&Bullet; physics 14, s57
By injecting momentum into the liquid around an object, researchers can freely switch between obscuring the object’s presence and canceling hydrodynamic forces on the object.
Among the most famous technologies of Star Trek’sSpaceships are their invisible cloaking devices and their shields. In real life, a limited form of invisibility can be achieved passively using metamaterials. Now Evgeniy Boyko from the Technion – Israel Institute of Technology and colleagues have developed an active method that also includes shields. Their technique works for an object sitting in a stream of liquid and lets them switch between the “camouflaging” and “shielding” modes at will  .
Hydrodynamic camouflage obscures the effects of an object on the fluid flowing around it. For example, a metamaterial with a certain structure can divert the flow around the object in order to change its interaction with the structure (see Synopsis: Hydrodynamic Cloaks).
The new method by Boyko and colleagues uses a different approach. Instead of using passive structures, they actively inject momentum into the fluid using a mechanism called electroosmosis. With this technique they can control the impulse of the surrounding liquid via electric fields, so that in stealth mode the flow outside the camouflaged area gives no indication of the presence of the object. Researchers can also switch to manipulating the flow of fluid around the object so that any hydrodynamic forces that the flow would exert on the object are eliminated. They call this suspension of forces the shielding mode.
The team describes the approach theoretically for a number of object shapes in a microscale flow and demonstrates it experimentally in a microfluidic chamber. The technique could have a number of uses, say the researchers, including acting as “tweezers” to hold soft objects – like cells – in a stream of fluid.
–Erika K. Carlson
Erika K. Carlson is Corresponding Editor for physics based in New York City.
- E. Boyko et al., “Microscale hydrodynamic camouflage and shielding by electroosmosis” Phys. Rev. Lett.126184502 (2021).