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


By jpeza - Posted on 29 Junio 2009

Fecha Publicación: 
19 Oct 2005
Nombre de Revista: 
Datos del paper
Autor Principal: 
Joseph L. Kirschvink
Volumen: 
13
Issue: 
5
Página Inicial: 
401
Página Final: 
411
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. 1992 Wiley-Liss, Inc.

Dirección del Autor: 
Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena

*Correspondence to Joseph L. Kirschvink, Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, CA 91125

Keywords: 
experimental controls ; biomagnetic effects ; coil designs ; Helmholtz coils
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[file] Bioelectromagnetics_1992_vol 13_num 5_pp401-11.pdf4.36 MB