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关键词： Harmonic analysis   Transponders   Measurement   Receiving antennas   Transmitting antennas   Performance evaluation   Loss measurement   Backscatter   conversion loss   dual band   frequency doubler   harmonic transponder   metrics   nonlinear circuits   patch antennas   over-the-air testing   RFID   wireless sensor  

摘要： Harmonic transponders are passive wireless devices that hold great promise for a variety of long-term tracking and sensing applications. These nonlinear devices receive an interrogation signal at one frequency (f) and backscatter harmonics (typically, 2f is of interest). The device's conversion loss is the change in power from what is received and what is transmitted. We show herein that conversion loss is dependent jointly on interrogation power, interrogation frequency, and interrogation angle. This coupled nature of the device's behavior necessitates performance metrics that capture these characteristics. We present a methodology to generically test these devices and propose metrics that capture the noted dependencies.

关键词： Human activity recognition   Radiofrequency identification   Skeleton   Data collection   Support vector machines   RFID tags   Monitoring   body RFID skeleton   machine learning   recurrent neural networks   graph convolutional networks  

摘要： Human Activity Recognition (HAR) has attracted much attention due to the application in consumer electronics. To address the shortcomings of existing HARs, such as no identification, privacy leakage, battery maintenance, low accuracy, and few recognized activities, we have proposed new bound-RFID HARs. Firstly, we have devised body RFID skeleton to sense human activity by collecting tag response records of the skeleton node, which form the human activity dataset suitable for a benchmark. Secondly, we propose data standardization to solve the problem caused by the differences in the size and the amount of the tag response signal feature data. Thirdly, some body RFID skeleton-based HARs are proposed by utilizing machine learning, recurrent neural networks, and graph convolutional networks. In these proposed HARs, the best HAR is an improvement on the state-of-the-art HAR in the computer vision. The experimental results show that the proposed best HAR improves 0.27% than the state-of-the-art HAR by utilizing RSSI, Phase, and Doppler Frequency with only 4.5MB parameters, and achieves a recognition accuracy of 98.52%. Therefore, the devised body RFID skeleton effectively senses human activities, and the proposed HAR recognizes human activities with high accuracy and fine granularity. The dataset and source code are available at https://***/BRS/.

关键词： RFID   sensor   additive manufacturing   structural health monitoring   direction of arrival estimation   machine learning   photoluminescence  

摘要： Monitoring object displacement is critical for structural health monitoring (SHM). Radio frequency identification (RFID) sensors can be used for this purpose. Using more sensors enhances displacement estimation accuracy, especially when it is realized through the use of machine learning (ML) algorithms for predicting the direction of arrival of the associated signals. Our research shows that ML algorithms, in conjunction with adequate RFID passive sensor data, can precisely evaluate azimuth angles. However, increasing the number of sensors can lead to gaps in the data, which typical numerical methods such as interpolation and imputation may not fully resolve. To overcome this challenge, we propose enhancing the sensitivity of 3D-printed passive RFID sensor arrays using a novel photoluminescence-based RF signal enhancement technique. This can boost received RF signal levels by 2 dB to 8 dB, depending on the propagation mode (near-field or far-field). Hence, it effectively mitigates the issue of missing data without necessitating changes in transmit power levels or the number of sensors. This approach, which enables remote shaping of radiation patterns via light, can herald new prospects in the development of smart antennas for various applications apart from SHM, such as biomedicine and aerospace.

关键词： Backscatter modulation   chipless radio-frequency identification (RFID)   differential radar cross section (RCS)   resonant scatterer   vibration sensing  

摘要： This article introduces multistate (M-S) chipless radio-frequency identification (RFID) tags that can be utilized to enhance the vibration sensing range and reading robustness in real environments. The proposed M-S chipless tag consists of a resonant scatterer trapped between two different dielectric layers, which causes the near-field boundary of the scatterer to be modulated during vibration and results in the appearance of multiple modulation states. The motion-induced near-field modulation provided by the M-S chipless tag is much more effective than the natural Doppler modulation caused by vibration, which significantly increases the modulated portion of the backscattered power, and consequently, enlarges the sensing range. The backscattering from the vibrating M-S chipless tag is studied using presented mechanical and electromagnetic models that are verified by simulations. The designed M-S chipless tag is implemented, and the concept is experimentally proven. The differential radar cross section (RCS) of the vibrating M-S chipless tag is 45 times greater than that of a vibrating classical chipless tag, which translates into an increase of factor 2.5 in the read range. The M-S chipless RFID tag is utilized to successfully detect a submillimeter vibration through a wall in an indoor environment at low microwave frequencies, while the vibrating tag is located at a 2.5-m distance.

关键词： Internal corrosion   permeability perturbation   radio frequency identification (RFID)   structural health monitoring  

摘要： Radio frequency identification (RFID) sensors for pipeline corrosion monitoring have been considered an attractive area due to the advantages of battery-free and maintenance-free. Due to the skin effect of high-frequency electromagnetic waves, existing RFID sensors can only detect the surface corrosion of pipelines. To realize internal corrosion monitoring, a magnetic permeability perturbation-based RFID sensing method was developed in this article. Under direct-current magnetization, internal corrosion causes magnetic field distortions, and incurs magnetic permeability perturbations in the skin layer of surface. These perturbations can be detected by the RFID sensor. Considering the resonance frequency shift (RFS) as a feature, a patch antenna sensitive to magnetic permeability was designed. Moreover, steel plates with artificial internal defects were simulated and tested to validate the feasibility of the proposed method. It was observed that the surface magnetic permeability perturbations caused by internal corrosions of different depths incur different RFS values. Finally, pipelines with artificial and natural internal corrosions were tested to validate the feasibility of the proposed method. The RFS caused by the natural corrosion was 4.26 MHz, and the RFS caused by the sound area was 1.63 MHz. The proposed magnetic permeability perturbation-based RFID method provides a promising method for pipeline internal corrosion monitoring with the application of RFID sensing technology.

关键词： Computational RFID   frequency scaling   intermittent computing   task rate   task throughput  

摘要： RFID (Radio Frequency Identification) computing devices in practical applications often suffer from their poor computing performance in terms of low task throughput (also known as task rate) due to scarce harvested power. For optimizing the task throughput, the basic idea is to choose an optimal processor clock frequency when executing a specific task (e.g., operate sensor) in order to maximize task execution rate. Existing methods are based on the common sense where the frequency and task throughput are directly proportional to each other, meaning that a higher frequency causes a higher task rate. In RFID-scale devices, however, we observe that the relationship between the frequency and task throughput overturns the common sense, in which if the device rises the frequency, the task throughput will increase first and then decrease due to intermittent task execution pattern on such devices. In this article, we present a systematic task throughput model to explain and formulate the non-monotonic relationship between the frequency and task throughput. Based on the throughput model, we further introduce dynamic optimal frequency scaling (DOFS) to calculate the optimal frequency for task execution and thus optimize the task throughput in the RFID-scale devices. The experimental results show that the task throughput can be improved by 45.8% on average compared to the existing best effort.

关键词： BIM   Blockchain   RFID   Digital twin   Material passport   Circular economy   Digital transformation   Circular construction  

摘要： This systematic review critically examines the intersection of digital transformation and circular economy (CE) principles within the built environment. While digitalisation has been shown to enhance efficiency, safety, and sustainability in construction, its role in fostering circularity is less established. This study analyzes literature from 2010 to 2022, focusing on how digital technologies such as open-BIM, digital twins, material passports, blockchain, RFID, and gamification can integrate into and enhance the circular building lifecycle. The findings reveal that while digital tools are pivotal in design and construction phases, their application to existing structures is less straightforward, with challenges including the absence of digital twins for demolished structures, the high costs of retrofit digitalisation, and the predominant focus on environmental benefits over practical implementation. The review also highlights the need for a unified digital transformation strategy and greater cross-industry collaboration. Future research directions are proposed, including the development of localized material banks, the application of RFID in circularity, the scope of Design for Disassembly (DfD) tools, digital inventory of existing buildings, the circularity of Life Cycle Assessment (LCA) databases, and policy implications for promoting circular construction practices.

关键词： RFID   Data cleaning   Edge computing   Single-tag   Multi-tag  

摘要： As the performance of Radio Frequency Identification (RFID) devices is susceptible to the influence of the surrounding environment, making the original data collected by RFID devices with uncertain, of which missed data and redundant data are the main source of uncertainty data, these uncertainty data will seriously affect the quality of RFID upper layer applications. Therefore, to solve the uncertainty in RFID data, the original data must be cleaned. For the shortcomings of tag dynamics detection in the traditional data cleaning algorithm named Statistical Smoothing for Unreliable RFID data (SMURF), an adaptive sliding window-based data cleaning algorithm for RFID single-tag is proposed. The method takes into account the influence of tag speed on tag integrity judgment, and divides sliding sub-windows to accurately detect tag changes and then reasonably adjusts the sliding window size. In addition, considering that the average reading rate of tags is affected by the collision between multiple tags, an RFID multi-tag cleaning method based on twice-tag number estimation is proposed. The method accurately estimates the number of tags by the twice-tag estimation method, controls the read period by the Markov chain, and reduces the occurrence of multiple tag collisions by using an unequal time slot optimization method. Experimental results show that the proposed method in this paper can form a complete set of RFID data stream cleaning algorithms, which effectively reduces the uncertain data and improves the data accuracy.

关键词： Global Positioning System   Delay lines   Spirals   Dipole antennas   Antennas   Resonant frequency   Radiofrequency identification   Artificial magnetic conductor (AMC)   circular polarization (CP)   cross-dipole   gain   radio frequency identification (RFID)   reader  

摘要： In this communication, a triple-band circularly polarized antenna backed with an artificial magnetic conductor (AMC) is presented for radio frequency identification (RFID) readers/Internet of Things (IoT)applications. The antenna is comprised of a spiral-shaped dipole pair that is printed on both sides of the dielectric substrate in a cross-dipole configuration. Delay lines are used in the designed antenna to connect the dipole elements and to achieve circular polarization (CP). The antenna is supported by a 4x4 AMC surface placed beneath it at a distanceof lambda(0)/10, where lambda(0)is the wavelength calculated at the lowest resonant frequency. The AMC backing results in gain enhancements of 3.06, 3.43,and 0.56 dB in the global positioning system (GPS) L1 (1.575), 2.45,and 5.8 GHz bands, respectively. Consequently, the reading range of the reader increases, as the gain increases. In the GPS L1 (1.575), 2.45,and 5.8 GHz bands, the proposed AMC-backed antenna has impedance bandwidths of (1.56-1.585 GHz), (2.39-2.53 GHz), and (4.7-5.9 GHz),respectively. The proposed antenna could be a suitable candidate forreal-time implementation in RFID readers/IoT applications.

关键词： information metasurfaces   low power consumption   nearly passive   radio frequency identification   remote control  

摘要： Information metasurfaces (IMSs) have been considered to be a revolutionary technology for improving the spectral efficiency of sixth-generation (6G) wireless communications due to their superior ability to manipulate electromagnetic (EM) waves. However, there are still problems to be solved before the widespread application of IMSs. The first is to reduce power consumption, and the second is to achieve a long-range remote control. In this paper, a long-range and nearly passive radio frequency identification (RFID)-controlled IMS is proposed. The proposed IMS comprises four RFID tags and 8 x 8 elements, each of which is integrated with a single-pole-double-throw switch chip to achieve 1-bit phase reconfigurability. With the remote control of the RFID system, the IMS can be programmed to switch between three functionalities, including beam splitting, beamforming, and EM-wave absorption. Experiments are performed and the beam-splitting functionality is demonstrated. The measurement results indicate that the wireless communication between the RFID reader and the IMS is robust within 21.7 m. Additionally, the power consumption of the IMS is as low as 0.576 mW, which can be negligible. The scheme presented in this paper paves the way for the large-scale applications of IMSs in 6G wireless communications.