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Signal Generators

Betsy Ancker-Johnson began a uniquely diverse and illustrious career in physics, engineering and public service just after World War II. Credited with a variety of inventions and achievements including the development of a type of high-frequency signal generator in the 1960s, she serves as one of the United States’ most distinguished role models for women as part of a generation that helped to change perspectives on gender roles and aptitudes in scientific fields.

Born on April 29,1927, Ancker-Johnson was inspired by her mother, a homemaker, who encouraged her to wholeheartedly pursue whatever was most interesting to her. She chose physics, attending Wellesley College where she earned a bachelor’s degree in 1949, then she moved to Germany to attend the University of Tuebingen where she completed her Ph.D. in physics in 1953.

She married Hal Johnson in 1958 and the couple had four children. Meanwhile she maintained a very active and fruitful career that began first with a position at the University of California, Berkeley, where she was a lecturer from 1953 to 1954; she moved on to the Inter-Varsity Christian Fellowship in Chicago from 1954 to 1956; she then became a Senior Research Physicist with the Microwave Physics Laboratory at Sylvania Electric Products in Palo Alto, California from 1956 to 1958. During these years she developed a specialization in plasma and published a number of important research papers related to the field.

Ancker-Johnson has described plasma as a fourth state of matter after liquids, solids and gases. Among her observations related to plasma studies were the occurrence of “pinching,” as well as the phenomenon of microwave emission from an electron-hole plasma — initiated only by the application of an external electric field. Her work in this area lead to subsequent findings that solid-state plasmas can serve as microwave sources of radiation.

During the 1960s, Ancker-Johnson worked for the David Sarnoff Research Center at RCA, as well as for the Plasma Physics Laboratory at the Boeing Science Research Laboratories in Seattle, and then as an Affiliate Professor of Electrical Engineering at the University of Washington from 1961 to 1973. Also during this time, she served as visiting scientist at Bell Laboratories, as well as supervisor in the division of Solid State and Plasma Electronics at the Boeing Corporation.

It was while working with Boeing that she developed her most famous invention — a type of signal generator based on her finding that if a low-density plasma is established in a piece of semiconductor material in the presence of a high-intensity electric field and low-intensity parallel magnetic field, very high frequency signals — well into the gigacycle range — may be generated.

Ancker-Johnson found that if a plasma can be generated such that the density of plasma varies from one portion of the semi-conductor material to another, a relatively high intensity electric field may be applied without the occurrence of impact ionization. Normally, impact ionization phenomena prevent the formation of low density plasma required for this invention to work effectively. The necessary gradation in plasma density can be created in numerous ways, including using semiconductor materials with either a gradient in relative purities, surface finishes, cross sectional area, or by applying appropriate electromagnetic radiation.

Ancker-Johnson was issued U.S. Patent #3,287,659 for “Signal Generators Using Semiconductor Material in Magnetic and Electric Fields” on Nov. 22, 1966. She has at least six other patents in this area.

With this achievement behind her, in 1973, Ancker-Johnson became the first female Presidential appointee in the U.S. Department of Commerce when she took on the role of Assistant Secretary for Science and Technology. She served until 1977 during the Nixon/Ford administration. From 1977 to 1979 she served as Associate Laboratory Director, Physics Research, at the Argonne National Laboratory in Argonne, Illinois. From there she moved on to General Motors where she was named Vice President of General Motors’ Environmental Activity Staff in 1979. This marked the first time a woman was named to the position of vice president in the U.S. auto industry.

Over the course of her career, Ancker-Johnson has written more than seventy scientific papers and has received a variety of honors and awards including membership in the American Association for the Advancement of Science as well as the Institute of Electrical and Electronic Engineers. In 1975, she was the fourth woman elected to the National Academy of Engineering (Lillian Gilbreth was the first, in 1965). She retired from General Motors in 1992. As of 1988 she has served as pro-bono Director of the World Environment Center.

[January 2005]