What Are Electromagnetic Countermeasures?
Electromagnetic Countermeasures are measures taken to prevent effects of electromagnetic radiation.
Electromagnetic waves are waves that travel through space where electricity flows, where radio waves fly, and where magnetic fields are generated, interacting with each other.
Electromagnetic waves are divided into ionizing and non-ionizing radiation. The boundary between them is 3000 THz, and ionizing radiation is what is usually referred to as radiation. The frequency range of electromagnetic waves covered by guidelines is from 10 kHz to 300 GHz. The lower and higher frequencies are divided into two categories: low frequency and high frequency.
Since the properties of electromagnetic countermeasures differ depending on the frequency, classification by frequency and countermeasures are necessary. Examples of low-frequency waves are power lines and electrical appliances, which operates at frequencies of is 50~60 Hz and wavelengths of 5000~6000 km. Examples of high-frequency waves include cell phones and microwave ovens, which have frequencies ranging from 800 MHz to 3 GHz and wavelengths from 10 to 40 cm. Electromagnetic waves are measured in terms of power density (mW/cm) and absorbed rate (SAR) (W/kg).
In terms of magnetic field strength, the global average of the geomagnetic field is about 46 μT. The World Health Organization (WHO) states that magnetic fields of 500 μT or less are not considered to have any biological effects.
Guidelines for electric and magnetic fields have been established by organizations such as the WHO and the International Commission on Non-Ionizing Radiation Protection (ICNIRP),. Electromagnetic countermeasures are achieved by absorbing, shielding, and attenuating outgoing and incoming electromagnetic waves.
Types of Electromagnetic Countermeasures
Not all frequencies of electromagnetic waves can be shielded, particularly at low frequencies.
Various types of electromagnetic countermeasures are used. Ferrite cores, capacitors, and common mode choke coils are used as filtering components to attenuate electromagnetic noise, while conductive tape, metal mesh, and shielding gaskets are used to shield incoming and outgoing electromagnetic waves.
In addition, electromagnetic shielding for the housings of home appliances and other products involves the application of metallic materials, electroless shield plating, vacuum deposition, coating with conductive paints, and the attachment of conductive fibers. Aprons made of conductive fibers are commercially available as a method to shield electromagnetic waves to the human body.
Principle of Electromagnetic Shielding
The principle of electromagnetic shielding is to attenuate electromagnetic wave energy based on the three properties of reflection, absorption, and multiple reflection of electromagnetic waves. Attenuation minimizes the adverse effects on the human body and equipment. Shielding performance is usually expressed in decibels, which is the logarithm (log) of the electric field strength after shielding / electric field strength before shielding or the magnetic field strength after shielding / magnetic field strength before shielding multiplied by 20 (in dB).