Cloaking a sensor.

We propose the general concept of cloaking a sensor without affecting its capability to receive, measure, and observe an incoming signal. This may be obtained by using a plasmonic sensor, based on cloaking, made of materials available in nature at infrared and optical frequencies, or realizable as a metamaterial at lower frequencies. The result is a sensing system that may receive and transmit information, while its presence is not perceived by the surrounding, which may be of fundamental importance in a wide range of biological, optics, physics, and engineering applications.