Methods of high current magnetic field generator for transcranial magnetic stimulation application

This paper describes the design procedures and underlying concepts of a novel High Current Magnetic Field Generator (HCMFG) with adjustable pulse width for transcranial magnetic stimulation applications. This is achieved by utilizing two different switching devices, the MOSFET and insulated gate bipolar transistor (IGBT). Results indicate that currents as high as ± 1200 A can be generated with inputs of +/-20 V. Special attention to tradeoffs between field generators utilizing IGBT circuits (HCMFG1) and MOSFET circuits (HCMFG2) was considered. The theory of operation, design, experimental results, and electronic setup are presented and analyzed

Optimization of Magnetooptic Device by Low Switching Field Domains

This paper expounds on the optimization of magnetooptic devices using preferential domains that switch at low field strengths. In particular, an all-optical switch for transparent networks based on theMach-Zehnder interferometer configuration is examined in detail. The switch utilizes bismuth-substituted iron garnets with a specific composition of (Bi1.1Tb1.9)(Fe4.25Ga0.75)O12 as Faraday rotators. It is proposed that switch figures of merit can be improved by preferentially choosing domains which align with applied fields at field strengths much lower than required by the bulk material. Measurement of magnetic domain orientation in the material and Faraday rotation within domains is reported. The domain behavior in low magnetic fields is also investigated to achieve a switch with lower switching times and higher extinction ratios

Interferometric Detection of Pinned Interactions in Bismuth-Substituted Iron Garnet

The utilization of a bismuth-substituted iron garnet as a magnetooptic Faraday rotator (MOFR) has been reported for all-optical networking purposes as well as for other applications. Our measurements and observations demonstrate that the MOFR saturates once a significantly large magnetic field (\u3e225 G) is applied. After the applied magnetic field enters the saturation region, the material\u27s magnetic domains can become pinned at intermediate levels of magnetization. Pinning in this form has not been reported nor well studied for this application. In this paper, a method to detect and describe anomalous pinning in terms of Faraday rotation is presented. Measurements on the changes in the state of polarization that a pinned material produces are examined. This paper will also present practical methods for unpinning the MOFR material, which are traditionally considered to be challenging

Synthetic Aperture Focusing Technique Using the Envelope Function for Ultrasonic Imaging

In traditional ultrasonic imaging systems, a transducer is scanned across the surface of a specimen at constant intervals. Synthetic aperture focusing techniques (SAFT) have been utilized extensively to process the RF data in order to enhance the signal-to-noise ratio of the image [1]. However, the implementation of the algorithm using sampled RF data has the disadvantage of requiring large memory and high-speed devices. These requirements can be reduced by using the envelope of the RF signal which involves processing the baseband signal. The envelope detection can be easily implemented as part of the receiver circuit

Philosophical and Educational Perspectives on Engineering and Technological Literacy, II

Unknown to each other two groups of engineers and engineering educators began to consider aspects of philosophy and engineering. One held a workshop of engineers and philosophers- “Engineering meets Philosophy” at Delft University and the other held a special session at the annual Frontiers in Education Conference on engineering education and philosophy. Since then the former has held a biannual workshop that have resulted in two impressive publications. The other continued its discussions through FIE and ASEE conferences. There are now regular sessions on philosophy and engineering education at the annual FIE conferences.https://lib.dr.iastate.edu/ece_books/1001/thumbnail.jp

Finite Element Modeling of Binary Acoustic Fresnel Lenses

Binary acoustic Fresnel lenses (BAFLs) have recently emerged as possible replacements for spherical lenses for applications in acoustic microscopy. BAFLs are surface relief structures that are relatively easy to manufacture compared to conventional spherical lenses. While the latter requires careful grinding and polishing, the former can be easily fabricated to sub-micron dimension accuracy using existing VLSI etching technology. The term binary arises from the fact that each masking step during the lens production creates two phase levels. Therefore, a total of 2 n phase levels are created in n masking etching steps. A special case is when n = 1 (2 phase levels), which corresponds to the conventional Fresnel lens (zone plate)

Philosophical Perspectives on Engineering and Technology Literacy, I

The belief that engineering and technology are beneficial to all and can improve human lives has inspired the tireless endeavors of many creative individuals throughout history. Engineers and technologists have generally believed that their actions and designs need to be scientifically justified and logically dependable. In addition, due to the pragmatic nature of the field there is also an emphasis on systematic approaches and defining standard practices in engineering. Such a positivist approach is seen in all aspects of engineering and technological ventures. Consequently, such an approach exists in most engineering educators’ perspectives and belief structures regarding the contents of the curricular, student training, and the overall goal of engineering and technological education.https://lib.dr.iastate.edu/ece_books/1000/thumbnail.jp

Evaluation of the Effects of Pulsed Magnetic Field Treatment as a Nondestructive Treatment for Magnetic Materials

Pulsed magnetic treatment has been suggested as a nondestructive treatment of magnetic materials for reducing microscopic stress and strain in the materials. Systematic studies have been made to test the effect of pulsed magnetic field treatments in a variety of magnetic materials including bulk nickel and magnetic thin film samples. The treatment involves the application of a low frequency, periodic magnetic field superimposed with a high frequency pulse component followed by demagnetization. Equipment for applying the pulsed magnetic field treatment has been designed and constructed, together with computer software which was developed to allow complete control of the waveform, frequency and amplitude of the pulsed magnetic field profile. Various characterization techniques, including magnetic hysteresis, Barkhausen effect measurements and magnetic force microscopy, were used to test the effects of the pulsed magnetic field treatment. Present results indicate that the stress relief effect of the treatment on the samples, if there is any, is much weaker than claimed in previous studies