Research On Novel Portable Microwave Permittivity Sensors

As an important property of chemicals and biochemicals,permittivity is useful for a variety of academic research and applications.Different information of specific material can be reflected through sensing permittivity.Different from mainstream industrial transducers,sensors based on RF and microwave technology have great potential to become a valuable and cost-effective tool in all aspect of industrial process owe to its accurate,strong penetrating and noninvasive nature.Conventional RF sensor need to work with vector network analyzer,which constrained by high cost and bulky size making them unsuitable for portable applications.Therefore,in this paper author focus on the design of portable RF sensor for dielectric sensing.Firstly,this work proposes a portable interferometry sensor based on voltage-controlled phase shifter.Using a CPWG component as the sensitivity element to hold the MUT.A down-conversion mixer is selected for mapping the change of the amplitude and phase of S₂₁to a DC voltage.Through controlling the phase between the ports of mixer by changing the biased voltage,the real and imaginary part of permittivity can be extracted.Moreover,according to the experimental result of several MUT,this prototype achieves a small measurement error within3%.Secondly,a time-domain pulse circuit based on reverse transmission line is introduced.It is suitable for narrow pulse circuit to work as the source of RF permittivity sensor because of its characteristic of wide frequency band.Through the analysis of the principle of the step recovery diode and modeling it in ADS,a narrow pulse circuit with the 10 d B bandwidth of 3.4 GHz is designed based on a short-circuit stub.Using time-domain pulse in RF permittivity sensors,the working bandwidth and efficiency is improved through getting rid of frequency sweep source.Finally,the way to expand the bandwidth of sensor has been studied.Since the sensitivity of the transmission line method for measuring the permittivity enhances with increasing frequency,it is necessary to further increase the center frequency of the pulse signal spectrum.The differentiator and up-conversion have been proved to broaden the frequency band effectively through co-simulation in ADS and HFSS.In this way,time-domain based RF sensors can extract complex permittivity of MUT in ultra-wide bandwidth.So,the pulse source can realize the portability of the signal source...