Vanishing Act for Water Waves: Cavities in Water Channels Demonstrate Perfect Absorption

Researchers discover a new technique to protect coastlines and reduce erosion using perfect absorption of water waves.

In a breakthrough discovery, researchers have demonstrated perfect absorption of water waves using cavities built into the sides of a narrow channel. This achievement opens up new possibilities for protecting coastlines and reducing erosion. The concept of perfect absorption, where waves are completely absorbed and do not reflect or transmit, has been previously demonstrated for light and sound waves. However, this is the first time it has been achieved for water waves. The researchers believe that with further development, this technique could be used to create an array of elements near coastlines to protect sensitive structures and harness wave energy.

The Quest for Perfect Absorption

Perfect absorption has been a subject of interest for researchers in various fields. The ability to completely absorb waves without any reflection or transmission has significant applications in controlling and manipulating wave energy. Previous studies have shown promising results in achieving perfect absorption for light and sound waves. However, the challenge of creating a perfect absorber for water waves has remained.

A New Approach

Inspired by their own mathematical work, a team of researchers from ESPCI Paris set out to engineer a resonant structure that would interact with incoming water waves, resulting in perfect absorption. Their approach involved analyzing how cavities could produce zero transmission at specific frequencies and then fine-tuning the setup to achieve zero reflection at those same frequencies. The team constructed a water channel with two small cavities built into the side, extending away from the channel wall by 4 cm and along the channel for 3 cm.

Experimental Results

The researchers conducted experiments using water waves in the lab to test their predictions. The results closely matched their calculations, with two dips in the transmission-vs-frequency curve. While the first dip nearly reached zero, the second dip reached around 40%. The discrepancies between theory and experiment were attributed to friction losses in the fluid and approximations used in the analysis. To achieve perfect absorption, the researchers distorted the cavities, making one extend slightly farther away from the channel wall than the other. This adjustment resulted in zero transmission and reflection at a frequency of 2.9 Hz.

Potential Applications

The discovery of perfect absorption in water waves has significant implications for coastal protection and erosion reduction. The researchers envision using this concept to develop a practical system that can protect coastlines from erosion. By creating a “protective belt” in the sea, the resonant structures could act as a barrier against wave energy, reducing the risk of overtopping. Additionally, the researchers suggest that this technology could be used to harvest ocean wave energy, further expanding its potential applications.

Conclusion:

The achievement of perfect absorption for water waves using cavities in a narrow channel marks a significant milestone in wave control and manipulation. The ability to completely absorb water waves without any reflection or transmission opens up new possibilities for protecting coastlines and harnessing wave energy. The researchers’ innovative approach and successful experimental results pave the way for further development and practical applications of this technology. As coastal erosion continues to threaten vulnerable areas, this breakthrough offers a promising solution for safeguarding coastlines and preserving valuable ecosystems.


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