Edmund Melson Clarke, Creator of Model Checking, Dies at 75

IEEE also mourns the loss of F.C. Kohli, India’s ‘Father of IT Industry,’ and others

7 min read
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Edmund Melson Clarke

Model-checking creator

Fellow, 75; died on 22 December

Clarke was a computer-science pioneer who helped develop model checking, an automated method for finding design errors in computer hardware and software. Intel, Microsoft, and other companies use the method to verify designs for integrated circuits, computer networks, and software.

He died from COVID-19 complications.

Clarke initially studied mathematics and received a bachelor’s degree in the discipline in 1967 from the University of Virginia, in Charlottesville, and a master’s degree in 1968 from Duke University, in Durham, N.C. But when he was a doctoral student at Cornell, he changed his field of study to computer science. He conducted his thesis research under the guidance of Robert L. Constable, a pioneer in making connections between mathematical logic and computing.

After graduating in 1976, Clarke joined Duke as a computer science professor. In 1978 he began teaching computer science at Harvard. While there, Clarke and his doctoral student E. Allen Emerson conducted research on methods that could be used to effectively verify how a system performs without errors. In 1981 they published a paper on model checking, “Design and Synthesis of Synchronization Skeletons Using Branching Time Temporal Logic,” in Logics of Programs.

In 1995 Clarke led a team that tested the method on an IEEE standard for interconnecting computer components. They discovered flaws in the standard’s design—which spurred the tech industry to use model checking on its systems.

Clarke, along with Emerson and computer scientist Joseph Sifakis, received the 2007 Association for Computing MachineryA.M. Turing Award.

In 1982 Clarke joined Carnegie Mellon, where he worked as a professor of computer science and electrical engineering. He was named an emeritus professor in 2015.

He served on the editorial board of IEEE Transactions on Software Engineering.

If you’ve had a family member who was an IEEE member pass away due to complications from COVID-19 and would like an obituary published by The Institute, contact the editors: institute@ieee.org.

Joseph R. Asik

Research scientist

Life senior member, 82; died 17 July

From a young age, Asik was rarely known to leave home without pens, pencils, and a Swiss Army knife, ready to tackle life’s problems, according to his obituary.

He was awarded several scholarships after graduating high school and received a bachelor’s degree in physics in 1959 from the Case Institute of Technology, now Case Western Reserve University, in Cleveland. During his time as an undergraduate, he was an intern one summer at the U.S. Department of Energy’s Oak Ridge National Laboratory, in Tennessee, where he worked on a secret atomic project, according to the obituary.

Asik was a research scientist at Ford for 30 years. While there, he was granted 22 U.S. patents.

After he left Ford, he joined Lawrence Technological University, in Southfield, Mich., as a part-time lecturer on automotive and electrical engineering.

Asik had many interests and hobbies including amateur radio, gardening, and cooking Hungarian food.

He received both a master’s degree and a Ph.D. in physics from the University of Illinois at Urbana-Champaign.

Robert F. Heile

Co-founder of an IEEE Wi-Fi standards group

Life member, 75; died 24 September

Heile was serving as chairman of the IEEE 802.15 Working Group for Wireless Specialty Networks at the time of his death. The group, which he co-founded in 1990, is developing standards for the Internet of Things.

After receiving a Ph.D. in physics from Johns Hopkins University, in Baltimore, Heile joined chemical manufacturer Union Carbide in Houston. He left there in 1980 and became vice president of business operations and transmission products at Codex, in Canton, Mass., where he oversaw development of modems and wireless networking devices. In the 1990s he was a vice president at several Massachusetts companies including TyLink and Windata.

He joined BBN Technologies, in Cambridge, Mass., in 1997 with the mission of developing business strategies to commercialize the company’s wireless technologies, according to his obituary. After the company was acquired by GTE—now part of Verizon—Heile left to become a consultant.

His work at BBN led Heile to get interested in technology standards, according to his obituary.

Heile helped create the ZigBee Alliance, an IEEE Industry Standards and Technology Organization group responsible for developing and promoting the Internet of Things. He served as its chairman and CEO until 2013, when he joined the Wi-SUN Alliance as director of standards and chief representative for business development in greater China.He received a bachelor’s degree from Oberlin College, in Ohio, and completed his master’s degree and doctorate in physics at Johns Hopkins.

Noah Hershkowitz

Plasma physicist pioneer

Fellow, 79; died 13 November

Hershkowitz’s research broadened the understanding of the fundamental properties of plasma. His pioneering work on emissive probes, which are small electrodes that are heated until they emit electrons, resulted in the development of a technique for determining plasma potential. This charge of electric and magnetic fields surrounding the plasma can be analyzed by the current emitted by the emissive probe. In 2002 Hershkowitz became the first to measure plasma potential throughout the sheath and presheath—the regions surrounding the plasma with positive ions and neutral atoms—in a weakly collisional plasma made from weakly charged particles.

Hershkowitz began his career in nuclear physics. He changed his field of study because plasma physics “looked like it would be more fun,” according to his obituary.

He was a professor at several institutions including the University of Colorado Boulder, the University of Iowa, and the University of Wisconsin–Madison, before retiring in 2012.

Mentor to more than 50 doctoral students, he was named professor emeritus at the University of Wisconsin after retiring.

He received numerous awards during his career, including the 2004 James Clerk Maxwell Prize for Plasma Physics, the highest honor afforded by the American Physical Society’s Division of Plasma Physics, and the 2015 IEEE Marie Sklodowska-Curie Award for innovative research and inspiring education in basic and applied plasma science.He received a bachelor’s degree in physics in 1962 from Union College in Schenectady, N.Y., and in 1966 earned a Ph.D. in physics at Johns Hopkins, in Baltimore.

Thomas D. Walsh

Power systems engineer

Life senior member, 90; died 13 November

Walsh joined Boston Edison in 1950 as an apprentice lineman and retired in 1993 as manager of transmission and distribution. After retiring, he worked as a consultant in the United States and Asia.

Walsh also was a professor at Quincy College, in Massachusetts, and he served on Northeastern University’s RE-SEED program committee, which aims to improve science education in public schools.

He holds several U.S. and Canadian patents and authored numerous technical papers and journal articles.

Walsh had been a Boy Scouts of America leader since 1969 and was awarded the 1999 Silver Beaver Award, which recognizes distinguished service in the organization.

He received a bachelor’s degree from Northeastern, in Boston, and a master’s degree from Lesley University, in Cambridge, Mass.

Pinar Boyraz Baykas


Senior member, 39; died 14 November

Boyraz Baykas was an associate professor at the Chalmers University of Technology, in Gothenburg, Sweden, at the time of her death. She conducted research in the applications of mathematical modeling, mechatronics, signal processing, and control theory.

After receiving her Ph.D. in mechatronics in 2008 from Loughborough University, in England, Boyraz Baykas joined the University of Texas at Dallas as a postdoctoral research associate. Her research focused on driver behavior modeling and active safety-system development.

She joined Istanbul Technical University as an assistant professor in 2010 and conducted research in applied robotics. In 2014 she was awarded a research fellowship from the Alexander von Humboldt Foundation, which aims to promote international scientific collaboration. Through the fellowship, in 2016 Boyraz Baykas joined Leibniz University Hannover, in Germany, where she continued her research.

“Her effort to survive in a competitive academic world will hopefully pave the way for younger generations of women and help improve gender balance in academia,” Marco Dozza, her research colleague at Chalmers, told The Institute.

She received two bachelor’s degrees in 2004—one in mechanical engineering and the other in textile engineering—from Istanbul Technical University.

F.C. Kohli

Former Tata Consultancy CEO

IEEE member, 96; died 26 November

Kohli is referred to as the “Father of the Indian IT Industry” for his contributions to establishing and growing the field through his leadership of Tata Consultancy Services. He led a team that installed a computer system to control the power lines between Mumbai and Pune.

Kohli received a bachelor’s degree from the University of the Punjab, in Lahore, India. During his final year at the school, he joined the Indian Navy. While waiting for his assignment, however, he applied for and was awarded a scholarship to Queen’s University in Kingston, Ont., Canada. He graduated with a bachelor’s degree in electrical engineering in 1948 and joined Canadian General Electric in Toronto. While working there, he pursued a master’s degree in electrical engineering at MIT.

After graduating in 1950, Kohli began working in power system operations at Ebasco, the Connecticut Valley Electric Exchange, and the New England Electric System. After a year, he returned to India and joined the Tata Electric Co. in Mumbai, where he helped set up a load-dispatching system to help manage the company’s operations. He was promoted to general superintendent in 1963 and eventually became deputy general manager. When he was promoted to director, he introduced advanced engineering and management techniques for power systems operations.

In 1969, at the request of J.R.D. Tata, chairman of the company, Kohli helped set up Tata Consultancy Services, a subsidiary that provides IT services and business solutions. It is now one of the world’s largest IT software services providers, according to an article on business news website Mint.

Through the new service, Kohli led the installation of the computer system between Mumbai and Pune.

Tata was only the third utility company in the world to install such a system, according to Kohli’s obituary.

Kohli became the company’s first CEO and spent 30 years in the position until stepping down in 1996.

He was the 1995–1996 president and chairman of NASSCOM, an Indian IT services advocacy body in New Delhi, and then served on the organization’s executive committee. He helped shape global partnerships and showcase opportunities to deliver IT services from India, according to the obituary.

Norman Abramson

ALOHAnet developer

Life Fellow, 88; died 1 December

Abramson led the team at the University of Hawaii at Manoa, in Honolulu, that developed ALOHAnet, which allowed computers to transmit packets over a shared channel as soon as they had information to send. ALOHAnet was the first use of wireless communications for a data network.

Abramson began his career as a research engineer in 1953 at Hughes Aircraft in Westchester, Calif. Two years later, he joined the faculty at Stanford and taught at the university for 10 years. Some of his early research was in radar signal characteristics, sampling theory, frequency modulation, digital communication channels, pattern recognition, machine learning, and computing for seismic analysis.

He was a visiting professor at the University of California, Berkeley, in 1966 before joining the University of Hawaii in 1968 as a professor of electrical engineering and computer science.

When he joined the university, he was tasked with developing radio technology to help the school send data from its remote geographic location to the continental United States, and vice versa, according to his obituary.

ALOHAnet was deployed in 1971, and its protocol is now widely used in nearly all forms of wireless communications.

Abramson retired in 1994 and helped found Aloha Networks in San Francisco, a communications technology supplier.

He received a bachelor’s degree in physics from Harvard in 1953, a master’s degree in physics in 1955 from the University of California, Los Angeles, and a Ph.D. in electrical engineering in 1958 from Stanford.

IEEE membership offers a wide range of benefits and opportunities for those who share a common interest in technology. If you are not already a member, consider joining IEEE and becoming part of a worldwide network of more than 400,000 students and professionals.

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The Inner Beauty of Basic Electronics

Open Circuits showcases the surprising complexity of passive components

5 min read
A photo of a high-stability film resistor with the letters "MIS" in yellow.
All photos by Eric Schlaepfer & Windell H. Oskay

Eric Schlaepfer was trying to fix a broken piece of test equipment when he came across the cause of the problem—a troubled tantalum capacitor. The component had somehow shorted out, and he wanted to know why. So he polished it down for a look inside. He never found the source of the short, but he and his collaborator, Windell H. Oskay, discovered something even better: a breathtaking hidden world inside electronics. What followed were hours and hours of polishing, cleaning, and photography that resulted in Open Circuits: The Inner Beauty of Electronic Components (No Starch Press, 2022), an excerpt of which follows. As the authors write, everything about these components is deliberately designed to meet specific technical needs, but that design leads to “accidental beauty: the emergent aesthetics of things you were never expected to see.”

From a book that spans the wide world of electronics, what we at IEEE Spectrum found surprisingly compelling were the insides of things we don’t spend much time thinking about, passive components. Transistors, LEDs, and other semiconductors may be where the action is, but the simple physics of resistors, capacitors, and inductors have their own sort of splendor.

High-Stability Film Resistor

A photo of a high-stability film resistor with the letters "MIS" in yellow.

All photos by Eric Schlaepfer & Windell H. Oskay

This high-stability film resistor, about 4 millimeters in diameter, is made in much the same way as its inexpensive carbon-film cousin, but with exacting precision. A ceramic rod is coated with a fine layer of resistive film (thin metal, metal oxide, or carbon) and then a perfectly uniform helical groove is machined into the film.

Instead of coating the resistor with an epoxy, it’s hermetically sealed in a lustrous little glass envelope. This makes the resistor more robust, ideal for specialized cases such as precision reference instrumentation, where long-term stability of the resistor is critical. The glass envelope provides better isolation against moisture and other environmental changes than standard coatings like epoxy.

15-Turn Trimmer Potentiometer

A photo of a blue chip
A photo of a blue chip on a circuit board.

It takes 15 rotations of an adjustment screw to move a 15-turn trimmer potentiometer from one end of its resistive range to the other. Circuits that need to be adjusted with fine resolution control use this type of trimmer pot instead of the single-turn variety.

The resistive element in this trimmer is a strip of cermet—a composite of ceramic and metal—silk-screened on a white ceramic substrate. Screen-printed metal links each end of the strip to the connecting wires. It’s a flattened, linear version of the horseshoe-shaped resistive element in single-turn trimmers.

Turning the adjustment screw moves a plastic slider along a track. The wiper is a spring finger, a spring-loaded metal contact, attached to the slider. It makes contact between a metal strip and the selected point on the strip of resistive film.

Ceramic Disc Capacitor

A cutaway of a Ceramic Disc Capacitor
A photo of a Ceramic Disc Capacitor

Capacitors are fundamental electronic components that store energy in the form of static electricity. They’re used in countless ways, including for bulk energy storage, to smooth out electronic signals, and as computer memory cells. The simplest capacitor consists of two parallel metal plates with a gap between them, but capacitors can take many forms so long as there are two conductive surfaces, called electrodes, separated by an insulator.

A ceramic disc capacitor is a low-cost capacitor that is frequently found in appliances and toys. Its insulator is a ceramic disc, and its two parallel plates are extremely thin metal coatings that are evaporated or sputtered onto the disc’s outer surfaces. Connecting wires are attached using solder, and the whole assembly is dipped into a porous coating material that dries hard and protects the capacitor from damage.

Film Capacitor

An image of a cut away of a capacitor
A photo of a green capacitor.

Film capacitors are frequently found in high-quality audio equipment, such as headphone amplifiers, record players, graphic equalizers, and radio tuners. Their key feature is that the dielectric material is a plastic film, such as polyester or polypropylene.

The metal electrodes of this film capacitor are vacuum-deposited on the surfaces of long strips of plastic film. After the leads are attached, the films are rolled up and dipped into an epoxy that binds the assembly together. Then the completed assembly is dipped in a tough outer coating and marked with its value.

Other types of film capacitors are made by stacking flat layers of metallized plastic film, rather than rolling up layers of film.

Dipped Tantalum Capacitor

A photo of a cutaway of a Dipped Tantalum Capacitor

At the core of this capacitor is a porous pellet of tantalum metal. The pellet is made from tantalum powder and sintered, or compressed at a high temperature, into a dense, spongelike solid.

Just like a kitchen sponge, the resulting pellet has a high surface area per unit volume. The pellet is then anodized, creating an insulating oxide layer with an equally high surface area. This process packs a lot of capacitance into a compact device, using spongelike geometry rather than the stacked or rolled layers that most other capacitors use.

The device’s positive terminal, or anode, is connected directly to the tantalum metal. The negative terminal, or cathode, is formed by a thin layer of conductive manganese dioxide coating the pellet.

Axial Inductor

An image of a cutaway of a Axial Inductor
A photo of a collection of cut wires

Inductors are fundamental electronic components that store energy in the form of a magnetic field. They’re used, for example, in some types of power supplies to convert between voltages by alternately storing and releasing energy. This energy-efficient design helps maximize the battery life of cellphones and other portable electronics.

Inductors typically consist of a coil of insulated wire wrapped around a core of magnetic material like iron or ferrite, a ceramic filled with iron oxide. Current flowing around the core produces a magnetic field that acts as a sort of flywheel for current, smoothing out changes in the current as it flows through the inductor.

This axial inductor has a number of turns of varnished copper wire wrapped around a ferrite form and soldered to copper leads on its two ends. It has several layers of protection: a clear varnish over the windings, a light-green coating around the solder joints, and a striking green outer coating to protect the whole component and provide a surface for the colorful stripes that indicate its inductance value.

Power Supply Transformer

A photo of a collection of cut wires
A photo of a yellow element on a circuit board.

This transformer has multiple sets of windings and is used in a power supply to create multiple output AC voltages from a single AC input such as a wall outlet.

The small wires nearer the center are “high impedance” turns of magnet wire. These windings carry a higher voltage but a lower current. They’re protected by several layers of tape, a copper-foil electrostatic shield, and more tape.

The outer “low impedance” windings are made with thicker insulated wire and fewer turns. They handle a lower voltage but a higher current.

All of the windings are wrapped around a black plastic bobbin. Two pieces of ferrite ceramic are bonded together to form the magnetic core at the heart of the transformer.

This article appears in the February 2023 print issue.