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1 Overview of RFID System Anti-Collision Technology
factor in engineering. It can be seen that only when the conductivity is 0, the electromagnetic wave will be lossless propagation in the medium, which does not exist
in the practical application. Similarly, the attenuation factor can significantly affect
the RFID system’s reading distance, which must be considered when deploying the
system.
In addition, when the antenna captures space electromagnetic waves, the attenuation coefficient of the antenna base material will also affect the decoding of the
system, thus causing obstacles to the reading. Therefore, when designing the antenna,
the lower the conductivity of the selected material should be, the better.
(3) Metamaterials and their electromagnetic properties
Metamaterial is a composite material that has an artificially designed structure and
exhibits supernormal physical properties not found in natural materials. In this
medium, the strength of the electric field, the magnetic field and the electromagnetic
wave vector comply with the left-hand rule, hence the term “left-handed material”.
When electromagnetic waves travel through metamaterials, they exhibit some
bizarre properties:
(1) The group velocity direction of the electromagnetic wave is parallel to the
phase velocity direction, that is, the direction of the wave vector is opposite to
the propagation direction of energy, and the left-hand law is satisfied between
electric field, magnetic field, and wave vector.
(2) Reversed Doppler effect. The observed change in frequency in the left-handed
material is the opposite of the effect in the right-handed material. In the righthanded material, when the observer moves toward the source, the observer
measures a higher frequency than the source vibrates, which is called the
Doppler effect. In the left-handed material, similarly, when the observer is
moving toward the source of the wave, the frequency measured by the observer
is lower than that of the source of the wave, which is the inverse Doppler effect.
(3) Reversed Snell refraction. The refractive index is negative. At the interface
between left-handed material and right-handed material, the refractive rays
and incoming rays are on the same side of the normal line. So you have what’s
called a perfect lens.
(4) Reversed Cerenkov radiation. When a charged particle moves in a medium,
an induced current is generated in the medium. By these induced currents,
secondary waves are excited. When the velocity of a charged particle exceeds
the speed of light in the medium, these secondary waves interfere with the
original electromagnetic field and can form a radiation electromagnetic wave.
This radiation is called Cerenkov radiation. In the right-handed material, the
electromagnetic-excited radiation scatters forward at an acute angle. In the lefthanded material, the radiation direction of the electromagnetic wave changes,
scattering backward at an obtuse ngle.
1 Overview of RFID System Anti-Collision Technology
factor in engineering. It can be seen that only when the conductivity is 0, the electromagnetic wave will be lossless propagation in the medium, which does not exist
in the practical application. Similarly, the attenuation factor can significantly affect
the RFID system’s reading distance, which must be considered when deploying the
system.
In addition, when the antenna captures space electromagnetic waves, the attenuation coefficient of the antenna base material will also affect the decoding of the
system, thus causing obstacles to the reading. Therefore, when designing the antenna,
the lower the conductivity of the selected material should be, the better.
(3) Metamaterials and their electromagnetic properties
Metamaterial is a composite material that has an artificially designed structure and
exhibits supernormal physical properties not found in natural materials. In this
medium, the strength of the electric field, the magnetic field and the electromagnetic
wave vector comply with the left-hand rule, hence the term “left-handed material”.
When electromagnetic waves travel through metamaterials, they exhibit some
bizarre properties:
(1) The group velocity direction of the electromagnetic wave is parallel to the
phase velocity direction, that is, the direction of the wave vector is opposite to
the propagation direction of energy, and the left-hand law is satisfied between
electric field, magnetic field, and wave vector.
(2) Reversed Doppler effect. The observed change in frequency in the left-handed
material is the opposite of the effect in the right-handed material. In the righthanded material, when the observer moves toward the source, the observer
measures a higher frequency than the source vibrates, which is called the
Doppler effect. In the left-handed material, similarly, when the observer is
moving toward the source of the wave, the frequency measured by the observer
is lower than that of the source of the wave, which is the inverse Doppler effect.
(3) Reversed Snell refraction. The refractive index is negative. At the interface
between left-handed material and right-handed material, the refractive rays
and incoming rays are on the same side of the normal line. So you have what’s
called a perfect lens.
(4) Reversed Cerenkov radiation. When a charged particle moves in a medium,
an induced current is generated in the medium. By these induced currents,
secondary waves are excited. When the velocity of a charged particle exceeds
the speed of light in the medium, these secondary waves interfere with the
original electromagnetic field and can form a radiation electromagnetic wave.
This radiation is called Cerenkov radiation. In the right-handed material, the
electromagnetic-excited radiation scatters forward at an acute angle. In the lefthanded material, the radiation direction of the electromagnetic wave changes,
scattering backward at an obtuse ngle.