Zutang Wu

Conventional particle image velocimetry (PIV) techniques face an inherent trade-off between temporal resolution and single-pulse laser energy, limiting their performance in shock wave measurements. This study develops a multi-channel parallel PIV system with programmable timing control to address this constraint. By distributing laser pulses across eight independent optical channels, the system decouples single-pulse energy from the repetition rate, enabling continuous velocity field measurements at microsecond temporal resolution with high signal-to-noise ratio. Experiments were conducted on a planar shock wave propagating over a trapezoidal step in a shock tube facility. The system captured velocity fields at seven consecutive time instants with a 1 μs pulse interval, revealing the curved evolution of diffracted shock fronts and transient flow separation induced by shock–boundary-layer interaction. Comparison with unsteady Reynolds-averaged Navier–Stokes simulations demonstrated that the PIV system resolves fine-scale post-shock perturbations and turbulent fluctuations that were numerically dissipated in computational fluid dynamics. The results verify that the parallel-channel architecture accurately captures unsteady flow structures during shock reflection and diffraction, offering a reliable diagnostic technique for investigations of shock wave dynamics.

Piezoelectric pressure sensors are commonly used as blast wave pressure sensors in explosion testing. Accurate measurement of blast wave overpressure is of great significance. In explosion testing, piezoelectric pressure sensors exhibit a baseline drift phenomenon. This paper analyzes the mechanism of the baseline drift phenomenon observed in explosion testing through experiments and simulation, identifying the mechanism behind it. From an experimental perspective, it is determined that the thermal effect of light induces the baseline drift phenomenon. Furthermore, modeling and simulation of the piezoelectric pressure sensor using COMSOL 6.2 Multiphysics software confirms that the photothermal effect causes changes in the temperature field within the sensor’s internal structure, which in turn brings the thermal stress. The thermal stress superimposes on the output of piezoelectric pressure sensors. This is the fundamental cause of the baseline drift phenomenon in piezoelectric pressure sensors. This research provides a crucial foundation for understanding the mechanisms by which explosions affect piezoelectric pressure sensors.

The generalized Radon–Fourier transform (GRFT) is a well-established coherent accumulation technique for high-speed and high-mobility target detection. However, this method tends to suffer from the difficulty of identifying the main lobe from multiple blind speed sidelobes (BSSLs) and the computational complexity is generally high. To address these challenges, we propose a new method, namely the BSSL Traction Particle Swarm Optimization (BTPSO), to robustly and accurately extract the main lobe. In the method, the relationship between the main lobe and the BSSLs is used to attract particles to potential positions of the main lobe in the group when trapped in local optimal, and a new termination criterion in which multiple particles should converge to the same optimal value is proposed to avoid local convergence. Simulation examples show that the proposed method can improve the probability of converging to the main lobe peak while reducing cost time, and its good adaptability to low signal-to-noise ratio (SNR) cases is well verified.

Hypertension is a very significant public health problem and has become a potential risk for cardiovascular and renal diseases. Blood pressure (BP) including systolic BP (SBP) and diastolic BP (DBP) is a vital parameter that should be monitored regularly for the early detection and prevention of chronic diseases. The traditional cuff-based BP monitors can cause discomfort to the users due to inflation and deflation. Here, a wearable and flexible photoplethysmography (PPG) patch sensor based on the polydimethylsiloxane (PDMS) substrate and double-layer serpentine structure with a closed loop that can omit the transfer printing process is proposed for cuffless BP estimation. Three models are adopted to estimate the BP. The accuracy of SBP and DBP obtained are 3.68 ± 2.37 and 4.9 ± 3.78 mmHg for the first model and 3.61 ± 2.62 and 4.72 ± 3.46 mmHg for the second model, respectively. The third model introduces the Kalman filtering to optimize the solution of the coefficients of the second model to forecast BP. As a result, the accuracy of SBP and DBP as high as 2.94 ± 2.35 and 3.41 ± 2.94 mmHg, respectively, is realized. The results show that the introduction of the Kalman filter algorithm to forecast BP can not only reduce the number of calibrations, but also improve the accuracy of BP estimation.

The electromagnetic particle velocity measurement technology is an important measurement method in the study of stress wave propagation. This paper analyzes the problem that the pulsed-magnetic-field-based electromagnetic particle velocity measurement technology will introduce additional induced electromotive force, and proposes an electromagnetic particle velocity measurement technology based on superconducting magnet. After considering the factors of electromagnetism, structure and heat distribution, a superconducting magnet with 500mm room-temperature bore was constructed, and the proposed electromagnetic particle velocity measurement system based on the superconducting magnet was designed subsequently. The experiment of filled explosion in PMMA was carried out, and high quality particle velocity and displacement signals were obtained, which verified the measurement performance of the system. The proposed method can provide a more powerful test means for the study of stress wave propagation.

Most of fiber-optic pressure sensors used in shock wave measurements are based on deformations of sensing elements. These approaches result in low dynamic pressure ranges for these sensors used in the air. A novel fiber-optic method based on the relationship between pressure and the acceleration of a diaphragm is proposed to obtain peak reflected pressure of shock waves in the air. The optical sensor is designed with a thin circular diaphragm as the sensing element, and the Fabry-Perot optical interferometry is used to detect the acceleration of the diaphragm. Shock tube and explosive-blast experiments prove that the proposed fiber optic method is feasible and has the advantages of no calibration, high precision and fast response time. The proposed fiber-optic pressure method has potential in practical applications for shock wave measurements.