What are transformers?
An impedance matching device is called a transformer. Instead of an abrupt change between the two media, a transformer provides a smoother, gradual transition from the old to the new medium. Depending upon the wave and the medium, different transformers, such as quarter-wavelength and tapered transformers, can be used to help minimize reflection.
An example of a tapered transformer can be found in soundproof rooms or sound studios. Any sound that is produced is supposed to be absorbed by the impedance matching material on the walls. Special foam, tapered in a V-like shape, is used as a transformer to gradually absorb all the sound into the walls. The gradual changeover from the air medium to the wall medium prevents sound from reflecting back into the air.
An example of a quarter-wavelength transformer can be found on many camera lenses and eyeglasses. The quarter-wavelength thick coating on a lens is used to reduce reflections off the lens surface, allowing more light into the lens.
Electrical transformers are also used to match impedances by changing the varying voltages and currents in an electronic circuit. Modern electronic circuits make very minimal use of transformers because of their weight and size.