6

Bioelectromagnetism

   

feld coexist together and travel through a vacuum at the speed of light (3 × 10⁸m/s). Tey are character­

ized by their wavelength λ measured in meters (m) and frequency f measured in Hertz (Hz).

According to quantum mechanics, electromagnetic waves have properties of both a wave and a par­

ticle (photon). Te photon energy of electromagnetic waves (U) is quantized with Planck’s constant (h)

times the frequency (f). Tis energy can be expressed in electron volts (1 eV = 1.6 × 10^–19 J). Te following

relationships hold for the electromagnetic wave.

˜ = / , =

 ,

= /  = h f k

c f U

h f T U k

/

where c is the speed of light (= 3 × 10⁸m/s), h is the Planck’s constant (= 6.63 × 10⁻³⁴ Js), k is the

Boltzmann’s constant (= 1.381 × 10⁻²³ J/K), the photon energy U in Joule (J), and T in Kelvin (K). It can

be observed that if the frequency increases or the wavelength decreases, the photon energy increases.

Te electromagnetic spectrum is the distribution produced when the electromagnetic waves are

decomposed into various frequency components. Diferent electromagnetic wave frequencies give dif­

ferent forms of electromagnetic radiation. Figure 1.1 shows the electromagnetic spectrum, which is usu­

ally divided into ionizing radiation or non-ionizing radiation along with the typical sources. Ionizing

radiation is the radiation that occurs when its frequency is higher than 3,000 THz. It includes hard UV

and higher frequency electromagnetic waves (X-rays, γ-rays). Tis frequency corresponds to a wave with

a wavelength of 100 nm (1 nm = 10⁻⁹ m), a photon energy of 10eV. Ionizing radiations cause severe dam­

age to the gene of living materials. Non-ionizing radiation refers to the electromagnetic felds ranging

from 0 Hz (static felds) to 3,000 THz. Tis wide frequency band, as seen in Figure 1.1, includes static

electric and magnetic felds, extremely low-frequency electromagnetic felds (ELF-EMF), intermediate

frequency electromagnetic felds, high-frequency feld and visible light. Te International Commission

on Non-Ionizing Radiation Protection (ICNIRP) has published the defnition of non-ionizing radiation

(ICNIRP, 2020b). Non-ionizing radiation refers to electromagnetic radiation and felds with a photon

energy lower than 10 eV, corresponding to frequencies lower than 3,000 THz and wavelengths longer

than 100 nm. It is grouped into diferent frequency or wavelength bands, namely UV radiation (wave­

lengths 100–400 nm), visible light (wavelengths 400–780 nm), radiofrequency electromagnetic felds

(frequency 100 kHz–300 GHz), low-frequency felds (frequencies 1 Hz–100 kHz) and static electric and

magnetic felds (0 Hz). Non-ionizing radiations have no high energy to cause severe damage to chemical

bonds. Non-ionizing radiations have diferent mechanisms of biological interactions depending on their

frequencies or wavelength.

In addition to the naturally occurring electromagnetic radiations, man-made sources of electromag­

netic felds produced afer the electrifcation began to exist in the human environments. Now, electro­

magnetic felds on earth are consists of two components, electromagnetic felds generated from natural

phenomena and man-made electromagnetic felds. Tese two diferently originated sources of non-

ionizing radiation exist together and around us. Electromagnetic radiations of broad frequency from

the non-ionizing range are used in biomedical imaging in medicine and biology.

1.2.2 Bioelectromagnetism

Bioelectromagnetism is the area of science that studies the interaction between electromagnetic phe­

nomena and biological systems. Te knowledge in electromagnetism based on classical physics and

quantum mechanics has led to understanding the basic phenomena in bioelectromagnetism. Tis is

due since electromagnetism and bioelectromagnetism have advanced together until now and they will

continue advancing together in the future. In the history of science so far, bioelectromagnetism has

been basically developed by connecting electricity, magnetism and electromagnetism to biology, medi­

cine, physics and engineering. MRI using static and time-varying magnetic felds and radiofrequency

electromagnetic felds is a typical example. In this sense, bioelectromagnetism is signifcantly difcult