| 摘要 |
<p>1,243,993. Piezo-electric crystals. HITACHI Ltd. 26 July, 1968 [2 Aug., 1967; 18 Sept., 1967], No. 35906/68. Heading HIE. [Also in Division H4] An electromechanical transducer utilizes the ferroelastic/ferroelectric properties of certain crystals, e.g. Rochelle salt, potassium dihydrogen phosphate (KDP), gadolinium molybdate (GMO) and methylammonium aluminium sulphate dodecahydrate (MASD). These crystals have the required properties at a temperature below a certain phase-transition point (Curie point) which may vary over a considerable range, e.g. for GMO it is 160‹ C., for KDP it is - 150‹ C. The Specification gives a list of crystal classes in which substances having the required properties are found and the relevant phenomena are discussed at length. The case of GMO is also discussed in Specification 1,243,994. The crystals exhibit E-field vs. E-polarization and stress vs. strain hysteresis characteristics whereby application of mechanical forces or electric fields comparable to the coercive stress or coercive field results in reversal of the spontaneous polarization or spontaneous strain of the crystal and it is stated that a large increase in electromechanical efficiency results from these reversals. The theoretical nature of "spontaneous polarization" and "spontaneous strain", are explained in the Specification. As shown in Fig. 7(a), a 5 mm. cube 1 of 45‹ Z-cut KDP (cut parallel to the surfaces [001], [110] and [110]) whose [001] surface is provided with an electrode 2 is disposed in a hollow cylindrical pressure cell 3 of pyroferrite. The arrangement is dipped in liquid N 2 and pressure applied by pistons 5. A voltage of about 5 kv is obtained across the electrodes and fed to a capacitor (Fig. 7b, not shown). The arrangement may be used as a transducer for closing the contacts of a relay (Fig. 8, not shown). The Specification describes a bimorph (Fig. 9, not shown), for use, e.g. in a pick-up, comprising two elongated GMO elements each cut from a single crystal perpendicularly to the c axis and affixed to either side of a resilient cantilever. The c axes are arranged in the same direction and electrodes arranged on the exposed faces. The bimorph operates in a bending mode. The Specification also describes a voltage transformer (Fig. 12, not shown), using two pairs of electrodes arranged on a 45‹ Z-cut GMO element (i.e. cut parallel to the [001] and [110] faces which are perpendicular to the c axis. The voltage ratio between the two pairs of electrodes is stated to be 100: 2.</p> |
