North-finding techniques involve detecting and calculating the azimuth angle, thus determining north using various kinds of sensors. North identification can be accomplished through the use of a digital magnetic compass. However, the accuracy of a magnetic sensor is easily degraded by spatial and temporal distortions due to ferrous material or electromagnetic interference. Moreover, GPS-based north-finding systems (NFSs) can accurately determine the azimuth by two separated GPS antennas. This still has a practical limitation in jamming or indoor environments, however. Therefore, an inertial NFS has been developed to replace the classic equipment used in estimating the fire direction of hand-carried projectile weapons such as with mortars. To improve the precision of seeking north with a middle grade gyro, multi-position method is implemented. Using only a single fiber optic gyroscope and two MEMS accelerometers on a rotary platform, the north orientation is accurately found by observing the horizontal component of the earth's rotation vector. With a minimum number of inertial sensors on a manual rotary platform, the NFS can be compact, light-weight, low-cost, and robust enough for easily portable mortar. Using additional auxiliary information which can be obtained by magnetic sensors, the time for locating north can be dramatically reduced. The test results compared with the navigation grade inertial navigation system show that a single digit mrad heading accuracy can be achieved. The operability of NFS mounted beside a mortar was tested in the field, in which the reference positions were acquired by DGPS (Differential GPS). To insure the durability in gun-fire shock, the drop-tower test was performed based on the shock profile measured in real mortar fire.

In this thesis, fabrication technology of a freestanding micro mechanical structure using electroplated thick metal with a high-aspect-ratio SU-8 mold was studied. A cost-effective fabrication process using electroplating with the SU-8 mold was developed without expensive equipment and materials such as deep reactiveion etching (DRIE) or a silicon-on-insulator (SOI) wafer. The process factors and methods for the removal of SU-8 were studied as a key technique of the thick metal micro mechanical structure. A novel method that removes crosslinked SU-8 completely without leaving remnants of the resist or altering the electroplated microstructure was utilized. The experimental data pertaining to the relationship between the geometric features and the parameters of the removal process are summarized. Based on the established SU-8 removal process, an electroplated nickel comb structure with high-aspect-ratio SU-8 mold was fabricated in a cost-effective manner. In addition, a freestanding micro mechanical structure without a sacrificial layer was successfully realized. The in-plane free movements of the released freestanding structure are demonstrated by electromagnetic actuation. This research implies that various types of MEMS devices can be developed at a low-cost with design flexibility.

No abstract

We report experimental behaviors of condensed 87 Rb atoms responding to changes in the trap potential of the atomchip. The two-types of adiabatic and non-adiabatic overall changes were implemented by changing the ramp-down speed of the chip-wire current, which can dominantly modify the one-axis magnetic field gradient. Under the adiabatic process, a pure condensate stayed in the initial spin state and collectively oscillated with both monopole and dipole modes, while an atomic cloud above the critical temperature exhibited sound waves in a dense ultracold gas. On the other hand, Bose-Einstein condensate atoms with non-adiabatic perturbation were split into spatially different positions by spin states through spin-flip. We investigated the split ratio among spin states depending on final evaporation frequency. Potential changes, of course, cause collective oscillations regardless of the changing process.