碩士 / 大葉大學 / 機械工程研究所碩士班 / 94 / ABSTRACT
SQUID （Superconducting Quantum Interference Device）is the most sensitive magnetometer now. It can detect the signal as small as 10-14 to 10-15 Tesla, which is one-billionth of terrestrial magnetism. Another, because of the unique properties of the voltage variation periodically with magnetic flux, SQUID has been applied in precision measurement, like the weak magnetic field, current, voltage, inductance, and magnetic susceptibility.
Based on the eddy current method, this work proposed the nondestructive evaluation of the metal conductor by using the combination of the transfer coil probe and SQUID magnetometer.
We developed all the experimental system including Dewar, magnetically shielding box, and coil. In Dewar, the G-10 fiberglass is used to manufacture the vacuum bottle of liquid nitrogen because of the property of thermal conductivity and non-metal to avoid the influence of the SQUID sensing.
In magnetically shielding box, mu-metal plate, copper net, and aluminum plate are used. The first is for anti- terrestrial magnetism and low frequency noise. The others are for isolating the electromagnetic wave of high frequency.
Besides, we designed excitation coil and pick-up coil as the gradiometer probe to detect the crack signal. Then the induced current in the gradiometer probe rebuilt the magnetic field inside the magnetically shielding box, which is sensed by SQUID. It has many advantages than the tradition method of the direct sensing by SQUID. For example, the active probe is more practical and convenient than the heavy and large Dewar with SQUID. And the sensitivity is improved due to no limitation of the space between SQUID and sample
| Identifer | oai:union.ndltd.org:TW/094DYU00488047 |
| Date | January 2006 |
| Creators | Chia Lung Lee, 李佳榕 |
| Contributors | cyhong, 洪振義 |
| Source Sets | National Digital Library of Theses and Dissertations in Taiwan |
| Language | zh-TW |
| Detected Language | English |
| Type | 學位論文 ; thesis |
| Format | 55 |
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