Any of the periodic signals can be expanded into a Fourier series, which is the sum of several harmonics (sine waves). According to this principle, a band-pass filter can be used to set the frequency band between 40-60Hz. .

Sine wave is the signal with the most frequency components, and the waveform of this signal is named after the mathematical sine wave. Any complex signal, such as a musical signal, can be viewed as a synthesis of many sine waves of different frequencies and sizes.

Unlike an amplifier circuit, a self-excited circuit is an electronic circuit that can generate an output signal without the need for an external signal. Therefore, it is often used as a signal generator to generate signals of various frequencies. Oscillator circuits are divided into sine wave and non-sinusoidal oscillators.

Extended information:

A sine wave is a single signal with the largest frequency component. The waveform of this signal is named after the mathematical sine wave. Any complex signal, such as a musical signal, can be viewed as a synthesis of many sine waves of different frequencies and sizes.

Unlike an amplifier circuit, a self-excited circuit is an electronic circuit that can generate an output signal without the need for an external signal. Therefore, it is often used as a signal generator to generate signals of various frequencies. oscillator.

An ideal square wave has only two values: "high" and "low". A signal whose current or voltage is rectangular is a rectangular wave signal.

Baidu Encyclopedia - Sine Wave

Baidu Encyclopedia - Square Wave