Zenmon Abe

NMR Fresnel transform imaging technique using a quadratic nonlinear field gradient

A new NMR imaging technique using a quadratic nonlinear field gradient is described. The center position of the nonlinear field gradient where the field intensity is minimum is moved spatially at a fixed amount in each imaging pulse sequence to produce nonlinear phase encoding as a function of position. A NMR image is reconstructed from the collected data by the computer data processing. The principle of this technique and many experimental results using a low field imaging system operating at 0.0192 T are presented. Theoretical and experimental comparison of the S/N of the image in this technique with that of the conventional Fourier imaging technique are made and the results show that both techniques have almost the same S/N. Moreover, the theoretical and experimental results show that this technique has a feasibility of a spatially localized imaging without using a conventional localization technique such as the use of the selective excitation in the presence of a linear field gradient.

A New Second Harmonic Type Ferroelectric Modulator for Electrometer

The authors examined the possibility of using a second harmonic type modulator made of ferroelectric material with an electrometer. It was established that if modulation is carried out at a temperature slightly above the Curie point utilizing the odd symmetry of the relationship between voltage and charge of a ferroelectric capacitor, then the delay in response to a large input signal (memory effect) is eliminated, both zero drift and noise are reduced, and carrier amplitude is diminished largely in contrast to the results obtained at room temperature. In the experiments, triglycine sulfate single crystal (TGS) whose Curie point lay around 50°C was used with a carrier frequency of 50 kHz, reducing zero drift to the order of 10 μV/day and realizing low noise as characterized by 6 μV p‐p with 1 MΩ input resistance and in the bandwidth from dc to 1 Hz. This modulator is solid state, and its input resistance is about 1013 Ω as determined by the specific resistance of a TGS single crystal. Owing to the absence...