Modeling And Design Of EMI Magnetic Probe

In recent years,as the integrated circuits become more intensive and the working frequencies become higher,the electronic device gradually enters the millimeter wave band.The size of electronic packages and chips will be comparable with the electromagnetic wavelength,and they will become transmitting antennas.The radiated noise will interfere with the normal operation of the surrounding components,making the electromagnetic interference(EMI)problem on the PCB serious.This kind of EMI problem can be solved by near-field scanning technology.Compared with expensive microwave anechoic chamber,near-field scanning technology has become the focus of relevant practitioners due to its low cost and high efficiency.With the growing maturity of near-field/far-field transformation,noise source modeling and other technologies,the accuracy of near-field scanning results has been gradually valued.The spatial resolution,sensitivity and the working bandwidth of the near-field scanning technology mostly depend on the electric/magnetic probe.It is of great significance to develop a high-performance electric/magnetic probe.This paper focuses on the design principle of the electric/magnetic probe and the coupling circuit model at first.1.The basic structure and working principle of tangential magnetic field probe,normal electric field probe and tangential electric field probe are studied and analyzed.For the tangential magnetic field probe,the equivalent circuit model is given,and the receiving power of the receiving load is calculated according to the model.The calculation results are valuable for predicting the trend of the sensitivity curve.At the same time,this paper also gives the effective calibration method of the tangential magnetic field probe,which can help convert the electrical signal into the magnetic field information.2.The equivalent circuit model of the magnetic field probe is improved,and the coupling effect of the tangential electric field E_l on the probe is added.It is proved that H_n and E_l fields to be measured have coupling effect on the magnetic field at the same time,which are equivalent to the induced voltage sources V_H and V_E respectively.And these voltage sources are in series.At the same time,the electric/magnetic coupling coefficientαandβis proposed,which represents the coupling of the probe to E_l field and H_n field respectively.The innovation of this method is that it breaks the traditional idea that the normal electric field E_z is the maximum interference field.And it clarifies the phenomenon that the influence of E_l field is higher than that of E_z field in high frequency band.According to the coupled circuit model of the tangential magnetic field probe,we analyze its sensitivity characteristic curve.From the perspective of working frequency,the difficulty in designing the tangential magnetic field probe appears in the two ends of the working frequency band.The sensitivity will be low at low frequencies,while parasitic resonance point and impedance mismatch will be found at high frequencies.Aiming at these difficulties,this paper designs the low frequency and high frequency probes respectively based on engineering application:3.A low frequency and high sensitivity magnetic field probe is designed and fabricated.For low frequency band 1(1MHz-100MHz)and low frequency band 2(3k Hz-1MHz),multi loops and active magnetic field probes are designed respectively,which can measure 0.1n T weak magnetic field with high sensitivity.The innovation of these probes is that it provides a solution to the problem of low sensitivity of magnetic field probe in low frequency band by using PCB technology.4.High frequency magnetic field probe is designed and fabricated.Single 0.1mm loop is designed to reduce the high frequency parasitic effect.At the same time,magnetic field probe connected with SMA and End-Launch are designed respectively to achieve impedance matching at high frequency.The test results show that it can work to 40GHz and 67GHz respectively,which is higher than the existing probe in other paper and commercial magnetic field probe products.The innovation is that those probes use laser technology in the detection part,and method of the grounding in the detection part is improved.In addition,the steeped grooves structure optimizes the impedance matching.