Poly(vinylidene fluoride-co-trifluoroethylene) (P(VDF-TrFE)) hydrophone emerges as a transformative candidate for future hydrophone designs for its exceptional sensitivity, good acoustic impedance matching with water, capability for large-area conformal arrays, lightweight structure, and cost-effectiveness. In this work, we present a planar hydrophone made from P(VDF-TrFE) piezoelectric material, including a six-element and one-dimensional flexible hydrophone array, and showcasing a leap in performance over traditional ceramic hydrophones. Furthermore, the device delivers remarkable acoustic wave reception across a frequency range of 10 kHz to 40 kHz, and achieves a sensitivity response of approximately -179 dB fluctuating within 4 dB. This research presents novel concepts and methodologies for large-area, conformal underwater acoustic sensing, and significantly propels the development of high-performance flexible hydrophones, which also addresses the critical needs of underwater platforms, such as submarines, unmanned underwater vehicles (UUVs), and underwater robots, enhancing their capabilities for detection, perception, and communication.

The time reversal (TR) method is applied to the localisation of microcrack based on the vibro-acoustic modulation (VAM) which is one of the effective non-linear ultrasonic testing approaches in this paper. The principle of the localisation combining the VAM and TR was analysed and deduced in theory. Then, the VAM experimental system was established and used to detect the aluminium plate and tube containing microcrack. The signals which were produced when the ultrasonic wave and vibration wave interact with the microcrack were received from different positions using the numbers of piezoelectric ceramic pieces. The non-linear components were extracted from the received signals by empirical mode decomposition method. Finally, the non-linear components were reversed in time domain and reloaded into the finite element model of the aluminium plate and tube. The location information of microcrack could be represented in the cloud image of aluminium plate and tube by focusing reversed non-linear signals. The experiment results have been shown that the obtained microcrack location information is closed to the actual location of microcrack in the tested specimen and the localisation method for microcrack is effective.

This paper proposes an underwater pulse transmission model and an optimization model for pulse compression to mitigate the problem of pulse broadening in underwater transmission, which reduces the data rate of underwater wireless optical communication (UWOC). Deriving from the Lorentz–Lorenz equation and the Schrödinger equation, the underwater pulse propagation model is established, from which we can obtain the temporal evolution of the pulse over time and propagation distance in water. To address the pulse broadening, a nonlinear optimization model is then developed to determine the optimal dispersion compensation parameters. The results demonstrate that this approach can effectively handle ultrafast laser pulses with an initial width of 50 fs, which undergo a 6.2-fold broadening as they propagate through water. The nonlinear optimization model provides targeted dispersion compensation for the broadened pulse, restoring its original width. The method presented in this paper offers substantial theoretical value and practical potential for high-speed UWOC applications.

The detection and quantitative evaluation of internal defects in polymer materials are critical for practical engineering applications. This paper introduces a method for the quantitative evaluation of defects in polymer materials using the ultra-sound thermal effect. Initially, a heat generation model for polymer materials under ultrasonic excitation is developed, and based on heat conduction theory, the mechanism by which defect characteristics affect the temperature distribution in infrared images is examined. A hybrid simulation and experimental approach is employed to analyze the variation patterns of infrared images on the surfaces of materials with various defects under the ultrasound thermal effect. A method is proposed to accurately assess the size and location of defects by measuring the width of the opening and the deepest concave point in the anomalous regions of infrared images. Local image frequency variations are assessed through normalized local gradients and variance, while an adaptive fractional-order model is developed to enhance the images. Morphological operations are employed to reconstruct grayscale images, with the resulting images serving as foreground markers for subsequent segmentation using the watershed algorithm. The convex hull algorithm is utilized to compute the width of the opening and the location of the deepest concave point in the infrared images, thereby facilitating quantitative defect analysis. This approach offers a novel perspective for the quantitative evaluation of internal defects in polymer materials.