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Uniform magnetic fields and double-wrapped coil systems: Improved techniques for the design of bioelectromagnetic experiments

Kirschvink, Joseph L. (1992) Uniform magnetic fields and double-wrapped coil systems: Improved techniques for the design of bioelectromagnetic experiments. Bioelectromagnetics, 13 (5). pp. 401-411. ISSN 0197-8462. doi:10.1002/bem.2250130507. https://resolver.caltech.edu/CaltechAUTHORS:20130624-100604074

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Abstract

A common mistake in biomagnetic experimentation is the assumption that Helmholtz coils provide uniform magnetic fields; this is true only for a limited volume at their center. Substantial improvements on this design have been made during the past 140 years with systems of three, four, and five coils. Numerical comparisons of the field uniformity generated by these designs are made here, along with a table of construction details and recommendations for their use in experiments in which large volumes of uniform intensity magnetic exposures are needed. Double-wrapping, or systems of bifilar windings, can also help control for the non-magnetic effects of the electric coils used in many experiments. In this design, each coil is wrapped in parallel with two separate, adjacent strands of copper wire, rather than the single strand used normally. If currents are flowing in antiparallel directions, the magnetic fields generated by each strand will cancel and yield virtually no external magnetic field, whereas parallel currents will yield an external field. Both cases will produce similar non-magnetic effects of ohmic heating, and simple measures can reduce the small vibration and electric field differences. Control experiments can then be designed such that the only major difference between treated and untreated groups is the presence or absence of the magnetic field. Double-wrapped coils also facilitate the use of truly double-blind protocol, as the same apparatus can be used either for experimental or control groups.


Item Type:Article
Related URLs:
URLURL TypeDescription
http://dx.doi.org/10.1002/bem.2250130507 DOIUNSPECIFIED
http://onlinelibrary.wiley.com/doi/10.1002/bem.2250130507/abstractPublisherUNSPECIFIED
ORCID:
AuthorORCID
Kirschvink, Joseph L.0000-0001-9486-6689
Additional Information:© 1992 Wiley-Liss, Inc. This research supported in part by the Electric Power Research Institute (EPRI) contract RP2965-8 and NIH grant GM41635. Contribution No. 5000 from the Division of Geological and Planetary Sciences of the California Institute of Technology. I thank two anonymous referees for their helpful comments.
Funders:
Funding AgencyGrant Number
Electric Power Research Institute (EPRI)RP2965-8
NIHGM41635
Subject Keywords:experimental controls; biomagnetic effects; coil designs; Helmholtz coils
Other Numbering System:
Other Numbering System NameOther Numbering System ID
Caltech Division of Geological and Planetary Sciences5000
Issue or Number:5
DOI:10.1002/bem.2250130507
Record Number:CaltechAUTHORS:20130624-100604074
Persistent URL:https://resolver.caltech.edu/CaltechAUTHORS:20130624-100604074
Official Citation:Kirschvink, J. L. (1992), Uniform magnetic fields and double-wrapped coil systems: Improved techniques for the design of bioelectromagnetic experiments. Bioelectromagnetics, 13: 401–411. doi: 10.1002/bem.2250130507
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:39047
Collection:CaltechAUTHORS
Deposited By: Tony Diaz
Deposited On:24 Jun 2013 17:14
Last Modified:09 Nov 2021 23:42

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