résonance

Résonance is the phenomenon in which a system exhibits a large amplitude of oscillation when driven by a periodic force at a frequency near the system's natural or resonant frequency. In an ideal undamped oscillator, the response diverges at resonance, but real systems include damping that limits the amplitude and determines the sharpness of the resonance peak. The efficiency of energy transfer is greatest when the driving frequency aligns with the natural frequency, so small forces can produce large oscillations.

Resonance appears in many domains. Mechanical resonance is seen in pendulums, vibrating rods, and bridges; acoustic resonance occurs in air columns and musical instruments; electrical resonance is observed in circuits containing inductors and capacitors; optical resonance takes place in cavities and nanostructures, and quantum systems exhibit resonant transitions when energy matches allowed levels.

Key concepts include the natural frequency, the driving frequency, damping, and the quality factor (Q), which measures how narrowly the system responds around resonance. Anti-resonance refers to frequencies where the response is suppressed. The resonance curve describes output amplitude versus frequency, and the width of the peak is related to damping.

Applications range from tuning and filters in electronics, acoustic design of rooms and instruments, to sensors and imaging techniques that exploit resonant interactions. Engineers must consider resonance to avoid unwanted amplifications that could cause structural failure, and may introduce damping or stiffness changes to suppress problematic modes.

Etymology: résonance derives from the Latin resonare “to resound,” and entered science through studies of vibrating systems.