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We review the inhomogeneous scalar Helmholtz equation in three-dimensions and the scattering of scalar wavefields from a scatterer of compact support. An asymptotic solution is then considered representing the effect of the frequency approaching zero when a ‘wavefield’ reduces to a ‘field’. The characteristics of ultra-low frequency Helmholtz scattering are then considered and the physical significance discussed of a model that is based on the scattering of Helmholtz wavefields over a broad frequency spectrum. This is equivalent to using a linear systems approach for modelling the propagation, interaction and detection of broad-band signals and provides an approach to the classification of a field from a wavefield that is intrinsically causal and thus, consistent with the basic principle of information theory. The approach leads to the proposal that all fields are derived from wavefields interacting over a broad frequency spectrum and that there are two principal field types:
(i) fields generated by low frequency scattering - a ‘gravitational field’;
(ii) fields generated by high frequency eigenfield tendency - an ‘electric field’.
Blackledge, J.: An Approach to Unification using a Linear Systems Model for the Propagation of Broad-Band Signals. ISATS Transactions on Electronics and Signal Processing. ISSN 1797-2329, issue: No. 1, Vol. 1, pages: 101-116, 2007.