Miniaturization of Delay Lines Through the Use of the Dielectric and Structural Properties of Plastics

A miniaturized delay line wound on a sectionalized plastic spool is described. The surfaces of the spool and flange separators are coated with a silver paint which serves as a capacitor electrode. The other capacitor electrode is a winding conductor and the capacitance is derived from the wire insulation. To raise the capacitance the spaces between turns of the windings and between the windings and the flange or-core are filled with an oil having a dielectric constant somewhat greeter than air. The surface electrical resistance of a silver paint electrode has a significant effect on the output voltage loss and the capacitance of the delay line. In general, the thinner silver paint electrodes result in less output voltage loss and also lower capacitance. In view of the output voltage and the delay time of this delay line, suitable surface electrical resistance is 15 to 25
/Omeg
/square, hence the effect of thickness of silver paint electrodes is discussed. The temperature coefficient of delay time is improved by using a filler oil with a negative temperature coefficient of dielectric constant. A further improvement is achieved by a newly developed packing method. The miniaturized delay line in a size of 11x14x45mm has a low output loss of 3 dB at 4 MHz.