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Barriers against radiated disturbances
Published in Mark van Helvoort, Mathieu Melenhorst, EMC for Installers, 2018
Mark van Helvoort, Mathieu Melenhorst
Magnetic (and electric) fields can be superimposed. The total net field is the sum of the individual fields. For low frequencies (roughly between DC and 5 kHz) this can be used for creating a field-free region, by purposely creating a field which counteracts the incident field as shown in Figure 7.28. Most often Helmholtz coils (Figure 7.29) are used, because they create a homogeneous field in a rather large volume in the center between the coils (Ruark and Peters 1926). The field in the center is oriented along the dash-dot axis. Its value at the center point is given by HHelmholtz=8125I×Nr
Magnetic Fields
Published in David Jiles, Introduction to Magnetism and Magnetic Materials, 2015
Often, when it is necessary to produce a uniform field over a large volume of space, a pair of Helmholtz coils is used. This consists of two flat coaxial coils, each containing N turns, with the current flowing in the same sense in each coil as shown in Figure 1.7. The separation d of the coils in a Helmholtz pair is equal to their common radius a.
Design and Study of Novel Tunable ELF-PEMF System for Therapeutic Applications
Published in IETE Journal of Research, 2022
Himani Kohli, Sangeeta Srivastava, Manan Oza, Satish Chouhan, Shivani Verma, Anju Bansal, Bhuvnesh Kumar, Sanjeev Kumar Sharma
The main property of the Helmholtz coil is that the magnetic flux becomes uniform in a reasonably large region with a rather simple coil system. Figure 5(a) represents the longitudinal field of a pair of Helmholtz coils in the plane as a contour plot. The contours depict the cross section of B (magnetic field strength) magnitude in a Helmholtz coil consisting of a coil pair, with one coil at the top and the other at the bottom. The contour plot shows that the field is uniform at 1 mT for most of the inner region. Figure 5(b,c) represents the magnetic field lines in a plane bisecting the current loops. The field is approximately uniform in between the coil pair. The arrows indicate the direction of the magnetic field strength. Figure 5(d) depicts the three-dimensional plot of the magnetic field of Helmholtz coil with radius and separation distance a = 0.15 m. As shown in the above graphs, the internal magnetic field distribution is very uniform. The magnetic flux density of the center region is approximately 0.9 mT, slightly less than the experimental value 1 mT. The computational magnetic field distribution was plotted along the distance from the center of the coil. Figure 5(e) illustrates the well-known uniformity of the magnetic field along the central axis of a Helmholtz pair with coil current fed to the coil as a variable parameter. The model clearly demonstrates the highly uniform magnetic field obtained in a Helmholtz coil.
Investigation of the magnetic field sensing properties of a magnetic fluid clad microfiber knot sensor
Published in Instrumentation Science & Technology, 2019
The experimental setup is shown in Figure 2. Light from a broadband source is launched into the sensor, and its transmission spectrum is monitored by an optical spectrum analyzer (Yokogawa AQ6370D). A uniform magnetic field is generated by a pair of Helmholtz coils. By controlling the magnitude of the supplied current to the coils, the strength of the applied field can be precisely adjusted. Meanwhile, a 360° rotating platform was employed to maintain the sensor head center-aligned within the air gap in the uniform magnetic field. By rotating the platform, the direction of the applied magnetic field with respect to the sensor may be adjusted. Moreover, the magnetic field strength is measured in close vicinity to the sensor in real time by the use of a gauss meter with a resolution of 0.1 Gs.
Highly sensitive modified giant magnetometer resistance measurement system for the determination of superparamagnetic nanoparticles in continuous flow with application for the separation of biomarkers
Published in Instrumentation Science & Technology, 2023
Manh Vu Xuan, Phu Nguyen Dang, Loc Do Quang, Hieu Nguyen Minh, Trinh Chu Duc, Tung Bui Thanh
The relationship between the output signal and the magnetic field in the sensitivity direction of the sensor was investigated. In the first experiment, only one pair of bias Helmholtz coils was implemented. First, a DC current was applied to the bias Helmholtz coils to generate a DC magnetic field in the sensor’s sensitive direction for the evaluation under static conditions. The magnetic field strength was changed by varying the current for the bias Helmholtz coils. The magnetic field strength was increased at a slow rate to the saturation level of the sensor and reversed the voltage polarization to gradually decrease the strength to zero. During the process of changing the magnetic field strength, the sensor’s output signal was recorded.