Chunhee Cho

Passive wireless antenna sensor for strain and crack sensing—electromagnetic modeling, simulation, and testing

This research investigates a passive wireless antenna sensor designed for strain and crack sensing. When the antenna experiences deformation, the antenna shape changes, causing a shift in the electromagnetic resonance frequency of the antenna. A radio frequency identification (RFID) chip is adopted for antenna signal modulation, so that a wireless reader can easily distinguish the backscattered sensor signal from unwanted environmental reflections. The RFID chip captures its operating power from an interrogation electromagnetic wave emitted by the reader, which allows the antenna sensor to be passive (battery-free). This paper first reports the latest simulation results on radiation patterns, surface current density, and electromagnetic field distribution. The simulation results are followed with experimental results on the strain and crack sensing performance of the antenna sensor. Tensile tests show that the wireless antenna sensor can detect small strain changes lower than 20???, and can perform well at large strains higher than 10?000???. With a high-gain reader antenna, the wireless interrogation distance can be increased up to 2.1?m. Furthermore, an array of antenna sensors is capable of measuring the strain distribution in close proximity. During emulated crack and fatigue crack tests, the antenna sensor is able to detect the growth of a small crack.

Wireless Mobile Sensor Network for the System Identification of a Space Frame Bridge

This research investigates the field performance of flexure-based mobile sensing nodes (FMSNs) developed for system identification and condition monitoring of civil structures. Each FMSN consists of a tetherless magnetic wall-climbing robot capable of navigating on steel structures, measuring structural vibrations, processing measurement data, and wirelessly communicating information. The flexible body design of the FMSN allows it to negotiate with sharp corners on a structure, and attach/detach an accelerometer onto/from structural surface. Our previous research investigated the performance of the FMSNs through laboratory experiments. The FMSNs were deployed to identify minor structural damage, illustrating a high sensitivity in damage detection enabled by flexible mobile deployment. This paper investigates the field performance of the FMSNs with a pedestrian bridge on the Georgia Tech campus. Multiple FMSNs navigate to different sections of the steel bridge and measure structural vibrations at high spatial resolution. Using data collected by a small number of FMSNs, detailed modal characteristics of the bridge are identified. A finite element (FE) model for the bridge is constructed. The FE model is updated based on the modal characteristics extracted from the FMSN data.

Thermal effects on a passive wireless antenna sensor for strain and crack sensing

For application in structural health monitoring, a folded patch antenna has been previously designed as a wireless sensor that monitors strain and crack in metallic structures. Resonance frequency of the RFID patch antenna is closely related with its dimension. To measure stress concentration in a base structure, the sensor is bonded to the structure like a traditional strain gage. When the antenna sensor is under strain/deformation together with the base structure, the antenna resonance frequency varies accordingly. The strain-related resonance frequency variation is wirelessly interrogated and recorded by a reader, and can be used to derive strain/deformation. Material properties of the antenna components can have significant effects on sensor performance. This paper investigates thermal effects through both numerical simulation and temperature chamber testing. When temperature fluctuates, previous sensor design (with a glass microfiber-reinforced PTFE substrate) shows relatively large variation in resonance frequency. To improve sensor performance, a new ceramic-filled PTFE substrate material is chosen for re-designing the antenna sensor. Temperature chamber experiments are also conducted to the sensor with new substrate material, and compared with previous design.

Design and simulation of a slotted patch antenna sensor for wireless strain sensing

In this work, a slotted patch antenna is employed as a wireless sensor for monitoring structural strain and fatigue crack. Using antenna miniaturization techniques to increase the current path length, the footprint of the slotted patch antenna can be reduced to one quarter of a previously presented folded patch antenna. Electromagnetic simulations show that the antenna resonance frequency varies when the antenna is under strain. The resonance frequency variation can be wirelessly interrogated and recorded by a radiofrequency identification (RFID) reader, and can be used to derive strain/deformation. The slotted patch antenna sensor is entirely passive (battery-free), by exploiting an inexpensive offthe- shelf RFID chip that receives power from the wireless interrogation by the reader.

Passive Wireless Frequency Doubling Antenna Sensor for Strain and Crack Sensing

This paper presents the design, simulation, and validation experiments of a passive (battery-free) wireless frequency doubling antenna sensor for strain and crack sensing. Since the length of a patch antenna governs the antenna’s resonance frequency, a patch antenna bonded to a structural surface can be used to measure mechanical strain or crack propagation by interrogating resonance frequency shift due to antenna length change. In comparison with previous approaches such as radio frequency identification, the frequency doubling scheme is proposed as a new signal modulation approach for the antenna sensor. The proposed approach can easily distinguish backscattered passive sensor signal (at the doubled frequency

A Slotted Patch Antenna for Wireless Strain Sensing

2{f}

Passive Frequency Doubling Antenna Sensor for Wireless Strain Sensing

) from environmental electromagnetic reflections (at original reader interrogation frequency

Strain Sensing Through a Passive Wireless Sensor Array

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An Eigenvalue Perturbation Solution for the Multiphysics Simulation of Antenna Strain Sensors

). To accurately estimate the performance of the frequency doubling antenna sensor, a multi-physics coupled simulation framework is proposed to aid the sensor design while considering both the mechanical and electromagnetic behaviors. Two commercial software packages, COMSOL and Advanced Design System (ADS), are combined to leverage the features from each other. The simulated performance of the frequency doubling antenna sensor is further validated by experiments. The results show that the sensor is capable of detecting small strain changes and the growth of a small crack.

Multi-Physics Modeling and Simulation of a Frequency Doubling Antenna Sensor for Passive Wireless Strain Sensing

This research studies the wireless strain sensing performance of a slotted patch antenna sensor. In our previous work, a folded patch antenna was designed for passive wireless strain and crack sensing. When experiencing deformation, the antenna shape changes, causing shift in electromagnetic resonance frequency of the antenna. The wireless interrogation system utilizes the principle of electromagnetic backscattering and adopts off-the-shelf 900MHz radiofrequency identification (RFID) technology. In this research, a new slotted patch antenna sensor is designed and tested. The antenna detours surface current using slot patterns, so that the effective electrical length is kept similar as previous folded patch antenna. As a result, the sensor footprint is reduced and the antenna resonance frequency is maintained within 900MHz RFID band. To accurately describe both mechanical and electromagnetic behaviors of the antenna sensor, a multi-physics coupled simulation approach is pursued. Implemented through a commercial software package, COMSOL, a multiphysics finite element model of the antenna uses the same geometry and meshing for both mechanical and electromagnetic simulations. Wireless strain sensing performance of the antenna is first simulated using the multi-physics model. In addition, experimental tensile tests are performed to investigate the correlation between wirelessly interrogated resonance frequency and the strain experienced by the antenna. The strain sensing performance is tested.