The directivity of the quasi-static component (QSC) is quantitatively investigated for evaluating the orientation of a micro-crack buried in a thin solid plate using the numerical simulation method. Based on the bilinear stress–strain constitutive model, a three-dimensional (3D) finite element model (FEM) is built for investigating the nonlinear interaction between primary Lamb waves and the micro-crack. When the primary Lamb waves at A0 mode impinge on the micro-crack, under the modulation of the contact acoustic nonlinearity (CAN), the micro-crack itself will induce QSC. The amplitude of the QSC generated can be used for directly charactering the micro-crack orientation. The finite element simulation results show that the directivity of the QSC radiated by the micro-crack is closely related to the orientation of the micro-crack, allowing for the characterization of micro-crack orientation without the need for baseline signals. The results indicate that the directionality of the QSC can be used for characterizing the orientation of the micro-crack. The amplitude of the QSC is affected by the contact area between two surfaces of the micro-crack. It is demonstrated that the proposed method is a feasible means for the characterization of micro-crack orientation.

Piezoelectric energy harvester (PEH) is being world widely studied by many researchers due to their excellent advantages over batteries. Therefore, how to improve the capability of energy harvesting has become a hot research topic. In this study, based on the theory that the electromechanical coupling coefficient is proportional to the difference of mode shape slopes at the two ends of a piezoelectric sheet made of macro fiber composite, a modified cantilever structure consisting of two segments is proposed. The piezoelectric sheet is affixed on the segment close to the fixed end, while the segment containing the free end is rotated by 90° along its axial direction. The mode shape of the cantilever structure is calculated based on the Euler-Bernoulli beam theory. Prototypes of the conventional and modified PEHs are fabricated and tested. Compared to the conventional one, the experimental result of the modified PEH demonstrates that the electromechanical coupling coefficient is enhanced by 600%, and the output power is increased by more than 300%. The proposed PEH is simple, highly efficient, and easy-realized.

The Chu’s limit imposes a significant challenge for traditional antennas operating at extremely low frequencies, as they require a large size due to the long operating wavelength, thus limiting their applicability. To reduce the antenna size, this paper proposes a vibrating beam system for long-wave communication that leverages the inverse piezoelectric effect, vibration theory, and Maxwell’s equations. A prototype utilizing beam structures is developed and examined experimentally. Furthermore, the frequency modulation of the vibrating beam system and signal transfer protocol are investigated in detail. The experimental results demonstrate that exciting different vibration modes of the vibrating beam system leads to varied electromagnetic signals in specific rules, enabling long-wave communications and ensuring confidentiality. This work offers valuable insights into the potential of local information exchange among close-range platforms. It also highlights the promising approach of integrating piezoelectric material and magnets within the vibrating beam system, showcasing their potential towards practical applications in long-wave communication.

Micro defects, such as pore and inclusions, inevitably appear in the forming process of three-dimensional (3D) printed materials, which would affect the mechanical properties of materials. Therefore, a nondestructive testing method is urgently needed to evaluate the effect of these micro defects on the mechanical properties of materials. In the present work, by using a nonlinear ultrasonic testing technology, mechanical test and characterization of material microstructure, the relationship between the relative acoustic nonlinearity parameter (RANP), tensile strength and material defect ratio of 3D printed aluminum alloy specimens under different scanning powers is investigated. The analysis results show that the greater the material defect ratio is, the smaller the tensile strength is and the greater the RANP is, and the RANP could be used to evaluate the strength of materials. Moreover, fatigue damage induced by high cycle fatigue loading test in the first stage of early performance degradation, the results of nonlinear ultrasonic testing show that the RANP presents an increasing trend as the fatigue load increases. By observing changes in material microstructure, it is found that the increasing acoustic nonlinearity parameter is due to the directional coarsening degree of the precipitated phase increasing, which shows that RANP is very sensitive to the change of material microstructure. The above results show that, the nonlinear ultrasonic testing technology can quantitatively evaluate and predict the mechanical performance and early performance degradation of 3D printing aluminum alloy.