Micah A. Lewis

Practical Microwave Meter for Sensing Moisture and Density of Granular Materials

A low-cost microwave sensor for rapid and nondestructive sensing of bulk density and moisture content in granular and particulate materials has been built and tested. The sensor was made with inexpensive, off-the-shelf components and operates at 5.8 GHz. Three permittivity-based algorithms were used to determine simultaneously bulk density and moisture content from dielectric properties measurement. Results obtained for wheat indicate the bulk density can be determined with less than 2% relative error and that moisture content can be determined with a standard error of calibration of 0.5%.

Embedded solution for a microwave moisture meter

In this paper, the conversion of a PC or laptop-controlled microwave moisture meter to a stand-alone meter hosting its own embedded system is discussed. The moisture meter is based on the free-space transmission measurement technique and uses low-intensity microwaves to measure the attenuation and phase shift of the sample, from which the dielectric properties are calculated. The dielectric properties are then used for instantaneous and nondestructive determination of the moisture content in the grain or seed sample. The previous system consisted of the moisture meter and measurement procedure being controlled via USB interface by an external laptop or PC. Though effective, the system lacked full portability and was susceptible to computer failure and interruptions in communication between the meter and computer. To improve the system, a microcontroller was selected in the design of an embedded system for the moisture meter, making it a stand-alone system. The microcontroller provides a graphical 144 × 32 pixel LCD and 16-button keypad to facilitate user interaction. The embedded system provides the following functionalities: user interface (input/output), event execution, process control, data acquisition and data storage. The integration of the embedded system with the microwave meter provides a portable, robust, and cost-effective solution for microwave moisture sensing.

Rapid and Nondestructive Determination of Moisture Content in Peanut Kernels from Microwave Measurement of Dielectric Properties of Pods

A method for moisture determination in peanut kernels from measurement of the dielectric properties of peanut pods at microwave frequencies is presented. The dielectric properties of peanut kernels and pods were measured in free space with a vector network analyzer and a pair of focused beam horn-lens antennas. A density-independent algorithm was used to determine moisture content in peanut kernels and pods. Moisture calibration equations with temperature correction were determined from a three-dimensional representation, and an explicit relationship between peanut pod moisture content and kernel moisture content was identified. Results presented at 6 GHz and temperatures ranging from 0.5 oC to 58 oC show that kernel moisture content can be predicted with a standard error of calibration of 0.79% and that of pods with a standard error of calibration of 0.95%.

Microwave Meter for Rapid, Nondestructive Determination of In-Shell Peanut Kernel Moisture Content from Dielectric Measurements on Cleaned and Uncleaned Pod Samples

A microwave moisture meter built with off-the-shelf components was developed, calibrated and tested in the laboratory and in the field for nondestructive and instantaneous in-shell peanut kernel moisture content determination from dielectric measurements on cleaned and uncleaned pod samples. The meter operates at a single frequency of 5.8 GHz and uses free-space transmission measurement principles for determining the dielectric properties of the peanut pods. From these properties, a permittivity-based algorithm provides the bulk density and moisture content of the pods, and the kernel moisture content. Field tests showed that moisture content of peanut kernels can be determined while still in the pod with a standard error of performance (SEP) of 0.82% moisture content for dielectric measurements on cleaned pods and an SEP of 0.86% moisture content for uncleaned pods compared to the official meter. When compared to the oven-drying standard method, values of the SEP were 0.51% for the official meter and 0.31% for the microwave meter.

Effects of "natural" water and "added" water on prediction of moisture content and bulk density of shelled corn from microwave dielectric properties.

Abstract Dielectric properties of samples of shelled corn of “natural” water content and those prepared by adding water were measured in free space at microwave frequencies and 23°C. Results of measurements of attenuation, phase shift and dielectric constant and loss factor at 9 GHz show no difference between the samples with “natural” water and those in which water was added artificially. Bulk densities and moisture contents predicted from calibration equations expressed in terms of dielectric properties of both natural and added water samples agreed closely, and standard errors were less than 1% for moisture content and relative error for bulk density was less than 5%.

Microwave Moisture Meter for Rapid and Nondestructive Grading of Peanuts

A low-cost microwave moisture meter made with off-the-shelf components was developed, calibrated and tested in the laboratory and in the field for the grading of peanuts. The meter allows rapid and nondestructive determination of kernel moisture content from measurements on unshelled peanut pods. The meter operates at a frequency of 5.8 GHz and uses the principle of free-space transmission measurement of the dielectric properties. Moisture content is determined independent of bulk density with a permittivity-based algorithm. Besides kernel moisture content, the meter provides simultaneously, from the same set of dielectric measurements, the bulk density and moisture content of the peanut pods.

Analysis of Stability and Type Independence of Three Density-Independent Calibration Functions for Microwave Moisture Sensing in Shelled and Unshelled Peanuts

A microwave dielectric method was used for nondestructive and rapid determination of moisture content in shelled and unshelled peanuts of various types from transmission measurements of their relative complex permittivities in free space at 23°C between 5 and 15 GHz. Moisture content was estimated, independent of bulk density, with three density-independent calibration functions and compared to standard oven moisture determinations; two of these functions are permittivity-based, and the other is expressed in terms of attenuation and phase shift. The effectiveness and stability of these three functions for type independence were evaluated over broad ranges of frequency, moisture content, and bulk density. While the performance of each function with individual type calibrations was reaffirmed, statistical analysis also showed high coefficients of determination in predictions with the combined type-independent calibrations. Therefore, with microwave moisture sensing technology, calibration equations can be used to accurately predict moisture content in peanuts with insensitivity to type; which is a characteristic lacking in todays commercial moisture meters.

Integrating an Embedded System within a Microwave Moisture Meter

In this paper, the conversion of a PC or laptop-controlled microwave moisture meter to a stand-alone meter hosting its own embedded system is discussed. The moisture meter uses low-power microwaves to measure the attenuation and phase shift of the sample, from which the dielectric properties are calculated. The dielectric properties are then used to determine instantaneously and nondestructively the moisture content in the grain or seed sample. The previous system consisted of the moisture meter being controlled via USB interface by an external laptop or PC. Though effective, the system lacked full portability and was susceptible to laptop crashes and interruptions in communication between the meter and laptop. To improve the system, a microcontroller was selected in the design of an embedded system for the moisture meter. The microcontroller provides a graphical 144 x 32 pixel LCD and 16-button keypad to facilitate user interaction. The embedded system provides the following functionalities: user interface (input/output), event execution, process control, data acquisition, and data storage. Initial testing shows that the moisture meter with the new embedded system maintains the performance and accuracy observed in the original PC or laptop controlled meter. The integration of the embedded system with the microwave moisture meter provides a cost-effective, portable, and robust solution for microwave moisture sensing.

Stability and Type-Independence Analysis of Density-Independent Calibration Functions for Microwave Moisture Sensing in Unshelled and Shelled Peanuts

Free-space-transmission measurements were used to measure the relative complex permittivities of shelled and unshelled peanuts of various types at 23°C between 5 and 15 GHz. Moisture content was estimated with three different calibration functions and compared to standard oven moisture determinations: two of these functions are permittivity-based, and the other is expressed in terms of attenuation and phase shift. The stability of these three functions for individual peanut types and type-independence was evaluated over broad ranges of frequency, moisture content and bulk density. Coefficients of determination and standard errors of calibration are presented for each function.

Type-Independent Calibration Method for Microwave Moisture Sensing in Unshelled and Shelled Peanuts

A microwave dielectric method was used for nondestructive and instantaneous determination of moisture content in shelled and unshelled peanuts from measurement of their relative complex permittivities in free space at 6.0 GHz and 23°C. Moisture content was determined independent of bulk density with the use of a density-independent calibration function. Statistical analysis provided the moisture calibration equations for each type with high coefficient of determination. The effectiveness of this method was further shown with the provision of a single moisture calibration equation for various types in shelled and unshelled peanut samples. Therefore, by using microwave moisture sensing, moisture content can be accurately predicted in different peanut types with a single calibration equation.