Análisis computacional de circuitos eléctricos y geometrías de bobinas para sistemas de estimulación magnética transcraneal

Transcranial magnetic stimulation systems have had a heyday in the last two decades, both in the development and commercialization of equipment, as well as in areas of application in medicine and research, which has made them tools for the diagnosis and treatment of important diseases of the nervous system. Most of the analyzes of the general operation are still limited to the separate study of the elements of the system. In this present work, the analysis is carried out through simulations of the electrical excitation circuit using the Matlab®/Simulink®and Micro-Cap tools, likewise, three coil geometries of transcranial magnetic stimulation systems are analyzed by using the finite element method in COMSOL Multiphysics®software. The computational analysis lies in studying the basic architecture of the electrical excitation circuit, which is made up of an RLC circuit with switching elements and power electronics, in charge of generating high-magnitude current pulses (between 1 and 3 kA) and short duration. (between 0.5 and 1250 ms). The magnitude of the current and the shape of the signal in the elements of the RLC stage are analyzed, performing a calculation of the power dissipated. This first stage is complemented with the analysis by means of the finite element method of the magnetic flux density and maximum operating temperature of three coil geometries commonly used for therapies. The computational analysis gives rise to a proposal for a system that reduces the maximum operating temperature of coil geometry by up to 20 %, maintaining the maximum magnitude of the magnetic flux density, which consists of the design of a single solenoid coil geometry with windings. concentric, which from the electrical point of view, are inductors in parallel.

Instantaneous Electromagnetic Torque Components in Synchronous Motors Fed by Load-Commutated Inverters

This paper proposes time-domain analytical expressions of the instantaneous pulsating torque components in a synchronous machine air gap when supplied by a load-commutated-inverter (LCI) system. The LCI technology is one of the most used variable frequency drives when very high power and low speed are required in applications such as pipeline recompression and decompression, as well as liquefied natural gas compression. In such applications, synchronous motors are used because of their high efficiency resulting from a separated supply of the current to their rotor through the excitation circuit. These applications usually have long and flexible shafts, which are very sensitive to torsional vibration excitation when their natural frequencies interact with any external torque applied to the shaft. A torsional analysis is required by international standards to assess the survivability of the shaft through the overall speed range of the motor. Therefore, the magnitude and frequencies of the motor air-gap torque are needed for such evaluation. The proposed developments are supported by numerical simulations of LCI systems in a large range of operation range. From the simulation results, torque harmonic families are derived and expressed in a parametric form, which confirm the accuracy of the proposed relationships.

Modern Hybrid Excited Electric Machines

The paper deals with the overview of different designs of hybrid excited electrical machines, i.e., those with conventional permanent magnets excitation and additional DC-powered electromagnetic systems in the excitation circuit. The paper presents the most common topologies for this type of machines found in the literature—they were divided according to their electrical, mechanical and thermal properties. Against this background, the designs of hybrid excited machines that were the subject of scientific research of the authors are presented.

An Excitation Circuit of the Cell in Optically Pumped Magnetometer

Cell is the key component in an optically pumped magnetometer. It is necessary to light the cell before measurement and to maintain the illuminated state. The accuracy and stability of magnetic values from the instrument are closely related to the brightness and stability of the cell. The cell is also the largest power dissipation component in the sensor probe, so the overall energy consumption of the magnetometer is highly correlated with it. This paper studies the excitation circuit of cell in the magnetometer. Firstly, we demonstrate the resistivity characteristic of a cell using simulations. After that, based on the combination of signal source impedance and transmission line impedance, the matching network of excitation circuit is analyzed. We demonstrate that both T-network and Π-network can achieve the impedance matching of the transmitter circuit by a simulation experiment, under the condition of 50MHz signal, 10Ω source impedance, and 50Ω transmission line impedance. T-network shows the best performance in frequency selectivity and energy transfer. Finally, the simulation experiment also proves that a circuit composed of a self-coupled coil and an LC parallel resonant network can realize the impedance matching and the passband selection of the receiver circuit by optimizing values of the inductance and capacitance, and turns of the self-coupled coil simultaneously. The power consumption of the whole high-frequency excitation circuit of cell in the optically pumped magnetometer is only about 6W.

An Novel Atomic Scalar Magnetometer Using Laser

The measurement precision of commercial atom scalar magnetometer is relatively backward compared with that of quantum magnetometer. However, the application of quantum magnetometers such as SERF requires more stringent environmental background requirements, which is not suitable for magnetic field measurement in the geomagnetic environment. The purpose of this paper is to design a 4He atom scalar magnetometer using ECDL laser. Compared with the conventional atomic scalar magnetometer, this magnetometer has higher measuring precision and can work normally in the geomagnetic environment. In order to achieve the above goals, the sensitivity formula of the atomic scalar magnetometer is first deduced and calculated, and the key physical factors that directly affect the sensitivity are the optical pumping rate, transverse relaxation rate, and longitudinal relaxation rate. Then, the light source and 4He cell are determined as key components which affect sensitivity. On this basis, the optical path of the 4He atomic scalar magnetometer using laser is designed in this paper. The light path ensures the stability of the laser wavelength of 1083.207nm by the saturation absorption spectrum method, and it ensures the circularly polarized light enters the 4He cell through the combination of various optical components. This paper also studies the electric excitation technology of the 4He cell. And, combined with simulation experiments, the High-Frequency discharge excitation circuit with high energy transfer efficiency and corresponding matching network are determined. Through the optical wavelength meter, it can be determined that the optical path designed in this paper can guarantee the wavelength stability of 1083.207nm for a long time. By analyzing the detection signals of PD, the circularly polarized light enters the 4He cell in the light circuit designed in this paper has a higher degree of polarization. The High-Frequency discharge excitation circuit designed in this paper can light up the cell smoothly, and the input power when the circuit works stably is about 6W. Finally, the static sensitivity of the magnetometer is 5pT/Hz1/2. The 4He atom scalar magnetometer using ECDL laser designed in this paper has high static sensitivity, which basically meets the design requirements, and the instrument can be used normally in the geomagnetic environment. However, the instrument still has a lot of room for improvement, including optical path and cell performance optimization, and we will continue to study in this direction.

Direct ablation and excision of myocardial scar in post-myocarditis ventricular aneurysm

The patient was a 34-year-old woman who developed multiple post-myocarditis ventricular aneurysms with ventricular tachyarrhythmia. After implantation of an intracardiac defibrillator, she experienced multiple episodes of counter-shock. An electrophysiological study demonstrated an early excitation circuit entering the septal aneurysm with the right ventricular aneurysm as an exit. A surgical ablation of the re-entry and left ventricular plasty with scar resection was performed. The operation was performed under direct, epicardial electrophysiological guidance. A cryoablation was performed along the right ventriculotomy and the margin of the left ventricular aneurysm. The left ventricle was closed using endoventricular aneurysmorrhaphy and the right ventriculotomy was closed directly. No recurrence of ventricular tachyarrhythmia has been encountered.