Structural health monitoring (SHM) is essential for modern large buildings and infrastructure. Radio frequency identification (RFID) widen a new paradigm for SHM in the Internet of Things (IOT) era. This paper introduces a low-cost intelligent RFID monitoring system for future IoT applications. Through adding a multi-parameter sensing strategy to the passive RFID tags that can be deployed on a large scale to form a sensor network, which expands the coverage of IOT in key positions health monitoring of buildings. In this work, a novel chipless RFID strain sensing tag is designed to characterize the magnitude and direction of metal surface strain, and a low-cost detection method suitable for large mechanical structures is proposed. The traditional strain antennas focus on identifying the strain characteristics without the function of encoding, and there are limitations such as the rigid measurement methods and the expensive measurement instruments. The tag designed in this paper integrates both strain sensing and encoding functions, and has the advantages of small size, high data capacity, and information reading is not easily affected by environmental noise. This paper proposes an economical and flexible tag spectrum extraction method, which realizes the intelligent collection and transmission of tag data by connecting lightweight vector network analyzer (VNA) with microcontroller. Combined with the IOT, this method can be well applied to the security assessment and damage detection of large infrastructure structures, which provides a new approach to modern building health monitoring applications from integrated tag design to intelligent detection and risk assessment schemes.

The rapid development of radio frequency identification (RIFD) technology has significantly changed the method of structural health monitoring (SHM). In this paper, a novel flexible chipless RFID tag sensor is proposed to monitor the change of relative humidity (RH) in the environment around structures. The tag is fabricated on a flexible substrate that can be transferred to a bendable metal surface and is fused with a high encoding capacity for tag recognition. In addition, a low-cost detection and wireless transmission scheme for dynamic spectrum data transmission is used, which is more flexible and automatical than traditional detection methods. The simulation and experiment results show that the humidity sensitivity of the tag sensor coated with a polyvinyl acetate (PVA) film is about 0.584 MHz/RH in the RH range below 60%, and about 2.03 MHz/RH in the higher RH range. Meanwhile, the tag can maintain stable sensing performances in a certain bending range, which may be very desirable in many application scenarios.

Chipless radio frequency identification (RFID) technology has been widely used in the field of structural health monitoring (SHM), but most of the current research mainly focuses on the detection of mechanical properties and there are few studies on the multi-physical parameters (for example, temperature and humidity) in the climatic environment around the structure. Thus, it is necessary to design a small and compact sensor for multi-parameter detection. This paper proposes a multi-parameter chipless RFID sensor based on microstrip coupling, which supports 4-bit ID code and integrates two detection functions of temperature and humidity. Through linear normalization fitting, the sensitivity of the sensor is about 2.18 MHz/RH in the ambient relative humidity test and the sensitivity of the sensor is about 898.63 KHz/°C in the experimental test of water bath heating from 24.6 °C to 75 °C. In addition, this paper proposes an engineering application detection method, designs a lightweight dynamic spectrum detection and wireless transmission platform based on a lightweight vector network analyzer (VNA) and realizes the real-time extraction and transmission of RFID spectrum sensing data. The means are more flexible and economical than traditional experimental scenarios.

A compact multiband tunable PIFA system using a varactor as an active tuning component is presented covering 88-2175 MHz. The antenna was designed to cover the mobile telephone bands (GSM850, 900, 1800, 1900, UMTS) by controlling the value of the capacitance across the gap in the slotted PIFA and two broadcast bands, FM radio (76-108 MHz) & mobile television DVB-H (470-702 MHz), were added by designing an appropriate matching circuit into the system. The antenna measured λ/15 × λ/43 × λ/19 at 470 MHz and was easily integrated into a small mobile phone handset. Simulations are verified by measurements.

Cognitive radio systems require antennas and microwave components to be actively tuned for different parts of the frequency spectrum. In this paper results of a study of three antenna tuning techniques are presented here. The first tunable antenna is a liquid crystal (LC) tuned microstrip patch antenna operating in the 2 GHz range. The simulated tuning range is 8% while the measurements showed a range of 3.8%. Losses in the LC material at these frequencies give rise to antenna efficiencies ranging from 25% to around 7% when the LC is in the unbiased state. The second antenna is a reconfigurable PIFA which is able to cover 7 frequency bands by controlling the combination of 4 MEMS switches mounted on the radiator. The third antenna is a dual-port antenna which is comprised of two capacitive-fed plates sharing one lower-band patch, operating for 5 mobile phone bands.