SPURIOUS RINGING IN PULSE NMR

The theory of electromagnetic generation of ultrasonic standing waves in metals is reviewed and applied to the problem of spurious ringing detected in pulse NMR. The theory predicts that the spurious signal is proportional to the transmitter pulse amplitude and the square of the static field intensity. It also depends on some material properties and geometrical factors. A table of pertinent properties for various metals is presented showing that aluminum is one of the worst materials. Experiments confirm that replacement of aluminum with other metals in the probe attenuates the spurious signal and that the ringing of the coil is attenuated by a judicious choice of wire size. © 1979.