Vladimir Genis

Cepstrum technique for multilayer structure characterization

The triple cepstrum, the third power of the inverse Fourier transform (IFT) of the logarithm of signal power spectrum, is used to characterize two-layer structures. The thickness of each layer can be found from the positions of the peaks in the triple cepstrum. Simulations and preliminary experiments have shown that the relative reflection coefficients can be reconstructed, in the ideal and lossless case, from the polarity and the amplitude of these peaks, as predicted by theory. The impedance pattern can be predicted even at low signal to noise ratio. A potential application of this method is to characterize blood vessel walls. The resulting thickness and impedance pattern could be useful in detecting and classifying plaques, particularly in the early stages.<<ETX>>

Computational Study of Kinematics of Capture of Magnetic Particles by Stent: 2-D Model

This paper presents a simple 2-D model to study the kinematics of capture of 1 μm diameter magnetic particles (MPs) by a periodic array of magnetic wires, which are aligned perpendicularly to Poiseuille flow in a rectangular 2-D channel in order to suggest improvements in the design of stent-assisted drug-targeting systems. The model examines the following: 1) the kinematics of particles near the wires; 2) the distribution of captured particles across the array of wires; and 3) the final position of particles that are not captured. An external homogenous magnetic field is applied perpendicularly to the axis of the wires and either perpendicular to or along the flow in order to magnetize the particles and the wires to saturation. The trajectories of MPs are determined using the first-order stiff ordinary differential equations that are solved numerically using MATLAB. These trajectories reveal that regardless of the orientation of external magnetizing field, it is always the first wire that captures the MPs. In addition, the particles that are not captured are found to be repelled to the center of the channel when compared with their starting position. This is an unexpected phenomenon indicating that the repulsive effect of the magnetic stent is stronger than the attractive effect, and the simplicity of our model allowed us to expose this previously undiscovered effect.

Environmental Control Plasma Educational Laboratory

The primary goal of the Environmental Control Plasma Educational Laboratory is to introduce students to the engineering principles of non-thermal plasma application for air cleaning from Volatile Organic Compounds (VOC) and other methods of VOC control and measurements, by combining hands-on laboratory experience with lectures. Specifically, during the laboratory sessions, the students learn the engineering and physical principles of non-equilibrium plasma systems operation using the unique pulsed corona system of the Drexel Plasma Institute Environmental Laboratory, carry out experiments on plasma cleaning of VOC contaminated air, measure dependence of Destruction and Removal Efficiency (DRE) of particular VOC on plasma power and other system parameters, and calculate the energy cost of VOC removal. In addition, the students are able to determine the air flow rate and VOC concentration in air stream before the treatment, after the scrubber, after the pulsed corona, and after the mist separator. Efficiency of VOC control by scrubbing is also discussed in details. The work in the laboratory enhances the fundamentals taught in the classroom sessions. Another goal of this laboratory course is to improve the students’ data gathering and communication skills. Therefore, a concise written report clearly describing all conclusions and comments is required within 7 days after completion of the laboratory session, upon which the students become familiar with basic VOC control techniques, gain hands-on experience with scrubbing and low-temperature plasma equipment, and are able to demonstrate the basic principles of low temperature plasma cleaning.

An Internet-Based Quality Control Laboratory via Integration of Remote Robotic Operation and Nondestructive Ultrasound Evaluation

This paper discusses the integration of a remote robot laboratory with nondestructive ultrasound evaluation (NDE) experiments. A remotely automated quality inspection system is designed to analyze dimensions as well as detect internal flaws of parts via an Internet-based NDE system. The remote quality inspection system includes: Internet controllable robot via Ethernet connection, multiple Web-cameras, Ultrasonic Automatic Flaw Detector, LabVIEW module, and computers with Internet access capable of remote connection. The uniqueness of the project lies in making this process Internet-based and remote robot operated. An Internet-based procedure such as the one we are developing will allow industrial companies involved in NDE procedures to increase productivity and profits by allowing an employee to monitor multiple operations over the Internet without having to be at a specified location. In addition, the utilization of remotely controlled robots for educational purposes is expected to increase the degree of immersive presence of the students engaging in such Internet-based laboratory exercises as well as the level of online interactivity between the faculty and students.Copyright

Chirp technique approach for objects' identification

Identification of inhomogeneities is of importance in the areas of tissue characterization, nondestructive evaluation and underwater acoustics. An approach to the identification of inhomogeneities by using a pulsed swept frequency technique (chirping) is presented. This technique allows frequency domain data to be determined directly from time domain data without using a Fourier transform algorithm and vice versa. The combined information contained in the time and frequency domain allows such parameters as size, shape, position, and structure of the object to be determined. The theoretical principles of the pulsed swept frequency technique are briefly outlined and the results of the experimental measurements from objects of simple geometry are presented. Preliminary experimental data indicate that the chirping approach can be successfully used in identification of differently shaped objects in water as well as objects embedded in tissue.<<ETX>>

A UNIVERSITY COURSE ON THE PHYSICAL PRINCIPLES OF ULTRASOUND NONDESTRUCTIVE EVALUATION

The ultrasound nondestructive evaluation (NDE) of materials course was offered to Applied Engineering Technology (AET) students at Drexel University for last two years. The main objective of this three‐credit (thirty‐hour) course is to introduce students to physical principles of ultrasound measurements and to demonstrate the basic principles of ultrasound nondestructive evaluation of materials by combining hands‐on laboratory experience with lectures. The work in the laboratory enhances the fundamentals taught in the classroom sessions.

Modified Born approximation for solving scattering problems

Scattering of ultrasonic waves in inhomogeneous media is described by the inhomogeneous differential equations. Such equations could be solved using a method of consecutive approximations, such as the Born approximation. The Born approximation is applicable when (n−1)<1 and 2ka(n−1)<1, where n is the refraction index and ka is the wave dimension of the scatterer. For the Born approximation, it is assumed that the acoustic field inside of a scatterer is substituted by the acoustic field of the incident wave, along with the wave number of the surrounding media. In this work, the modified Born approximation is used, where the acoustic field inside of a scatterer is substituted by the acoustic field of the incident wave, along with the wave number of the scatterer. A similar approach is used for solving the scattering problems of multilayered scatterers, which have weak scattering properties. The computed and experimental scattering characteristics for the elastic scatterers with various acoustical impedance ...

Parametric mechanism of subharmonic generation by the microbubble contrast agents

Contrast agents, consisting of gas‐filled microbubbles, are widely used in biomedical ultrasound for enhancing the capabilities of ultrasound imaging. The behavior of contrast agents has been shown to lead to the generation of harmonic and subharmonic components in the backscattered signal. The mechanism of subharmonic generation is not quite understood. It is known that the oscillation of gas‐filled bubbles is described by nonlinear equations. In this work, the parametric approach to solving this problem is introduced, where the nonlinear equation is substituted by the linear equation with time‐varying parameters, such as flexibility of the bubble. The equation describing the oscillation of the bubble is reduced to the Mathieu equation, and conditions for unstable solutions are presented. It has been demonstrated that the regions of instability occur in the vicinity of the frequencies w=1/2 wo, w=3/2 wo, etc., which correspond to generation of the first and higher subharmonics. Criteria for determining t...

Sound scattering by Gauss beam from cylindrical objects

Practically, when diagnosing vessels by focusing array, the vessel is radiated not by the plane wave, but a time‐limited beam. Here one can see the results of theoretical and experimental research of Gauss beam sound scattering from cylindrical objects with wave resistance different from the medium. Well‐known results of sound scattering on cylinders with limited sizes are wrong in reality, because of limiting the vertical size of the cylinder. In fact, all the objects, including the cylinder, are radiated by a nonconcentrated beam, like a Gauss beam. Theoretical and experimental results of Gauss beam scattering in the band of parameter α=a/w (where a‐cylinder radius; w‐Gauss beam width on e−1 range) from 10−6 (quasiplane wave) to 100 (super‐narrow beam) show, that a scattered wave spectrum changes very substantially. This point needs caution, and immediately changes classic results for the plane wave. Also, the sound beam echo‐signal spectrum in the reverse direction gives one the ability to classify and...

Sound scattering and transmission through cylindrical layer with concentrated defects

An experimental method of defect detection in a cylindrical shell is proposed. Defects are the cylindrical hollows (the projections) on the outside or the inside of the shell, filled up, and encircled by water. The defect diameter makes up 1–2 mm (0–0,95) h long, where h—is a shell thickness. The inverse sound scattering field and pass wave field on the shell axis were measured in the sound acoustic beam. Experimental investigations were compared with theoretical investigations by changing the shell wave dimension in the 2–20 range (the 3‐D resilience theory). The presence of the shell resonance clears surges and its inside liquid pillar as lengthening of the defect gradually results in their being illegible. The long defects reduce discrimination of the resonance system shell water. The through defect and the Helmholtz resonator are similar. The measurement results of the shells with defects and without were compared, when the shell was radiated by narrow sound beam (the beam width 10–15 times as much as...