One application of capacitors for filtering includes the use of safety capacitors for EMI suppression. EMI suppression is the removal of high frequency signals which can cause noise generation. Safety capacitors are a special application of capacitors which filter the high frequency noise and allow the low frequency pass through. These safety capacitors must meet strict criteria mandated by regulators like UL, CSE, ENEC and CQC, for the prevention of injury should the circuitry fail. Another application which is common for filtering is in RF circuits like radios and cell phones. In this application, the high frequency signals are allowed to pass thru while blocking the DC voltages. The top picture on this slide depicts an EMI filtering application and the use of X and Y safety capacitors. It is interesting to note that the capacitors provide filtering for noise generated from outside the circuit (EMI Susceptibility) as well as filtering any noise generated from inside the equipment (EMI Emissions/Radiation). The lower portion of this slide shows what used to happen to the television reception when a hair dryer was turned on. The dryer generated noise and the TV was susceptible to the noise generated, creating static on the screen.