Focusing a radio signal and simultaneously nulling it at another location using time-reversal: Experimental results

The time-reversal beam-forming technique utilizes the multipath in a cluttered environment to focus beyond the Rayleigh limit. This method makes use of the reciprocity of wireless propagation channels. Time-reversal can also be used to null signals, either to reduce unintentional interference or to prevent eavesdropping. Previous analytical work has also shown the ability to focus a signal at a location while simultaneously nulling it at a different location. We now present experimental results showing time-reversal focus and nulling in a cluttered environment.