Precision manufacturing faces an invisible enemy inside high-voltage chips, where microscopic defects threaten electric vehicles and aerospace hardware. A research team led by Professor Chang Jin Ho at the Department of Electrical, Electronic, and Computer Science at DGIST developed a screw lens-focused ultrasound transducer. By etching a threaded structure onto the side of the lens, the team has successfully neutralized internal noise that previously degraded high-resolution acoustic imaging.
Power semiconductors operating in harsh automotive environments must withstand extreme thermal loads and high voltages. Standard non-destructive testing often relies on X-rays or optical inspection, but acoustic testing provides superior penetration capabilities to detect hidden structural flaws like tiny cracks and internal voids without damaging the devices. Industrial sites typically run these scans using a water column waterfall method. However, physical space limitations constrain sensor sizing, triggering a persistent engineering headache known as edge noise. Reflected ultrasonic waves bounce internally within the compact lens assembly, interfering with each other and washing out image clarity.
Etching the Screw Thread Solution
Drawing inspiration from the sound-absorbing wedge structures built into anechoic chambers to eliminate acoustic echo, Professor Chang and his team engineered a physical fix. They densely engraved slanted, screw thread-shaped grooves straight onto the smooth side surface of the acoustic lens. When rogue ultrasonic waves head toward the side walls, they strike the inclined surfaces of these threads and scatter in multiple directions. This geometry breaks up the coherent wave reflection that creates internal interference.
Through iterative computer simulations, the researchers locked down optimal thread specifications that balance noise suppression with manufacturing feasibility. The design requires a thread height of 500 micrometers and an inclination angle of 30 degrees. Because the modification targets only the outer surface of the lens, it drops directly into conventional compact industrial inspection equipment without requiring a complete redesign of internal core components or changing the overall sensor footprint.
Revealing Sub-Hair Microstructures
Testing the newly developed transducer on automotive power module chips yielded striking visual evidence. The upgraded sensor mapped internal microstructures that remained completely obscured by baseline noise on standard equipment. Fine metal wires measuring just one-quarter the thickness of a human hair, alongside microscopic internal voids and bubbles, appeared with a clarity that rivals computed tomography scans.
“This research is significant because it solved the problem of internal lens noise—the greatest challenge in designing ultrasonic sensors optimized for industrial inspection equipment—simply by machining the lens shape,” stated Professor Chang. He noted that the advance lays the groundwork required for mass-producing ultra-high-frequency ultrasonic transducers operating at 100 megahertz or higher.
Next-Generation Non-Destructive Testing
The DGIST team published their findings in NDT & E International, a prestigious international journal considered the most authoritative in the field of non-destructive testing. Postdoctoral researcher Kang Sungwoo and integrated master’s-Ph.D. student Park Hyunkyu served as co-first authors on the study. Financial backing came from the STEAM program via the Korean Government’s Ministry of Science and ICT alongside the National Research Foundation of Korea, the InnoCORE program, and the AI Star Fellowship Support program managed by the Institute of Information & Communications Technology Planning & Evaluation.
Moving forward, the research lab plans to run collaborative trials with semiconductor manufacturers. These tests will evaluate real-world production defects to speed up the development of next-generation non-destructive testing systems tailored to on-site needs.
