The Method For Strain Measurement And Crack Detection Of Metallic Structure Based On Microstrip Antenna Sensor

In the long-term load bearing process,a variety of damage and defects can be seen on metal structure.When the damage and defects accumulate to a certain level,the structure's load-carrying capacity and anti-fatigue performance will be impaired,which may lead to extremely serious consequences.To ensure the safe operation and prolong the lifespan of metal structure,a common method is to use sensors to monitor the structure's health status.The traditional structural health monitoring(SHM)technology has been under development for decades and has formed a relatively complete system,in which some sensors are commonly used including metal foil strain gauge,optical fiber sensor,ultrasound-based sensor,eddy-current sensor,piezoelectric sensor,etc.These sensors can meet actual engineering needs in certain circumstances,but there are still some drawbacks that limit their application and promotion.Microstrip antenna sensor is a new type of SHM sensor that appears in recent years.It can be used to wirelessly and passively measure strain and identify cracks of metal structure.Microstrip antenna sensor has broad application prospect due to its advantages of simple configuration,light weight,easy fabrication,low cost,etc.In this work,we designed a microstrip antenna sensor and studied its strain measurement and crack identification performance by mathematical theory,finite element simulation and experimental verification.The main research contents are as follows:(1)According to “transmission-line model”,the sensor parameters were designed,and the theoretical relationship between the sensor's resonant frequency and the applied strain was deduced.The analytical solution of the electromagnetic field inside the sensor was derived based on "cavity model",and the analytic expression of the current density on the surface of the patch and the ground plane was obtained.Then the sensor's crack identification principle and the mechanism of strain-crack coupling effect on the resonant frequency were analyzed.(2)Ansoft HFSS was used to simulate the strain measurement and crack identification of the microstrip antenna sensor,and the senor's resonant frequency response to varying strain and crack was studied.A "Mechanics-Electromagnetism" dual-physics model of the sensor was built in COMSOL Multi-physics to analyze the resonant frequency response under the strain-crack coupled conditions.(3)The experimental setup was established,and several microstrip antenna sensor specimens were fabricated.Firsly,the sensor's resonant frequency response under different strain level or crack condition alone was measured.Then the resonant frequency behavior in strain-crack coupled situation was tested.The experimental results were discussed and compared with the finite element simulation to reach the main conclusions for microstrip antenna sensor being used in SHM.The above work demonstrated the feasibility of using microstrip antenna sensor in SHM,and quantitatively presented the sensor's characteristics in strain measurement and crack identification.This research has significant academic value in the feld and will lay the foundation for the practical engineering application of microstrip antenna sensor.