A probe includes an elastic element having first andsecond ends, a transmitter, one or more receiving antennas andone or more narrow-band amplifiers. The transmitter is coupledto the first end and is configured to transmit signals in agiven range of frequencies. The one or more receiving antennasare coupled to the second end and are configured to receivethe signals. The one or more narrow-band amplifiers have apass-band that matches the given range of frequencies and areconfigured to amplify the signals received by the one or morereceiving antennas, respectively.
