The Korea Research Institute of Standards and Science (KRISS, President Lee Ho-seong) has developed an ultrasonic sensor technology that applies a waveguide to detect defects in all directions without directly attaching sensors to the inspection target.
By enabling remote ultrasonic excitation and reception, the technology is expected to help prevent industrial accidents and eliminate inspection blind spots in high-risk industrial facilities where direct sensor installation has been challenging due to heat, toxic gases, or other hazardous environmental conditions.
Waveguide: A tubular structure designed to guide waves or physical energy along a defined path. Depending on its geometry, a waveguide can control ultrasonic propagation direction, manage reflection and refraction phenomena, and optimize the directionality and energy efficiency of transmitted waves.
Non-Destructive Testing (NDT) is a safety inspection technique that uses ultrasonic signals to detect internal defects without damaging the structure under examination. It is regarded as a critical technology for ensuring structural reliability in safety-critical industries such as aerospace, nuclear power, and large-scale industrial plants.
However, conventional ultrasonic sensors for NDT have been difficult to deploy in extreme environments, such as high-temperature piping in nuclear power plants or storage facilities containing hazardous chemicals. Because these sensors must be directly attached to the surface of the inspection target, they are frequently damaged by intense heat or corrosive substances. In addition, in restricted high-risk areas where human access is limited, sensor installation itself is often impossible.
Conventional ultrasonic transducers designed for full 360-degree inspection have typically relied on segmented configurations, in which multiple sensing elements are arranged circumferentially. However, combining wave signals from these segmented sources often leads to interference and distortion, reducing inspection accuracy.
To overcome this limitation, the KRISS Non-Destructive Metrology Group introduced a waveguide as an intermediate medium. By transmitting ultrasonic waves through the waveguide, the sensing region can be installed remotely without direct contact with the surface under inspection. This approach enabled the development of a new type of ultrasonic sensor capable of operating under high-risk conditions while maintaining precise defect detection performance.
The core innovation lies in generating torsional vibration within a cylindrical waveguide—much like twisting a towel—and then uniformly transferring this vibration to the surface under inspection. Through this mechanism, ultrasonic waves propagate evenly in all directions, enabling precise defect detection even when the sensor is installed at a distance from the target structure. Notably, the waveguide can be fabricated using various materials and geometries, and its end can be machined to conform to curved structural surfaces. This flexibility allows stable operation under diverse environmental conditions and on complex structural shapes.
Experimental results demonstrated that the developed sensor achieved approximately 95% directional uniformity and high-purity wave propagation, enabling consistent signal capture across the entire inspection range. Signal amplitude was also improved by more than 13.7 times compared to conventional segmented configurations, allowing rapid scanning of wide areas and high-resolution imaging.
This technology is expected to enable real-time monitoring of structures in extreme environments where conventional NDT methods have been impractical, significantly enhancing industrial safety. In addition, by replacing multiple high-cost sensors with a single sensor integrated with a low-cost waveguide structure, the system can inspect large areas efficiently while substantially reducing inspection costs.
Dr. Seung Hong Min of the Non-Destructive Metrology Group at KRISS said the newly developed sensor also demonstrates excellent signal performance in liquid environments, enabling precise inspection of large submerged structures. “Based on its high reliability and versatility, the technology can be readily applied to accident prevention systems across various industrial facilities. By detecting previously inaccessible inspection blind spots, it has the potential to significantly contribute to the prevention of large-scale industrial disasters,” he added.
This research was supported by the KRISS Basic Research Program and was published in December in Mechanical Systems and Signal Processing (Impact Factor: 8.9), a leading international journal in the field of mechanical engineering.
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