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Acoustic diode could improve ultrasound images

05 Nov 2013

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Researchers in China's Nanjing University have developed a theoretical model for an acoustic diode, a device that facilitates one-way transmission of sound waves in a method similar to how an electrical diode manages the one-way transmission of electrical impulses. The device has the potential to enhance future ultrasound images and improve diagnosis and therapy. The researchers based the framework on a material called a near-zero index metamaterial (ZIM) and a prism to generate high-transmission efficacy acoustic waves that strike a reflective boundary from two opposite sides.

Most people know about ultrasound through its role in prenatal imaging. A new technology called an "acoustic diode," as envisioned by researchers in China's Nanjing University, may improve future ultrasound images by changing the way sound waves are transmitted.

In the journal Applied Physics Letters, the scientists describe the theoretical framework for an acoustic diode, a device that achieves a one-way transmission of sound waves in the same way as an electrical diode controls the one-way transmission of electrical impulses.

The one-way flow of sound would provide brighter and clearer ultrasound images by eliminating acoustic disturbances caused by sound waves going in two directions at the same time and interfering with each other, explained researcher Jian-chun Cheng.

"The propagation direction of the output wave would be controlled freely and precisely," Cheng said. "These features are crucial for the medical ultrasound applications of the resulting devices."

Sound waves flow in two directions. Yet in nature, total reflection of sound in one direction is known to occur at the air-water interface. This gave investigators the idea that an acoustical diode could be constructed by transmitting acoustic waves using an asymmetric prism to create total unidirectional reflection.

The team developed its theoretical model based on a material not found in nature called a near-zero index metamaterial (ZIM) and a prism to create high-transmission efficacy acoustic waves that strike a reflective boundary from two opposite sides.

In theory, explained Dr. Cheng, "This would produce a unique tunnelling effect and an unprecedented property that the output waveform is kept consistent with those of the waves traveling towards a boundary."




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