Frequencydependent

Frequency-dependent describes a property that changes with the frequency of an input signal. In many disciplines, the response of a system is not constant across frequencies due to inertia, delays, resonance, or the distribution of time constants.

In biology, frequency-dependent selection occurs when the fitness of a phenotype or allele depends on its frequency relative to others in the population. Negative frequency-dependent selection favors rare variants and can maintain genetic diversity, while positive frequency-dependent selection favors common variants and can reduce diversity. Examples include prey or parasite dynamics where a rare phenotype has a selective advantage, or mimicry systems where the benefit of mimicking a model depends on how common the model is.

In physics and engineering, properties such as impedance, refractive index, and dielectric constant are often frequency-dependent. A system's transfer function or impedance can vary with angular frequency ω, and frequency response is characterized by magnitude and phase as functions of ω (as in Bode plots). This underlies filters, resonant circuits, and communication channels, where attenuation, phase shift, and delay depend on frequency.

In materials science and acoustics, viscoelasticity and dielectric relaxation produce frequency-dependent behavior, with mechanical loss and dielectric loss varying with frequency. Measurements are typically carried out in the frequency domain, using techniques such as impedance spectroscopy or dynamic mechanical analysis.