A batch-mode assembly and packaging technology for 3-axis tri-fold inertial measurement units
This paper reports a batch-mode generic 3-D precision assembly and wafer-level packaging technology for 3-axis tri-fold inertial measurement units (IMUs) using silicon mounting jig wafers with embedded vacuum channels. This approach allows use of optimized single-axis IMUs without manufacturing and structural constraints of forming 3-axis in a chip, and improving the overall yield by testing the chips prior to 3-D assembly. The 3-D chip assembly is performed by a controlled sequence of vacuum through the channels and bottom access holes, ambient pressurization, and raise of temperature to form permanent rigid tri-fold bond to the jig wafer.
Study of environmental survivability and stability of Folded MEMS IMU
This paper presents a study on the structural rigidity of an Inertial Measurement Unit (IMU) implemented using the Folded MEMS approach. For such folded structures, environmental survivability and stability is a natural concern. We investigated IMUs of 35 mm3 (small) and 130 mm3 (medium) in volume, in the shape of a cube and a pyramid, and considered the reinforcement methods, including epoxy, eutectic solder, and silicon welding. Experimental characterization of a medium cube with eutectic reinforcement showed the maximum tilt of 0.2 mrad on the cube's sidewalls under temperature variation 25°C–90°C and the tilt of 0.2mrad under 10Hz to 20kHz vibration. An IMU error model was implemented, with the target sensors performance of tactical-grade, using in-run bias stability and scale factor (SF) stability for gyroscope (1°/hr, 100ppm) and for accelerometer (100µg, 100ppm), and a pre-defined trajectory with 122s flight time. The 0.2 mrad misalignment for the medium eutectic-soldered cube corresponded to a Circular Error Probable (CEP) rate of 1.25 nmi/hr, and a typical tactical grade IMU corresponded to CEP rate ≤1nmi/hr. We also concluded that the 35mm3 eutectic-bonding reinforced cubes will survive the mechanical shock under 10,000g, while silicon welding reinforced cubes of 35 mm3 would survive the shocks of 20,000g.
Centrifuge modelling of effects of shield tunnels on existing tunnels in soft clay
With the rapid development of the subway network,the phenomena of shield tunnels going across the adjacent tunnels are becoming more and more common.The interaction between shield tunneling and nearby tunnels is more complicated than the ordinary shield tunneling in intact soil strata.Based on the project of Shanghai Bund Passage crossing Metro Line 2,the method of centrifuge modeling together with the field measurement is employed to study the effects shield tunneling on nearby strata and existing tunnels.In centrifugal model tests,the effects simulation techniques considering the unloading of excavation,ground loss and grouting are developed to analyze the longitudinal settlement of the shield tunnel and the existing tunnel induced by the shield tunneling.Besides,the deformation distribution and settlement curves of the existing tunnels during shield construction are studied by using the monitoring data.