Location: Quality and Safety Assessment Research Unit
2017 Annual Report
Objectives
1. Enable new commercial sensor-in-system flowing-grain microwave moisture and density meters for precision farming and yield monitoring.
2. Enable a portable, commercial microwave meter to create capacity for rapid grading in-shell almond and peanut by determining moisture content, meat content, and foreign material contents.
3. Enable new commercial microwave sensors for monitoring controlled drying of grain, peanuts and other seeds.
Approach
I: To enable a new commercial sensor for flowing grain microwave moisture and density, dielectric-based algorithms for bulk density and moisture content determination at microwave frequencies will be tested in flowing situations. In designing a flowing-grain system, the frequency must be higher than 3 GHz, free-space transmission techniques will be used for on-line applications, and measurements will be performed in the near field to keep the system compact. At least three cultivars each of wheat, corn, and soybeans will be obtained from certified seed with some geographic and seasonal diversity. Moisture, density, and temperature will be varied for model development and then validated on flowing grain. Next, a prototype sensor made with off-the-shelf components will be assembled and tested. Then a user-friendly, step-by-step software programs will be developed to control the measurements with moisture predictions within 0.2% to 0.5%, and bulk density will be within less than 2% relative error.
II: The above system will next be developed for rapid grading of in-shell almond and peanut by determining moisture content, meat content, and foreign material contents. First dielectric properties data will be collected with laboratory grade instrumentation on un-cleaned and cleaned in-shell almonds and peanuts of different varieties and from different locations and compared to oven-drying moisture and meat content. Measurements will also be collected on almond and peanut kernels alone. The data will comprise of dielectric properties corresponding to frequency, temperature, moisture content, bulk density, meat content, and foreign material content. The next step is to develop a microwave prototype for moisture content, meat content, and foreign material content in in-shell almonds and peanuts which will be externally controlled with a laptop computer and ultimately packaged to satisfy grading requirements and withstand working conditions at buying stations.
III: The last approach is to use the microwave moisture sensors developed above to monitor and record moisture content of grain, peanuts and other seeds in real-time during drying while improving efficiency through control of drying and minimizing energy consumption when compared to existing drying controls. To accomplish this, a microwave moisture meter will be combined with three temperature sensors and a relative humidity sensor to monitor peanut drying in a quarter scale-model drying wagon to optimize the drying process by determining real time in-shell kernel moisture content in different zones of the trailer. Similar work will be performed with cereal grains and oilseeds stored and dried in large, farm storage bins. Varying temperature and moisture profiles will be evaluated during the drying process. Through feedback control, the system will optimize the drying process to better ensure even drying throughout the trailer (for peanuts) and bin (for grains). Once successful, the microwave moisture meter(s) will then be integrated with all other sensors in one single unit including a microcontroller, an LCD, and mass storage device.
Progress Report
Development of portable sensors for in the field rapid determination of moisture content and bulk density of grain, seed, and nuts requires the measuring system to be compact, lightweight, and provide repeatable and accurate readings. Using microwave antennas, classical free space systems require the sample to be placed in the far field for accurate determination of the dielectric properties which are used for moisture and density determination. While such setup is excellent for laboratory investigation, it is not practical for field applications. Therefore, one attractive option to reduce the size of the measuring device is to perform the measurements in the near field where the sample to be tested is placed one wavelength from the transmitting and receiving antennas. Near-field measurements of the dielectric properties are challenging and there is very limited data, if any, published in the literature for grains, seeds, and nuts. Data were collected in the near field with a pair of inexpensive patch antennas operating at 5.8 GHz for wheat, corn, soybeans, and peanuts for practical ranges of temperature, moisture content and bulk density. The measurements were performed in static and flowing regimes. This database will constitute the backbone for the development of calibrations for both portable static sensors and in-stream flowing systems used for grains, seeds, and nuts. These calibrations will be for instantaneous determination of bulk density and moisture content from measurement of the dielectric properties at a single microwave frequency. Several algorithms correlating these properties with moisture content and bulk density were used successfully and provided bulk density results with a standard error of calibration of less than 0.05 grams per cubic centimeter and moisture content with a standard error of calibration of less than 0.8%, on wet basis.
Free space measurement can be performed in transmission and/or reflection mode(s). Transmission-mode measurements have the advantage of providing information relative to the volume interacting with electromagnetic wave. However, in some instances, reflection measurements are the only option, in particular when only one side of the material is accessible. Several open-ended inexpensive, lightweight antennas were simulated with commercial software and then built and tested in house. These antennas were tested both on static and flowing granular and particulate agricultural products. In particular, a portable microwave sensor made with off-the-shelf components and a six-port system, made in house, for measuring the reflection coefficient was assembled, calibrated, and tested successfully for liquids, gels, grains, and sawdust. This versatile device can be easily adapted for measurements on a variety of materials including liquids, gels, granular and particulate materials, and meat products.
Measurements of dielectric properties of peanut kernels, in-shell peanuts, almond kernels and in-shell almonds were performed with a vector network analyzer and a microwave sensor prototype operating at 5.8 GHz for temperature ranging from 5 to 35 degrees Celsius, moisture ranging from 8% to 19% for peanuts and from 5% to 14% for almonds, and density ranging from loosely packed to highly packed. In addition, for in-shell nuts, trash content varied between 0% and 15%. Graphical and statistical analysis showed promising correlations between the dielectric properties and the different variables for both peanuts and almonds. This database will be instrumental in developing algorithms for moisture content, meat content, and trash content prediction from measurement of the dielectric properties at a single microwave frequency.
Drying uniformity of peanuts was investigated in the laboratory in a quarter-scale drying system and in the field by placing peanut drying monitoring systems, developed by ARS scientists at Athens, Georgia, at two locations in 45-ft semitrailers (10 ft from the front and 10 ft from back). The drying monitoring systems were built in house and comprise sensors for real time measurement of the relative humidity and temperature of the air blown in the peanut bed, relative humidity and temperature of air exhaust from peanuts, temperature of air near the antennas, and in-shell moisture content. The network of sensors is driven by a microcontroller and the data is stored on a memory disk for the entire drying period. Under certain ambient temperature and humidity conditions, the monitoring system surprisingly identified situations where moisture actually increased during drying which indicates that driers should not remain on at all times. This will result in significant energy savings and thus increase the benefit margin for the peanut growers.
A microwave sensor system, operating at 3 GHz and comprising four open-ended substrate-integrated waveguides, was used for measurements on sawdust moving on a conveyor belt. The speed varied between 0.15 meter per second and 0.35 meter per second and the sawdust moisture content ranged from 6% to 36%. While moving on the conveyor belt, the bulk density changes. Thus a density independent algorithm was used for moisture prediction from measurements of the dielectric properties in reflection mode by switching electronically between the four open-ended substrate-integrated waveguides. Moisture accuracy was in the 1-1.5% range and the same sensor system can be implemented for materials flowing in pipes or chutes.
Accomplishments
1. Portable microwave moisture sensor for granular and particulate agricultural products. Rapid determination of moisture content of granular and particulate agricultural products is needed for pricing, determining conditions for safe storage, and for process control. ARS researchers in Athens, Georgia, developed a new, low-cost microwave sensor for instantaneous determination of moisture content in granular and particulate agricultural products. The new sensor operates at a single microwave frequency, is only presented to one side of the sample (reflection only) and has a much smaller sampling area than traditional microwave systems. Furthermore, the six-port measuring paradigm produces very accurate results. The system shows great promise for further development and commercialization.
Review Publications
Lewis, M.A., Trabelsi, S., Nelson, S.O. 2017. Real-time monitoring of peanut drying parameters in semitrailers. Drying Technology: An International Journal. 35(6):747-753.
Stuart, N.O., Trabelsi, S. 2016. Use of material dielectric properties in agricultural applications. Journal of Microwave Power and Electromagnetic Energy. 50(4):237-268.
Julrat, S., Trabelsi, S. 2017. Density-independent algorithm for sensing moisture content of sawdust based on reflection measurements. Biosystems Engineering. 158:102-109.
Trabelsi, S., Mckeown, M.S., Nelson, S.O. 2016. Dielectric properties-based method for rapid and nondestructive moisture sensing in almonds . Journal of Microwave Power and Electromagnetic Energy. doi:10.1080/08327823.2016.1190153.
Mckeown, S.M., Trabelsi, S., Nelson, S., Tollner, E.W. 2017. Microwave sensing of moisture in flowing biomass pellets. Biosystems Engineering. 155:152-160.
Sakol, J., Trabelsi, S. 2017. Density-independent algorithm for sensing moisture content of sawdust based on reflection measurements. Biosystems Engineering. 158:102-109.
Ellison, C., Mckeown, M., Trabelsi, S., Bolder, D. 2017. Dielectric properties of biomass/biochar mixtures at microwave frequencies. Energies. 10(4):502.
Mckeown, M.S., Julrat, S., Trabelsi, S., Tollner, E.W. 2017. Open transverse-slot substrate-integrated waveguide sensor for biomass permittivity determination. IEEE Transactions on Instrumentation and Measurement. 66(8):2181-2188.
Julrat, S., Trabelsi, S. 2017. Portable six-port reflectometer for determining moisture content of biomass material. IEEE Sensors Journal. 17(15):4814-4819.
Trabelsi, S., Lewis, M.A., Nelson, S. 2016. Microwave sensing of moisture content and bulk density in flowing grain. Transactions of the ASABE. 59(2):429-433.
Lewis, M.A., Trabelsi, S., Nelson, S. 2016. Assessing the utility of microwave kernel moisture sensing in peanut drying. Applied Engineering in Agriculture. 32(6):707-712.
