Which factor does NOT influence the resonant frequency in a cavity?

The resonant frequency in a cavity is determined by factors that directly influence the physical characteristics or dimensions of the cavity that can resonate with electromagnetic waves. The material used affects the dielectric constant, which in turn influences the resonant frequency. The physical size of the cavity is crucial because larger cavities have lower resonant frequencies, while smaller ones resonate at higher frequencies. The shape of the cavity also plays an important role, as different geometries can alter the modes of resonance available within the cavity.

Ambient temperature, while it can affect the properties of materials (such as changing their resistance or dielectric properties), does not directly alter the fundamental resonant frequency established by the cavity's size, shape, or the materials used. Thus, changes in temperature have a lesser impact on the intrinsic resonant frequency established by the cavity's fixed dimensions and geometric configuration, making it the factor that does not have a direct influence on resonant frequency in this context.