Page 8 - Spring 2009

Fig 6. Photograph of Jim West, Jim Flanagan, and Gerhard Sessler at the launch of Apollo 17 on December 7, 1972. They were recording the acoustic signal from the launch using a large electret sensor (approximately 3 inches in diameter) that was capable of recording to very low frequencies. (Source: Bell Labs Archive)
Canaveral, Florida is about 950 miles (nearly 1800 km), and the acoustic signal from the Saturn V was detectable at low fre- quencies where the excess absorption was apparently low enough. The time delay between the launch and the signals at Murray Hill was just over 1.2 hours. An interesting historical note here is that Jim and Gerhard were asked not to publish this finding since a similar method was used to confirm atmospheric nuclear explosions. In the photo, Jim and Gerhard were attempting to confirm their measurements at the source, but condensation on the electrometers resulted in not being able to get data on the last of the Apollo launches.
Gerhard Sessler left Bell Labs in 1975 and headed to the Technische Hochschule of Darmstadt (now the University of Darmstadt) in Germany. The reasons for his move were interesting. First, he felt that Bell Labs was a place where experience was not valued as highly as at a university. Second, he also saw the beginning of the pendulum swing where the word “relevance” was introduced when reviewing research projects. At Darmstadt, Sessler continued to explore acoustic transducers and played a pivotal role in the research and development of silicon-based microphone systems. When asked what inspired him to move into the silicon microphone, Sessler responded “it was in the air.” Having a good sense of smell apparently is a good attribute for a researcher. Sessler fortunately happened to have an academic
to how the electret was ignored cannot be overlooked.
As one can see, there is a strong historical thread that binds the invention of the microphone in 1876 to today’s MEMS silicon microphones. Gerhard Sessler and Jim West played key roles in the invention of the current ubiquitous electret and the future silicon MEMs microphones for con-
sumer microphone applications.
Stata and micro-electro-mechanical-systems (MEMS)
After graduating from the Massachusetts Institute of Technology (MIT) in 1957 Ray Stata pursued his ambition to create a company that would be a place for creative engineers to develop innovative electronic components. In 1959, he had a chance meeting in Harvard Square with Matthew Lorber, a former MIT classmate. They started a company called Solid State Instruments which they sold to Kollmorgen Corporation soon thereafter. Mr. Stata became a vice presi- dent of marketing with Kollmorgen’s Inland Controls Division. With the nest egg from the sale of Solid State Instruments and the experience at Kollmorgen, Stata and Lorber founded Analog Devices Inc. (ADI) in January 1965. Their first product was a general-purpose operational ampli- fier—a hockey-puck sized module used in test and measure- ment equipment. The focus from the very beginning was on high performance operational amplifiers that delivered real value to their customers (see Figs. 7-8).
Analog Devices continued to grow. In 1969, with annual sales in excess of $8.7M, the company went public generating the cash it needed to become an integrated circuit (IC) man- ufacturer. In parallel with other product innovations, the acquisition of Pastoriza Electronics began what would even- tually become Analog Devices’ domination of the analog-to- digital and digital-to-analog converter marketplace.
Throughout these early years Ray Stata wanted to create an engineering-driven technology company where engineers could focus on product performance. With this focus in the core areas of operational amplifiers, analog to digital and dig- ital to analog converters and digital signal processors (DSPs) Stata created a set of products with very broad usage in the audio and acoustics world today.
Since founding ADI, Ray Stata has continuously fostered a strong sense of “entrepreneurship” in the company. New ideas are encouraged and many are given space and funding
colleague and friend who was head of the silicon fabrication facility at Darmstadt. The link to silicon bulk machining was made and Sessler and his student Dietmar Hohm produced the first working silicon condenser microphone devices
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An interesting sideline here is that Bell Labs was also working on its own silicon microphone. However this effort dissolved without much success after the initial devices showed poor acoustic per- formance due to a diaphragm that was too stiff, (even after extensive doping in an attempt to lower the bending stiff- ness). Bell Labs also was an early innovator in using Micro- Electro-Mechanical Systems (MEMS) and actually experi- mented in MEMS microphones, but these devices remained laboratory experiments since there was no interest in the company to produce actual devices for the market. Parallels
based on bulk machining of silicon.
Condenser Microphones 7