<P> At frequencies greater than 200 GHz, waveguide dimensions become impractically small, and the ohmic losses in the waveguide walls become large . Instead, fiber optics, which are a form of dielectric waveguides, can be used . For such frequencies, the concepts of voltages and currents are no longer used . </P> <P> Alternating currents are accompanied (or caused) by alternating voltages . An AC voltage v can be described mathematically as a function of time by the following equation: </P> <Dl> <Dd> v (t) = V p e a k ⋅ sin ⁡ (ω t) (\ displaystyle v (t) = V_ (\ mathrm (peak)) \ cdot \ sin (\ omega t)), </Dd> </Dl> <Dd> v (t) = V p e a k ⋅ sin ⁡ (ω t) (\ displaystyle v (t) = V_ (\ mathrm (peak)) \ cdot \ sin (\ omega t)), </Dd>

Is the number of cycles per second of an ac sine wave