Dielectrophoresis Tutorial: Inspired by Hatfield's 1924 Patent and Boltzmann's Theory and Experiments of 1874

The first patent to describe dielectrophoresis (DEP) as a means and process to separate particles from a mixture was granted by the US Patent Office to Henry Stafford Hatfield in 1924. The novel methods of sample preparation and designs of electrode geometry covered by the patent's disclosures and claims describe the basis for most present-day applications of DEP as a method of particle separation. Hatfield had clearly acquired a deep understanding of DEP, not only from the perspective of the potential energy of the target particle to be separated from others but also from consideration of the conservation of energy of the electrical system. He cites no prior art or supporting theory of what he would have known as the action of the ponderomotive force. There is no record of his publishing this work, but efforts to find the source of his knowledge led to the retrieval of his Ph.D. thesis from the archives of the University of London. It describes innovative applications of DEP to separate impurity particles from powdered mineral ore and refers to the theoretical and experimental studies by Boltzmann of the ponderomotive force acting on small spheroidal samples of insulating material. This early background theory and experimentation by Boltzmann is described here and, together with the rules and methods so clearly and simply described in Hatfield's patent, forms the core of a tutorial for those engaged in DEP but who might lack formal training in physics.