Research On Wireless Sensing-transmitting Cantilever-based Current Sensor

With the rapid development of digital society and energy economy,the demand for electricity from all walks of life is increasing year by year.There are new requirements for the stability,security and reliability of the power systems and related application equipment.Among the various electrical parameters(such as current,voltage,capacitance and etc.),current is one of the most important parameters to ensure the stable operation of power systems and the safety of power transmission.If wireless sensor nodes can be embedded in key parts of electrical equipment,early warning and accurate positioning can be achieved to avoid economic losses due to unplanned power outages.It is therefore of great significance to study the sensing mechanism and measurement technology of current,and in recent years,it has become a research hotspot in scientific research institutions at home and abroad.This article is oriented to the field of current monitoring applicable to wireless sensor networks.Aiming at the cantilever-based direct current sensors have weakness of that they cannot realize wireless transmission of signals and continuous monitoring of direct current,a wireless sensing-transmitting scheme by integrating a magnetic cantilever with a microstrip antenna is proposed and designed.It has advantages of low power consumption,low cost,simple structure,small size,real-time sensing of DC and transmitting signals synchronously and etc.,the content of this article is clarified as follows:Firstly,the induced magnetic field distribution model around the current-carrying two-core wires is established and the magnetic force F_Y applied to the permanent magnet due to the induced magnetic field is analyzed.After modeling,the relationship between the magnetic force F_Y and the current I to be measured is obtained.Then,the relationship between the magnetic force F_Y and the strain?_Aon the microstrip antenna is obtained in the cantilever bending model.Meanwhile,the relationship between the strain?_Aon the microstrip antenna and the deflectionof the cantilever free end is obtained.Then,the relationship between the normalized frequency shift of the microstrip antenna and the strain?_Aon the microstrip antenna is established.And the relationship between?f/f_?Land?_Ais discussed when the microstrip antenna suffers strain along the length direction and the width direction.Finally,after equation transformation,the relationship between the normalized frequency shift?f/f_?Lof the microstrip antenna and the current I in the current-carrying two-core wires is established.Secondly,Theoretical models are established from three aspects of microstrip antenna parameters,cantilever parameters,permanent magnet and two-core wires parameters respectively,to qualitatively analyze the influence of these parameters of the proposed wireless sensing-transmitting cantilever-based current sensor on the sensitivity of the theoretical models.The microstrip antenna and cantilever are designed,and then the designed microstrip antenna is optimized in the finite element simulation software HFSS to determine the final dimension.Based on the above qualitative analysis,the parameters of the proposed current sensor are preliminarily determined.Then,the multi-physics coupling simulation model COMSOL of the proposed current sensor was established.It is found that the current I to be measured is quadratically varied with the normalized resonance frequency shift?f/f_?Lof the microstrip antenna.After exploration,it is found that the phenomenon of the quadratic relationship is due to the dynamic distance b between the center of the magnet and the center of the toroidal current coil.Therefore,a feedback model is proposed to correct the theoretical model.On this basis,the effect of the parameters on the sensitivity,such as the distance b between the center of the magnet and the center of the toroidal current coil,the size parameters of the toroidal current coil,the size parameters of the permanent magnet and the size parameters of the cantilever are studied and analyzed quantitatively,respectively.Furthermore,an influence evaluation model was established to quantitatively analyze the influence degree Var_??of each parameter on the sensitivity.The results show that the thickness of the cantilever h_c has the greatest influence on the sensitivity.The length l_c and width w_c have the least influence on the sensitivity.Based on the above quantitative analysis,the proposed current sensor with optimized dimension is determined,and after optimization,the current sensitivity is increased by 213%.In addition,for the case where the current sensitivity of the proposed current sensor is a quadratic function,a conversion model is established and the sensitivity function is transformed into a linear straight line for subsequent comparison.Finally,the experimental plan and experimental steps are designed to verify the feasibility of the proposed current sensor.The strain on the cantilever fixed end and the strain on the microstrip antenna are collected respectively by a data acquisition instrument.After preprocessing the experimental test results,the relationship between the strain on the proposed current sensor and the current I to be measured is obtained.The test results verify the correctness of the quadratic relationship in the simulation model and the necessity of establishing a feedback correction model.At the same time,the strain transfer efficiency is measured to be 61.4%.In this paper,a wireless sensing-transmitting cantilever-based current sensor is proposed,deigned and verified,which realizes continuous monitoring of current and wireless transmission of signals,expands the application field of cantilever-based sensors,and improves the possibility of applying cantilever-based current sensors to wireless sensor networks.