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United States Department of Agriculture

Agricultural Research Service

Related Topics

Research Project: Sensing Methods & Instrumentation for Rapid Determination of Moisture Content... and Other Quality Attributes of Grains, Seeds, & Nuts

Location: Quality and Safety Assessment Research Unit

2013 Annual Report


1a.Objectives (from AD-416):
1. Develop cost-effective systems and sensors for rapid and nondestructive measurement of moisture content and density of cereal grains, oilseeds and nuts that can be used in static and dynamic situations (on line and in process applications). 2. Develop a portable system for moisture measurements of shelled and unshelled peanuts that can be used in the field and at peanut grading stations.

3. Improve peanut grading processes by developing a rapid system for nondestructive determination of peanut kernel moisture from measurements on pre-cleaned samples and samples consisting of a mixture of pods and foreign materials.

4. Develop methods for monitoring water migration in almonds and other nuts and its effect on their quality by dielectric and spectroscopic methods.


1b.Approach (from AD-416):
Developing a cost-effective microwave system for rapid moisture measurement will require analysis of existing dielectric properties data to determine the optimum frequency and measurement parameters. From these results, microwave components will be specified, assembled into a low-cost rapid prototype, compared to a network analyzer, then calibrated and validated for moisture content of wheat, corn, soybeans, almonds, oats, sorghum, and barley.

For peanuts, dielectric properties from 2 to 18 GHz on Runner, Spanish, Valencia, and Virginia will first be collected on shelled and unshelled peanuts. As with the other grains above, these data will then be analyzed to determine the optimum dielectric properties parameters and associated algorithms for a density- and variety-independent measure of peanut moisture content, and a prototype low-cost rapid peanut moisture measurement system will be developed. From these measurements and system development for peanut moisture content of shelled and unshelled peanuts, further development of a system to measure the moisture content of peanut kernels without shelling will be developed. Additional dielectric properties of both the unshelled and shelled kernels will be collected as needed, along with the moisture content of both the shells and the kernels. From these data, moisture algorithms will be developed. Additional dielectric properties measurements on unshelled peanuts with and without foreign material will also be collected for development of moisture models that are also independent of foreign material (trash). Models will be developed for both pod and kernel moisture contents. Besides kernel moisture content, meat content and percentage of foreign material are also important grading parameters. Attempts to correlate the dielectric properties data with these parameters will also be made.

For almonds, since no dielectric properties data exists, fundamental dielectric properties measurements of almonds of varying varieties, growing locations in California, and moisture contents will be collected with a network analyzer. Correlations between moisture content and dielectric properties data will be developed. To investigate the dynamics of water migration in the almond kernels, known amounts of water will be sprayed on almond kernels of known moisture content, mixed, and then sealed in a Styrofoam box. The sealed box will then be placed between two horn-lens antennas for free-space measurement of the dielectric properties between 2 and 18 GHz at room temperature. Changes in the dielectric properties will be recorded over time as water moves from the almond surface to water in equilibrium inside the kernels. The next stage will be the use of these dielectric spectroscopic methods to monitor water migration inside the almonds under controlled conditions of humidity and temperature. In this instance, the water will permeate the almonds from the atmosphere for varying relative humidities from 20 to 80% in a controlled environmental chamber. Additionally, measurements will be repeated over varying temperatures from 0 to 50 oC in 5 oC increments.


3.Progress Report:
A microwave sensor prototype made with off-the-shelf components and operating at 5.8 GHz was assembled, tested, and calibrated for simultaneous and independent determination of bulk density and moisture content in peanut kernels, peanut pods, and corn. Density and moisture calibration equations with temperature compensation were established. The standard errors of performance ranged from 0.01 to 0.02 gram per cubic meter for bulk density and from 0.3% to 0.6% for moisture content. Evaluation of two microwave circuits showed that the standard error of performance could be decreased by as much as 30%. A quarter-scale drying system including a microwave sensor prototype was developed to provide an automated solution to the peanut drying process and to monitor in-shell kernel moisture content in real-time. The automated drying system monitors ambient air temperature and relative humidity and controls the dryer accordingly. Using a microwave moisture meter, the system is able to monitor the kernel moisture content of the drying peanut pods in real time without having to shell the peanuts. This drying system is expected to reduce overdrying and underdrying, preserve peanut quality, and minimize energy consumption. A new microwave sensor for measuring complex dielectric properties of liquids, powders, and semi-solid biological materials at radiofrequency and microwave frequencies has been developed. In addition, a new calibration method for determining the material dielectric properties from measurement of the microwave propagation constant has been developed. The sensor has been integrated with laboratory microwave hardware, allowing measurements to be efficiently and conveniently made. Measurements of several reference liquids showed that the new sensor and calibration technique is very accurate. Dielectric properties of oats, soybeans, barley, and corn were measured with a free-space system and a vector network analyzer between 2 GHz and 18 GHz for samples of different moisture content, temperature and bulk density. For each material, different varieties and different growing locations were considered. The data compiled were used in different calibration algorithms for simultaneous and independent determination of moisture content and bulk density. Dielectric data collected with a vector network analyzer at microwave frequencies for different peanut types (Georgia Runner, Texas Runner (high oleic), Valencia, and Virginia) were used to generate density-independent and type-independent moisture calibration equations. The standard error of performance for moisture determination in peanut kernels and pods ranged from 0.26% to 0.36%. Dielectric properties measurements on chicken breast meat, to track the effect of aging on meat over a 14-day period, were performed using a vector netwok analyzer and a coaxial probe between 200 MHz and 20 GHz at room temperature (about 24 C). The effect of aging was particularly noticeable in the lower frequency range (below 1 GHz). Also, effect of marination on dielectric properties of chicken meat was investigated. As expected, effect of marination was evident in the frequency range between 200 MHz and 1.5 GHz.


4.Accomplishments
1. An automated quarter-scale peanut drying system. The current peanut drying process utilizes model-based decision support software that requires substantial human interaction to adjust dryer settings based on both kernel moisture (requiring shelling) and environmental parameters. These conditions increase the likelihood of peanuts being overdried or underdried. An automated drying system, integrating atmospheric-condition sensors and a microwave moisture sensor for in-shell peanuts, was developed. Real-time monitoring of peanut kernel moisture content and environmental conditions allows the drying time to be controlled automatically. Implementation of such a system will reduce overdrying and underdrying, preserve peanut quality, and minimize energy consumption.


Review Publications
Lewis, M.A., Trabelsi, S. 2012. Integrating an embedded system in a microwave moisture meter. Applied Engineering in Agriculture. 28(6):923-931.

Trabelsi, S., Nelson, S.O. 2012. Microwave dielectric properties of cereal grains. Transactions of the ASABE. 55(5):1989-1996.

Trabelsi, S., Nelson, S.0., Paz, A.M. 2013. Microwave dielectric method for the rapid, non-destructive determination of bulk density and moisture content of peanut hull pellets. Biosystems Engineering. 115(3):332-338.

Trabelsi, S., Nelson, S.O. 2012. Microwave Dielectric Properties of Cereal Grains. Transactions of the ASABE. 55(5):1989-1996.

Samuel, D.D., Trabelsi, S., Karnuah, A., Anthony, N., Aggrey, S. 2012. The use of dielectric spectroscopy as a tool for predicting meat quality in poultry. International Journal of Poultry Science. 11(9):551-555.

Lewis, M.A., Trabelsi, S., Nelson, S.O., Tollner, E.W., Haidekker, M.A. 2013. An automated approach to peanut drying with real-time microwave monitoring of in-shell kernel moisture content. Applied Engineering in Agriculture. 29(4).

Last Modified: 10/30/2014
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