This paper presents a passive wireless humidity sensor for concrete monitoring. After discussing the transmission of electromagnetic wave in concrete, a novel architecture of wireless humidity sensor, based on Ultra-High Frequency (UHF) Radio Frequency Identification (RFID) technology, is proposed for low-power application. The humidity sensor utilizes the top metal layer to form the interdigitated electrodes, which were then filled with polyimide as the humidity sensing layer. The sensor interface converts the humidity capacitance into a digital signal in the frequency domain. A two-stage rectifier adopts a dynamic bias-voltage generator to boost the effective gate-source voltage of the switches in differential-drive architecture. The clock generator employs a novel structure to reduce the internal voltage swing. The measurement results show that our proposed wireless humidity can achieve a high linearity with a normalized sensitivity of 0.55% %RH at 20 °C. Despite the high losses of concrete, the proposed wireless humidity sensor achieves reliable communication performances in passive mode. The maximum operating distance is 0.52 m when the proposed wireless sensor is embedded into the concrete at the depth of 8 cm. The measured results are highly consistent with the results measured by traditional methods.

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Asset management was a common RFID-based Internet-of-Things (IoT) application scene. RFID tags in the equipment warehouse were usually large, and the communication between the reader and the tag was prone to data collision problems, which affected the recognition efficiency of the device. In practical applications, due to the structural characteristics of the micro-strip UHF RFID tag antenna, the traditional inter-coupling impedance expression had large errors and insufficient accuracy in predicting the mutual coupling effect, such as system frequency shift. In this paper, the 3D initialization model of the tag was used to indirectly extract the electrical parameter values by the ANSYS HFSS software. At the same time, the dualtag was taken as an example to derive the transimpedance expression between the dense tags to extract the corresponding coupling parameters. Finally, various tag-intensive scenarios in the actual environment were tested and the derivation formula was verified, and the dual-tag UHF RFID near-field frequency shift affected by the environmental factors, such as relative position, attachment, and the stacking method, was discussed. The mutual coupling effect on the minimum transmit power of the reader antenna was also studied. The experimental results showed that the average error of the formula calculated by this method was significantly smaller than that of the traditional formula. When the tag spacing was less than 30 mm, the derived mutual impedance expression was applied to the frequency shift calculation error range (1.6-7.3 MHz). For dense tag systems, the error was less than 9.8% when the number of tags was greater than 7, and the prediction accuracy was higher than the superposition method. The research results provided a theoretical and practical basis for the rapid identification and location of power assets during the dense RFID tag environment. INDEX TERMS UHF RFID, Internet of Things, power asset management, frequency shift, mutual couple effect, mutual impedance.

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Low temperature combustion was developed using a four-cylinder light vehicle diesel engine. Operating conditions considered were 1600 rpm, 1bar and 3bar IMEP. Both EGR and split injection strategy were optimized in order to obtain the lowest BSFC accompanied with a low level of emissions. It was found that a late injection strategy with high levels of EGR rate was required for simultaneous reduction of NOx and soot. However, the fuel consumption remains higher than the conventional combustion regime. Thus, the optimization study of injection parameters to improve the trade-off between NOx and soot emissions while maintaining good fuel efficiency was performed. Several injection pressures were tested. The results showed that as injection pressure increased, NOx emissions increased slightly, soot initially decreased sharply, but further increase of injection pressure on soot was not obvious at low temperature atmosphere, and might lead to increased BSFC. Next, split injection strategy was adopted, optimized pilot injection conditions for minimizing fuel consumption were found at late pilot injection timing with big injection quantity, but little amount of pilot injection could make better comprehensive performance of diesel engine. Through multi-parameter collaborative optimization, the emission reduction path was proposed at operating condition of partial load. Low NOx and soot emissions could be obtained with slightly increase of fuel consumption.