By sion932 
What is the working principle of a resonant circuit? HVHIPOT specializes in the production of series resonance, with a wide range of product selection and professional electrical testing. To find series resonance, choose HVHIPOT.
The voltage waveform when resonance occurs in a series circuit. When a voltage square wave is applied to an LC series circuit, both the front and rear edges of the square wave will excite the LC series circuit (i.e. receive energy), and after each excitation, damping oscillation (i.e. energy loss) will occur. When the rise rate dv/dt value of the input voltage waveform is greater than the rise rate of the resonant circuit waveform (sine wave), the circuit will generate excitation; When the rise rate dv/dt value of the input voltage waveform is less than the rise rate of the resonant circuit waveform, the circuit will generate damping.
Due to the fact that the energy of the oscillation circuit has not been completely consumed after each excitation, a new excitation is then applied to superimpose the oscillation voltage time and time again. If the phase of the excitation can be synchronized with the phase of the oscillation waveform, the amplitude of the oscillation voltage will increase until the energy excited is equal to the energy lost in the circuit. Therefore, when the quality factor Q value of the resonant circuit is high, the resonant voltage can also rise very high. Ideally, if the Q value is infinitely high (i.e. the antenna has no loss), the amplitude of the resonant voltage will also rise infinitely high, but this situation does not exist.
The voltage amplitude during resonance in an LC series circuit is closely related to the phase of the excitation waveform, while it is not particularly correlated with the amplitude of the excitation waveform. If the phase or period between voltage square waves is not strictly kept equal, the waveform will experience severe jitter, and the amplitude of the resonant voltage will also decrease significantly. Therefore, some measurement methods cannot objectively measure the electromagnetic field strength of interference signals in a certain space.
In addition, it should be pointed out that the receiving antennas used for testing are also divided into electric field induction wires, magnetic field induction antennas, and electromagnetic field induction antennas.
We only analyzed the principle of the interference signal receiving antenna. In practical applications, the antenna does not specifically distinguish between the receiving antenna and the transmitting antenna, and both can use the same antenna. Therefore, any charged conductor or conductor through which current flows in a circuit can be regarded as a transmitting antenna.
The magnitude of radiation interference generated by electronic devices is not only related to the amplitude of the interference signal, but also to the size of the induction capacitors C1 and C2, that is, it is related to the area of electric field radiation (capacitance is proportional to the area) and the area of magnetic field radiation. Therefore, minimizing the radiation area of interference signals is a good way to reduce radiation interference, which is the working principle of resonant circuits.