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