METHOD AND MEANS FOR SENSING STRAIN WITH PIEZOELECTRIC STRAIN SENSING ELEMENT

摘要

1378633 Sensing strain electrically GENERAL DYNAMICS CORP 18 May 1973 23816/73 Heading G1N In a strain sensing device Piezo-electric material is disposed between an inner conductor and a surrounding flexible outer conductor such that when the material is subject to strain by flexure of the outer conductor an electric charge is generated proportional in amplitude and polarity to the amount of strain. As shown in Fig.1, the device is in the form of a circular cross-section cable having conductors 12, 16 and Piezo-electric material 14. Examples of materials are given. A rectangular, Fig.2 (not shown) square or oval cross-section may be provided. An additional layer of Piezo-electric material and a further conductor may be provided for greater sensitivity, Fig.4 (not shown). An outer insulating jacket may be provided around the outer conductor, Fig.3 (not shown) and a protective layer may be provided between the outer conductor and the jacket, Fig.5 (not shown). As shown in Fig.6, an amplifier 54 is connected to the first conductor and to a tape recorder, measuring instrument or oscilloscope 56 or alternatively a threshold device 58 and alarm 60. The device may be used as an intruder detector, or in a strain gauge system. It can be used to sense strains in the soil or other granular material, bridges, buildings, fences, walls, machines, or vehicles. If the cable is of large length it may have active sections and intermittent non-active sections.