Manipulating microscopic objects without actually touching them is a challenge in many micro and nanotechnology applications. While there are techniques that utilize surface acoustic waves (SAW), they often depend on ultrasonic waves in the MHz range, which are particularly difficult to generate. Researchers at Leti came up with a workaround that involves using a very special type of wave: evanescent acoustic waves.

What sets evanescent acoustic waves apart is the fact that they propagate emission-free, which eliminates energy losses in the substrate. The waves are effectively confined to the vicinity of the emitting substrate with a very low wavelength gradient, making them easier to control and giving them more force, even at low frequencies.

Here, the researchers produced evanescent waves using a device made up of a very thin glass plate attached to an annular piezoelectric ceramic material with concentric circles of bacteria on it.

The research, published in Nature Communications Physics, will create opportunities in biotechnology. The solution developed is easy to make and cost effective. In its current form it can move and pattern micro-objects accurately and contact-free. For bacteria and cells, the advance could make certain biological tests faster, saving precious time.