Inductors are used extensively in analogue circuits and signal processing. Inductor in conjunction with capacitors and other components form tuned circuits which can emphasize or filter out specific signal frequencies. Two (or more) inductors which have magnetic flux form a transformer, which is a fundamental of every electric utility power grid. An inductor is used as the energy storage device in a switched mode power supply. Inductors are also employed in electrical transmission systems, where they are more commonly referred to as reactors. As inductor tend to be larger and heavier than other components, their use has been reduced in modern equipments. Solid state switching power supplies eliminate large transformers, and circuits are designed to use only small inductors. Large values are simulated by use of "gyrator" circuits which uses a capacitor and active components to behave similarly to an inductor.