No abstract

Nuclear magnetic resonance (NMR) is a fundamental research tool that is widely used in many fields. Despite its powerful applications, unfortunately the low sensitivity of conventional NMR makes it difficult to study thin film or nano-sized samples. In this work, we report the first NMR spectrum obtained from general thin films by using magnetic resonance force microscopy (MRFM). To minimize the amount of imaging information inevitably mixed into the signal when a gradient field is used, we adopted a large magnet with a flat end with a diameter of 336 μm that generates a homogeneous field on the sample plane and a field gradient in a direction perpendicular to the plane. Cyclic adiabatic inversion was used in conjunction with periodic phase inversion of the frequency shift to maximize the SNR. In this way, we obtained the 19F NMR spectrum for a 34 nm-thick CaF2 thin film.

We describe a magnetic resonance force microscopy experiment carried out using both a fast-relaxing spin system and a frequency-modulation mode detection method, presenting a validation of the measured signal and sensitivity. The detection method applied along with a self-excited cantilever oscillation worked stably without any serious interference due to spurious cantilever excitation despite application of first-harmonic microwave modulation, and thereby successfully created almost the maximum available signal. The signal could be measured without distortion while the magnetic field was swept at a rate of 1.9 G s−1. The measured sensitivity approached the thermal noise limit of the cantilever with a high quality factor. The experimental results for both signal and noise were in good agreement with theoretical predictions.

Liquefied natural gas (LNG) is liquefied at -162°C at atmospheric pressure and stored in the inner shell. Due to the transport and storage characteristics of such low temperature conditions, 9% high nickel steel, which shows excellent strength and toughness even at low temperatures, is used for the inner wall. On the other hand, the base material of the inner wall has a tempered martensite structure, whereas the weld metal has an Inconel- based austenite structure with high damping properties in acoustics. Also, the weld metal is composed of an anisotropic structure completely different from the base material. These are considered obstacles in non-destructive testing. We applied automated phased array ultrasonic testing(PAUT) as a replacement of radiographic testing in inspection of LNG storage tank. To obtain the reference value data, a reference specimen for each thickness was prepared, and an automatic scanning device was designed and manufactured. Also, a customized phased array(PA) probe was developed and applied. All parts are integrated and operated as one system, and the data is analyzed and stored through an operating program developed in-house. The current system has proven its performance through field application to a much-improved level in the existing scanning device, probe and application method. In conclusion, it was proved that our technology can be commercialized by showing excellent detection ability.