Plant Biomass Estimation Using Dielectric PropertiesMotivation for Estimating BiomassSlide 3BackgroundSlide 5Slide 6Slide 7Slide 8Slide 9System DesignSlide 11Preliminary Known Sample TestingKnown Sample ResponseFrequency Selection ExampleResponse to Plant MaterialSlide 16Slide 17Characteristic Curve with Plant Material (30.5 cm antennae)Influence of Extraneous MaterialPredicting Water Content and Biomass (30.5 cm antennae)ConclusionsPlant Biomass Estimation Using Dielectric Properties2006 Annual International MeetingPortland, OregonJuly 9 - 12Paper Number: 063092C. L. Jones Asst. Professor , ASAE memberN. O. Maness Professor - Horticulture M. L. Stone Regents’ Professor, ASAE FellowJ. B. Solie Sarkey’s Professor, ASAE FellowG. Brusewitz Professor Emeritus, ASAE FellowMotivation for Estimating Biomass–Chemical application decisions–Yield prediction –Grazing managementPaper Number: 063092Plant Biomass Estimation Using Dielectric PropertiesAnswer the following:–Using a free-space system, can electromagnetic response (300 to 900 kHz range) be used to detect volumetric moisture of spinach?–Using this system, what is the optimum frequency within this range for detecting volumetric moisture of spinach in situ? –What is the relationship between the electromagnetic transmission attenuation and moisture content (biomass) of spinach plants?Paper Number: 063092BackgroundDielectric properties…–measure of polarizability when subjected to electric field (Von Hippel, 1954)–Represented by relative complex permittivity•ε = ε′ - j ε″•ε′ …material’s ability to store energy (dielectric constant)•ε′ = C·C0-1 (capacitance of system with and without sample) (Sacilik et al., 2006)•ε″…material’s ability to dissipate energyPaper Number: 063092BackgroundInfluential factors…–Water: influential factor due to polar nature–Bulk density–Frequency–Temperature–Chemical composition –Permanent dipole moment association between water and constituent molecules(Nelson, Nelson and Stetson, Von Hippel)Paper Number: 063092BackgroundFree water (non-bound)•ε = ε′ - j ε″ = ε∞ + (εs - ε∞ )(1 + iωt)-1(Debye, Hasted)•ε∞ : permittivity at high frequencies…no polarization•εs : permittivity at zero frequency•t: relaxation time, ω: radian frequency (2pf)•Biomaterial contains both bound and free water•Dielectric properties of bound water: between ice and free water depending on how tightly water is boundPaper Number: 063092BackgroundBiomaterials (free and bound water)•ε = ε′ - j ε″ = ε∞ + (εs - ε∞ )(1 + iωt)-ά(Cole-Cole Equation)•ά = breadth of time constant distribution (single relaxation = 1, infinitely broad distribution = 0)•Dependent on temperature, pressure and chemistryPaper Number: 063092BackgroundTesting biomaterials–Potential difference measurements of elements of known permittivity...compare to test material(ex: water ε′ = 80)–OR…correlation of transmission potential difference between 2+ quantities of sample material with gravimetrically determined water content of samples(Berbert et al, Boldor et al, Jorgensen et al, Kim et al, Kraszewski, Nelson, Lawrence, Noh, Stetson, Sokhansanj, Trabelsi….)Paper Number: 063092Background•Area of investigation–300 to 900 khz–Minimize the Maxwell-Wagner effect (Kittel)–Reduced interaction with plant geometry (1 km - 333 m wavelength)• Radiofrequency spectrum AM radio - 535 kilohertz to 1.7 megahertz Paper Number: 063092System Design Paper Number: 063092Equivalent CircuitSystem DesignElectrostatic Free-Space System–Parallel aluminum plates (sizes tested in FEMLAB)•12.7 cm x 12.7 cm x 0.32 cm - and - 30.5 cm x 30.5 cm x 0.32 cm •Sensed volume: 0.6 m x 1 m x 1m–Vector Network Analyzer (VNA): Agilent 8712ET Paper Number: 063092Preliminary Known Sample Testing•Response of system with known quantities of water•Measured signal attenuation modulus K = 10log10(P0Pz-1) where:P0 = incident power Pz = power at receiving antenna•Ksample = Ktest - KspacePaper Number: 063092Known Sample ResponsePaper Number: 06309230.5 cm plates 12.7 cm platesFrequency Selection ExampleDetermining frequency – known water samplesPaper Number: 063092Response to Plant Material•Flat of healthy spinach presented to system on plastic holder•Randomly chosen samples harvested, weighed, and placed in oven for moisture content analysis•With all vegetation removed, attenuation was recorded of the empty flatPaper Number: 063092Response to Plant MaterialGreenhouse-grown spinach, 12.7 cm antennaePaper Number: 063092Response to Plant MaterialGreenhouse-grown spinach, 30.5 cm antennaePaper Number: 063092Characteristic Curve with Plant Material(30.5 cm antennae)Paper Number: 063092( )� �� �� �� �� �� �� �x - ln ln2 - 97.6y = - 49.4 exp - exp -160.1• R2 was equal to linear relationship, 0.95• Curve appeared linearInfluence of Extraneous Material•Tested with plant material samples•Placed at lower limit of sensing areaPaper Number: 063092Predicting Water Content and Biomass(30.5 cm antennae)Paper Number: 063092Conclusions•Electromagnetic Free-space System shows promise for estimating water content in situ (biomass in homogenous samples)•450 to 500 kHz is appropriatePaper Number:
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