Abstract: A method of driving an electric motor having at least one coil winding comprising using a switching operation when the current in the winding is to be switched from a first state to a second state. The switching operation has at least first and second switching steps, the interval between which is approximately equal to half the period of a dominant frequency of vibration of the motor (or to an integral multiple of the period plus a half). This reduces vibrations causing acoustic noise, enabling the motor to be operated more quietly. One or more intermediate steps may be included in the switching operation.

Abstract: An electromagnetic acoustic transducer for generating ultrasound waves in an electrically conducting sample comprises a magnetic element for producing a static magnetic field, and a coil through which brief current pulses are passed to create a dynamic magnetic field, the interaction between the fields and the sample generating ultrasound waves. The current pulses are produced by an input circuit, and their characteristics are arranged so that the frequency content of the ultrasound generated is broadband. Output pulses produced as a result of the input pulses are then also brief (substantially the same duration as the input pulses) so that accurate measurement of the interval between one output pulse and the next is relatively easy. The transducer can therefore be used to measure accurately the thickness of very thin samples, and to detect near surface defects. The generating transducer may also be used for detection of the output pulses, or a similar but separate detecting transducer may be used.

Abstract: An apparatus for inspecting single crystal specimens comprises an x-ray generator which supplies x-rays to a collimator. The collimator has a matrix of apertures to produce a plurality of parallel x-ray beams which are directed onto a surface of the specimen. An x-ray detector detects the x-ray beams diffracted from the surface of the specimen, corresponding to each of the parallel x-ray beams. At each symmetry pole of an overall Laue pattern an accurately predictable pattern of spots is produced on the x-ray detector, if the orientation and shape of the specimen crystal is known. Each spot corresponds to where one of the diffracted beams strikes the detector. A disarrangement of one or more of the spots indicates a difference in crystal orientation.