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Foil Electret Microphone
In the 1960s, a pair of Bell Labs scientists, James Edward
West and Gerhard M. Sessler, worked together to produce the
foil electret microphone. This type of microphone remains
one of the most affordable and commonly used microphones today,
with nearly 90 percent of all microphones made currently built
based on principles developed by the duo.
West was born on February 10, 1931 in Prince Edward County,
Virginia. He attended Temple University, completing his B.S.
degree in physics in 1957, and began working for the Acoustics
Research Department at Bell Labs in Murray Hill, New Jersey,
where he had participated in internships as a college student.
An acoustical scientist, he specialized in electroacoustics,
physical and architectural acoustics.
Sessler was born on February 15, 1931 in Rosenfeld, Germany.
He studied physics at the University of Freiburg, and later
at the Universities of Munich and Goettingen. He completed
his Ph.D. at Goettingen in 1959. Shortly thereafter he moved
to the United States to begin working for Bell Labs.
In 1960, the men were charged with an assignment to create
a new technology for making highly sensitive, durable and
compact microphones that would be inexpensive to manufacture.
Microphones, which convert sound waves into electrical voltages,
were first developed in the mid-19th century. The first was
a telephone transmitter invented by Emile Berliner in 1876.
In the early 1960s, condenser microphones were the standard
in telephony, but these were expensive and required a rather
large battery source. Commonly used in the recording industry,
they were impractical for widespread use in applications such
as telephones or toys.
West and Sessler pioneered the design of electret transducers
— they knew that an electret, which employed an inexpensive,
thin, plastic film (they used Teflon), could, after being
exposed to a strong electrical field, retain its electrical
polarization without requiring a power source. According to
West’s description, “the film is drawn taut like
the head of a drum and is suspended just above a metal surface.
As you talk into the microphone, pressure fluctuations in
the air distort the film. Charges in the metal surface experience
fluctuating forces as the polarized electret moves above it.
As a result of these forces, a very small current flows from
the metal surface through a wire that touches it.”
The electret microphone was inexpensive and could be made
in extremely small sizes to be used in such devices as hearing
aids, telephones, camcorders and tape recorders. Its design
was finalized in 1962, and by 1968, it had gone into widescale
production. It quickly found broad use in telecommunications,
recording and acoustic measuring equipment worldwide.
In 1999, West and Sessler were inducted into the National
Inventors Hall of Fame for their invention of the “Electroacoustic
Transducer/Electret Microphone” (Patent Number 3,118,022).
Sessler stayed on at Bell Labs until 1975 when he returned
to Germany to become professor of electroacoustics at the
University of Darmstadt. There in the 1980s, he developed
the first condenser microphones based on silicon micromachining.
He holds over 100 U.S. and foreign patents. Sessler’s
honors include the George R. Stibitz Trophy and the Helmholtz
Medal, the highest award of the German Acoustical Society.
He is also a Fellow of the IEEE.
West left Bell Labs in 2001 as a retired Distinguished Member
of Technical Staff and Bell Labs Fellow. His numerous distinctions
include Fellowship in the IEEE and membership in the National
Academy of Engineering, National Patent Law Association, the
Electrochemical Society of America, the Acoustical Society
of America and the National Society of Black Engineers. In
1997, he was named president-elect of the Acoustical Society
of America (ASA).
West has more than 40 U.S. and over 100 foreign patents
and has authored or contributed to more than 100 technical
papers and several books on acoustics, solid-state physics
and materials science. He is especially active in programs
designed to inspire minorities and women to enter fields in
science, technology and engineering. As of 2003, he has served
as a research professor at the Whiting School of Engineering
at Johns Hopkins University in Baltimore. He was named Divisional
Diversity Council of the Whiting School in the fall of that