Helmholtz Coils and Magnetic Fields (original) (raw)
2020
The objectives of the experiment are to determine the magnetic field along the horizontal x-axis that passes through the centre of a single solenoid coil, and to determine the magnetic field along the horizontal x-axis that passes through the centre of the Helmholtz coil. Helmholtz coil is a device that produces a region of a nearly uniform magnetic field. It consists of two solenoids that are parallel to each other on the same axis. Both solenoids are separated by a distance, d. Each coil carries an equal electric current in the same direction. The entire experiment is conducted via a simulator software provided. For Experiment I, the graph of B vs x is obtained alongside with the logarithmic graph of B vs the square of x. The comparison of the experimental and the theoretical logarithmic graphs allows the determination of the turns of wire, N of the hypothetical single coil. That is, N = 1717.5. It is managed to obtain the best value for B_0 through the standard deviation as the uncertainty in a single measurement with 70% confidence. That is, B_0 = (4.1267 x 10-3) ± (9.2236 x 10-5) T. The experimental μ_0 is deduced and it is given by μ_0 = (2.5292 x 10-7) T m A^-1. The determination of the experimental μ0 yields a percentage error of 79.9%. For Experiment II, the graph of B vs x is obtained for all d = R, d = 1.5R and d = 0.5R. Two major things found out in this part are, firstly, the mathematical erratum in either the simulator or in the laboratory manual is very substantial, and secondly, the erratum has caused such an ambiguity that a thorough quantitative analysis has become cumbersome given the time constraint as the deviation between the experimental and the theoretical values are of logarithmic. Next, the graph of B_0 vs d is also obtained for both the experimental and the theoretical values. Nothing much could be done on the quantitative aspect of it. However, qualitatively, it is observed that as d increases, B decreases. This may explain the lesser incident flux density as the coils move further apart. Lastly, the slope of the experimental data has a greater rate of change as opposed to that of the theoretical values.
Related papers
EXPERIMENT EM3 LORENTZ FORCE AND MAGNETIC FIELD OF PAIRED COILS IN HELMHOLTZ ARRANGEMENT
This experiment is investigating the current balance or force acting on a current-carrying conductor and the magnetic field in a pair of Helmholtz arrangement. In first part, the experiment is testing about the relationship between the force and the current while in second test, the experiment is testing on the various strength of the magnetic flux density in various parameters which are the separation distance between two coils, the radius from the centre in 0 degree and 90 degree position, and the radial component of the Helmholtz arrangement.
The Use of Helmholtz Coils Designed for 50 Hz at Higher Frequencies
Annals of the University of Craiova, Electrical Engineering series, No. 44, Issue 1, 2020; ISSN 1842-4805, 2020
Helmholtz coils (HC) are used in order to generate and control uniform magnetic fields for a variety of research applications. They can be easily constructed and their fields can be easily calculated. This makes them especially useful in calibrating magnetic field sensors. Such a calibration system with large Helmholtz coils (1x1m) can be found in ICMET Institute, designed to operate only at a frequency of 50 Hz. There has recently been a request for the calibration of several measuring sensors operating at frequencies up to 10 kHz used in industrial applications such as induction hardening of metal parts. The paper aims to determine the conditions under which this low frequency HC system can be used at frequencies at least 100 times higher. The first part of the paper describes a theoretical analysis on the volume confining the space where the magnetic field components have a predetermined deviation (a 2% threshold) from the center of the HC system followed by a comparison with a 3D FEM simulation and measurement of HC field. The second part describes the identification of the HC parameters at higher frequencies and the resonant methods used to achieve the excitation power required at these frequencies.
Effects of crossing saddle coil conductors: Electric length X mutual inductance
Concepts in Magnetic Resonance Part B-magnetic Resonance Engineering, 2010
In magnetic resonance imaging (MRI), either on human or animal studies, the main requirements for radiofrequency (RF) coils are to produce a homogeneous RF field while used as a transmitter coil and to have the best signal-to-noise ratio (SNR) while used as a receiver. Besides, they need to be easily frequency adjustable and have input impedance matching 50 Ω to several different load conditions. New theoretical and practical concepts are presented here for considerable enhancing of RF coil homogeneity for MRI experiments on small animals. To optimize field homogeneity, we have performed simulations using Biot and Savart law varying the coil's window angle, achieving the optimum one. However, when the coil's dimensions are the same order of the wave length and according to transmission line theory, differences in electrical length and effects of mutual inductances between adjacent strip conductors decrease both field homogeneity and SNR. The problematic interactions between strip conductors by means of mutual inductance were eliminated by inserting crossings at half electrical length, avoiding distortion on current density, thus eliminating sources of field inhomogeneity. Experimental results show that measured field maps and simulations are in good agreement. The new coil design, dubbed double-crossed saddle described here have field homogeneity and SNR superior than the linearly driven 8-rung birdcage coil. One of our major findings was that the effects of mutual inductance are more significant than differences in electrical length for this frequency and coil dimensions. In vitro images of a primate Cebus paela brain were acquired, confirming double-crossed saddle superiority. © 2010 Wiley Periodicals, Inc. Concepts Magn Reson Part B (Magn Reson Engineering) 37B: 193–201, 2010
Loading Preview
Sorry, preview is currently unavailable. You can download the paper by clicking the button above.