DE1572996

1,173,374. Non-contact-making relays; electro-mechanical networks. INTERNATIONAL BUSINESS MACHINES CORP. 3 April, 1967 [29 April, 1966], No. 15117/67. Headings H3B and H3U. [Also in Division H1] A resonator comprises a semi-conductor body 60 and an electrical heating element 70 formed in or on the body for causing mechanical strain due to differential expansion of the body. If the electrical, and hence the thermal, excitation is varied at a suitable frequency the body will resonate mechanically, producing a large mechanical strain. The heating element may be an electrical resistance element at the surface of the semi-conductor, an electrical resistance established through the semi-conductor body, a forward biased PN junction or a transistor operated to cause collector power dissipation. In each case the arrangement is such that more heat is supplied to the upper surface of the body than to the lower, so that the substrate bends. Alternatively, heaters may be provided on both surfaces and driven electrically out of phase. It is also suggested that the Peltier effect could be used. Strain in the substrate is detected by means of one or more piezo-resistors 72, 74, 76, or piezo PN junctions, or by reflecting light from the free end of the substrate towards a light detector. In the arrangement shown the piezoresistors are connected in series to a voltage source, with 72 in the middle, and an output voltage is detected at the junction between 72 and 74. By using resistors 72, 76 which have an equal and opposite temperature coefficient to resistor 74 output variations due to temperature changes are eliminated. In Fig. 8 the heating element 70 is a transistor and a control voltage is applied to its base to vary the emitter-collector current and hence the heating effect. Transistor and resistor devices 82, 83 are provided for amplifying the control and output signals 84, 85 being input and output connection tabs. A modification is referred to in which four piezo-resistors are connected to form a bridge circuit. Instead of operating in a flexual mode the device may be constructed to operate in a torsional or an acoustic mode. In a torsional arrangement the body is cylindrical and has the excitation and sensing elements arranged on a helical line at 45 degrees to the axis of the cylinder. In an acoustic arrangement the excitation and sensing elements are mounted on opposite end faces of the substrate which is attached to a support by way of the excitation element. A