The Giants Behind the Signal: Honoring the Pioneers of Eddy Current Testing

When we talk about eddy current testing (ECT) today—automated scanners, phase-angle crack sizing, AI-enhanced signal recognition—it’s easy to forget that the roots of this technology stretch back nearly 200 years. Before digital impedance planes and touchscreen flaw detectors, there were the giants—scientists, engineers, and experimenters—who laid the electromagnetic groundwork we still use today.

In a riveting historical address at the 1977 NBS Workshop on Eddy Current Testing, Dr. Robert C. McMaster, one of America’s leading NDT thinkers, walked attendees through this scientific lineage. What follows is a condensed tribute to the lesser-known (and some well-known) names who helped shape ECT as we know it.

🔭 The 1800s: From Curiosity to Core Laws

• Hans Christian Ørsted (1820) noticed that a current could deflect a magnetic compass. That simple spark of curiosity launched the entire field of electromagnetism.

• André-Marie Ampère, working almost immediately after Ørsted, showed how currents interact—foundational to how we design coil pairs in differential eddy current systems today.

• Michael Faraday didn’t just discover electromagnetic induction—he practically wrote the playbook. If you’ve ever used a probe to detect lift-off or tried to size a surface crack, you’re using principles Faraday documented in the 1830s.

• Lenz, Neumann, and Helmholtz contributed the math, showing that induced fields oppose the cause and can be expressed in equations. These laws weren’t just scientific decoration—they explain why flaws create unique, interpretable signals.

• James Clerk Maxwell unified it all with his equations in the late 1800s. Without him, the impedance plane as we know it would not exist.

⚙️ Early 1900s: From Theory to Practice

ECT didn’t take off immediately. It was the power industry, transformer design, and radio that gave it a reason to exist.

• David Hughes ran early experiments that could differentiate coins using electromagnetic response—a primitive precursor to alloy sorting.

• Charles Steinmetz revolutionized the way we represent AC systems using phasor diagrams and complex impedance—a concept every Level III today still uses to analyze eddy current responses.

🧪 Mid-Century: The Instrumentation Era

Fast-forward to the 1920s–40s: steel mills and naval engineers wanted better quality control tools. Enter the pioneers of practical ECT.

• Ross Gunn (U.S. Naval Research Lab) developed new coil configurations for inspecting war-critical materials.

• Charles Burroughs, Carl Kinsley, Archibald Davis, and Alfred Sharpies designed some of the earliest production-line eddy current machines in the U.S., testing steel tubes and bars.

Their systems were crude by today’s standards, but they proved that ECT could deliver reproducible results on real-world parts.

🧠 Post-War Innovation: The Förster Revolution

After WWII, the field exploded—thanks in large part to Dr. Friedrich Förster, a German physicist who single-handedly revolutionized eddy current testing. His work:

• Formalized phase-plane analysis

• Introduced lift-off compensation systems

• Built the first truly quantitative flaw detectors

• Was compiled into the original ASNT Nondestructive Testing Handbook.

McMaster called Förster the “father of modern ECT”, and with good reason. His designs were so influential that multiple U.S. companies entered licensing agreements just to commercialize his instruments.

U.S. Thinkers Catch Fire

Inspired by Förster’s work, American researchers ramped up:

• Hugo Libby led the charge at Hanford, developing multifrequency ECT and paving the way for frequency-mix analysis.

• Caius Dodd and J.A. Deeds at Oak Ridge modeled eddy currents in complex geometries—efforts still cited in modern probe design.

• Richard Hochschild and Ron Botsco helped transfer Förster’s tech to the U.S., then pushed ECT into new arenas like microwave NDT.

🛰️ What We Owe Them

ECT has become a high-tech field—phased arrays, digitized signal stacks, AI auto-analysis—but every inch of progress stands on their shoulders.

Without Ampère, we wouldn’t have differential coils.

Without Faraday, we wouldn’t understand probe lift-off.

Without Förster, we wouldn’t have the impedance plane or modern instruments.

💡 Call to Action

Want to dive deeper into these historical giants and how their insights affect your work as an ECT professional?

Visit eddycurrent.com — your one-stop resource for everything eddy current, from classic theory to cutting-edge tools. We’ve curated educational archives, legacy documents, and modern applications so you can keep pushing this field forward—just like they did.

🧲 Explore the past. Master the present. Build the future.