Finding an efficient way for underwater communication with a portable antenna at very-low frequency (VLF 3-30 kHz) is challenging since the conventional electrical antennas require the size to be larger than 1/10 of the wavelength. Recently, acoustically driven antennas were proposed to realize portable VLF communication in air but lack the demonstration in a lossy environment. Here, we reported the first VLF underwater communication system based on a pair of acoustically actuated magnetoelectric (ME) antennas with small size of 10 cm in length. A theoretical analysis of reflection and radiation performance of the ME antenna was conducted, where the electromechanical resonance (EMR) frequency and effective magnetic dipole moment were estimated, and a near-field coupling model of a pair of ME antennas was further established. The results of theoretical predictions and finite element (FEM) simulations were then compared with experimental measurements and their differences were discussed. A prototype of underwater communication system based on the ME antenna pair was finally presented, where a binary digital modulation with a bit rate of 100 bps has been demonstrated, confirming the feasibility of ME antennas for portable underwater communication.

Acoustically actuated magnetoelectric (ME) antennas based on resonant magnetoelectric coupling within ferromagnetic/piezoelectric ME laminated composites have recently been considered as a promising solution for antenna miniaturization. However, its radiation performance has been theoretically overestimated, since the negative effects on performances due to the magnetization saturation and the nonlinear mechanical behavior that occur from high-field driving have not been paid enough attention. This work presents a unique equivalent-circuit-based numerical method to analyze the near-field resonance radiation performances of ME antennas driven by high electric fields. In this method, we establish an equivalent circuit of the converse magnetoelectric effect for a ME laminated composite to describe the operating principle of acoustically actuated electromagnetic radiation. The equivalent parameters related to resonance characteristics are determined by fitting the circuit model to the data from frequency response measurements of the near-field magnetic flux density. The validity of the model is verified by comparing the theoretical predictions with the experimental results, in the view of the volume fraction dependence of the mechanical resonance-related radiation characteristics of the fabricated ME composites. Based on the proposed model, the influence of driving voltage amplitude on near-field radiation performances is further analyzed by experimental fitting to the model, and the potential limiting factors of ME antennas are discussed according to the driving-amplitude dependence of parameters obtained from the fit. This work provides an effective and engineering-friendly approach to predict the evolution of ME antenna performances, leading a way to improve the performance limit for resonant magnetoelectric coupling.

Very low frequency (VLF, 3-30 kHz) electromagnetic (EM) waves are widely used in areas such as mining, underwater communications, etc., because of their relatively large skin depth that enables long distance propagation in lossy medium. Mechanical antennas driven by acoustic oscillation or external mechanical movements have been proven to be promising candidates for low frequency transmitter. Unfortunately, the mechanical relaxation in modulation caused by the motion inertia of mechanical antennas limits modulation rates. Here, we developed a high-rate active phase modulation (APM) scheme that can eliminate the mechanical relaxation and approach the theoretical maximal bit rate in a magnetoelectric (ME) antenna. The proposed magnetoelectric antenna is based on a three-layered acoustic resonator with the length of only 8 cm, with a total efficiency of 3.59×10 ^-14 , which is closer to the Chu’s limit. The proposed APM is realized by the 180° phase reversal of the bias magnetic field that provided by a modulating coil. High bit rate of 18 kbps at the resonant frequency of 27.75 kHz is demonstrated by using APM, one order of magnitude higher than that of passive phase modulation due to the effective suppression of mechanical relaxation in such 180° phase variation.

In smart grid, the topological relationship between the transformers and the consumers in a low-voltage distribution network is crucial for powerline loss analysis, fault locating, and power dispatching, etc. The state-of-the-art method for topological relationship identification relies on the precision detection of weak characteristic current with a frequency of ~833 Hz. In this work, we design a magnetoelectric sensor based on the cantilever beam that made of Metglas/Ni/PZT composite and NdFeB permanent magnets, whose second-order resonant frequency is comparable to the frequency of characteristic current. Due to the resonant-enhanced sensitivity of the magnetoelectric sensor, weak characteristic current at μA level is detectable with a high sensitivity of about 111 mV/A in a non-intrusive manner. The proposed magnetoelectric current sensor doesn't require power supply and is able to detect weak currents as low as 0.43 μA. Theoretical calculations, finite element simulations, laboratory and field experiments have verified the effectiveness of the sensor, showing great potential for practical applications in non-invasive characteristic current detection.

The development of advanced magnetoelectric (ME) composites necessitates high-performance materials that are capable of achieving high levels of ME coupling, minimal magnetic loss, and absence or limited reliance on external excitation sources. In this paper, a (2-2) connectivity ME laminate integrates multiple layers of FeSiB alloy (Metglas) and Pb (Mg, Nb) O₃-PbTiO₃ (PMN-PT) single crystal, achieving a remarkable ME coupling coefficient of 2033.4 V/Oe·cm (sevenfold rise) by laser thermal annealing treatment. Here, the laser-induced nanostructures on Metglas, with an oxidized insulation layer and soft and hard magnetic dipole layer improve the Magneto-electric-mechanical coupling with a mechanical quality factor (Q_m) exceeding 350. More importantly, the interaction between amorphous and nanocrystalline dipoles triggers an Exchange Bias (EB) effect, leading to a self-biasing performance of 67.45 V/Oe·cm. Furthermore, the composite exhibits an excellent passive DC magnetic detection limit of 22 nT, and an improved weak AC magnetic detection limit down to 383 fT. These explorations offer the potential to enhance passive current measurement, and underwater communication, extend weak magnetic positioning and brain magnetic detection.

Mechanical antennas that driven by external mechanical oscillation and acoustic self-resonance have been demonstrated for portable VLF electromagnetic wave transmitting. However, the mechanical relaxation, caused by the energy transition between mechanical and electromagnetic energies during signal modulation, limits the modulation rate of mechanical antennas. Here, we use direct antenna amplitude modulation (DAAM) to enhance the modulation rate of the proposed magnetoelectric (ME) antenna. First, we construct a nonlinear converse magnetoelectric equivalent circuit model to optimize the DC magnetic field and operating frequency. The relaxation of Young’s modulus of the magnetic layer is gradually eliminated with the increase of modulation rate, until the Young’s modulus and radiation intensity of the ME antenna are no longer changed. Ideally, the modulation rate of DAAM is the half of the carrier rate, but the actual value is lower than the ideal value due to the overshoot and ringing from the modulation coil. Under the carrier frequency of 27.6 kHz and the modulation frequency of 6 kHz, the bit rate of DAAM reaches up to 12 kbps, which is 6 times higher than that of the conventional electrical modulation. Our work demonstrates the potential of portable ME antenna for practical high-rate VLF electromagnetic communication.