introduction to Resonance
Resonance is a phenomenon that occurs in many fields, including electronics. A resonance device produces a broadening and dampening effect. In electronics, resonant circuits pass desired frequencies and reject all others. The ability of a series or parallel combination of XL or XC to produce resonance provides a number of unique applications. Resonant circuits make it possible for a radio or television receiver to tune in and receive a station at a particular frequency. The tuning circuit consists of a coil of wire in parallel with a capacitor. Parallel tuned circuits have maximum impedance at resonant frequencies. Tuned circuits are vital to a variety of types of communication equipment, from radios to radar.
Resonance occurs when a circuit’s inductive reactance and capacitive reactance are balanced. Previously, it was mentioned that inductive reactance increases with frequency, and capacitive reactance decreases with frequency. If both inductive and capacitive components are in an AC circuit, at one particular frequency their reactances will be equal but opposite. This condition is referred to as resonance, and a circuit that contains this characteristic is called a resonant circuit. Both inductance and capacitance must be present for this condition to occur.
In any resonant circuit, some resistance is usually present. Though the resistance does not have an effect on the resonant frequency, it does affect other resonant circuit parameters that are explained later in this text.
The value of inductance and capacitance deter- mines the specific frequency of resonance of a circuit. Changing either or both results in a different resonant frequency. Typically, the larger the value of inductance and capacitance, the lower the resonant frequency
Therefore, the smaller the value of inductance and capacitance, the higher the resonant frequency.
Above and below the resonant frequency of any LC circuit, the circuit behaves as any standard AC circuit. Resonance is desired with radio frequencies in tuning receivers and transmitters, certain industrial equipment, and test equipment. It is undesired in audio amplifiers and power supplies. Resonant circuits are not used in the audio bands of frequencies.