| 摘要 |
A method and an apparatus for transmitting and receiving electromagnetic ultra-sound, especially in non-destructive testing of electrically conductive material, comprising the steps of generating one or more magnetic fields by means of one or more electromagnets (1,2,3,4) and supplying a transmitter coil (8) in said magnetic field with a supersonic frequency, and scanning a receiver coil (56) in said magnetic field. In known apparatuses, especially in the testing of non-magnetic material, the signal/noise ratio of a received signal is unfavorable. According to the present invention said ratio is improved in that said magnetic field is generated during a short time compared with the time between two successively occurring magnetic fields, and that a number of pulses of well-defined length of supersonic frequency are supplied to the transmitter coil (8) when the magnetic field or fields have a sufficient strength. The receiver coil (56) is scanned after each such pulse, and the different receiver signals are summed up in an integrator (60). The said pulses each have a preferred length of a complete sinusoidally-shaped cycle, whereafter the respective pulse is extinguished entirely. |
