among others, T. J. E. (Tim) Miller—was concerned with the use of superconductors in electrical machines, a salient topic at the time, while later papers show a growing focus on stepping motor work, much of this being led by Austin Hughes (figure 5), who had joined the Leeds machines group in 1971. Coincidentally, both Austin and Tim met Peter while he was a consultant on superconducting motors at International Research and Development in Newcastle; he later claimed that it was best to have the people who asked awkward questions on his own team!

    Figure 5.

    Figure 5. Leeds International Stepping Motor Conference and Exhibition, 24 July 1974. Left to right: Dr Austin Hughes; Professor Peter Lawrenson; Mr J. Blommaert (CRIF, Belgium); Mr Syd Spracklan (engineering vice president, Novatronics, Canada). Photograph courtesy of the University of Leeds.

    Meanwhile, Peter's interest in the problems of computing and solving electromagnetic field problems clearly continued, as evidenced by his published papers and in an updated (1973) second edition of Analysis and computation of electric and magnetic field problems, again co-authored with Ken Binns.

    Another contemporary university photograph (figure 6) is striking in that it shows Peter in a more casual pose, in contrast to the more formal and serious—perhaps even austere—image he would sometimes project in later professional settings. This still-youthful portrait hints at a less public, more flamboyant and cosmopolitan side of Peter's character: the man who had a passion for colourful silk ties and stylish suits, who loved modern art, good food and wine, and who had truly catholic tastes in music. These ranged from classical (he introduced the author to Henryk Górecki's Symphony of sorrowful songs) through to a remarkably diverse range of popular and rock music, not least an impressive collection of albums by Bob Dylan.

    Figure 6.

    Figure 6. Peter Lawrenson, ca 1974; University of Leeds staff photograph. Photograph courtesy of the University of Leeds.

    Peter's sense of humour was recalled (Harris et al. 2017) by his close friend Martyn Harris. They first met at AEI/Metropolitan Vickers, after which–like Peter–Martyn left industry for academia, initially researching electrical machines at University College, London. Martyn was to become a life-long friend, with joint family holidays a rich source of anecdotes. It was during one such that Martyn recalled he and Peter attempting to purchase an electric lawnmower for use at the Lawrenson's holiday cottage. Having been challenged about the improbably large power rating claimed for its small motor, the salesman (not knowing the men's professional background) unwisely insisted `Ah, but these are American watts, sir!' Needless to say, on that particular occasion, a sale was not concluded, and the two academics returned to the cottage in fits of giggles. Peter's daughter Isobel also recalls the two men sharing an idiosyncratic sense of humour, and says they were even known to hold covert competitions to see which one could make the other laugh during important meetings!

    Following Professor Carter's retirement in 1974, Peter took over as head of department for the next 10 years, working to expand the School of Electrical and Electronic Engineering and in particular establishing strengths in the new and rapidly growing areas of computing and digital processing. Peter was also instrumental in extending the university's links with industry. Initiated by the head technician, C. S. (Sidney) Petch, the department had been running an electronics trade show for some years, and the Leeds Electronic Exhibition was already established as a regular summer fixture of the UK industry's calendar, attracting senior industry figures as well as a diverse range of electronic component and instrument manufacturers. Leetronex, as it later became known, continued and expanded under Peter's tenure, latterly in collaboration with the flamboyant exhibition organizer and publicist Evan Steadman. Peter also collaborated with Steadman in devising the UK's annual Drives, Motors and Controls technical conference and exhibition, showcasing the rapidly developing technologies, markets and industrial importance of electronically controlled motors and associated motion control equipment. The inaugural event in 1982 was appropriately held at Leeds (12) (Anon. 1982) and the conference continues to this day, now an international event, under the aegis of the IET as ‘Power Electronics, Machines and Drives’ (PEMD).

    Peter remained head of department at Leeds until 1984 (being succeeded by microwave semiconductor specialist Dr Michael J. Howes), but retained his Chair and continued to work for the university until 1991. In its own obituary of Peter (Anon. 2017), the University of Leeds noted that:

    From 1974 to 1984—the period of the ‘Great Debate’ about the purpose of public education and of unsettling change for institutions and academics—Peter served as a dynamic and pragmatic Head of Department, retiring from the University in 1991, although he continued to be active and influential in the wider engineering field.

    During his 30 years’ affiliation with the university, Peter was also active on many committees at Leeds, and he expended considerable energy in encouraging the university to become more accessible to the public. This was exemplified by his support for public open days, as originally proposed by press officer Ian Morrison. Peter also persuaded the university to improve its organization and to adopt a more dynamic and, as he saw it, realistic relationship with the changing society outside.

    Origins of the switched reluctance (SR) motor

    What is now clearly recognizable as a crude SR motor was first demonstrated in Aberdeen as early as 1842 by Robert Davidson (Anderson 2018; Reid n.d.). Unfortunately, his ideas were too far ahead of their time; viable storage batteries had yet to be developed, as had generators adequate to power his machine—and electronic diodes (which would have eliminated troublesome sparking and reduced the associated power losses) would not be available until the early twentieth century. Davidson failed to secure financial backing, and his ideas were eclipsed by later developments in direct current (DC) and alternating current (AC) motors, so that, for well over a century, his machine remained little more than a scientific curiosity.

    Figure 7.

    Figure 7. Replica of a 1967 prototype switched reluctance motor.

    However, in his 1992 President's Address to the IEE (17), Peter recalled that, by 1965, his own work on AC reluctance motors had already resulted in a viable commercial product, presumably (based on correspondence from his own archive) working in collaboration with major local manufacturer Brook Crompton of Huddersfield. He also noted that, although this product offered better performance than had hitherto been possible in this type of motor, ‘the commercial attraction lay […] in their synchronous properties rather than in dramatic levels of performance. The original question persisted […]’. That ‘question’ boiled down to whether further improvements in motor performance—notably in power output, efficiency and/or controllability—could be made by utilizing the reluctance forces to the full (17):

    A final-year undergraduate project in 1967 demonstrated that they could, together with the additional possibility of continuous control (including reversal) of speed—as would be confirmed later, fully equivalent to the separately-excited DC machine.

    This seminal prototype motor (figure 7) was initially described as a ‘variable reluctance’ motor to distinguish it from the conventional AC reluctance motor. Peter subsequently coined the term ‘switched reluctance’—hence ‘SR’—motor, arguably a better description, and one that distinguished it from the closely related stepper motor (also classed as a variable reluctance motor).

    The 1967 prototype SR motor is very simple, comprising just one electrical circuit or ‘phase’ with a mechanical commutator for switching the stator winding current. Later, this commutation function would be implemented electronically, but the design illustrated here is noteworthy in allowing simple but nonetheless effective mechanical control of the rotor angles at which the stator current is switched on and off. By sliding the two brush contacts in an axial direction, the switch-on and switch-off points—technically, the ‘commutation angles’—could be independently controlled, a key feature of SR motor control methods even today.

    Work on the SR motor seems to have slowed at this point, there being little further mention of it in published papers until 1977, when the department's Annual Review refers to a research project on ‘Switched Reluctance Motors’, which were

    ‘being investigated [as] an attractive alternative to conventional variable-speed drives. Industrial support has provided funds to extend earlier research to drives for battery electric vehicles’ (8).

    This ground-breaking work was led by Michael Stephenson, who deserves much of the credit for developing a proper theoretical understanding of the SR motor and a methodology for its design. Michael had himself studied electrical engineering at Leeds in 1958, and (like Peter) had joined the department staff in 1961 at Geoffrey Carter's invitation, after completing a graduate apprenticeship at British Thomson Houston in Rugby. While Peter certainly provided much of the impetus for the subsequent commercialization of the SR machine, it was Michael who laid the necessary technical foundations in terms of its electromagnetic design.

    SR machine research with the University of Nottingham

    The early 1970s saw rapid and unprecedented increases in the price of oil, resulting in a renewed interest in electrically powered road vehicles (EVs). At the time, a serious limitation to the commercialization of EVs was the cost of the incumbent brushed DC motor and its requisite electronic controller. Together with the battery, these were far more expensive than a mass-produced internal combustion engine. Nevertheless, Chloride Technical Ltd, then a major UK-based manufacturer of batteries, believed that battery-electric road vehicles had serious commercial potential, which, if realized, would also lead to growth in the market for rechargeable batteries (which of course they hoped to supply).

    Chloride therefore initially approached the University of Nottingham—a leading centre for power electronics research—and asked them to explore the feasibility of replacing the then-standard but expensive and mechanically complex DC motor with a lower-cost brushless machine—perhaps an induction motor. The Chloride enquiry initially landed on the desks of Nottingham electronics and control researcher William F. (Bill) Ray, and power electronics expert Rex Davis, who identified a further motor possibility: Peter Lawrenson's SR motor.

    A specific advantage of the SR motor was that, although (like any variable-speed brushless motor) it required high-power electronics for control of its winding currents, it could be operated from pulses of direct current. Consequently, electronic control of the SR machine could, if desired, be achieved using just one semiconductor switch per phase, rather than the two needed by a conventional AC motor. As power electronic components were then relatively expensive, this facilitated significant cost savings in the overall drive system. Furthermore, the motor's inherent characteristics—high starting torque and the ability (with appropriate control) to deliver its full rated power across a wide range of speeds—were well-matched to the needs of an electric vehicle. A small motor was thus built at Nottingham to establish the basic validity of the concept.

    Chloride Technical was impressed by Nottingham's exploratory work, and agreed to fund the design and construction of a prototype vehicle powered by an SR motor. However, although they had extensive electronic controls know-how, neither Rex Davis nor Bill Ray was an electrical machine specialist. The obvious solution, however, was not far away at Leeds, where Peter's group had already developed a significant understanding of the SR motor. In 1977 a research contract was agreed, sponsored by Chloride and bringing together the two universities and four academic consultants—that is, Peter Lawrenson and Michael Stephenson at Leeds, Bill Ray and Rex Davis at Nottingham. Two research associates were also recruited, Norman Fulton at Leeds and Roy Blake at Nottingham. Peter, as the senior academic, became head of the team. Two initial patent applications were made, one related to the power electronic circuits and one to the excitation of the motor.

    At the IET memorial event held in Peter's honour in 2017, Bill Ray recalled that Peter led the initial commercial and patent negotiations with characteristic acumen and dexterity (Harris et al. 2017):

    Intellectual property rights are always a tricky subject where Universities are concerned. Chloride was only interested in the rights to exploit SR technology for battery powered applications. The consultants were keen to retain the rights to exploit the technology for other applications, and the Universities eventually agreed to this in return for royalties. It took many months, but Peter eventually clinched a very good deal, without which the subsequent commercialisation of the SR machine would not really have been possible.

    The prototype vehicle (based on a converted Bedford van) was a success, and the work resulted in some seminal papers (9, 10), but commercial interest in electric vehicles had waned as oil prices fell, and Chloride—now itself in financial difficulties—brought the project to a closein 1984.

    By this time, however, the research team had acquired a substantial knowledge base and various key design tools had been developed, not least a suite of computer programs for designing the motor and accurately predicting its performance. Such optimization tools were essential if the new drive systems were to be commercially viable—the technology not only had to function in a research context, but also had to be attractive in terms of cost and performance when compared with the incumbent mature motor technologies.

    Commercialization of the SR motor—Switched ReluctanceDrives Ltd

    Based on their extensive research efforts, Peter and his colleagues saw that the SR machine had significant advantages that could benefit a wide range of motor applications—not only electric vehicles—and were keen to exploit this potential commercially (13). Having secured acceptable intellectual property agreements with their respective universities, in 1980 Peter, Michael, Bill and Rex jointly established a limited company, Switched Reluctance Drives Ltd (SRDL), with the aim of commercializing the SR motor and its control.

    From the outset, SRDL's business model was to license SR technology and know-how to existing motor manufacturers and to businesses using electric motors in their products (the so-called “original equipment manufacturers”, or OEMs). This approach was chosen because enormous financial investment would otherwise have been needed to make motors on an industrial scale for even a single market application. The high capital costs involved, together with the sheer diversity of applications they foresaw, effectively ruled out establishing a manufacturing facility from scratch.

    The breakthrough first licence agreement was struck with Lowestoft manufacturer TASC Drives Ltd, whose existing core product—an adjustable eddy-current coupling—was obsolescent, not least owing to its very poor energy efficiency. The first commercial SR product was therefore the TASC ‘Oulton’ general-purpose industrial motor and matching variable-speed controller, rated at 10 kW (figure 8). Larger and smaller variants soon followed, and the Oulton range of SR motors and controls quickly became known for their high energy efficiency and accurate, responsive speed control (14) (Anon. 1983). They were notably popular in the water industry, where variable-speed pumping could eliminate the crude and inefficient bypass valves that had hitherto been used for flow and pressure control. Even at 1980s' energy prices, this resulted in considerable energy cost savings—an early example of ‘green’ engineering.

    Figure 8.

    Figure 8. The first commercial switched reluctance motor and matching controller.

    Interest from other motor manufacturers and users quickly followed, with enquiries from Prestolite (machine tools), Mawdsley's (large industrial drives), Anderson Strathclyde (mining applications) and GEC Traction (for rail and tram propulsion).

    Over the ensuing years, only a small proportion of the many enquiries and associated customer-funded projects resulted in long-term products and associated lucrative technology licences; such is the nature of speculative research and development. However, the successful demonstration and testing of prototype motors in a diverse range of applications was highly valuable to the company, not only in terms of the resulting credibility and publicity, but also in the additional technical experience and knowledge gained by the team throughout their development. Potential licensees were expected to contribute to the engineering development costs, and the resulting income was an important source of revenue.

    SRDL was initially legally registered to Peter's home address in Spen Lane, Leeds, with the four directors working as consultants from their respective university departments as and when time permitted. By 1984, however, the two former research assistants (Dr Roy Blake and Dr Norman Fulton) had been appointed as full-time employees, and the business was in a sufficiently secure position to justify the leasing of office and laboratory space in Springfield House, an attractive and then new ‘technology park’ development on the edge of the university campus at Leeds. Springfield House was conveniently close to the Department of Electrical & Electronic Engineering, where both Peter and Michael still had full-time jobs, and furthermore allowed easy access to the University's computing centre, mechanical workshop and other research facilities. This was the heyday of mainframe computing—the small desktop machines then available (such as the Acorn BBC Micro and Sinclair's ZX Spectrum) were inadequate for serious scientific purposes—and, for its motor design work, SRDL initially paid for use of the University's computing resources.

    In 1985, in recognition of their pioneering work on the novel and energy-efficient SR technology, the four directors jointly received the prestigious Esso Energy Award from the Royal Society (figure 9).

    Figure 9.

    Figure 9. Presentation of the Esso Energy Award at the Royal Society, 1985, with (among others) SRDL's other three founding directors. Back row, left to right: Dr J. M. (Michael) Stephenson; Mr Rex Davis; Professor Peter Lawrenson; Mr Bill Ray; Professor T. H. R. Skyrme FRS; Professor J. G. Thompson FRS. Front row, left to right: Professor J. B. Gurdon FRS; Dr D. Kalderon; Dr A. Klug FRS; Professor J. Argyris; Sir Jack Lewis FRS; Professor R. Penrose FRS. Photograph © Godfrey Argent Studio.

    Expansion of SRDL

    SRDL continued to grow steadily throughout the 1980s and early 1990s, adding to both its technical and administrative staff and greatly extending its portfolio of customers, designs and applications experience. The latter included domestic appliances, power tools, coal mining equipment, industrial machinery, aerospace, automotive auxiliaries and notably—in a successful return to a topic of Peter's Manchester research—textile machinery. Motor power levels ranged from tens of watts—a motor that would fit in the palm of one hand—to enormous machines weighing many tonnes and rated at over a megawatt: a diverse range indeed.

    Additional business units within Springfield House were eagerly occupied as and when they became vacant, providing much-needed extra laboratory and office space, while external investment from the venture capital group 3i (Investors in Industry) provided welcome additional funding and financial security. Some of the key applications and customer relationships established in this period would endure for many years, with a few continuing long after the business was sold by the original four directors. The associated technology licences, while not as numerous or lucrative as the company would have liked or indeed foresaw in its 1985 business plan (15), nevertheless generated long-lasting royalty streams for the company.

    Technology acceptance

    For all its accolades and apparent advantages, the novel SR motor was not always warmly received or accepted by other academics and electrical machine research groups around the world, and Peter sometimes had an uphill struggle to secure a fair hearing for the company's ideas and technology. This was especially the case in the USA, where, despite publishing some seminal results (e.g. (16)), he experienced considerable scepticism and even, on a few occasions, a degree of antipathy—echoes of which persist, remarkably, to this day (Bose 2022).

    To be fair, given the rather conservative nature of the electric motor industry at the time, where most of the incumbent technologies were already mature, Peter's proud and sometimes bold claims for the SR motor (even when fully valid) could provoke scepticism from academic rivals and even in potential customers. Furthermore, the SR motor's advantages also came with something of an ‘Achilles heel’ in the form of acoustical noise and vibration, an unfortunate and largely inherent feature of its harmonic-rich time-varying radial forces and torque. Acoustical noise mitigation—which was critical in some applications—consumed a considerable amount of the company's engineering attention and effort over many years, and although significant improvements were certainly made, acoustical noise and vibration remain features of the SR motor that have, arguably, not yet been fully resolved. In particular, attempts to improve acoustical noise, whether through design of the motor or by electronic control means, tended to impair other aspects of performance (notably energy efficiency, size, weight and/or cost).

    Nevertheless, the SR motor's unique properties—especially its inherent robustness and simplicity, high starting torque, low material cost and high energy efficiency across a wide range of operating conditions—steadily earned it a valid position in the industry's portfolio of recognized and accepted variable-speed motor technologies.

    Sale of the SR business—and retirement

    SRDL's full-time staff now numbered some 20 people, all of whose livelihoods depended on a continuous stream of incoming work—a responsibility that (as his widow Shirley recalls) Peter felt very keenly. At the same time, the number of existing client companies and projects—with all their associated requirements, expectations and inevitable difficulties—had also grown substantially. With SRDL's turnover for 1990 approaching £1 million, it became clear to Peter that the hitherto part-time involvement of the academic directors was no longer sufficient, and in 1991 he took the doubtless difficult decision, after 30 years in academia, to resign his chair at the University of Leeds and to devote the final years of his career to SRDL as full-time managing director. This he did with his usual energy and enthusiasm, while—remarkably—at the same time maintaining his significant involvement with the IEE—later to become the IET. The IEE had, meanwhile, awarded him its prestigious Faraday Medal in 1990 (figure 10) ‘for notable scientific/industrial achievement, for services rendered to the advancement of engineering/technology and/or for lifetime achievement in science, engineering or technology’. Peter was also to serve (as the university later noted in its own obituary of Peter: Anon. 2017) ‘with great distinction’ as IEE president 1992–1993.

    Figure 10.

    Figure 10. Receiving the IEE Faraday Medal from IEE president Dr James Smith (right) in 1990. Photograph from the Lawrenson family collection; copyright unknown.

    SRDL's success—especially during this era of rapid growth in variable-speed, electronically controlled motor technologies and applications—had attracted the attention of several major players in the electric motor industry, and as the four original directors were at least approaching retirement age, the prospect of selling the company inevitably had its attractions. Consequently, several potential business ‘suitors’ discreetly visited Springfield House in the early 1990s and, after protracted negotiations, SRDL was eventually sold to US-based multinational corporation Emerson Electric in July 1994 (Anon. 1994). Peter stood down as managing director (handing over to long-standing Emerson employee Bill Schnyder, who was despatched to Leeds from their St Louis headquarters), but continued to serve in an advisory capacity until his final retirement in 1997.

    SRDL under Emerson

    Emerson initially invested heavily in SRDL, and quickly applied for a remarkable number of patents to protect its newly acquired intellectual property. It is worth commenting that the sheer cost of filing patents, together with the difficulty—as a small, independent business—of policing them even if granted, had hitherto discouraged SRDL from widespread patenting of its inventions.

    Limited office and laboratory space at Springfield House in Leeds had also become an issue, and in 1996 Emerson financed a much-needed move to larger and newly refurbished premises in Harrogate, some 15 miles to the north. By a curious but apt coincidence, the buildings they acquired—East Park House, on Otley Road—had previously served as the northern research laboratories of the UK Central Electricity Generating Board, where one of the first modern, if crude, battery-electric passenger cars (the Electra) had been developed in the early 1970s.

    For many years following its acquisition by Emerson, SRDL's business model continued along much the same lines as before, that is, providing switched reluctance machine know-how, product designs, prototypes and research facilities, but now with the various divisions of Emerson as its primary customers. Notably, Emerson group companies were required to become licensees if they wanted to use the new SR technology, an arrangement conceived to safeguard the financial interests of SRDL's existing paid-up licensees (for whom Emerson was a potential competitor) by maintaining a somewhat level commercial ‘playing field’. This business model, necessary though it was, unfortunately also acted as something of a disincentive to the various Emerson motor companies, which were generally responsible for their own profitability and were also largely technically autonomous. The requirement to pay royalties, whilst simultaneously becoming somewhat technically reliant on an external business unit, was thus not universally welcomed. On the other hand, from SRDL's perspective the arrangement allowed the company to continue seeking and supporting the business of external clients wherever these did not conflict with the interests of its new parent organization. This benefit was to prove important later, when Emerson's enthusiasm for SR technology rather waned after a (perhaps inevitable) initial post-acquisition ‘honeymoon period’.

    Another commercial issue—relevant to many potential customers, not just Emerson—was that the SR machine utilized a quite different internal construction from conventional electric motors. This meant that existing designs of lamination (the thin sheets of steel from which almost all electric motors are built) could not be used, and potential SR motor manufacturers were thus faced with the substantial capital cost of new tooling, both for stamping the laminations and for winding the assembled motor cores. This was less of a concern where a completely new or bespoke motor would have been needed in any case (for example, application-specific designs to be made in large quantities), but was significant in the general-purpose market where motor manufacturers were accustomed to re-using standardized ‘platform’ laminations and repurposing existing production lines.

    Emerson and SRDL nevertheless collaborated in developing a very successful SR motor for use in domestic appliances (then a major market for Emerson in North America). Launched in 1997, this was used for several years by Maytag Corporation in their Neptune horizontal axis washing machine, with cumulative sales amounting to several million units before being replaced by an electronically controlled (but otherwise conventional) AC induction motor.

    Meanwhile, the competitive landscape was far from static. In SRDL's early days, electronic control of the incumbent AC induction motor had been expensive and of relatively poor performance. By the mid 1990s, however, this was no longer the case, with digital micro-computer techniques facilitating high-quality variable-speed control of industry-standard AC motors. Despite lacking some of the SR machine's advantages, these motors were already in mass production, and were technically familiar, and electronic control could often be added with little modification to the basic motor design. Electronic component manufacturers were quick to respond with wide ranges of low-cost parts, many of which were unfortunately not suited to the SR motor, so rather placing it at a commercial disadvantage. This was especially significant in mass-market applications where integration and standardization of the electronics was key to keeping costs low. At the other end of the market, applications requiring high power or high precision could now use conventional industrial AC motors controlled by off-the-shelf electronic inverters. These background developments meant that SRDL was increasingly forced to focus on applications where its technology had specific, often niche, advantages over conventional motors.

    In 1999 the company nevertheless expanded into small-scale manufacturing of SR motors and power electronic controls, utilizing the significant floorspace that was available in Harrogate. This not only allowed the company to support its licensees with low-volume series production (while simultaneously generating much-needed additional income), but also greatly enhanced its prototyping capabilities thanks to the on-site availability of motor and controls manufacturing facilities, and the skilled labour needed to operate them.

    SRDL post-script

    The Harrogate-based SRDL business unit became a wholly owned subsidiary of Nidec Corporation of Japan in 2010, when Emerson sold its entire US-based motor manufacturing interests (to which, for management purposes, SRDL had been attached). The company was later transferred to the US- and China-based Nidec Drive Systems division in 2016, and sadly was much reduced in size and scope in 2019 when Nidec ended all manufacturing at the Harrogate site and largely disbanded the hitherto comprehensive engineering team. While—at the time of writing—the residual business unit focuses primarily on other motor technologies (notably brushless permanent magnet machines), Nidec continues to supply small quantities of SR motors and inverters, albeit only for customer-specific industrial and off-road vehicle applications.

    Switched reluctance motors continue to be widely used, however, in textile weaving machinery—an application first developed with great success by SRDL in the early 1990s—and for diverse but niche industrial applications, including high-speed industrial pumps and propulsion of large off-road vehicles and rail service locomotives. The technology continues to attract interest worldwide thanks to its combination of high energy efficiency, good dynamic performance (with characteristics well-suited to electric vehicle use) and a complete absence of permanent magnets. The latter often require rare-earth minerals, with associated high costs, geopolitical supply problems, environmental pollution during mining and refining and difficulties of effective recycling.

    Notable research is still taking place at the universities of Sheffield and Newcastle in the UK, with the latter having recently spun out a new business, Advanced Electric Machines Ltd, focused (as was SRDL in its early days) on vehicle propulsion (Advanced Electric Machines n.d.). Peter's dream of the SR machine seeing widespread use in electric vehicles—a return to the technology's roots, so to speak—may yet be fulfilled.


    After his retirement in 1997, Peter continued to keep himself busy. He and Shirley had moved from their long-standing Leeds home in Spen Lane, Far Headingley, to an attractive Arts and Crafts house in Linton, near Collingham, a few miles north of Leeds. Here he spent many hours tending their substantial gardens, being especially fond of sweet peas. He continued to play tennis, bridge and chess, became president of the Linton Antiques Society, and was chairman of the Steering Group for the Collingham with Linton Parish Plan & Village Design Statement. He also enjoyed walking with Shirley and had many enjoyable overseas trips, especially to Italy with daughter Ruth and son-in-law Giorgio Bisotti.

    Meanwhile, American recognition of Peter's lifetime achievements in the field of electric motors and drives finally came from the Institution of Electrical and Electronic Engineers (IEEE), which awarded him its prestigious Edison medal in 2005 ‘for outstanding contributions to the field of electrical machines, most notably the development and commercialization of switched reluctance drives’ (ETHW 2022). In making this award, the IEEE added Peter's name to a truly illustrious collection of scientists, engineers and inventors—a list that notably includes electrical machine pioneers such as Ernst Alexanderson, Nikola Tesla and George Westinghouse.

    In reviewing Peter's substantial personal archive, still in possession of the Lawrenson family, one cannot help but be struck by the extent to which he retained a keen interest in the SR machine and the company he founded, long after his own retirement. His continued passion for the technology and for his life's work is amply evidenced through copies of published papers, journal articles and press releases that extend well into the Nidec era.

    Illness and death

    In September 2011 Peter was diagnosed with Alzheimer's disease. Unsurprisingly, he found the symptoms of this illness enormously frustrating, but his strength of character and perseverance continued undaunted (figure 11). Shirley devoted her time to care for him, encouraging and assisting him to continue the activities he enjoyed, visiting friends, travelling overseas and pottering around the garden. He continued to enjoy playing chess with his grandson, Andrew, who would patiently remind him of the rules—one of the few people to beat him.

    Figure 11.

    Figure 11. Peter and Shirley Lawrenson, pictured in 2015.

    Eventually he required more care at home than could be provided by Shirley, and in September 2016 he moved into a specialist dementia care home, where he enjoyed daily visits from family and friends. He passed away peacefully in the early hours of 27 October 2017 with his family by his side. A private cremation was followed by two separate memorial services: the first was held at the IET, Savoy Place, London, on 8 December 2017, and the second on 21 December at St Oswald's Church, Collingham, where his ashes are interred.

    Honours and accolades

    Peter was a fellow of the Institution of Electrical Engineers (now IET) and the Institute of Electrical and Electronics Engineers. His research, innovation and services to electrical engineering were formally recognized by his election to fellowship of the Royal Academy of Engineering in 1980, and to the Royal Society in 1982.

    Other significant honours and distinctions included his delivery of the Faraday Anniversary Lecture (‘Faraday's induction: birthright and legacy’) in 1981 (11); the James Alfred Ewing Medal in 1983 (an award of the Institution of Civil Engineers, on the joint nomination of the ICE president and the President of the Royal Society); the Esso Energy Gold Medal of the Royal Society (as already noted) in 1985; and the IEE Faraday Medal in 1990. He served as president of the IEE from 1992 to 1993, and in 2005 was awarded the IEEE Edison Medal for his outstanding contributions to the field of electrical machines. In the same year, the Royal Academy of Engineering presented him with the Sir Frank Whittle Medal for engineering innovations in energy—only the fifth time that the medal had been bestowed.


    My sincere thanks to the Lawrenson family—especially Peter's widow Shirley and their daughter Isobel—for providing many insights and personal recollections, and for allowing me prolonged and unfettered access to Peter's extensive archive. I must also thank Shirley for her continued skills in proofreading, for keeping me on the straight and narrow path of historical accuracy in regard of Peter's family and home life, and not least for her perpetual kindness and hospitality. The late Bill Ray's recollections—which he fortunately shared with me in written form ahead of the IET memorial reception in Peter's honour—were invaluable in recalling the research that led to the formation of SRDL, and in telling the story of the company's early days. My thanks also to Qona Wright and her colleagues at the library of the University of Leeds for generous assistance in locating, reviewing and obtaining permission to use photographs from the university's collection.

    The photographs of figures 1 to 4 and figures 9 to 11 are from the Lawrenson family's private collection. Figures 5 and 6 are reproduced courtesy of the library at the University of Leeds. Figure 7 was taken by the author (of a prototype motor in possession of the Lawrenson family), and figure 8 was scanned from an original TASC Oulton brochure in the author's collection.

    The frontispiece portrait photograph is © 1992, The Institution of Engineering and Technology.

    Author profile

    Inline Graphic

    Michael Turner first studied at the University of Leeds during Peter's tenure as head of department, receiving an honours degree in electrical and electronic engineering in 1985. Having begun his engineering career with the BBC in London, he soon returned to Leeds, where he joined SRDL in 1987 as a junior development engineer. Mike worked with Peter Lawrenson for many years, eventually becoming technical director for both SRDL and a sister manufacturing business, SR Drives Manufacturing Ltd. His 32 years with the company (latterly under US/Japanese owners Emerson Electric and Nidec Corporation) provided Mike with a rich and continually evolving learning experience across a diverse range of engineering disciplines, as well as significant exposure to global research, business operations and management. Throughout this time, however, he also retained a keen hobby interest in audio electronics and music, and a growing realization that his hard-won experience of motor design, feedback control systems and dynamics was readily transferrable to loudspeakers led to a part-time PhD in voice coil motor control, being supervised at Leeds by Peter's former colleagues Dr David Wilson and Dr Austin Hughes. Since 2019 Mike has operated his own consulting and technology licensing business, Active Transducer Research Ltd (ATRL), which, in addition to his active loudspeaker intellectual property, also offers his consulting expertise in electronics, motor control, system design and analysis. He has published a number of papers concerned with motor control, power electronics and audio, presented at many international conferences and internal company events and is the author of 22 patents in related fields. He is a UK chartered engineer, a member of the IET, IEEE and Audio Engineering Society, and received Emerson Electric's Prolific Inventor award in 2001.


    * Numbers in this form refer to the bibliography at the end of the text.

    Published by the Royal Society. All rights reserved.


    References to other authors

    The following publications are those referred to directly in the text. A full bibliography is available as electronic supplementary material at


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