This paper investigates the effect of gas flow in holes on the squeeze film damping of perforated structures. An infinite perforated plate with circular holes is analyzed with an analytical model. The results show that there is a minimum damping ratio for a certain size ratio. The corresponding hole size can be defined as a critical size. When the hole size is smaller than the critical size, the hole effect dominates. The damping ratio increases drastically with hole size decreasing when the size ratio keeps constant. Some finite two-dimensional structures are analyzed with an equivalent circuit model. Similar results are obtained. The finite two-dimensional structures and some quasi three-dimensional structures are also simulated with ANSYS/FLOTRAN. The results are presented.
Presented in this paper is an experimental study of squeeze- film air damping in rare air. Experimental beam-mass devices with different gap distances have been designed and fabricated for the experiments and a glass apparatus has been design and set up for measurement in quality factor in low pressure range. The piezoresistive bridge on the beam facilities the measurements of quality factor in vacuum. The pressure coverage in the study is in the range of 105 Pa to below 0.1Pa. The experimental results of quality factor do not agree well with the existing model proposed by Christian, but agree much better with a new model using energy transfer scheme instead of the momentum exchange scheme used by Christian.
Conventionally, a one-dimensional vibratory gyroscope is excited into vibration int the x-direction and detection is made for an angular rate around the z-axis by measuring the induced vibration in the y-direction. Proposed in this paper is a novel operation mode. In this operation mode, excitation is made in both the x- and y-directions and the angular rate around the z-axis causes the phase variation of the vibrations. Therefore, the angular rate signal can be detected by measuring the phase change of the output signal of the gyroscope in one of the directions. This operation scheme features high accuracy, high immunity against interference and low temperature coefficient. A bulk micromachined gyroscope with piezoresistive sensing elements is used as a test carrier for the two-dimensional excitation operation and phase detection scheme. Experimental results are presented.
Described in this paper is a micromachined vibratory gyroscope fabricated by combining anisotropic etching and DRIE process. The gyro consists of two chips, the sensor chip and the bottom chip. Two identical cantilever beam-mass structures are fabricated in the sensor chip and driving electrodes are made on the bottom chip. The beam-mass structure has two vibration modes: the vertical vibration mode for driving and the lateral vibration mode for sensing. Piezoresistive sensing elements are made on the surface of the beams to monitor the vertical and the lateral vibration. Gyroscopes can be formed using a single beam-mass structure or using two beam-mass structures (the dual beam-mass gyroscope). The effect of acceleration can be rejected if a differential operation mode is used for a dual beam-mass gyroscope. The gyroscope can operate in an atmospheric pressure due to the high Q value in lateral vibration mode dominated by slide-film air damping. Piezoresistive sensing avoids the difficulties caused by small capacitance detection. The packaging and testing costs can be reduced significantly. Preliminary results for a working device with a single beam-mass structure show that the sensitivity for angular rate signal is found to be about 15.6(mu) V/$DEG/sec/5V in an atmospheric pressure environment.
Described in this paper are a novel composite beam-mass structure and a micro gyroscope based on the structure. The composite beam consists of two sections: a section of vertical beam with a cross-section vertical to the wafer surface and a section of horizontal beam near the wafer surface. As the two sections have two orthogonal compliant directions, the structure has two orthogonal vibration modes: a vertical vibration mode decided by the horizontal beam and a lateral vibration mode decided by the vertical beam. Therefore, a vibratory gyroscope can be developed by this composite beam structure with a mass attached. As the composite beam is a multilevel structure that can hardly be fabricated by a conventional anisotropic etching technology, a novel 'maskless etching' technology for <100> vertical steps has been developed for the structure. Piezoresistive bridges on the surfaces of the horizontal and the vertical beams are used to monitor the driving vibration and to sense the output signal. Testing shows that the sensitivity from the piezoresistive bridge is 0.22 (mu) V/(degrees/sec) under a 6V AC driving with a DC bias. The special advantage of the sensor is the ability of working in an atmospheric environment.
A novel singled-sided multilevel island-beam-diaphragm structure has been designed and fabricated for an extremely high sensitivity pressure transducers by using a novel anisotropic etching technology called masked-maskless anisotropic etching technology. The structure consists of two small islands for overrange protection, two shallow masses for stress concentration, three thin beams on a deep-etched thin diaphragm for piezoresistors location. A prototype pressure transducer of 400 pa operation range and 0.6% nonlinearity has been tested.
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