Patent GB-753617-A (GB)
Title: Bending-responsive electromechanical transducer device
IPC: H04R17/00
Filed: 1954-03-15
Abstract: 753,617. Piezo-electric transducers. CLEVITE CORPORATION. March 15, 1954 [March 18, 1953], No. 7448/54. Class 40 (8). A piezo-electric transducer adapted to respond in a flexual mode comprises a structurally non-composite body of ceramically-bonded polycrystalline material, e.g. barium titanate, which is made up of two outer thickness portions 52, 53, Fig. 3, joined by at least three laterally-separated webs or connecting portions 51, electrodes 54, 55, 56 being applied to the inner and outer surfaces of the outer portions 52, 53. By means of suitable connections to the inner and outer electrodes a permanent or prepolarizing potential may be applied in opposite directions to the two thickness portions 52, 53, the signal field being applied across the outer electrodes 54, 55 so as to produce oppositelydirected stresses in the two portions with consequent bending of the body. Alternatively, a uniform polarizing field may be applied between the outer electrodes and the signal field applied in opposite directions in the two portions by connecting the signal source in parallel to the inner and outer electrodes. In the case of a rectangular body the flexing occurs both about the longitudinal and lateral axes of the body and linear oscillatory motion may be produced in response to an oscillatory electric signal by anchoring the body along one edge and attaching a stylus or other member to the opposite edge (Figs. 1, 4, not shown). In the transducer of Fig. 3 the connecting portions 51 run the whole length of the body and are separated by holes of either rectangular or circular (Fig. 2, not shown) section. In a modified structure, Fig. 5, the holes run at right-angles to each other, the connecting portions 84 being distributed uniformly. A further structure (Fig. 6, not shown), having uniformly-distributed connecting portions of cylindrical form is described. The curved side walls of the various structures may be removed without affecting the mode of operation. Disc-shaped structures may also be made; e.g. the structure of Fig. 5 may be modified by grinding away the edges to form a disc which is supported at its edges and suffers cup-shaped deformations on application of a signal. The following dimensional proportions for maximum response are given: (a) the lateral distance between any point on a laterally exposed interior surface of a connecting portion and the closest adjacent laterally exposed surface of another connecting portion must be less than half the overall width of the body. (b) This lateral distance must be less than five times the thickness of the smaller of the two outer thickness portions measured at its thinnest region. (c) No point on either of the two outer electrodes must be separated from one of the inner electrodes by a distance through the body greater than twice the thickness of the intervening thickness portion measured at its thinnest region. (d) The thickness dimension of the interior thickness portion (i.e. the thickness of the connecting portions) must be between one quarter and one half of the overall thickness. Specifications 590,688, 648,404, 663,423, 753,618 and 753,619 are referred to.