GB764017A - Capacitors - Google Patents

Abstract

764,017. Capacitors. TECHNOGRAPH PRINTED CIRCUITS, Ltd. Dec. 13, 1954, No. 36072/54. Class 37. A capacitor has its two electrodes, which form integral parts of the conductive pattern of a printed circuit in which the capacitor is incorporated spaced apart on the same side of a dielectric layer, and includes an electrically isolated conductive bridge at least part of which is on the opposite side of the dielectric layer and overlaps both the electrodes. The electrodes 10, 11 (Fig. 2) form integral parts of the conductive pattern of a printed circuit of which the dielectric layer 12 comprises the insulating base. The rigid conductive bridge 13 is disposed on the opposite side of base 12; in the case of a fixed capacitor it is fixed to the base 12, but in the case of a variable capacitor, it is movable so as to vary the area by which it overlaps the electrodes. The conductive bridge 13 may alternatively be of flexible material in which case it may be rolled on to the surface of the dielectric 12, as shown in Fig. 3, in order to vary the overlap. If the element 10, 11, 12 also be flexible, it and the flexible bridge 13 may be wound together from different directions about a common axis, to form a spiral coil, the bridge overlapping the electrodes only in the portions which are wound together. Another alternative construction is shown in Fig. 5 in which the two electrodes 10, 11 are mounted on one side of a dielectric sheet 12, an insulating backing-sheet 16A (thick compared with 10, 11, 12) being provided on the other side of the electrodes. The conductive bridge 17A is secured to the other surface of the sheet 16A, the capacity of the unwound band then being negligible. However, when the band is wound upon itself in a spiral coil the conductive layer 17A in one turn is separated from the electrodes 10, 11 in the adjacent turn by the thickness of the dielectric sheet 12 only and consequently the wound portion is effective as a capacitor, the capacity of which is variable by winding up more or less of the band. Fig. 6 illustrates another modification in which the conductive bridge takes the form of two arrays 26 and 27 of closely-spaced conductive strips each array overlapping one of the electrodes 24, 25, the strips being secured to the dielectric layer. One or more of the strips of each array may be connected together and to a similar number of the strips of the other array by a movable conductive member 28. Alternatively individual leads may be taken from each of the strips 26, 27 and the connections between the strips may then be effected at the remote ends of these leads.