Feedthrough EMI Filters Syfer / Knowles Feedthrough EMI Filters offer an extensive range, covering threaded and solder-in panel mounting versions, and an ever-expanding range of surface mount types. Syfer / Knowles Feedthrough EMI Filters are designed using a multilayer ceramic element, and manufactured using a unique 'Wet Process'. Dielectric materials used in these Feedthrough EMI Filters include the ultra stable C0G and stable X7R types, which ensure excellent insertion loss performance is provided up to full rated voltage and to the extremes of rated temperature. Capacitance values up to 2.2μF are offered, with working voltages up to 3kVdc.