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United States Department of Agriculture

Agricultural Research Service

Related Topics

Research Project: SENSING MOISTURE CONTENT AND QUALITY OF GRAIN AND OTHER AGRICULTURAL PRODUCTS BY DIELECTRIC PROPERTIES

Location: Quality and Safety Assessment Research Unit

2005 Annual Report


1.What major problem or issue is being resolved and how are you resolving it (summarize project aims and objectives)? How serious is the problem? What does it matter?
Rapid means of sensing product quality, such as moisture content in cereal grains, is needed for real-time on-line monitoring of quality characteristics. Techniques for instantaneous sensing and measurement of moisture content in wheat, corn, and other cereal grains, and soybeans, peanuts, and other oilseed crops are being developed for reliable moisture measurement for on-line applications. These techniques utilize the electrical characteristics of grain and seed known as dielectric properties. The dielectric properties, which determine the interaction with electric fields, are highly correlated with moisture content and can be sensed with appropriate electronic instruments. These techniques will provide reliable moisture content information that is essential for yield monitoring on harvesting equipment when combined with global positioning systems for precision farming operations and in preserving the quality of cereal grains, their products, and other agricultural products during transfer for storage and during processing. Moisture content is the single most important quality characteristic that determines the safe storage potential for cereal grains and oilseeds. Grain that is too high in moisture content is subject to attack by grain storage fungi and stored grain insects. These infections and infestations produce spoilage and loss of value that reach significant proportions every year. Fungi produce toxins such as aflatoxins and fumonisins that are serious health hazards to man and animals that use these products for food and feed. Therefore, better information on the moisture levels of products such as cereal grains can be of significant value in maintaining quality and preventing losses and contamination. In addition, the moisture monitoring techniques will provide for better control of processing for value added applications and improved end product quality. They will provide more precise moisture information that can be used in optimizing grain drying with resulting higher quality products and significant energy savings in grain drying operations. Reliable on line moisture monitoring will also fill important needs in highly automated operations in agriculture, such as precision farming, yield monitoring, and in other industries as well, where real time moisture content information is essential to efficient operations. Accurate and reliable monitoring of moisture content is also essential for fairness in trading of grain and oilseeds, for efficiency in processing, and in providing healthful food products to the consuming public.


2.List the milestones (indicators of progress) from your Project Plan.
12-Month Milestones a. Microwave dielectric properties of wheat, corn, oats, soybeans, sunflower, safflower and canola measured as functions of frequency moisture content, temperature, and bulk density. b. Testing of initial patch antennas completed and required design selected. c. Procurement of components initiated for assembling time-domain spectroscopy (TDS) system. d. Dielectric properties measured for several fruits and vegetables over broad frequency range.

36-Month Milestones a. Preferred frequency ranges established for reliable sensing of moisture content in static samples of major grain and oilseed crops. b. Degree of calibration-function universality established for major grain and oilseed crops. c. Improved patch antennas integrated with microwave circuits needed for moisture meter evaluation. d. Papers presented and submitted for publication. e. Completion of TDS system assembly and software development initiated for dielectric properties measurements. f. Additional products identified and evaluated for potential quality sensing studies.

60-Month Milestones a. Calibration equations developed as a universal density-independent moisture predictor or for classes of grain and seed crops. b. Performance on flowing grain samples evaluated and recommendations formulated for technology transfer. c. Published papers and new paper submitted. d. Working prototype microwave moisture meter evaluated for performance on static grain and seed samples and recommendations formulated for technology transfer. e. Working TDS system with broadband dielectric properties data on several agricultural products. f. Paper presentations and papers submitted for publication.


4a.What was the single most significant accomplishment this past year?
Title: Measurement of kernel moisture content in unshelled peanut pods. We demonstrated that kernel moisture content can be determined by microwave measurements on unshelled peanut pods. Current practice requires the shelling and cleaning of peanut samples before kernel moisture can be determined with electronic moisture meters. In most peanut drying operations, samples are hand shelled and cleaned, thus requiring significantly more time and expense than needed for direct nondestructive moisture determination on unshelled pod samples. This was accomplished by microwave measurements of the dielectric properties of both shelled and unshelled peanuts, developing a density-independent moisture calibration function for both shelled and unshelled peanuts and equating the two calibration functions and solving for kernel moisture content in terms of the measurement on unshelled pod peanuts. Because of its rapid and nondestructive nature, a microwave moisture meter for pod peanuts would result in significant savings in time and expense, which also includes loss of sample material, throughout the industry. Development of new microwave peanut moisture meters could provide significant benefits to producers, handlers, processors, and consumers.


4b.List other significant accomplishments, if any.
1. Use of inexpensive patch antennas for sensing grain moisture content. We demonstrated that inexpensive patch antennas can be used in place of expensive microwave horn/lens antennas for reliable measurement of grain and oilseed dielectric properties and consequent determination of moisture content. This is an important step toward the development of a practical moisture meter to implement research findings showing that grain and oilseed moisture content can be sensed better at microwave frequencies than at the lower frequencies currently utilized by commercial grain moisture meters. Moisture content is provided independent of the density of the grain, so that reliable moisture sensing in moving grain can be achieved. The microwave frequencies are also not affected by variations in ionic conductivity, which is responsible for errors in moisture measurement at lower frequencies. These findings will help provide the stimulus that is needed to encourage development of practical microwave moisture meters for monitoring grain and seed moisture content to assist in preserving such crops, maintaining high quality, and improving yield monitoring in precision agriculture. 2. Microwave sensing of bulk density in granular materials. The same measurement of microwave dielectric properties of grain and oilseeds that permits moisture content sensing can also be used to determine the bulk density, or packing density of the grain and seed. This provides a new technique for monitoring bulk density in granular materials, which can be useful in monitoring mass flow for grain and other materials. Bulk densities of corn, wheat, oats, soybeans and peanuts were determined from measurements of microwave dielectric properties with sufficient accuracies for practical use. While the application of this finding has not been fully explored, it may eventually be useful in the monitoring of mass flow for granular materials in precision farming and other applications.

3. Electrical behavior of water in grain and seed. New understanding of the electrical or dielectric behavior of bound water in grain was achieved. This is important because the dielectric behavior of grain, which is used in sensing moisture content, is dominated by the dielectric behavior of bound water. At normal moisture contents, the water in grain is chemically bound to other molecules in the kernels. By conditioning wheat at very low temperatures and tracking the dielectric properties as it warmed to room temperature, two kinds of bound water were revealed. And by moistening wheat and tracking the dielectric properties as the added water diffused into the kernels, it was revealed that the dielectric properties reached equilibrium conditions within two to four hours. Furthering the understanding of the behavior of bound water in grain and seed permits the improvement of moisture sensing in these granular materials through research.

4. Broadband electrical spectroscopy of fruits and vegetables. The electrical characteristics, or dielectric properties, of nine fruits and vegetables were determined previously in the frequency range from 10 to 1,800 MHz and their temperature-related behavior was analyzed. Dielectric properties analysis may offer means for nondestructively sensing such quality factors as maturity or defects. The dielectric properties are also important in research on food processing by high frequency and microwave dielectric heating for cooking and pasteurization. The behavior of the dielectric properties of fresh apple, avocado, banana, cantaloupe, carrot, cucumber, grape, orange and potato tissue over this range of frequencies at temperatures from 15 to 95 degrees C was established, thus providing necessary background data for further research. Further analysis revealed linear relationships between the log of the dielectric loss factor and both temperature and the log of frequency. This research has provided new dielectric properties data important in the modeling of radio-frequency and microwave dielectric heating processes for such foods and also of value in future research on fruit and vegetable maturity and defect sensing with electromagnetic fields.

5. New fitting procedure for electrical or dielectric spectroscopy data. With the cooperation of a theoretical physicist at Kazan State University, Tatarstan, Russian Federation, dielectric spectroscopy data for fresh fruits and vegetables and similar data over a different frequency range for adult insects of four stored-grain insect species, were fitted with seven parameters which can be used to express the dielectric properties of these biological materials as a function of frequency and temperature. This accomplishment has scientific significance, because it provides an excellent fitting of the data for potential use in practical applications such as the detection of quality characteristics in fruits and vegetables. The analysis was based on known behavior of dielectric properties of matter and advanced mathematical techniques for developing the fitting parameters. The work must be considered exploratory, and the technique must be applied to new dielectric spectroscopy data taken for the purpose of distinguishing important characteristics in products for evaluation.


4c.List any significant activities that support special target populations.
None.


4d.Progress report.
This report serves to document research conducted under a specific cooperative agreement 58-6612-1-212 between ARS and The University of Georgia. Additional details of the research can be found in the report for the sibling project 6612-44000-024-01S. Methods for rapidly and reliably sensing product quality, such as grain moisture content, are needed for on-line monitoring of quality characteristics. Techniques based on measurement of the microwave dielectric properties of corn, wheat, oats, soybeans, and peanuts provided moisture content independent of the material bulk density, and the techniques also can provide bulk density of the grain or seed independent of moisture content. Promising results were obtained with a single moisture calibration equation for these four commodities. A universal moisture calibration for grain would provide a significant advantage, thus, providing an incentive for development of practical microwave grain moisture sensors.


5.Describe the major accomplishments over the life of the project, including their predicted or actual impact.
Techniques have been developed for measuring the electrical or dielectric properties of grain and oilseed over the frequency range from 2 to 18 GHz with a microwave network analyzer. These techniques are especially well suited for on line measurements to determine moisture content through use of the dielectric properties. Techniques have been developed for reliable moisture sensing in grain independent of bulk density (grain packing). At microwave frequencies, measurements on wheat, corn, oats, soybeans, and peanuts over wide ranges of frequency, moisture content and bulk density have provided reliable moisture determination. Advanced techniques have been explored for obtaining the best calibrations for sensing grain moisture content. The new techniques for grain moisture sensing should result in development of improved moisture monitoring instrumentation that can be applied for more accurate and reliable yield monitoring on combine harvesters for precision farming and in many grain processing and product drying applications. Over the past year, efforts were concentrated on developing the foundation for reliable moisture sensing in grains and oilseeds by microwave measurements and exploiting the substantial advantages that microwave frequencies offer for this application. Good progress has been made in developing density-independent moisture calibrations that promise universal applicability for grain and oilseed and in identifying cost reductions for eventual production of economically feasible practical instruments. Limited measurements on fruit and vegetable tissues have provided an initial database on the dielectric properties of several fruits and vegetables and revealed their frequency- and temperature-dependent characteristics. They include a frequency between 10 and 120 MHz where the dielectric constant does not depend at all on temperature and a linear model for the dielectric loss factor of nine fruits and vegetables over the frequency range from 10 to 300 MHz. These provide a background for future research on quality sensing in fruits and vegetables by radio-frequency and microwave electric fields.


6.What science and/or technologies have been transferred and to whom? When is the science and/or technology likely to become available to the end-user (industry, farmer, other scientists)? What are the constraints, if known, to the adoption and durability of the technology products?
A major manufacturer of farm equipment has a new grain moisture sensor in production on its grain combines, which uses principles developed by ARS research. Consultation was provided by ARS engineers to the designers and developers of this new moisture sensor. Principles outlined in United States Patent No. 6,691,563, “Universal dielectric calibration method and apparatus for moisture content determination in particulate and granular materials,” Samir Trabelsi, Stuart O. Nelson and Andrzej W. Kraszewski.,issued February 17, 2004, have been incorporated into microwave moisture sensing equipment supplied by an instrument manufacturer in Iceland. Many reprints of published papers have been distributed in response to inquiries from all over the world. Most of these inquiries are from scientists, engineers, and graduate and undergraduate students interested in moisture sensing, microwave processing, applications of RF and microwave energy for insect control or seed treatment, and basic dielectric properties of materials and their measurement. Informal consultation was provided to representatives of a major agricultural instrument manufacturer relative to possible development of microwave grain moisture meters. Informal consultation was also provided to two foreign companies, one manufacturing industrial microwave moisture sensing equipment and another interested in sensing quality of fruits and vegetables. Research papers and consultation have been provided for companies interested in developing high frequency and microwave equipment for nonchemical stored grain insect control purposes in The United States, the United Kingdom, and the Ukraine. Constraints for the moisture sensing applications consist mainly of costs of developing suitable practical equipment, ascertaining reliability of the measurements, and unknown market potential for the equipment. Constraints for the insect control application are economic, including both costs of equipment for large-scale treatment and costs of operation when less expensive chemical controls are available.


7.List your most important publications in the popular press and presentations to organizations and articles written about your work. (NOTE: List your peer reviewed publications below).
None.


Review Publications
Nelson, S.O. 2004. Agricultural applications of dielectric spectroscopy. Journal of Microwave Power and Electromagnetic Energy. 39(2):75-85.

Nelson, S.O., Trabelsi, S. 2004. Microwave dielectric properties of shelled and unshelled peanuts. Transactions of the ASAE. 47(4):1215-1222.

Nelson, S.O., Trabelsi, S. 2005. Permittivity measurements and agricultural applications. Chapter 18. In: Kupfer, K., editor. Electromagnetic Aquametry. Berlin, Heidelgerg.

Nelson, S.O. 2004. Useful relationships between dielectric properties and bulk densities of granular and powdered materials. In: Proceedings of the American Institute of Chemical Engineers Annual Meeting. Fourth World Congress on Microwave and RF Applications. New York. p. 136-140. CDROM.

Nelson, S.O. 2005. Dielectric spectroscopy of fresh fruits and vegetables [abstract]. American Association for the Advancement of Science. p. A134.

Nelson, S.O. 2005. Dielectric spectroscopy of fresh fruits and vegetables. In: Proceedings of the 22nd IEEE Instrumentation and Measurement Technology Conference. p. 360-364.

Trabelsi, S., Nelson, S.O. 2005. Dielectric study of temperature-dependent behavior of bound water in grain. In: Proceedings of ISEMA 2005 6TH International Conference on Electromagnetic Wave Interaction with Water and Moist Substances, May 29-June 1, Weimar, Germany. p. 41-46.

Nelson, S.O., Trabelsi, S. 2005. Universal microwave moisture sensor. In: Proceedings of ISEMA 2005 6th International Conference on Electromagnetic Wave Interaction with Water and Moist Substances, May 29-June 1, Weimar, Germany. p. 231-235.

Nelson, S.O. 2005. Frequency and temperature dependence of the permittivity of fresh fruits and vegetables. In: Proceedings of the 6th International Conference on Electromagnetic Wave Interaction with Water and Moist Substances, May 29-June 1, Weimar, Germany. p. 391-398.

Nelson, S.O. 2005. Granular and powdered material permittivity-density relationships. In: Proceedings of 6th International Conference on Electromagnetic Wave Interaction with Water and Moist Substances, May 29-June 1, Weimar, Germany. p. 448-455.

Trabelsi, S., Nelson, S.O. 2005. Comparing near-field and far-field dielectric properties measurements for accuracy of bulk density and moisture content determination in grain. In: Proceedings of the Sixth Conference on Electromagnetic Wave Interaction with Water and Moist Substances, May 29-June 1. Weimar, Germany. p. 462-470.

Nelson, S.O. 2005. Some applications for dielectric spectroscopy in agriculture [abstract]. URSI Digest, USNC/CNC/URSI North American National Radio Science Meeting, July 3-9, Washington, DC. Session 105-4 CDROM.

Nelson, S.O. 2005. Dielectric spectroscopy studies on fresh fruits and vegetables. In: Proceedings of the IEEE Antennas and Propagation Society Digest. Session 148-8. CDROM.

Trabelsi, S., Nelson, S.O. 2005. Microwave dielectric study of bound water behavior in granular materials [abstract]. URSI Digest, USNC/CNC/URSI North American National Radio Science Meeting, July 3-9, Washington, DC. Session 105-1. CDROM.

Nelson, S.O. 2005. Temperature and frequency dependence of the dielectric properties of fresh fruits and vegetables. In: Proceedings of the 39th Annual Microwave Symposium, July 13-16, Seattle, WA. p. 11-14.

Nelson, S.O., Trabelsi, S. 2005. Microwave moisture sensing in cereal grains and oilseeds. In: Proceedings of the 39th Annual Microwave Symposium, July 13-16, Seattle, WA, p. 101-104.

Trabelsi, S., Nelson, S.O. 2005. Microwave dielectric properties of cereal grain and oilseed. In: Proceedings of the American Society of Agricultural Engineers, St. Joseph, MI. Paper no.056165.

Trabelsi, S., Nelson, S.O. 2005. Microwave dielectric methods for rapid, nondestructive moisture sensing in unshelled and shelled peanuts. In: Proceedings of the American Society of Agricultural Engineers, St. Joseph, MI. Paper no. 056162.

Nelson, S.O. 2005. Dielectric properties measurement for agricultural applications. In: Proceedings of the American Society of Agricultural Engineers, St. Joseph, MI. Paper No. 053134.

Trabelsi, S., Nelson, S.O. 2004. Calibration methods for nondestructive microwave sensing of moisture content and bulk density of granular materials. Transactions of the ASAE. 47(6):1999-2008.

Nelson, S.O. 2005. Dielectric spectroscopy in agriculture. Journal of Non-Crysitaline Solids. 351:2940-2944.

Trabelsi, S., Nelson, S.O. 2005. Effect of non-equilibrated moisture on microwave dielectric properties of wheat. In: Proceedings of the 22nd IEEE Instrumentation and Measurement Technology Conference. Ottawa, Ontario, Canada. p. 369-371.

Last Modified: 4/16/2014
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