Brendan Scaife

Brendan Kevin Patrick Scaife FTCD, MRIA, Boyle Laureate (/skeɪf/; born 19 May 1928), is an Irish academic engineer and physicist who carried out pioneering work on the theory of dielectrics. Scaife founded the Dielectrics Group in Trinity College Dublin where he is Fellow Emeritus and formerly Professor of Electromagnetism, and previously to that a professor of engineering science.

Scaife showed that in a linear system the decay function is directly proportional to the autocorrelation function of the corresponding fluctuating macroscopic variable, and proved how the spectral density of the dipole moment fluctuations of a dielectric body could be calculated from the frequency dependence of the complex permittivity, ${\displaystyle \epsilon (\omega )=\epsilon '(\omega )-i\epsilon ''(\omega )}$. It was independent of Ryogo Kubo who in 1957 developed the corresponding theory for magnetic materials. The work was published prior to the work of Robert Cole in 1965 which is often cited.

Scaife was born in London on 19 May 1928 and just after World War II he began his undergraduate studies in the Department of Electrical Engineering at Queen Mary College, University of London; he graduated in 1949. At Queen Mary College there was a high-voltage laboratory run by Hans Tropper, whose lectures on electromagnetic theory inspired Scaife. After graduation, he began research into the properties of insulating materials under Tropper's direction. Scaife's doctoral research broke new ground in the study of dielectrics.

Scaife was the first scientist to successfully measure the complex permittivity of a number of polar liquids such as eugenol, glycerol and water as a function of pressure up to 12 kbar. This is published in a research note in Proc. Phys. Soc. B, 68 (1955) 790. Up to that time, Chan and Danforth working in Bridgman's laboratory in the US, had measured essentially the equilibrium relative permittivity ε(ω) of a number of liquids. At the time the experimental facilities in this area of research were severely limited. Commercial bridges for measuring complex permittivity were not available. A three terminal transformer coupled ratio arm bridge based on Blumlein's invention prior to the War had been constructed at Queen Mary by an Indian student S. Sharan for his PhD work. This bridge was applied successfully to measurements of samples subjected to high pressures. After completing this work and a brief period of employment with GEC in Wembley, he returned with his Irish parents to Ireland where he remained for the rest of his career in spite of many offers from abroad.

Scaife joined the Dublin Institute for Advanced Studies in 1954. Here Prof. Erwin Schrödinger was still a Senior Professor as was Cornelius Lanczos. The work of these two leading theoretical physicists of the 20th century was a source of great inspiration to him and helped in shaping his future work. In 1961 he joined the School of Engineering at Trinity College.

His interest in the theory of dielectrics led to a collaboration with Herbert Fröhlich at the University of Liverpool, where he was a regular visitor in the 1950s and 1960s. He developed a lifelong friendship with Fröhlich and the members of his research group. Scaife sought to apply the work of Callen and Welton (1951) on the Fluctuation-dissipation theorem to Frohlich's work on dipole moment fluctuations in dielectric bodies. This work on the theory of dielectrics culminated in a long report in 1959 published by the Electrical Research Association (now ERA Technology Ltd) on "Dispersion and fluctuation in linear systems with particular reference to dielectrics". In this he pointed out that, in a linear system, the decay function was directly proportional to the autocorrelation function of the corresponding fluctuating macroscopic variable. He showed how the spectral density of the dipole moment fluctuations of a dielectric body could be calculated from the frequency dependence of the complex permittivity ε(ω) = ε'(ω) – iε"(ω). This work was later published in Progress in Dielectrics, 1963. It was independent of Ryogo Kubo who in 1957 developed the corresponding theory for magnetic materials. The work was published prior to the work of Robert Cole in 1965 which is often cited.

The theory of the equilibrium relative permittivity ${\displaystyle \epsilon (\omega )}$ of dipolar substances had been developed by Kirkwood (1939) and Fröhlich (1948), who built on the pioneering work of Debye (1913) and Onsager (1936). It was hoped that the results of his 1959 report could be used to generalise the work of Onsager, Kirkwood and Fröhlich and to obtain a theory for the frequency dependence of the complex permittivity ${\displaystyle \epsilon (\omega )=\epsilon '(\omega )-i\epsilon ''(\omega )}$. The first step was to clarify the concept of the reaction field introduced by Onsager. Once this had been done it was possible to see how a generalisation of Onsager's equation for ${\displaystyle \epsilon (0)}$ to the frequency-dependent case would be obtained. Such an equation was published in a short note in 1964 in the Proceedings of the Physical Society of London 84, 616. The justification of this equation had first appeared in an Electrical Research report, which Scaife published in 1965. A more extended version was given in Complex Permittivity published in 1971.

In the work published up to 1965, inertial effects had not been fully taken into account. An early attempt to remedy this deficiency was made by Rocard in 1933. A major advance was made by Sack (1953,1957) and Gross (1955). Sack's work was based on the Fokker Planck equation governing the temporal evolution of the orientational distribution for molecules. In an attempt to clarify the physical aspects of the problem, Scaife derived Sack's results by starting from the stochastic Langevin equation (1908) of molecular rotational brownian motion.