IEEE Circuits and Systems Magazine - Q4 2022 - 63

the Rockefeller Foundation, and who suggested the subject
of this research " [3]. During his visit he prepared
an article for the Journal of Applied Physics, which he
only submitted after his return to Göttingen in November
1931 [5]. Also following Brune's results, in 1932 he
submitted the article " The Poisson integral for functions
with positive real part " to the Bulletin of the American
Mathematical Society [6]. In 1931, Cauer introduced a
very important step in circuit theory by proposing the
use of " approximations in the Chebyshev sense " . In his
memoir, Sidney Darlington described it thus: " At Bell
Laboratories, a number of us first learned about some
of Cauer's canonical circuits and his Chebyshev approximations
at a conference on Cauer's proposed sale
of some of his patents. It was an important event in my
professional life " [10]. When AT&T offered Cauer $5,000
for the US and Canadian patent rights, he accepted.
Back in Germany he was able to hire a personal research
assistant, Ernst Glowatzki, who helped him with
the filter calculations until 1935. At the end of his visit,
he worked for Wired Radio, Inc. for three months before
returning to Germany by ship in August 1931.
Cauer's first book " Siebschaltungen " was completed
during his visit to MIT and published after his return to
Germany in 1931 [4]. Then, he tried to find a university
position where he hoped for a change to obtain one of
the free professor positions of Jewish mathematicians.
Although Cauer published other well-regarded papers
with mathematical and electrotechnical contributions
to filter design, it became clear by 1934 at the latest that
he would probably not be able to get a professorship
because of his Jewish origins. So, he applied for positions
in electrical engineering companies such as Telefunken,
Siemens and Philips and aircraft manufacturers
such as Henschel, Donnier, and Junkers. Finally, in
July 1935, Cauer was employed by the Fieseler aircraft
company in Kassel, but in 1936 he moved again to Mix
& Genest Berlin, where he became head of the laboratory.
In order to be able to give lectures there, Cauer had
to pass the habilitation requirement at TH Berlin. The
common method to get a professorship at a German university
is the habilitation (teaching thesis). It consists
of a postdoctoral thesis, the habilitation treatise, and a
public lecture. From 1938 to 1942 he gave lectures about
" Mathematical foundations of the theory of elasticity " ,
" Theory of transient processes " , and " Theory of linear
AC circuits " . In 1939, he was appointed extraordinary
professor at the TH Berlin.
Even before he left Göttingen, he published some results
about his analog computer, but soon he presented
the first publications in the technical journal of Mix &
Genest. In 1939, based on the pioneering work of Edward
Norton, Cauer developed a new type of filter design
FOURTH QUARTER 2022
method, which is now called insertion loss theory, simultaneously
and independently with Hans Piloty and
Sidney Darlington. However, since 1934 Cauer wanted to
write a book about analysis and design of AC circuits and
finally in 1940 before he signed a contract by a book publisher.
In 1941 the first volume of his famous monograph
" Theorie der linearen Wechselstromschaltungen " was
published [7]. It was the last publication during his lifetime,
because Cauer was not able to publish any results
in the last two years of the war. For although he collected
the material for the second volume, the manuscript was
twice destroyed. A first version of Cauer's second volume
was destroyed in March 1943 during an Allied bombing
attack on Mix & Genest. Cauer prepared another version
of this book that was lost when he died shortly before
the end of World War II in April 22, 1945, when Soviet
troops took his Berlin district of Marienfelde. He had
only recently left his family, who were in relative safety in
Witzenhausen near Göttingen. He had only received temporary
permission to leave Berlin and therefore wanted
to return to Berlin out of a sense of duty.
Thanks to the energy of Cauer's wife, Karoline Cauer,
and the kind editorial help of E. Glowatzki, G. E. Knausenberger,
W. Klein, and F. Pelz, some papers were published
posthumously. A revised and expanded version
of Volume 1 of Cauer's book appeared in 1954, and using
Cauer's estate and parts of Cauer's second volume that
had remained with colleagues, Glowatzki collected material
for a second volume, which appeared in 1960 [9].
Already in 1958 these both volumes together with a lot
of further material were collected to a volume " Synthesis
of Linear Communication Networks " by W. Klein, and
F. Pelz as well as G. E. Knausenberger and J. N. Warfield
[8]. In the closing remarks of this book, Karoline Cauer
wrote: " Cauer's work was then internationally recognized
as pioneering. He had opened an important discipline
of electrical engineering to exact mathematical
treatment " . One may envisage from these words some
of the difficulties he had to meet. For the electrical engineers
he used too much mathematics; for the mathematicians
he used too much electrical engineering. " Faced
by such criticisms, Cauer once laughingly pointed at the
efforts as he was burdened with because of his work in
two such specialized fields " [8].
References
[1] W. Cauer, " Die Verwirklichung von Wechselstromwiderständen
vorgeschriebener Frequenzabhängigkeit, " AEÜ Int. J. Electron. Commun.,
vol. 17, no. 4, pp. 355-388, 1926.
[2] W. Cauer, " Untersuchungen über ein Problem, das drei positiv definite
quadratische Formen mit Streckenkomplex in Beziehung setzt, "
Mathematische Annalen, vol. 105, pp. 86-132, Dec. 1931.
[3] O. Brune, " Synthesis of a finite two-terminal network whose drivingpoint
impedance is a prescribed function of frequency, " MIT J. Math.
Phys., vol. 10, pp. 191-236, Apr. 1931.
(continued on page 72)
IEEE CIRCUITS AND SYSTEMS MAGAZINE
63
https://peoplepill.com/people/hans-piloty https://en.wikipedia.org/wiki/Sidney_Darlington https://en.wikipedia.org/wiki/Edward_Lawry_Norton https://en.wikipedia.org/wiki/Edward_Lawry_Norton
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