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The History of Bioelectromagnetism
non-viable bioflms of bacteria (Grimnes and Martinsen, 2000). Particles suspended in a liquid will
experience torque in a rotating E-feld (Arnold and Zimmerman, 1982).
Sen-ichi Masuda (1926–1995), professor at the University of Tokyo, and his co-workers were the frst
to report on the manipulation of biological particles using rotating traveling electric felds (electric cur
tain) with three-phase voltage frequencies between 0.1 and 100 Hz (Masuda et al., 1987, 1988). Using
relatively low frequencies in his original papers, the technique of electrophoresis was predominant. Te
electrical traveling waves in non-uniform AC electric felds can also be used for the manipulation of par
ticles in 1988. An important point is that the selected particles move in a stationary supporting fuid in
the separation process. His technique was improved to use traveling-wave dielectrophoresis with higher
frequencies to separate viable yeast cells from non-viable yeast cells (Talary et al., 1996). Employing this
traveling feld dielectrophoresis, Pethig’s group of the University of Wales, UK, separated red and white
blood cells and selectively viable yeast cells (Burt et al., 1998).
Schoenbach and his co-workers at Old Dominion University, USA, discovered the induction of apop
tosis by nano-second pulsed electric felds in cancer cells, in 1999. Since these observations, there has
been increasing numbers of studies of the electrical behavior of cell membranes by nano-second pulsed
electric felds. For example, the electroporation is used as a universal tool for drug deliveries and genes
into living cells for electrochemotherapy and gene therapy in medical application (Schoenbach et al.,
2001, 2004).
2.5.2 Biomagnetism
Biomagnetism is simply the study of the interactions between magnetic felds and biological systems.
Various biomagnetic phenomena for diferent magnetic feld strengths and their frequencies are shown
in Figure 2.13. It is important to know the strengths and frequencies of the magnetic felds involved in
biomagnetic phenomena. For example, the so-called magnetophosphene is a visual sensation elicited by
exposing the head to a low-frequency (around 10–70 Hz) magnetic feld of around 10–20 mT. Te signal
is generated in the retina. Magnetic stimulation of the human brain and heart has been used for the
purpose of both research and clinical treatment. Using SQUID magnetometers, the very weak magnetic
felds from the brain, heart, and lung can be measured from outside the body. Since the beginning of the
history of biomagnetism, there are now Magnetic Resonance Imaging (MRI), functional MRI (fMRI),
Transcranial Magnetic Stimulation (TMS), etc. related to medical applications.
Te understanding of biomagnetism is based on the concept of magnetism. Magnetism is mainly
characterized by three variants, ferromagnetism, paramagnetism, and diamagnetism. Ferromagnetism
has its own magnetic poles and exerts force on each other as a magnet. Te magnetic susceptibility
of ferromagnetism is positive and large. Paramagnetism produces weak magnetization parallel to the
direction of the magnetic feld. Diamagnetism is a substance that exhibits weak magnetization in the
opposite direction to the magnetic feld and a force proportional to the product of the magnetic feld
strength and its gradient is produced in the direction of repulsion to the magnet. Te magnetic suscep
tibility of diamagnetism is negative in the order of 10−6 to 10−5(SI). Te magnetic susceptibility of para
magnetism is positive in the order of 10−5 to 10−3(SI).
2.5.2.1 Magnetic-Related Phenomena
In the past, the magnetic feld strength of a permanent magnet was too weak to demonstrate the mag-
netic-related phenomena of diamagnetism and paramagnetism. Around the 1980s, the magnetic feld
strength of a permanent magnet increased drastically due to the development of neodymium magnets.
Tis opened a new era for the study of the magnetic properties of every material in high magnetic
felds. In the presence of a neodymium magnet, the magnetic properties of diamagnetic materials can be
observed with the naked eye. With neodymium magnets, apples, eggs, carbon, bismuth, etc. can be levi
tated. A neodymium magnet is a rare earth magnet (Nd2Fe14B) consisting mainly of neodymium, iron,
and boron. It was invented by Masato Sagawa and others at Sumitomo Special Metals (later, Hitachi