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.

In this paper, we report a barbell-shaped piezoelectric energy harvester (BSPEH) operating in a d₃₃ mode and aiming for mechanical vibration energy harvesting in a high temperature (H-T) circumstance. BSPEH is composed of a ring-shaped multilayer piezo-stack, a tip mass, and an elastic shaft connecting them together. The piezo-stack is made of bismuth scandium lead titanate (BiScO₃-PbTiO₃) ceramic with a large piezoelectric coefficient of d₃₃ = 450 pC/N and a high Curie temperature point T_c of around 450 °C. Experimental results show that the BSPEH works effectively and steadily in a wide temperature range from room temperature (R-T) till T_c/2. Furthermore, it is found that under a constant mechanical vibration excitation, the power output of the BSPEH at 200 °C is even two times higher than that at R-T. The proposed harvester shows a great potential for applications as a self-power source of wire-less sensor system in H-T circumstance.

The magnetic flux gate sensors based on Faraday’s Law of Induction are widely used for DC or extremely low frequency magnetic field detection. Recently, as the fast development of multiferroics and magnetoelectric (ME) composite materials, a new technology based on ME coupling effect is emerging for potential devices application. Here, we report a magnetoelectric flux gate sensor (MEFGS) for weak DC magnetic field detection for the first time, which works on a similar magnetic flux gate principle, but based on ME coupling effect. The proposed MEFGS has a shuttle-shaped configuration made of amorphous FeBSi alloy (Metglas) serving as both magnetic and magnetostrictive cores for producing a closed-loop high-frequency magnetic flux and also a longitudinal vibration, and one pair of embedded piezoelectric PMN-PT fibers ([011]-oriented Pb(Mg,Nb)O₃-PbTiO₃ single crystal) serving as ME flux gate in a differential mode for detecting magnetic anomaly. In this way, the relative change in output signal of the MEFGS under an applied DC magnetic anomaly of 1 nT was greatly enhanced by a factor of 4 to 5 in comparison with the previous reports. The proposed ME flux gate shows a great potential for magnetic anomaly detections, such as magnetic navigation, magnetic based medical diagnosis, etc.