Beamformers are also called spatial filters or virtual sensors. They have the advantage that the number of dipoles must not be assumed a priori. The output y(t) of the beamformer is computed as the product of a 3 × N (each Cartesian axis is considered) spatial filtering matrix W T with m(t), the N × 1 vector representing the signal at the array at a given time instant t associated with a single dipole source, i.e. y(t) = W T m(t). This output represents the neuronal activity of each dipole d in the best possible way at a given time t.
