Microwaves sense grain moisture, impacting harvest, storage and price.

A technique that uses microwaves to determine moisture levels in grain crops is available for licensing from USDA-ARS scientists. In the process, an antenna transmits microwaves into such grains as corn, wheat, barley or soybeans that have been placed in an oven or vessel.

The microwaves pass through the grain and are received by another antenna on the other side of the vessel. The alternating of the microwaves themselves as they pass through the grain determines how much moisture is actually in the grain. The technique automatically adjusts for different types of grain.

Researchers have established the usefulness of the microwave measurements for sensing the moisture content of several kinds of grain in the laboratory. They have used a sample that is a layer of grain, a few inches thick. From measurements that determine the dielectric properties of the grain, investigators determine moisture content independently of the bulk density of the granular material and with a single moisture calibration that appears to be applicable to corn, wheat, oats and soybeans.

Because of the density-independent nature of the technique, it should be applicable to moving grain. Some further research and developmental work to build a practical grain moisture meter is required, but the scientists expect that instrument development is a project for private industry.

Grain moisture is important because the level of water in grain is a key factor in determining when harvest should occur. If harvesting occurs when moisture levels are too high, the combines can damage the grain in the threshing and shelling processes. If the moisture content is too low, there is the risk of damage occurring from shattering and kernel breakage. Moisture information is also essential in determining whether grain can be safely stored without spoilage and in calculating its selling price.

Currently, a separate calibration must be made for each kind of grain, and corrections must be made to account for differences in the temperature of the grain and its bulk density. In many instances, samples must be collected and tested in handheld moisture testers or taken to grain elevators for more accurate testing.

The new technique eliminates the need for making several calibrations and compensates for grain density and temperature. The technique has potential for use on combines and on grain handling or conveying equipment, and it could find use in any application that requires continuous moisture monitoring.

Grain handlers could have better information for managing their operations. If commercialized, the system is expected to be cost-effective because no other sensor is needed for making density measurements, and calibration maintenance is simpler.

Patent. 6,147,503--Method for the simultaneous and independent determination of moisture content and density of particulate materials from radio-frequency permittivity measurements. Issued: Nov.14, 2000. Inventors: Stuart Nelson, et al. Assigned to USDA. This patent covers a method for simultaneously and independently measuring the moisture content and bulk density of particulate materials using radio-frequency measurements. These measurements allow for on-line, real-time monitoring and control. Moisture and density are determined by measurements of complex permittivities. This technique is based on using the dielectric properties of the materials for density and water content determination.

Further information. Stuart Nelson, USDA-ARS Richard B. Russell Research Center, P.O. Box 5677, Athens, GA 30604; phone: [phone]; fax: [phone]; email: [e-mail].