The origin of low-order and high-order impedance-coupled resonant modes in piezoelectric-excited millimeter-sized cantilever (PEMC) sensors: Experiments and finite element models

The characteristics of both low-order and high-order resonant modes exhibited by piezoelectric-excited millimeter-sized cantilever (PEMC) sensors were investigated to determine the coupling between electrical impedance and resonant modes observed experimentally. Experimentally measured frequency response spectra correlated well (<5% difference; n = 10 sensors) with three-dimensional (3D) finite element model (FEM) calculations. FEM frequency response and eigen frequency analyses revealed the sensor's resonant modes were complex, and characterized by combinations of transverse, torsional, longitudinal, buckling, and lateral motion. The magnitude of average integrated charge and current density change in the piezoelectric (lead zirconate titanate; PZT) layer at resonance directly correlated with coupling of resonant modes to electrical impedance measurement. Of the 32 resonant modes predicted by eigen frequency analysis in the frequency range 0-1 MHz, only a subset of 17 modes produced charge and current density changes in the PZT layer greater than off-resonance values. Thus, only the subset of resonant modes was coupled to electrical impedance changes and could be exploited for sensing. Transverse, longitudinal, and lateral motion of the piezoelectric layer coupled strongly with the PZT electrical impedance, while torsional and buckling motion did not. Electrically decoupled resonant modes were made measurable by introducing minor geometric asymmetry in composite layer alignment. High-order modes were shown experimentally to exhibit sub-femtogram sensitivity to mass-changes in air. Such modes consisted of combinations of transverse and longitudinal modes in both sensor layers.     

压电作动器在基于声辐射模态的ASAC中的应用

控制作动器的选取和设计是实现主动结构声学控制的关键一环。利用压电材料的逆压电效应,选择矩形压电片作为控制作动器应用于基于声辐射模态的主动结构声学控制中,提出了基于声辐射模态的压电作动器主动控制策略,并得到了最佳控制电压的获取方法。以简支板为例,通过压电作动器控制效果分析,揭示了压电作动器控制的内在规律;通过与单点力控制效果的比较分析,验证了压电作动器控制策略的优越性。     

Modelling load-settlement behaviour of piles using high-order neural network (HON-PILE model)

An accurate estimation of pile response to loading is a challenging task due to the complexity of the soil-pile interactions and uncertainties in the soil properties. Conventional methods of predicting pile load-settlement relationship either oversimplify the problem or require the parameters that are difficult to determine in the laboratory. In this study, a high-order neural network (HON) is developed to simulate the pile load-settlement curve using properties of the pile and SPT data along the depth of pile embedment as inputs. The results indicated a significant improvement in the quality of HON predictions over that of BPN, RBF and GRNN models. Based on the comparisons with the predictions of elastic and hyperbolic models, the proposed HON model provides better predictions than existing theoretical models.     

Dynamics of a rotating flexible and symmetric spacecraft using impedance matrix in terms of the flexible appendages cantilever modes

The subject of this work is the dynamics of a rotating spacecraft. The spacecraft is modeled as a main rigid body connected to two flexible solar panels. The orbital motion of the whole spacecraft with a constant angular velocity is considered, interacting with small rigid motions of the main body, and small elastic deformations and infinitesimal vibrations of the solar panels. A continuum approach based on the Rayleigh–Ritz discretization is used to describe the distributed flexibility in the spacecraft. Rayleigh–Ritz discretization functions used are the clamped modes of the solar panels. This method enables us to construct the impedance matrix of the whole system relating to the displacement of the main body and the external torque. A spectral expansion of this impedance matrix, in terms of these clamped modes is obtained in the frequency domain. The numerical results presented show that for small values of orbital angular velocity, the vibration motion frequencies of the flexible parts (solar panels) are not perturbed substantially. Moreover, when great values of orbital angular velocity are simulated, these frequencies change considerably. The present investigation based on the Rayleigh–Ritz discretization shows the effect of the interaction between the orbital motion of the whole spacecraft and the vibration motions of the flexible parts.     

Model ensemble for the simulation of plankton community dynamics of Lake Kinneret (Israel) induced from in situ predictor variables by evolutionary computation

This study addresses the need for operational models in view of rapidly advancing in situ sensor technology that puts lakes into online surveillance mode. A model ensemble for simulating plankton community dynamics in Lake Kinneret (Israel) from 1988 to 1999 has been induced from electronically-measurable predictor variables (EMPV) such as water temperature, pH, turbidity, electrical conductivity and dissolved oxygen by the hybrid evolutionary algorithm HEA. It cascade wise predicts the total nitrogen to total phosphorus ratios TN/TP, concentrations of chlorophyta, baccilariophyta, cyanophyta and dinophyta, as well as densities of rotifera, cladocera and copepoda solely from EMPV. The best coefficients of determination (r²) have been achieved with 0.6 by the dinophyta model, 0.45 by the rotifera model and 0.44 by the bacillariophyta model. The worst coefficients of determination (r²) have been produced by the cladocera model with 0.24 and by the TN/TP model with 0.28. Despite the differences in the r² values and apart from the cladocera model, the remaining models matched reasonably well seasonal and interannual plankton dynamics observed over 11 years in Lake Kinneret.The model ensemble developed by HEA also revealed ecological thresholds and relationships determining plankton community dynamics in Lake Kinneret solely based on in situ predictor variables.     

Development of a new fluorescent sensor based on a triazolo-thiadiazin derivative immobilized in polyvinyl chloride membrane for sensitive detection of lead(II) ions

A new sensor membrane based on a novel triazolo-thiadiazin derivative immobilized in polyvinyl chloride has been developed for the determination of Pb(II) ions that displays excellent performance. The parameters involved in the preparation of the optode and determination of Pb(II) were optimized. Under the optimal conditions, the proposed sensor displays a calibration response for Pb(II) over a wide concentration range of 5.0 × 10⁻⁸ to 3.8 × 10⁻⁴ M with the detection limit of 2.2 × 10⁻⁸ M. In addition to high reproducibility and reversibility of the fluorescence signal, the sensor also exhibits good selectivity over common metal ions. The optode membrane developed is easily prepared, stable, rapid, and simple for the determination of Pb(II). The accuracy of the proposed sensor was confirmed by analyzing standard reference materials of natural water and surface water. The sensor was successfully used for the determination of Pb(II) ions in water samples with satisfactory results.