Lamb waves manipulation by piezoelectric metasurface with tunable diffraction orders

In this paper, a piezoelectric metasurface is proposed to manipulate the anti-symmetric mode Lamb wave by altering the diffraction order. The metasurface attached to a host plate is symmetrically arranged by out-of-plane polarized piezoelectric patches connected with synthetic inductance circuits. Without changing the physical configuration, the transmitted phase of the anti-symmetric mode Lamb wave can be shifted arbitrarily in 0 ∼ 2π range by the metasurface. Furthermore, the relationship between the phase gradient and diffraction order is investigated, and different orders of diffraction waves can be obtained by adjusting the shunting inductance circuits. The symmetric transmission and asymmetric transmission from a couple of axis symmetric incident waves can be realized by utilizing +1st-order and −1st-order diffraction. Moreover, omnidirectional wave reflection and wave trapping in channelized waveguides can also be realized by utilizing the 0th-order diffraction. The results indicate that the proposed piezoelectric metasurface has great potentials in manipulating guided waves with a large incident angle and isolating wave propagation

Lamb waves manipulation by piezoelectric metasurface with tunable diffraction orders

In this paper, a piezoelectric metasurface is proposed to manipulate the anti-symmetric mode Lamb wave by altering the diffraction order. The metasurface attached to a host plate is symmetrically arranged by out-of-plane polarized piezoelectric patches connected with synthetic inductance circuits. Without changing the physical configuration, the transmitted phase of the anti-symmetric mode Lamb wave can be shifted arbitrarily in 0 ∼ 2π range by the metasurface. Furthermore, the relationship between the phase gradient and diffraction order is investigated, and different orders of diffraction waves can be obtained by adjusting the shunting inductance circuits. The symmetric transmission and asymmetric transmission from a couple of axis symmetric incident waves can be realized by utilizing +1st-order and −1st-order diffraction. Moreover, omnidirectional wave reflection and wave trapping in channelized waveguides can also be realized by utilizing the 0th-order diffraction. The results indicate that the proposed piezoelectric metasurface has great potentials in manipulating guided waves with a large incident angle and isolating wave propagation.</jats:p

The summer-fall anticyclonic eddy west of Luzon: Structure and evolution in 2012 and interannual variability

The Conductivity-Temperature-Depth (CTD) and acoustic Doppler current profiler (ADCP) measurements along 18 degrees N off the western Luzon in the South China Sea (SCS), collected during a cruise from August 12-14,2012, were used to explore the vertical structure of an anticyclonic eddy (AE) during the observational period. Further, the French Archiving, Validation and Interpretation of Satellite Oceanographic data (AVISO) sea level anomaly (SLA) and corresponding anomalous surface geostrophic velocity were used to study the temporal evolution of the AE. The vertical structure of the AE along 18 degrees N in August 2012 showed a trough located near 117.5 degrees E. The AE extended vertically downward and its distinct feature was identifiable to 200 m depth. Seasonal variations of SIA indicate that the AE lasted for 5 months (June to early November), going through the growth and nearly stationary period from mid-June to late August and then propagating westward along 18 degrees N with varying phase speeds and shapes to the continental slope off the southeastern Hainan Island during late September to November. Furthermore, T-S characteristics suggest that the AE was generated off the western Luzon. Interannual variations of the summer (July-September) SLA presented by Empirical Orthogonal Function analysis, indicates that the local circulation was enhanced by the anomalous anticyclonic eddy along 18 degrees N in the years of 2008, 2010, 2012 and 2013 during the period from1993 to 2014. (c) 2017 Elsevier B.V. All rights reserved

Theoretical analysis of guided waves propagation in periodic piezoelectric plates with shunting circuits

The tunable manipulation of guided waves in plates brings out great potential applications in engineering practices, and the electromechanical coupling effects of piezoelectric material with shunting circuits have exhibited powerful tunability and flexibility for guided wave propagation. In this paper, a theoretical model is established to analyze the guided wave propagation in one-dimensional periodic piezoelectric plate constructed from a periodic array of anisotropic piezoelectric materials under periodic electrical boundary conditions. The extended Stroh formalism incorporating with the plane wave expansion method is developed to transform the wave motion equations of the periodic piezoelectric plate into a linear eigenvalue system, and a more concise and elegant solution of generalized displacement and generalized stress can be derived. There are various dispersion relations in terms of the altering electrical boundary conditions to be acquired, if the thin electrodes with shunting circuits are attached periodically to both surfaces of the piezoelectric plate. Analytical results show that the coupling of the local electric resonant mode and propagating elastic wave modes can induce hybridization bandgaps, and the bandgaps of Lamb waves and SH waves in the piezoelectric plate can be tuned by designing appropriate material polarization orientations and shunting circuits. In addition, the Bragg bandgaps can also be influenced by the external circuits. Results indicate that the proposed theoretical model can effectively analyze the performances of guided waves in periodic piezoelectric plate and provide useful theoretical guidance for designing smart wave control devices.</jats:p

Exercise-Induced Excessive Blood Pressure Elevation Is Associated with Cardiac Dysfunction in Male Patients with Essential Hypertension

Objective. Cardiopulmonary exercise testing (CPET) has been used to explore the blood pressure response and potential cardiovascular system structure and dysfunction in male patients with essential hypertension during exercise, to provide a scientific basis for safe and effective exercise rehabilitation and improvement of prognosis. Methods. A total of 100 male patients with essential hypertension (aged 18–60) who were admitted to the outpatient department of the Center for Diagnosis and Treatment of Cardiovascular Diseases of Jilin University from September 2018 to January 2021 were enrolled in this study. The patients had normal cardiac structure in resting state without clinical manifestations of heart failure or systematic regularization of treatment at the time of admission. Symptom-restricted CPET was performed and blood pressure was measured during and after exercise. According to Framingham criteria, male systolic blood pressure (SBP) ≥210 mmHg during exercise was defined as exercise hypertension (EH), and the subjects were divided into EH group (n = 47) and non-EH group (n = 53). Based on whether the oxygen pulse (VO2/HR) plateau appeared immediately after anaerobic threshold (AT), the EH group was further divided into the VO2/HR plateau immediately after AT (EH-ATP) group (n = 19) and EH-non-ATP group (n = 28). The basic clinical data and related parameters, key CPET indicators, were compared between groups. Result. Body mass index (BMI) visceral fat, resting SBP, and SBP variability in EH group were significantly higher than those in non-EH group. Moreover, VO2/HR at AT and the ratio of VO2/HR plateau appearing immediately after AT in EH group were significantly higher than those in the non-EH group. The resting SBP, 15-minute SBP variability, and the presence of VO2/HR plateau were independent risk factors for EH. In addition, work rate (WR) at AT but also WR, oxygen consumption per minute (VO2), VO2/kg, and VO2/HR at peak were significantly lower in the EH-ATP group compared to the EH-non-ATP group. Peak diastolic blood pressure (DBP) increment and decreased △VO2/△WR for AT to peak were independent risk factors for VO2/HR plateau appearing immediately after AT in EH patients. Conclusion. EH patients have impaired autonomic nervous function and are prone to exercise-induced cardiac dysfunction. EH patients with exercise-induced cardiac dysfunction have reduced peak cardiac output and exercise tolerance and impaired vascular diastolic function. CPET examination should be performed on EH patients and EH patients with exercise-induced cardiac dysfunction to develop precise drug therapy and effective individual exercise prescription, to avoid arteriosclerosis and exercise-induced cardiac damage. The retrospective study protocol was approved by medical ethics committee of the First Hospital of Jilin University (AF-IRB-032-06 No. 2021-015). The study was registered with the Chinese Clinical Trials Register, registration number: ChiCTR2100053140

Reconfigurable metamaterial for asymmetric and symmetric elastic wave absorption based on exceptional point in resonant bandgap

AbstractElastic wave absorption at subwavelength scale is of significance in many engineering applications. Non-Hermitian metamaterials show the ability in high-efficiency wave absorption. However, the single functionality of metamaterials is an important limitation on their practical applications for lack of tunability and reconfigurability. Here, we propose a tunable and reconfigurable non-Hermitian piezoelectric metamaterial bar, in which piezoelectric bars connect with resonant circuits, to achieve asymmetric unidirectional perfect absorption (UPA) and symmetric bidirectional perfect absorption (PA) at low frequencies. The two functions can be arbitrarily switched by rearranging shunted circuits. Based on the reverberation-ray matrix (RRM) method, an approach is provided to achieve UPA by setting an exceptional point (EP) in the coupled resonant bandgap. By using the transfer matrix method (TMM) and the finite element method (FEM), it is observed that a non-Hermitian pseudo-band forms between two resonant bandgaps, and the EP appears at the bottom of the pseudo-band. In addition, the genetic algorithm is used to accurately and efficiently design the shunted circuits for desired low-frequency UPA and PA. The present work may provide new strategies for vibration suppression and guided waves manipulation in wide potential applications.</jats:p