The range of applications using microvibration isolation equipment is being extended to devices for which the influence of vibration had not previously been considered. As a representative example, the application of active microvibration isolation equipment using an air spring actuator, suitable for MRI and NMR that operate in a strong magnetic field, is examined. In order to be used in a strong magnetic field, the active microvibration isolation equipment needs to have an actuator made from a nonmagnetic material. The servo valve that controls the air pressure in the actuator, however, must be installed away from the strong magnetic field since it cannot be fabricated from a nonmagnetic material. This necessitates the use of a long air supply tube to connect the servo valve to the actuator. Since this long tube affects the actuator characteristics, adequate vibration isolation performance cannot be attained with a controller designed using the conventional equipment model. In this study, a new equipment model is proposed by analyzing the characteristics of the active microvibration isolation equipment, and the control system is designed for the model using the model matching technique. The equipment model and control technique are validated by simulation and experiment.

Nowadays there are demands on the refrigerator which will be used under maintenance-free condition. In particular, it is hoped that the thermoacoustic refrigerator will be used in artificial satellites, air conditioners, and so forth because of its simplicity and high reliability. This refrigerator has no mechanical parts in its system which cause friction loss and is similar in its refrigeration process to the basic-type pulse tube refrigerator. In this paper, a thermoacoustic refrigerator has been manufactured and its performance is discussed both experimentally and analytically. In experiments investigating the basic performance of this refrigerator, the stacks (which correspond to the regenerator of the pulse tube) of both the stainless-steel parallel plate and the ceramic capillary tube were installed in the resonance tube of quarter-wavelength. The temperature profiles were measured 50 mm apart along the tube. From experimental results, a COP of 0.334 has been obtained. In addition, the theoretical analysis using an advanced enthalpy flow model has been performed. A comparison between predicted and experimental performances was made, a qualitative agreement between them was obtained, and, finally, the effectiveness of the model was confirmed.

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