| Summary: | 碩士 === 中華大學 === 機械工程學系碩士班 === 100 === This research uses MEMS technology to integrate a thermal convection accelerometer on a RFID tag with flexible substrate such as a plastic or polyimide. Thus the accelerometer becomes a wireless sensor, the usage is very large. The fabrication process is a low temperature process. Firstly, use Cr and Ni metal thin films to make heater, and then let a standard electric current flowing through the resistor as heat source. Then deposit P-Type polysilicon in both sides of heater as thermistors. Repeat the above processes, we can use two pairs of modules to make a differential Wheatstone bridge circuit, the bridge circuit output voltage can be used to detect the vehicle acceleration. The advantage is to increase the output signal, and reduces the common mode noise and disturbance. Repeated three modules, we can measure three-dimensional acceleration motion. Such structure is very simple and without any movable parts. Besides, the heat dissipate to the environment is smaller than traditional silicon chip, because the thermal conductivity of plastic material is much smaller than that of silicon.
Moreover, the key technology of this research is to integrate thermal convection accelerometer with a wireless RFID tag on the same substrate. The heater and temperature sensors are directly adhered on the substrate surface without using the traditional floating structure. So, the structure is more simple, cheaper and reliable. It can be applied for larger acceleration conditions. This research uses xenon gas for conduction the heat, its molecular weight is larger than that of carbon dioxide, so it is more inert, and can increase the sensitivity performance. Besides, the internal chamber uses semi-cylindrical rather than the conventional rectangular. The sensitivity of the new design can also increase the sensitivity and response speed.
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