EMI Catalog - Spectrum Control

MultilayerDiscoidal CapacitorApplication GuidelinesCeramicdielectricElectrodesSources of EMIElectromagnetic interference occurs naturally from terrestrialsources such as lightning discharges, precipitation,and sand and dust storms, in addition to cosmic noiseemanating from sources within and outside our solarsystem. Man-made sources include power lines, rotatingmachinery, ignition systems, television and radio receivers,fluorescent lights, power amplifiers, computing devicesand transmitters of all types.Interference SuppressionFilter networks suppress electromagnetic interferencein two basic ways. The capacitor elements shunt theinterference to ground, and the series inductor elementsraise the impedance of the line making the shuntcapacitor elements even more effective.Capacitor ElementsThe types of capacitors used in Spectrum Control filtersare often referred to as feed-thru capacitors due to theirphysical geometry.The feed-thru design results in greatly reduced selfinductancecompared to standard leaded capacitors.Also, this design effectively prevents radiation from theinput coupling directly with the output of the capacitor,unlike leaded or chip capacitors. The combination oflow inductance and high input/output isolation providesexcellent shunting of EMI for frequencies up to andbeyond 1 GHz.The simplest feed-thru type is a ceramic tube that mayhave buried electrodes and can be constructed as a singlecapacitor or as two capacitors, as used in a Pi sectionfilter. This type of device can have capacitance values from10 pF to 0.1 µF and typical working voltage ratings up to2500 VDC. Due to the simple construction, these capacitorsare very efficient at frequencies up to 10 GHz andexhibit no pronounced resonances.Multilayer monolithic discoidal capacitors are used forvery high capacitance parts in standard sizes or for smallerfilters where the required capacitance cannot be achievedby a ceramic tube. This type of capacitor consists of alternatelayers of opposite polarity electrodes separated by aceramic dielectric. Typical capacitance values from 100 pFto 10 µF are available with working voltages up to 400 VDC.Embedded ElectrodeTubular CapacitorElectrode “E 1 ”Ground “G”Electrode “E 2 ”ResinSealedFilterPottingCircularFilteredConnectorMediumtempsolderjointsPottingTerminalBushingFerritebeadPi sectiontubularcapacitorHermeticallySealed FilterGlass sealCapacitorCoilCoil wirePlanarcapacitorsInterfacial sealHardinsertInductive ElementsFerrite sleeves are used with tubular capacitors sincethey can be conveniently accommodated inside the tubeto provide a very compact filter. They are also used withdiscoidal capacitors in some applications. Wound inductorsare used with discoidal capacitors to provide very highperformance filters.PottingFerritebeadSPECTRUM CONTROL INC. • 8031 Avonia Rd. • Fairview, PA 16415 • Phone: 814-474-2207 • Fax: 814-474-2208 • Web site: www.spectrumcontrol.comSPECTRUM CONTROL GmbH • Hansastrasse 6 • 91126 Schwabach, Germany • Phone: (49)-9122-795-0 • Fax: (49)-9122-795-5811