Showing papers by "Ajit Mal published in 2002"

A Thermally Re-mendable Cross-Linked Polymeric Material

Abstract: We have developed a transparent organic polymeric material that can repeatedly mend or "re-mend" itself under mild conditions. The material is a tough solid at room temperature and below with mechanical properties equaling those of commercial epoxy resins. At temperatures above 120 degrees C, approximately 30% (as determined by solid-state nuclear magnetic resonance spectroscopy) of "intermonomer" linkages disconnect but then reconnect upon cooling, This process is fully reversible and can be used to restore a fractured part of the polymer multiple times, and it does not require additional ingredients such as a catalyst, additional monomer, or special surface treatment of the fractured interface.

Interaction of focused ultrasound with biological materials

Abstract: This work is motivated by possible medical applications of focused ultrasound in minimally invasive treatment of a variety of disorders. The mechanical and thermal effects caused by high-frequency ultrasound in different material systems are calculated using a finite element based program called PZflex. The pressure distributions generated by plane as well as focused ultrasound beams are presented. For the focused beam, the temperature distribution in the focal zone is also calculated. The results indicate that the heating efficiency of the ultrasound energy in the focal region depends on the exciting frequency and the geometry of the focal zone depends on the material being tested. At higher excitation energies, cavitation and nonlinear effects need to be included in the simulations. These effects are under current investigation.© (2002) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Transcutaneous spine trauma and disorders treatment using ultrasonically induced confined heat zone

Abstract: A method of heating a tissue using pulsed focused ultrasonic waves, and an apparatus for carrying out the method. The method comprises depositing an amount of ultrasound energy sufficient to heat the selected site without adversely damaging other parts of the tissue. The apparatus comprises an ultrasonic source for producing pulsed ultrasonic waves, a lens for focusing the ultrasonic waves, and a controller for controlling wave frequency and transmission parameters of the ultrasonic waves. The method and apparatus can be used to treat spine or other joint disorders associated with lax ligamentous tissues, i.e., soft tissue disruption.

Interaction of high intensity focused ultrasound with biological materials

Abstract: This work is motivated by the possible medical application of focused ultrasound in minimally invasive treatment of a variety of disorders including those associated with soft tissue or disk element disruption in the vicinity of the spine causing impingement on the spinal cord.

Stress relaxation of a patterned microstructure on a diaphragm

Abstract: Stress relaxation of a patterned thin film on diaphragms of different material and thickness was investigated through experimental study and numerical simulation. The diaphragm deflections, caused by relaxation of the residual stress in a patterned thin film residing on top, were measured using a Twyman-Green laser interferometer. The first diaphragm used was a Si 3 N 4 (top)/SiO 2 /Si composite diaphragm and the second a 0.5-μm-thick Si 3 N 4 membrane. Custom-written simulation software, which uses a novel numerical algorithm named Nonlinear Sequential Analysis (N-LISA), was utilized to calculate the stress distribution in the patterned thin film and the diaphragm substrate. Agreement between the model and the experimental results was satisfactory. Simulation of the system balance between a tensile-stressed circular Ti film and a stress-free Si substrate of different thickness clearly shows a transition in the substrate behavior from a pure plate to a pure membrane. Interestingly, the deflection of the Si substrate caused by the residual stress in the Ti film reaches its maximum at a certain substrate thickness where plate and membrane characteristics coexist. This study addresses some basic mechanics issues involved in modern devices dealing with thin diaphragms.

Ultrasonic waves in an open cell foam

Abstract: This paper is concerned with the nondestructive materials and defects characterization of foams using ultrasonics. Propagation of ultrasonic waves in a thick plate made out of highly porous, open cell, carbon foam is studied in an effort to understand their relationship with the elastic properties of the material. The foam is assumed to have a tetrakaidecahedral structure and its geometric and overall elastic properties are determined from microscopic data and wave propagation experiments. A simple, one-dimensional model, based on a periodic spring-mass system is proposed for propagation in the through-thickness direction. Due to the difficulty in performing experiments under dry coupling conditions, ultrasonic experiments were carried out with the foam immersed in fluid in a test bed. The wave speed in the fluid filled foam is calculated after obtaining the average elastic moduli of the fluid saturated medium. The calculated wave speed is found to be in good agreement with that measured in the experiment. Significant discontinuities within the plate are also detected through ultrasonic and radiographic experiments. The present models can be employed effectively to characterize any open-cell foam.© (2002) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.