"Bridges and buildings need to be checked over time to identify weaknesses or abnormalities. While the existing inspection method is similar to an annual health checkup, our structural health monitoring is a technology that continuously observes the condition of structures, like a smartwatch. By using sensors to constantly observe how much a structure shakes and moves, we can detect small abnormalities early and prevent major accidents."
Sohn Hoon, professor of civil and environmental engineering at the Korea Advanced Institute of Science and Technology (KAIST) and recipient of the June Korea Science and Technology Award, made these remarks Tuesday about his high-precision displacement sensor technology. The award is hosted by the Ministry of Science and ICT (MSIT) and co-organized by the National Research Foundation of Korea and Seoul Economic Daily.
More than 98 percent of facilities worldwide are small and medium-sized structures, where displacement occurs at the millimeter level, making precise observation essential. Displacement refers to the change in distance and direction an object moves from its initial position to its final position. It is a measure of how minutely a bridge or building has moved from its original position due to external impacts. However, existing high-priced equipment costs more than 40 million won per unit, limiting field deployment. This has left numerous small structures unattended in safety blind spots.
The sensor developed by Professor Sohn dramatically lowers the cost burden to under 1 million won per unit, one-fortieth of the existing price. It also achieves world-class precision with an average displacement error of 0.026㎜. "Existing GPS-based measurement technology had high equipment costs and measurement accuracy of only about 10㎜, limiting its ability to precisely measure small movements in small and medium-sized structures," Sohn said. "The sensor we developed reduces power consumption and includes wireless communication functions, allowing structures to be monitored continuously over long periods."
The key to commercializing the new technology lies in combining two sensors of different characteristics to offset their weaknesses. The sensor applies an original technology that fuses millimeter-wave radar with a low-cost MEMS accelerometer. "Radar can easily measure the displacement of slowly moving structures but can miss rapid vibrations," Sohn explained. "On the other hand, the accelerometer captures rapid vibrations well but cannot accurately capture slowly accumulating movements that occur over time." He added, "By analyzing inexpensive accelerometers and radar together, we can effectively reduce errors and achieve highly precise displacement measurements."
Professor Sohn's research team installed the sensor on Sejong's Yi Eung Bridge for about three years to verify its long-term performance and applicability in actual field conditions. The team also applied it to overseas sites, including a highway in San Jose, U.S., a parking building at Stanford University, and a bridge in Weifang, China. Through more than 13 field demonstrations at home and abroad, the sensor has proven its world-class reliability. "The developed sensor has been verified in actual field conditions through cooperation with research institutions in various countries, including the United States, China, and France," Sohn said. "In particular, we are expanding field applications and commercialization possibilities in the U.S. through the National Research Foundation of Korea's Global Basic Research Laboratory program and the Ministry of Land, Infrastructure and Transport's international cooperation R&D project."
The technology is expected to expand to areas previously difficult to address with existing sensors, including structural health monitoring of small and medium-sized structures, monitoring during construction, precision construction, and load-bearing capacity testing. "To apply the sensor widely to small and medium-sized structures, not only equipment prices but also installation and maintenance costs had to be lowered," Sohn said. "To this end, we designed the sensor to transmit data wirelessly and operate without separate measurement equipment, enhancing installation convenience."
The team also focused on building a sensor system capable of long-term operation. "We embedded decision-making functions inside the sensor so that, rather than sending all data collected in the field, only the necessary results are transmitted," Sohn said. "This allows managers to easily oversee many structures." He added, "We sought to implement a field-oriented system capable of long-term operation by reducing the power supply burden through battery use and solar panel integration."
The research outcome is a case in which original technology developed through MSIT's Basic Research Program — the Leader Researcher and Basic Research Laboratory (BRL) initiatives — led to actual commercialization and technology transfer. The findings were published in the international journal Mechanical Systems and Signal Processing in January 2023.
Professor Sohn is an authority on civil engineering and structural safety diagnostics who was named KAIST's youngest tenured professor in his early 40s. For the past two years, he has concurrently served as director of the Korea National Railway's Railway Innovation Research Institute, working to apply advanced technologies to the national facility safety management system. He recently took on the role of director of the Railway Infrastructure Innovation AX Research Group, leading the construction of national smart infrastructure. "The sensor technology is significant in that it has laid the technological foundation for the precise management of small and medium-sized facilities that had been excluded from continuous monitoring," Sohn said. "Going forward, I will continue AI-based digital twin research to lead a paradigm shift in the safety diagnosis market through automation, unmanned operation, and intelligence, contributing to public safety and disaster prevention."
