Radar returned signals are processed by stretch processing, resulting in mixer outputs. Based on the time-frequency decomposition of the cross S-method (CSM) of two adjacent mixer outputs, a range-spread target detector is proposed in this paper. As a preparatory work, we propose a signal synthesis method (SSM) based on the singular value decomposition. The SSM synthesizes two signals in their normalized forms from their cross Wigner distribution (CWD) and concentrates their energy on two singular values. This detector consists of three steps. First, we derive the CSM from the S-method (SM). The CSM is close to the sum of the CWDs of the components in one mixer output and their counterparts in the other. Second, we can decompose the CSM by the SSM, thereby obtaining singular values. Third, the time-frequency decomposition feature, i.e., the ratio of the sum of several biggest singular values to the median or mean of the rest, is defined to demonstrate the concentration of the singular values and used to detect the range-spread target. The proposed detector is evaluated by the raw radar data without range migration correction. Results show that it outperforms the conventional detectors. In addition, we prove that the proposed detector has the constant false-alarm rate (CFAR) property.Index Terms-Cross S-method (CSM), constant false-alarm rate (CFAR), range-spread target detector, signal decomposition, singular values.
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.
This paper presents a novel monolithic pressure sensor tag for passive wireless applications. The proposed pressure sensor tag is based on an ultra-high frequency RFID system. The pressure sensor element is implemented in the 0.18 µm CMOS process and the membrane gap is formed by sacrificial layer release, resulting in a sensitivity of 1.2 fF/kPa within the range from 0 to 600 kPa. A three-stage rectifier adopts a chain of auxiliary floating rectifier cells to boost the gate voltage of the switching transistors, resulting in a power conversion efficiency of 53% at the low input power of −20 dBm. The capacitive sensor interface, using phase-locked loop archietcture, employs fully-digital blocks, which results in a 7.4 bits resolution and 0.8 µW power dissipation at 0.8 V supply voltage. The proposed passive wireless pressure sensor tag costs a total 3.2 µW power dissipation.
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