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'Acoustic Tweezers' Pick Up Objects Using Only Sound Waves

The technology could be use to levitate tiny objects for medical applications.

Scientists from Tokyo Metropolitan University (TMU) in Japan developed a new method for levitating and manipulating small objects using only sound waves, a press statement explains.

The team was able to make objects rise off reflective surfaces using acoustic levitation, potentially leading to new technologies that move and manipulate physical objects using only sound.

Though the technology, known by the name of "acoustic tweezers", would likely never be feasible for objects larger or heavier than a tiny ball, it has great potential for medical uses, such as guiding a small object through the human body without contact. 

Sound wave technology has shown potential across a wide variety of surprising use cases, meaning that we may have only seen the tip of the iceberg when it comes to potential applications.

In 2019, for example, researchers at the University of Sussex published a paper showing how they produced a "hologram" by lighting tiny objects that were manipulated via ultrasound waves.

Creating a reliable 'sound trap'

Though the concept of acoustic tweezers was first discovered in the 1980s, there are many challenges in the way of widespread adoption.

Early concepts used hemispherical arrays of acoustic transducers to create a "sound trap" of sound waves that could carry an object. However, such concepts were never quite able to reliably control objects in real-time, as it is very difficult to create and adapt just the right sound field as the object moves, especially if it is next to a surface that reflects sound.

For their study, the TMU engineers developed a hemispherical acoustic array that could lift a 3-millimeter polystyrene ball from a reflective surface.

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They split their transducer array into manageable blocks and used an inverse filter that finds the best phase and amplitude in order to make a sound trap.

"The phase and amplitude of each channel are optimized using the sound reproduction method," the scientists wrote in their paper. "This creates an acoustic trap at only the desired position, and pick up can thus be realized on the rigid stage. To the best of our knowledge, this is the first study to demonstrate non-contact pickup using this approach."

Though the team notes it still needs to work to improve the reliability of the machine, it has the potential to transform the way we use sound to manipulate small objects — a development that could lead to previously unimagined medical and scientific applications.

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