Small Number Of Measurement Points Research Articles

Damage Detection Using Optical Measurements and Wavelets

The paper presents an application of the wavelet transform for damage detection based on optical measurements. A number of important issues that need to be considered when image sequences are used for vibration analysis are discussed. These include: correspondence of image features from image to image, image calibration and spatial resolution. The principles of image edge detection are discussed and a comparison between the wavelet approach and the classical method is presented. A novel damage detection method based on optically measured mode-shape data is proposed. The method is illustrated using a simple cantilever beam experiment. The major advantage of the method is the significantly increased number of discrete points used to describe mode shapes. This is in contrast to classical techniques where in practice a small number of measurement points are obtained from a limited number of sensors.

A Modified Approach to the Characterization of EM Environments Irradiated by Unknown Sources

This paper presents a modified approach to the characterization of Electromagnetic (EM) environments irradiated by unknown sources. The approach based on application of Finite difference method (FDM) for the solution of Maxwell's equations subject to the constraints imposed by the measured values of the field at a relatively small number of measurement points and by the specified boundary conditions. The resulting III-conditioned system of equations is solved using Conjugate Gradient Method (CGM) which proves to be an accurate method for extraction of maximum information from minimum measurement effort. The applicability of the approach to EM environment characterization is demonstrated through two dimensional and three dimensional examples.

Reconstruction of two-dimensional current distribution from tangential MCG measurement

We describe a two-dimensional reconstruction method for tangential magnetocardiograms (MCGs). This method is based on two-dimensional Fourier analysis, and we used a new type of window function for tangential MCG to solve the problem of the small number of measurement points. By using this method, cardiac activity can be estimated as a two-dimensional current distribution. To determine the effectiveness of this method, we measured tangential MCGs of normal subjects, and compared the estimated current distribution with the actual cardiac muscle activity. Using this method, we were able to clearly show cardiac activity.

Minimization of bias error due to windows in planar acoustic holography using a minimum error window

Bias errors in the prediction of a sound field using planar acoustic holography are due to aliasing and window effects. It is noteworthy that aliasing is negligible in the forward predictions if the sampling space is less than a quarter wavelength. However, bias error induced by a window is the major concern for accurate holographic prediction because of the small number of measurement points in the planar acoustic holography. For the reduction of this error, a new class of window, the MEW, is proposed and compared with Hann, Gaussian, and Kaiser–Bessel windows. It is built by modifying the method that Papoulis proposed by minimizing the second-order moment of the window spectrum. The characteristics of the MEW vary with the number of weighting values and the number of higher-order moment terms to be eliminated. The applicability of the MEW on planar acoustic holography is demonstrated.

A New Approach to Volumes Irradiated by Unknown Sources

We suggest an approach to the characterization of electromagnetic (EM) environments irradiated by unknown sources. The approach is based on the numerical solution of Maxwell's equations subject to the constraints imposed by the measured values of the field at a small number of measurement points and by boundary conditions. A thorough examination of a method for the numerical solution is presented. The examples attempted demonstrate the approach but reveal deficiencies in the numerical method. Possible future directions are suggested.