An asymptotic estimate for the effective radius of a concentric bipolar electrode

A concentric bipolar electrode (CBE) (consisting of a central disc and an o uter annulus) has been proposed as an approximate method of measuring the s urface Laplacian of the body surface electrical potential distribution. The derivation of the surface Laplacian approximation, in terms of the potenti al difference measured with the bipolar electrode, contained an unspecified parameter which has been dubbed the 'effective radius' of the concentric b ipolar electrode. This paper presents an asymptotic analysis to derive an e xpression for the effective radius in terms of the physical dimensions of t he electrode (the radius of the central disc and inner and outer radii of t he annulus). Also studied is the way in which the value of the effective ra dius affects the behaviour of the relative error in the surface Laplacian m easurement at various dipole source locations within a conducting medium. ( C) 1999 Elsevier Science Inc. All rights reserved.