Communication is all the process of transferring information from sender to receiver. Since ancient times, information, like matter and energy, has been one of the basic resources on which human beings depend for survival and development. The history of human communication can be traced back to ancient times. Words, beacons, beacon, and post are the main communication methods, which have lasted for thousands of years. The history of the development of telecommunications began in 1837 when the American Morse invented the artificial telegraph device, and it has been only 170 years. Opening a thick history of telecommunications and following the footsteps of history, driven by technology and market demand, only a hundred years of history in telecommunications has undergone tremendous changes and achieved amazing glory. achievement.
Wireless communication system (WIReless CommunicaTIon System): Also called radio communication system, it is composed of three parts: sending equipment, receiving equipment, and wireless channel. It uses wireless electromagnetic waves to realize the transmission of information and data. It is classified according to working frequency band or transmission method, and can be divided into medium wave communication, short wave communication, ultra-short wave communication, microwave communication and satellite communication.
1 Low frequency induction communication theory
Low-frequency inductive communication is that after the data to be transmitted is modulated by a low-frequency carrier, signal amplification, and power amplification, a certain alternating current is generated at the transmitter. The alternating current is used to generate an alternating magnetic field, and the electric field generated by the alternating magnetic field. Therefore, the induced electromotive force is generated in the receiver. After filtering, demodulation, decoding and other signal processing, the transmitted information can be accurately received at the receiving end to complete the communication process. Because it uses the principle of electromagnetic induction to realize communication, it is called induction communication. When the distance is short, induction communication is relatively easy to realize.
Inductive communication uses the alternating current in the transmitting coil to generate a changing magnetic field. After the electromotive force is induced in the receiving coil, the transmitted signal is restored through a series of signal processing processes, thereby achieving the purpose of communication.
The strict theory of inductive communication is based on Maxwell's equations. Maxwell's equations are obtained through expansion and promotion on the basis of analyzing and summarizing the experimental laws of macroscopic electromagnetic phenomena. He revealed the interrelationship between electric field and magnetic field, electromagnetic field and electric charge and electric current, which is the general law followed by all macro electromagnetic phenomena. The differential form of Maxwell's equations is as follows:
The Maxwell equations in a passive, linear, uniform, and isotropic conductive medium are:
Let the propagation constant of electromagnetic waves in a passive, linear, uniform, and isotropic conductive medium be γ = β-jα, where α is the constant representing the attenuation of electromagnetic waves per unit distance, called the attenuation constant, and β represents the electromagnetic waves per unit distance The lagging phase is called the phase constant. According to the theory of electromagnetic field:
ε is the dielectric constant of the medium, σ is the conductivity of the medium, μ is the magnetic permeability of the medium, and ω is the working angular frequency.
Whether the medium is a dielectric or a good conductor is not only related to the medium parameters, but also related to the operating frequency. It can be seen that the better the conductivity of the medium (the greater the conductivity), the higher the operating frequency, the greater the attenuation of electromagnetic waves, that is, the high-frequency electromagnetic waves decay very quickly in good conductors, often decay to the nearest within a distance of microns It's zero. In general, the operating frequency of inductive communication in conductive media must be in the low frequency band, which is a very important feature of inductive communication systems in good conductor media.
Children Toy Car,Kids Electric Cars,Mini Cars For Kids,Toy Cars For Toddlers
Jinan Huajiang environmental protection and energy saving Technology Co., Ltd , https://www.hjnewenergy.com