A team at RMIT University in Melbourne have successfully combined two different types of sound waves to produce a new hybrid, so-called “surface reflected bulk waves.” Not only is this the first type of sound wave created for over 50 years, but this breakthrough has implications for a completely different field of research: stem cell therapy. The remarkable findings are published in the journal Advanced Materials.
Bulk waves, also known as Lamb waves, are special types of waves that move along a single surface. Regular sound waves are “longitudinal waves” that move particles forward in the same direction as the movement of the wave. “Transverse waves” move particles at right angles to the travel direction of the wave. Bulk waves are similar, but the particles move at right angles to their original surface, rather than the direction of the wave.
Due to this property, bulk waves allow the entire material to vibrate as one interconnected wave. Surface waves, on the other hand, only cause the surface to vibrate. You can think of surface waves as a light ocean wave, whereas a bulk wave is more akin to holding a carpet at one end and shaking it up and down. The researchers hoped to combine the two sound waves for the first time in human history.
An example of a surface wave. Dan Russell. CC BY-NC-ND 4.0
In order to do this, a new device was created, one that uses the vibrational properties of a piezoelectric chip. These chips can convert electrical charge into mechanical energy, and vice versa. By carefully manipulating this effect with extreme precision, a sound wave can be generated that combines the properties of both bulk and surface waves – hence the name “surface reflected bulk waves.”
This new wave, fired from a novel device called HYDRA (HYbriD Resonant Acoustics), allows the user to manipulate substances and objects in ways that were simply not possible before. The key example of this ability demonstrated in the study was how HYDRA could break liquids into an inhalable spray over a very short period of time.
“The combination of surface and bulk wave means they work in harmony and produce a much more powerful wave,” said Dr. Amgad Rezk, who co-authored the study, in a statement. “It's basically 'yelling' at the liquid so it vibrates, breaking it down into vapor.”
The vaporization, or “nebulization,” is a common technique used to deliver medical substances to those in need – for example, for those who require asthma medication. Using this new, energetic soundwave, the process was dramatically sped up. “As a result,” Rezk noted, “instead of administering or nebulizing medicine at around 0.2 milliliters per minute, we did up to five milliliters per minute. That's a huge difference.”
The Respite device uses HYDRA technology to deliver medicine. RMIT
This means that doses of medicine that would take 30 minutes to administer through nebulization can now take as little as 30 seconds. Not limited to just pharmaceutical drugs, HYDRA could potentially deliver stem cells straight to a specific site within the lungs to repair damaged tissue.
The device is already being used to develop a new nebulizer at RMIT called Respite. It’s cheap, portable and lightweight – perfect for personal use – and can deliver a range of treatments to patients, from precise drug doses for asthma sufferers, to insulin for diabetes patients, and needle-free vaccinations to infants.
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