The Development Of 8 Mm-band Biomass Moisture Content Test Device

With the shortage of fossil fuels and the increasingly serious environmental pollution problem,biomass energy has become the preferred alternative.In the application of biomass combustion for power generation and biomass solid fuel,the water content of biomass is strictly required.Therefore,the realization of low-cost,fast and accurate measurement of biomass moisture content is of great significance to the promotion and application of biomass energy.At present,millimeter wave technology is developing rapidly,and the millimeter wave frequency band is less affected by environmental interference.Compared with the low frequency antenna of the same size,the millimeter wave antenna has better directivity.The millimeter-wave test device can theoretically realize a high-reliability biomass moisture content test,and only requires a small sample volume.This paper compares and analyzes the 8 mm-band biological moisture content test plan,and develops an 8 mm-band biomass moisture content test device based on the attenuation test.The main work of the thesis is as follows:1.Based on the existing literature,a mathematical model of biomass moisture content and permittivity is deduced,and the test method for the permittivity of powdered and granular biomass is analyzed.Two 8 mm-band biomass water content test methods based on dielectric constant test and attenuation test are given.Considering the cost and test accuracy comprehensively,the 8 mm-band biomass moisture content test method based on the attenuation test is determined for the moisture content test method of this subject,and the test device design plan is given.2.Development of 8 mm-band frequency source.The X-band frequency source,Xband bandpass filter,8 mm-band quadruple frequency multiplier and 8 mm-band bandpass filter,which compose the 8 mm-band frequency source,are separately developed.The X-band bandpass filter adopts the CQ cross-coupling structure to introduce transmission zero points,which has good out-of-band suppression.The 8 mm bandpass filter adopts a 7-order H-plane waveguide diaphragm structure,which has good out-of-band suppression and an insertion loss of less than 1.5d B.The two filters have good suppression of the output spurious of the X-band frequency source and quadruple frequency multiplier.Finally,the 8 mm-band frequency source is swept output in the frequency range of 33.4 GHz-36.6 GHz,the output power of each frequency point is greater than 8 d Bm,the spurious suppression is greater than 58 d Bc,and the phase noise is about-94 d Bc/Hz@100k Hz.3.Development of 8 mm-band power detection module.In order to meet the 8 mmband signal power test requirements,an 8 mm-band power detection module was developed and the calibration in required frequency point was completed.The detection error is less than 0.1 d B within the input power range of-30 d Bm to 15 d Bm.4.The test device is set up.In order to facilitate the test and calibration of the test device,a movable antenna and sample box holder are designed.The distance between the antenna and the sample box is determined by simulation.The test device is improved to reduce the influence of multipath interference.Finally,the 8 mm-band biomass moisture content test device was built according to the design plan.5.Test and analysis of bark moisture content.An empirical formula for bark moisture content and attenuation was established through experiments,and the test results were analyzed.The test device designed in this paper can achieve high-precision measurement of bark moisture content.The water content test range covers 9.2%-38.4%,and the standard test error is 0.61%.