Absorptive Lines as RFI Filters

A new class of ":distributed constant" filters has been recently developed using the normal propagation path of the electrical current in a wire, a cable, or a line to suppress interference. The three basic characteristics are the following: 1) Instead of using lumped reactive components (inductors, capacitors) connected to the wire, one superposes the suppressive effect to the normal straight and flexible conductor without any additional components. 2) The problem of mismatch at the interfaces with the generator and with the load (for example, a classical π filter connected to a reactive load) is nonexistent, because the suppression is due to an absorption of the critical frequency components. The Q factor of such a line is substantially equal or less than unity in the frequency range considered. 3) In the case of nonsheathed cables (general case), if the suppression of the conducted interference is sufficiently high along the line (for example, a 20-dB attenuation is obtained for a linelength equal to a tenth of the wavelength at the considered frequency), radiation and induction of parasitic frequencies is automatically suppressed. The necessary absorption can be introduced on the cable or the line by using separately or together three different physical effects: 1) Absorption due to magnetic and dielectric losses. These losses are achieved by the use of special products, like magnetic ferrites with high Fe and Zn content, semiconductive and ferroelectric dielectrics, and with bulk or synthesized dispersive effects.