The author was trained as an electrical engineer. He got his first degree in the Department of Electrical Engineering, University of Hong Kong. He is interested in electronic engineering, especially HiFi audio equipment such as loudspeakers. For example, a good reference for loudspeakers was published by Martin Colloms (1948- ) [1]. He is also interested in magnetism and magnetic materials. In 1982, he was in USA. He bought a copy of the October 1982 issue of Scientific American. He was fascinated by an article with the title of “Magnetic fluids” [2]. The author was Ronald E. Rosensweig (1932- ). Please note that “magnetic fluids” are also known as “ferrofluids”. For example, in 2013, Stefan Odenbach (1964- ) published an article with the title of “Ferrofluids and their applications” [3]. A magnetic fluid is basically a colloid of magnetic nanoparticles. Thus magnetic fluid technology can be considered as some sort of magnetic nanotechnology. In this article, the author will try to focus on the application of magnetic nanotechnology to improve loudspeakers.
The first scientist known for R&D of magnetic fluids was Solomon Stephen Papell (1918-2015). He was an engineer working for NASA (National Aeronautics and Space Administration), USA. In 1963, he applied for US patent with the title of “Low viscosity magnetic fluid obtained by the colloidal suspension of magnetic particles” [3]. The patent was granted in 1965. The purpose of this invention was to create liquid rocket fuel that can be drawn toward a fuel pump in a weightless environment by applying a magnetic field. S.S. Papell suggested to use a mixture of liquid fuel and a magnetic fluid as liquid rocket fuel. He and R.W. Graham applied for another US patent with the title of “Liquid storage tank venting device for zero gravity environment” [4]. The patent was granted in 1967. The two patents were complementary for the above purpose.