Abstract: Commutation device to connect and disconnect a current or voltage generator and a coil adapted to create a gradient of magnetic field in a measurement chamber of an NMR apparatus. The device comprises a switch (1) mounted in the supply circuit (2) of the coil (3), actuated by a control signal and adapted, in open position, to isolate totally the coil (3) from the generator (4). The switch is a double switch (1) adapted to separate, upon opening, the supply circuit (2) into a portion (5) connected to the generator (4) and a portion (6) connected to the coil (3), independently of each other. Alternatively the switch can be a high speed switch comprising at least one field effect transistor.

Abstract: A hyperfrequency generator comprising a source element (5) of negative resistance adjacent to a cylindrical resonant cavity (2) closed at opposite ends by two transversal closure plates (4, 7) for the purpose of tuning over a frequency band. The source element (5) is installed directly in the resonant cavity (2) such that there is a direct coupling between the source element (5) and the resonant cavity (2). One of the closure plates (7) is movable toward and away from the other for rough tuning.