A single plate captures multiple frequencies at once

It has long been considered common sense that a single device performs only one function. Just as tuning a radio to a different frequency changes the channel, systems that manipulate waves have traditionally been designed to operate at only one specific frequency, requiring different devices for different frequencies. Now, however, researchers have opened up a new possibility: a single thinplate can simultaneously distinguish elastic waves of multiple frequencies and precisely direct each of them to different locations.

A research team led by Professor Junsuk Rho of the Department of Mechanical Engineering, Department of Chemical Engineering, Department of Electrical Engineering, and the Graduate School of Convergence Science and Technology at POSTECH (Pohang University of Science and Technology), together with integrated PhD student Geon Lee and Dr. Wonjae Choi of the Korea Research Institute of Standards and Science (KRISS), has developed the world’s first “frequency-multiplexed elastic metasurface.” This technology successfully enables simultaneous control of elastic waves at multiple frequencies without relying on complex structures and was recently published in the international journal Nature Communications.

The research began with a focus on elastic waves—vibrations that propagate through structures when they are mechanically excited. Elastic waves are widely used in non-destructive testing, a technique that evaluates the condition of structures such as buildings and machinery without causing damage. However, even small changes in frequency can significantly alter wave speed and mode shape, making precise control extremely challenging.

As a result, conventional technologies have been limited to handling only a single frequency with a given structure. Much like a radio can clearly receive only one channel at a time, mechanical systems have been designed to operate optimally at a specific frequency. When exposed to other frequencies, the intended functionality often breaks down.

The research team addressed this limitation by focusing on a seemingly simple parameter: plate thickness. When elastic waves propagate through a thin plate, their phase—that is, their arrival timing—depends sensitively on the plate’s thickness. The team recognized that by carefully tailoring the thickness profile, it would be possible to induce completely different responses for different frequencies. This principle is analogous to how a prism separates white light into a rainbow by bending each wavelength at a different angle.

Based on this idea, the researchers first designed the target focal positions for each frequency and then implemented them in a physical plate structure. As a result, a single metasurface was able to precisely focus elastic waves at distinct frequencies—40 kHz, 60 kHz, and 80 kHz—onto different spatial locations. By placing piezoelectric elements at these focal points to convert mechanical vibrations into electrical signals, the team demonstrated that the signal intensity at a target frequency could be enhanced by up to 48 times compared to other frequencies. This clearly demonstrated that frequency information can be separated and read out using only a single thin metal plate.

The significance of this technology lies in its integration of processes that previously required multiple devices and complex measurement systems. Wave control, frequency separation, spatial routing, and electrical signal conversion are all realized within a single metasurface structure.

Professor Junsuk Rho stated, “This work represents a technological turning point that breaks the conventional belief that one structure can perform only one function.” He added, “Without the need for expensive equipment, this platform enables frequency-selective detection and amplification of structural vibrations, making it a core technology with broad potential applications in industry, defense, energy, and sensing.”

This research was supported by the POSCO Holdings N.EX.T Impact Program, the Mid-Career Researcher Program of the National Research Foundation of Korea (NRF) funded by the Ministry of Science and ICT, the Presidential Science Scholarship, the Hyundai Motor Chung Mong-Koo Foundation Fellowship, and the NRF/Ministry of Education Graduate Student Support Program in Science and Engineering.