A Mechanical Antenna With Frequency Multiplication and Phase Modulation Capability

This article reports on a novel direct frequency multiplication and phase modulation (PM) scheme for mechanical antennas operating at the very-low-frequency band (3-30 kHz) and lower. This antenna is intended as a transmitter for underwater and underground communication applications. In mechanical antennas, instead of using signal generators to drive the antenna for radiation, the radiation is induced by accelerating (rotating) electric charges or permanent magnets. One important challenge for mechanical antennas is to find an approach to modulate the information signal with sufficient bandwidth. We propose a novel PM scheme by rotating a permanent magnet which is sandwiched between two pairs of orthogonal bow-tie shape high- μ magnetic material plates. By moving the angular position of the magnetic plates, it is shown that the phase and amplitude of the EM signal can be modulated. The amplitude modulation is significant and this provides an additional important feature, which allows the antenna to generate higher harmonics of the rotation frequency, and thereby it facilitates radiation at a much higher frequency than the rotational frequency of the magnet. Hence, higher range and more radiated power can be achieved. Here, the performance of proposed mechanical antenna with its PM and frequency multiplication capability is first verified analytically and through numerical simulations using ANSYS Maxwell. Then, a prototype of the antenna is fabricated with the aid of low cost 3-D-printing technology and its performance is measured. Measurements are in good agreement with the simulation predictions.