Location: Quality and Safety Assessment Research Unit
2016 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
Measurement of moisture content and bulk density of flowing grains are of interest at different stages from harvest all the way to the storing facility. The research goal is to develop a low-cost microwave sensor for real-time determination of moisture content and bulk density in flowing grain by measuring their dielectric properties at a single microwave frequency. To achieve this goal, several factors influencing the accuracy of these parameters have to be addressed. Since it is desirable to perform these measurements with minimal process disturbance, microwave free-space techniques were selected. In free space, accurate measurements are achieved if the material is placed at a far distance from the transmitting antenna which usually dictates samples with large dimensions. Since this is not always possible in real-life situations, measurements were collected with the antennas placed in close proximity of the material with a technique known as near field. Measurement accuracies of the dielectric properties were investigated at microwave frequencies between 2.0 GHz and 18.0 GHz.
Simulations were conducted with varying microwave frequencies, sample thicknesses, and distances from the antennas to the sample interfaces. From these simulations, it was concluded that the sample should be placed at least one wavelength from the transmitting antenna and one wavelength from the receiving antenna and that the sample thickness should be selected to ensure enough attenuation to avoid the effects of multiple reflections within the material.
Experimentally, a sample holder filled with corn was placed between two high-gain patch antennas connected to an instrument known as a vector network analyzer. Measurements were collected while moving the antennas symmetrically from the sample holder interfaces and the dielectric properties were calculated for samples of known moisture contents and known bulk densities. The dielectric properties values remained constant at a distance greater than one wavelength from sample holder interfaces confirming the simulations. Next calibration equations for simultaneous determination of bulk density and moisture content from measurement of the dielectric properties at a single frequency provided density predictions with a standard error of calibration 0.03 grams per cubic centimeter and moisture content predictions with a standard error of calibration of 0.5%, wet basis.
Peanut (almond) grading requires the determination of several parameters including moisture content, meat content, and trash content. Developing low-cost microwave sensor for rapidly and nondestructively determination of these parameters from measurement of the dielectric properties at a single microwave frequency requires the fundamental step of collecting the dielectric properties of these materials for varying levels of moisture content, meat content, and trash content and generating calibration equations for their determination with acceptable levels of accuracy. Since dielectric properties are also dependent on bulk density and temperature, their influence was also investigated and taken into account in any of the calibration equations for moisture content, meat content, and trash content. Dielectric properties of unshelled and shelled almonds and peanuts samples of different moisture content and different bulk densities were measured at varying frequencies and temperatures. A sample holder made of Styrofoam was filled with almonds and placed between two microwave antennas. The dielectric properties of each sample were determined from measurement of the attenuation and phase shift at each temperature. At this stage, this database will allow the development of moisture and density calibration equations with temperature compensation for unshelled and shelled almonds and peanuts.
There is a need for improving the efficiency of peanut drying by minimizing energy consumption and reducing human interaction. Several units for real-time monitoring of peanut drying were built with off-the-shelf components and tested in the laboratory on a quarter scale drying system and in the field with three different semitrailers. Each unit comprised a microwave moisture meter and sensors for monitoring temperature of the ambient air, the peanut bed near the microwave moisture meter, temperature of the inlet air blown into the airspace, and the relative humidity of the ambient air. The microwave moisture meter was used to monitor the pods and kernels moisture content every 12 seconds. The drying was terminated once the ideal kernel moisture content dropped below 10.5%. The pod and kernel moisture contents were within 0.5% moisture when compared to oven moisture content determination. In addition, a system was built to move the moisture meter antennas longitudinally and transversally in the quarter-scale drying system. This will allow a mapping of the pods and kernels moisture content inside the laboratory scale trailer and thus a better understanding of the drying profile.
Novel substrate integrated sensors were developed and tested on liquids, gels, and sawdust. They allowed moisture determination from measurement of the reflection coefficient at a single microwave frequency. These sensors have the advantage of being inexpensive and can be integrated easily for in-process measurement of moisture content.
Accomplishments
None.
Review Publications
Trabelsi, S., Lewis, M.A., Nelson, S.O. 2016. Microwave moisture meter for in-shell peanut kernels. Food Control. 66: 283-290.
Nelson, S.O., Trabelsi, S. 2016. Historical development of grain moisture measurement and other food quality sensing through electrical properties. IEEE Instrumentation & Measurement Magazine. pgs. 16-23.
Trabelsi, S., Nelson, S.O. 2016. Microwave sensing of quality attributes of agricultural and food products. IEEE Instrumentation & Measurement Magazine. pgs. 36-41.
