One common method of changing the frequency of an electromagnetic wave is to use a frequency converter. A frequency converter is a device that takes an input signal at one frequency and converts it to an output signal at a different frequency. This is typically achieved by using a combination of electronic circuits and filters to select and amplify the desired frequency components.
Another method of changing the frequency of an electromagnetic wave is to use a frequency shifter. A frequency shifter is a device that changes the frequency of a signal by adding or subtracting a fixed amount of frequency. This can be achieved by using a variety of different techniques, such as phase-locked loops (PLLs) or digital signal processing (DSP).
Finally, it is also possible to change the frequency of an electromagnetic wave by changing the physical characteristics of the medium through which it is propagating. For example, the frequency of a light wave can be changed by changing the refractive index of the material through which it is passing. This can be achieved by using a variety of different techniques, such as changing the temperature or density of the material.
