Creating a reconfigurable space-time cloak in real time

While hiding an object from electromagnetic or acoustic detection seems the stuff of sci-fi and fantasy, researchers are working to make cloaking a reality. One of the common approaches, spatial cloaking, involves the smooth guidance of waves around an object in a designated surrounding region, arriving perfectly restored to the receiver without backscattering. This perceived hole in space may, theoretically, be achieved by spatially manipulating the material in the cloaked region. A transformation-based spacetime cloak in a linear system was originally proposed by McCall and Kinsler. Called a temporal cloak, this application involves hiding an event of finite duration by manipulating the medium in space and time, creating an analogous hole.

Or Lasri and Leabeilkin Sirota present a method of achieving a temporal acoustic cloak using an active closed-loop control approach.

“The required space and time-dependent properties, such as effective mass density and bulk modulus in the cloaked region, as well as additional cross-coupling terms of pressure and flow velocity, are created by the controllers in a real-time measurement-based feedback operation,” said author Leabeilkin Sirota.

The resulting array of transducers and controllers is fully linear, programming the change in medium parameters into the controllers.

“The innovative part of our work is the approach of active real-time feedback control to realize the event cloak. In particular, the fact that this approach enables a fully linear solution, that it does not require a change in the properties of the actual propagation medium, and that the cloak parameters can be reprogrammed by the user without the need to refabricate anything,” said Sirota.

Source: “Active control approach to temporal acoustic cloaking,” by Or Lasri and Leabeilkin Sirota, Applied Physics Letters (2023). The article can be accessed at https://doi.org/10.1063/5.0152144 .