![\"Breaking](\"https:\/\/www.europesays.com\/uk\/wp-content\/uploads\/2025\/04\/breaking-a-century-old.jpg\" "\\"(a)")
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(a) Schematic of the experimental setup featuring a cylindrical granular particles\u2014small solid rods made of quartz (b) Displacement field within a single particle as a function of contact position (\u03bc). (The dashed box highlights the displacement pattern associated with the polarization-protected BIC.). Credit: POSTECH<\/p>\n
A joint research team has successfully demonstrated the complete confinement of mechanical waves within a single resonator\u2014something long thought to be theoretically impossible. Their findings, published<\/a> on April 3 in Physical Review Letters, mark a major breakthrough in the century-old mystery of bound states in the continuum (BIC). The team is from POSTECH (Pohang University of Science and Technology) and Jeonbuk National University.<\/p>\n Many technologies around us\u2014from smartphones and ultrasound devices to radios\u2014rely on resonance, a phenomenon in which waves are amplified at specific frequencies. However, typical resonators gradually lose energy over time, requiring constant energy input to maintain their function.<\/p>\n Nearly a century ago, Nobel laureates John von Neumann and Eugene Wigner proposed a counterintuitive concept: under certain conditions, waves could be trapped indefinitely without any energy leakage. These so-called bound states in the continuum (BIC) are like whirlpools that remain in place even as a river flows around them. But for decades, scientists believed this phenomenon could not exist in a compact, single-particle system.<\/p>\n Now, the research team has broken this long-standing theoretical boundary by successfully realizing BIC in a single particle.<\/p>\n Using a system of cylindrical granular particles\u2014small solid rods made of quartz\u2014the researchers built a highly tunable mechanical platform. By precisely adjusting how the cylinders touch each other, they could control the way mechanical waves interact at the contact boundaries.<\/p>\n Under special alignment, a wave mode became fully confined within a single cylinder without any energy escaping into the surrounding structure. This so-called polarization-protected BIC was not just theoretical\u2014it was observed in real experiments. Even more remarkably, the system achieved quality factors (Q-factors) of over 1,000, a measure of how efficiently a resonator stores energy with minimal loss.<\/p>\n What happens when many of these special cylinders are connected in a chain? The team discovered that the trapped wave modes could extend throughout the chain without dispersing\u2014a phenomenon known as a flat band.<\/p>\n “It’s like tossing a stone into a still pond and seeing the ripples remain motionless, vibrating only in place,” said lead author Dr. Yeongtae Jang. “Even though the system allows wave motion, the energy doesn’t spread\u2014it stays perfectly confined.”<\/p>\n This behavior is described as a bound band in the continuum (BBIC) and opens new possibilities for energy harvesting, ultra-sensitive sensors, and even advanced communications.<\/p>\n “We have broken a long-standing theoretical boundary,” said Professor Junsuk Rho, who leads the research. “While this is still in the fundamental research phase, the implications are significant\u2014from low-loss energy<\/a> devices to next-generation sensing and signal technologies.”<\/p>\n More information:<\/strong> \n\t\t\t\t\t\t\t\t\t\t\t\t\tProvided by \t\t\t\t\t\t\t\t\t\t\t\t\t\t<\/a>\n\t\t\t\t\t\t\t\t\t\t\t\t\t\t\t\t\t\t\t\t\t\t\t\t\t\t\t\t\t\t\t\t\t\t\t\t\t\t\t<\/p>\n \n\t\t\t\t\t\t\t\t\t\t\t\tCitation<\/strong>: \n\t\t\t\t\t\t\t\t\t\t\t This document is subject to copyright. Apart from any fair dealing for the purpose of private study or research, no
\n\t\t\t\t\t\t\t\t\t\t\t\tYeongtae Jang et al, Bound States to Bands in the Continuum in Cylindrical Granular Crystals, Physical Review Letters (2025). DOI: 10.1103\/PhysRevLett.134.136901<\/a>. On arXiv: DOI: 10.48550\/arxiv.2410.16209<\/a><\/p>\n
\n\t\t\t\t\t\t\t\t\t\t\t\t\t\t\t\t\t\t\t\t\t\t\t\t\t\t\tPohang University of Science and Technology<\/a>
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\n\t\t\t\t\t\t\t\t\t\t\t\tBreaking a century-old physics barrier: Scientists achieve perfect wave trapping with simple cylinders (2025, April 11)
\n\t\t\t\t\t\t\t\t\t\t\t\tretrieved 11 April 2025
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