Figure 6.
Wavenumber spectrum of a single dipole source. The dipole moment oscillates at f = 3 Hz. Potentials at 11 electrodes were calculated using a four concentric spheres model. The standard model parameters are given in the caption for Fig. 1. In each figure the upper plot shows the time series at the 11 electrodes (spaced by 2.5 cm). The lower plot shows the wavenumber spectrum at f = 3 Hz. The wavenumber spectra are shown in solid black lines over the range that can be estimated accurately with the 11 electrodes; dashed grey lines indicate the spectrum at lower wavenumbers which are wavelengths longer than the array size. (a) Tangential dipole located under electrode six at a depth of 2.2 cm (r = 7.0 cm) and oriented in parallel to the electrode array. (b) Radial dipole located under electrode 6 at a depth of 2.2 cm (r = 7.0 cm). (c) Radial dipole located under electrode 9 at a depth of 2.2 cm (r = 7.0 cm).