_ Section Nano antennas (Rectenna)
Researcher and author: Dr. Afshin Rashid
Note: In general, in order to receive the electromagnetic wave in the space, the dimensions of the antenna must be in the order of the wavelength of the input to its surface. Due to the very small dimensions of nano sensors, nano antennas need to have a very high working frequency to be usable. The use of graphene helps to solve this problem to a great extent. The speed of propagation of waves in CNTs and GNRs can be 100 times lower than its speed in vacuum, and this is related to the physical structure, temperature and energy.
Accordingly, the resonant frequency of graphene-based nano-antennas can be two times lower than nano-antennas based on nano-carbon materials. It has been proven mathematically and theoretically that the quasi-metallic carbon nanotube can emit terahertz radiation when a time-varying voltage is applied to its sides. Nanocommunications includes electronic devices and tools. It is possible that one of their dimensions is about one to several hundred nanometers. Based on this, if the antennas used in nano parts are to be in this range, it should be expected that the electromagnetic waves used in 5> The communications of these systems and devices should be about several tens of terahertz, which will include infrared, visible and ultraviolet wavelengths. Antenna as a tool The initial absorption of electromagnetic waves in space has been discussed and has its related engineering knowledge, which is very developed and extensive.
One of the most important parameters of any nano antenna is the current distribution on it. This characteristics of the radiation pattern, radiation resistance and reactance, and many important characteristics of the antenna determine. despite the facilities It is possible to make nanotubes with a length of several centimeters. At first glance, nanotube antennas give us the impression that they are similar to Dipole antennas designed in small dimensions. But in fact it is not the case. In the main theory of Dipole antennas to determine the current distribution on the antenna, that the Dipole radius is larger than the skin depth and also Kinetic inductance per unit length of the nanotube ten thousand It is equal to the magnetic inductance per unit length of conventional antennas. Therefore, the speed of the wave will be 100 times smaller than the speed of light. The efficiency of a classic nanotube antenna is around -90dB, which is due to resistive losses. Meanwhile, the dimensions of the antenna and nano system or nano sensor set, operating frequency, power losses, the scope and dimensions of the sensor network, the structure and facilities of the power supply system and the physical communication platform between different parts of a nano system, major factors and parameters are that each of them is decisive in some way and determines the ability to build and the performance of the final system.is completely excluded. Because here the electrons are only allowed to move along the conductor string and therefore the current distribution is effectively one-dimensional. In addition to the fact that the electrons only move in one dimension, there are two important issues. Also happens, large inductance and resistance. These characteristics create a very different behavior for nanotube antennas compared to classical antennas. The main difference is that the current distribution is alternating with a wavelength that is 100 times smaller than the free space wavelength for a certain thermal frequency. The wavelength of current distribution depends on the wave speed in that mode. If the speed of the wave is the same as the speed of light, the wavelength of the current distribution is the wavelength of electromagnetic waves in free space. On the other hand, the wave speed in nanotubes is about one hundred times lower than the speed of light. This is because in circuit theory, the wave speed is equal to the inverse of the square root of the capacitive capacitance per unit length multiplied by the inductive capacitance per unit length. In one-dimensional electrical conductors such as nanotubes, the skin-depth mode . Considering that the nanodipole L/d is significantly reduced, it cannot be used The resistance loss is so low that it can be ignored.
Conclusion :
In general, in order to receive the electromagnetic wave in the space, the dimensions of the antenna must be in the order of the wavelength of the input to its surface. Due to the very small dimensions of nano sensors, nano antennas need to have a very high working frequency to be usable. The use of graphene helps to solve this problem to a great extent. The speed of propagation of waves in CNTs and GNRs can be 100 times lower than its speed in vacuum, and this is related to the physical structure, temperature and energy.
Researcher and author: Dr. Afshin Rashid
Specialized doctorate in nano-microelectronics