Microwave Moisture Sensor Research Articles

Investigating the Influence of Grain Variety on Calibration of Microwave Moisture Sensors

<b>Highlights</b> <list list-type=bullet><list-item> Dielectric properties of wheat and corn were measured at 10 GHz and 25°C. </list-item><list-item> Moisture content was determined with a dielectric-based density-independent calibration function. </list-item><list-item> No Influence of variety in calibrating microwave moisture sensors was observed for wheat and corn. </list-item><list-item> A unified calibration for moisture determination in wheat and corn provided moisture content with SEC of 0.87%. </list-item></list> <b>Abstract.</b> Microwave moisture sensors represent a sound solution for real-time, nondestructive determination of moisture content in grains, seeds, nuts, and other agricultural products. One of the most critical phases in developing these sensors is their calibration against standard methods, in this instance, the oven-drying technique. In this study, dielectric properties of different varieties of wheat, and corn were measured at 10 GHz and an average room temperature of 25.2°C to investigate the influence of variety in calibrating microwave moisture sensors. Dielectric properties measured for all varieties tested for a given material were nearly superimposed, and the same was observed when plotting density-independent calibration function, , as a function of moisture content. Performance of individual moisture calibration equations in predicting moisture content was compared to that from a single moisture calibration equation established for all varieties combined through computation of the standard error of calibration (SEC). In most instances, for both wheat and corn the SEC corresponding to individual varieties were nearly the same as that corresponding to all varieties combined. In addition, it was observed that a unified calibration can be established for both wheat and corn whereby moisture can be predicted from a single moisture calibration equation based on measurement of the dielectric properties at a single microwave frequency. Here, such an equation provided moisture content in wheat and corn with a SEC of 0.87%.

Investigating the Influence of Grain Drying with Ambient Air Versus Heated Air within an Eighth-Scale Grain Drying Bin

HighlightsDrying of corn and wheat was monitored and controlled in real-time via the eighth-scale grain drying systemHeat and mass transfer during drying were simulated for corn and wheat when dried with heated and ambient airSimulated results provided prediction of preheating, constant-rate, and falling-rate periods at different heights within the drying grainMoisture content determined from simulation compared well with empirical data; root mean square error (RMSE) for corn and wheat (heated and ambient) were 0.61%, 0.45%, 0.61%, and 0.50% moisture content w.b., respectivelyAbstract. The choice of whether to use heated or ambient air during grain and oilseed drying is often complex, and it has a great effect on the overall quality of the product. A significant problem when drying with heated air is overdrying the bottom layer in attempting to dry the top layer. This is possible because grains or oilseeds within a storage bin can be more than 15.2 m deep. However, while the bottom layer is less likely to be overdried when using ambient air, there is a risk that the upper layers could be subject to mold and degradation if moisture is not removed quickly enough. An eighth-scale grain drying bin was equipped with temperature, moisture, and relative humidity sensors at different heights to observe temperature and moisture migration throughout the 60-cm deep bed as corn and wheat were dried. For both commodities, trials were run where they were dried with heated air and ambient air. Likewise, thin-layer drying models were applied to the deep bed, and the drying process was simulated using the finite difference method for both commodities using ambient and heated air. The absolute humidity, air temperature, grain temperature, and moisture content were modeled throughout the drying bed with respect to location and time. Data obtained from the simulations compared well with the experimental data. When comparing the moisture content determined from simulation with the same measured with the microwave moisture sensor within the drying system, root mean square error (RMSE) values for corn and wheat were 0.61 (heated air), and 0.45% and 0.50% (ambient air) moisture content wet basis (w.b.), respectively. A 30% increase in drying time was observed when ambient air was used to dry wheat. A 2-% increase in ending moisture content was observed when drying with ambient air for both commodities. The empirical results obtained from the eighth-scale drying system confirmed the results obtained from simulation for each trial. While results obtained may be unique to the current study, the effectiveness of the models was demonstrated. Keywords: Drying modeling, Grain drying, Heat transfer, Mass transfer, Microwave sensing.

Portable Wireless Yield Monitoring System on Conventional Rice Combine

Abstract. A simple, portable, and rugged instrumentation system has been successfully developed and field demonstrated to monitor, measure, and record the harvested crop yield and selected machine field performance parameters from the typical rice combines in Malaysia. The complete system comprises of two ultrasonic sensors located at the combine header to measure the cutting width, microwave solid flow, and microwave moisture sensors at the combine clean grain auger to measure the flow rate and moisture content of the cleaned grains going into the grain tank, electromagnetic detector on the combine grain elevator drive shaft to monitor the grain elevator rotational speed, and lastly a DGPS receiver on the combine console roof to indicate the travel speed and geo-position in the field. All these measured parameters were made to display in-real time on the touch panel screen of the embedded system on-board the combine for the interest of the combine operator and also made to display in-real time on the monitor of the toughbook at the on-ground base station for the interest of the system controller. Static calibrations on the individual sensors showed excellent measurement linearity having R2 values within 0.8760 to 1.000 ranges. The wireless communication between the embedded system on-board the combine and the toughbook at the on-ground base station could be sustained to a maximum distance of 185 m apart. Site specific variability maps of crop yield, harvested grain moisture content, combine cutting width, combine traveling speed, combine field capacity, and combine field efficiency within the harvested area could be produced from the data obtained with the instrumentation system using a GIS software. Keywords: Grain harvesting, Paddy mechanization, Precision farming, Wireless data transmission, Yield monitoring.

Design and Analysis of Dual Frequency Microwave Moisture Sensor Based On Rectangular Microstrip Antenna

The two proposed design microstrip patch antenna as a sensor are analysed with the help of CST software for detecting the moisture. The proposed design is T-Shape rectangular shape with slotted in the ground plane and without slotted in the ground plane. It is operated at two frequencies 2.2GHz and 4.6GHz. It is designed on FR4 substrate and thickness is 1.676mm. The moisture can be detected with the help of oven drying technique. It will be helpful for measuring the moisture content. This technique is very easy, less time consuming, versatile and compact. The ground parameter of the proposed design is 20mm, as well as the length and width of the patch dimensions are 15mm and 10mm, which will be very portable. The designs is simulated on CST software and gets the good return loss, which is -16dB at 2.2GHz and -45dB at 4.6GHz. The gain is also the important parameter of the sensor; the proposed slotted ground plane design gain is 4.99dB at 4.6GHz as well as without slotted ground plane design gain is 5.1dB at 4.6GHz. It will be fabricated and measure the moisture in rice grains with the help of vector network analyser. The calibration equation and regression equation is also the important role of detecting the moisture content.

Application of Microwave Moisture Sensor for DOC and Animal Feed

Measurement of moisture is of paramount importance for optimising energy consumption as well as increasing product quality and shelf life in process industries. Details of a comprehensive design for building a microwave-based moisture sensor along with calibration methodology and field demonstration of this concept is presented. Calibration, which is an essential step before field deployment, has been demonstrated using a waveguide method. The methodology presented connects the calibration performed using the waveguide method to that of free space methods employed in the field. Results for two field tests in De-oiled cake (Soya) and Animal feed (cattle feed) processing plants are analysed. The deficiencies and capabilities of the method to perform density-independent measurements have been demonstrated in these real-world scenarios.

Performance Comparison of Three Density-Independent Calibration Functions for Microwave Moisture Sensing in Unshelled Peanuts during Drying

HighlightsReal-time, free-space transmission measurements of relative complex permittivity in unshelled peanuts during dryingDynamic application: temperature, density and moisture content changing during dryingThree density-independent calibration functions evaluated for accuracy in real-time moisture content determinationReal-time moisture content determination with standard error of performance (SEP) = 0.55% moisture content for all calibration functionsCalibration function most commonly used with microwave moisture sensor was determined to be most accurate; SEP = 0.448% moisture contentAbstract. A microwave moisture sensor, developed within USDA ARS, has been used to determine moisture content in unshelled peanuts during drying. Relative complex permittivities of the peanuts obtained from free-space transmission measurements at 5.8 GHz are used for the moisture determination. Due to variations in density caused by drying, it is advantageous to estimate moisture content independent of bulk density. Therefore, moisture content was estimated with three density-independent calibration functions to assess which one provided optimal accuracy. One of the functions is based on the measured attenuation and phase shift, and the other two are permittivity based (one of which is commonly used with the microwave moisture sensor). The sensor was calibrated for peanut pod moisture content determination over a temperature range of 10°C to 40°C and a moisture content range of 6.5% to 19% wet basis (w.b.). Statistical analysis showed high coefficients of determination (r2), = 0.97 for the calibration with each function. Peanut pod moisture content was determined with the sensor in real-time as peanuts dried, and estimated moisture content was compared to the reference oven drying method. While the standard error of performance (SEP) for the three functions was = 0.55% moisture content, the calibration function most commonly used with the microwave sensor was observed to be the most accurate (SEP = 0.448% moisture content). Microwave sensing is a viable solution for nondestructive, real-time determination of moisture content in peanuts in dynamic situations such as drying. Keywords: Complex permittivity, Dielectric properties, Free-space measurements, Microwave sensing, Moisture content, Peanut drying.

Calibration Algorithm for Rapid and Nondestructive Moisture Sensing in In-Shell Nuts

A new calibration algorithm is presented for instantaneous and nondestructive determination of moisture contents of in-shell nuts and kernels from measurement of the dielectric properties of in-shell nuts at a single microwave frequency. The new calibration algorithm relies on the use of a density-independent function, expressed in terms of the dielectric properties, and the existence of a direct relationship between the in-shell nut oven moisture content and kernel oven moisture content. Results of measurement by using a microwave moisture sensor operating at 5.8 GHz are presented, and kernel moisture calibration equations are established for peanuts and almonds.

Density-independent calibration functions for nondestructive moisture sensing in flowing grain

In many agricultural and industrial applications, moisture content needs to be determined in real time while the material is moving. For granular and particulate materials, density-independent calibration functions were used in microwave moisture sensors to minimize the effect of bulk density changes. Three of these calibration functions expressed in term of the attenuation, phase shift and the dielectric properties were investigated for moisture determination in flowing grain and seed samples. To simulate in the laboratory measurements on flowing grain, a flowing system was designed and assembled. The flowing-grain system consisted of a conical stainless steel hopper connected to a polycarbonate chute and an iris diaphragm-type valve placed at the bottom. The iris can be manually adjusted to provide different flow rates. The flowing system was calibrated by using static samples which were placed in the polycarbonate chute between two patch antennas operating at 5.8 GHz and connected to a vector network analyzer. Measurements at room temperature on grain and seed samples flowing at varying flow rates showed that moisture content can be predicted with density independent calibration functions with a standard error of performance (SEP) of less than 1% moisture content.

An ‘isolated diffusion’ gravimetric calibration procedure for radar and microwave moisture measurement in porous building stone

Information about the presence and movement of water is crucial to understanding stone deterioration and rock weathering but hard to obtain. Non-destructive, non-invasive measurements of electromagnetic phenomena can provide proxy data on water contents within porous stone and rock. Commercial geophysical devices, such as radar and microwave moisture sensors, produce raw data or readings in arbitrary units, but can be related to absolute water contents through gravimetric calibration. Calibration procedures typically either equilibrate samples to a set of relative humidities (RH%) using salt solutions or environmental chambers (requiring specialised equipment), or monitor ambient drying which yields less homogenous moisture distributions and takes time. This study proposes and tests a cost- and time-effective ‘isolated diffusion’ gravimetric calibration procedure in which a set of samples are sealed at specific water contents and equilibrated. The procedure is compared to ambient drying over 120 h for three United Kingdom building stones and evaluated with modelled reflection coefficients and relative permittivities. The calibrations determined from isolated diffusion more closely follow modelled behaviour than those from ambient drying, as the calibrations developed from the latter were affected by uneven distributions of moisture. Calibrations for radar measurements developed from two types of back interfaces (air and metal) were very similar to one another, suggesting that measurements are consistent regardless of the type of back interface used. The isolated diffusion calibration procedure provides a cost-effective and simple method to facilitate comparison between different non-destructive testing methods and enables accurate measurement of water contents in porous geomaterials.

Development of an Eighth-scale Grain Drying System with Real-time Microwave Monitoring of Moisture Content

Abstract. After being harvested, cereal grain and oilseed are stored and dried in large cylindrical storage bins. Drying is necessary to prevent spoilage and degradation; however, because of the significant depth of material in the drying bin, a common problem in grain and oilseed drying is overdrying the bottom layer while trying to dry the top layer. This is due to insufficient knowledge of moisture throughout the bin. In some cases, an operator is limited to probing reachable locations to determine moisture content. However, this does not lend to observing the dynamics of moisture content within the bin continuously, and the lower layers of grain or seed within the bin are susceptible to being overdried. Temperature and/or moisture cables to monitor conditions throughout the bin are more widely used. These sensors use a correlation between grain moisture content and temperature and relative humidity. However, error in moisture content determination increases greatly at high relative humidity and/or temperature. By using a microwave moisture sensor operating at 5.8 GHz, developed within USDA ARS, the moisture content of the cereal grain or oilseed can be measured continuously, providing real-time moisture content with 12-s resolution. An automated, eighth-scale grain drying system was developed utilizing temperature and relative humidity sensors at different heights within the grain bin and the microwave moisture sensor to observe drying parameters and moisture migration as the grain or seed dried. Grain and seed moisture content was determined in real-time with a standard error of calibration of = 0.54% moisture content when compared to the reference oven-drying method. Overall evaluation showed that the automated grain drying system is an effective solution for real-time monitoring of moisture content and other parameters during drying. Keywords: Dielectric properties, Grain drying bin, Moisture content, Microwave sensing, Real-time monitoring, Sensors.

Using Microwave Sensing to Investigate Kernel Moisture Content at the Front and Back of Semitrailers during Peanut Drying

Abstract. Several factors influence the effectiveness of peanut drying. Such factors include temperature and relative humidity of the air used for aeration, air velocity through the peanuts, and the presence of foreign material that could obstruct air flow. All of these factors can vary at any location in a semitrailer holding 20 to 25 tons of peanuts being dried. Therefore, it is highly unlikely that a volume of peanuts &amp;gt;71 m3 (2500 ft3) will dry uniformly. During the drying process, an operator removes samples of peanuts for kernel moisture content testing every 3 to 4 h to validate the estimated drying time determined by peanut-drying models used in the peanut industry. However, if samples are only taken from one location, it is likely that other locations differ in kernel moisture content. To investigate kernel moisture content near the front and back of the semitrailer, two peanut drying monitoring systems, each equipped with a microwave moisture sensor, were deployed at a peanut buying point in central Georgia during the 2014 and 2015 peanut harvest seasons. Each system monitored in-shell kernel moisture content and drying parameters in real-time, every 12 s. In-shell kernel moisture content was determined with a standard error of prediction of 0.55% moisture when compared to the reference oven-drying moisture tests. The two monitoring systems were placed in 13.7-m (45-ft) drying semitrailers, one 3 m (10 ft) from the front and the other 3 m (10 ft) from the back. Data from the measurements were time-stamped and reconciled accordingly, and they were analyzed to compare the moisture loss in real-time at both locations in the trailer. The 12-s resolution provided a continuous moisture profile to analyze rather than the discrete profile currently provided by sampling every few hours. Results show that moisture loss, and therefore resulting kernel moisture content, can vary from one end of the trailer to the other during peanut drying. Therefore, systems that monitor peanut drying at various locations throughout the semitrailer would improve peanut drying efficiency. Keywords: Dielectric properties, In-shell kernel moisture content, Microwave sensing, Peanut drying, Real-time monitoring, Sensors.

Assessing the Utility of Microwave Kernel Moisture Sensing in Peanut Drying

<abstract> <b><sc>Abstract. </sc></b>Presently in the peanut industry, peanut pods (unshelled peanuts) have to be shelled for kernel moisture content determination with the official moisture meter. This makes kernel moisture content determination laborious and limits efficiency during peanut drying. For field testing during the 2013 and 2014 peanut harvest seasons, a microwave moisture sensor was placed in several 45-ft (13.7-m) drying semi-trailers at a buying point in central Georgia to monitor kernel moisture content as the peanuts dried. Laboratory investigation of the accuracy of the portable microwave moisture sensor showed that peanut kernel moisture content can be determined from measurements on unshelled peanuts with a standard error of performance ≤ 0.55% moisture content when compared to the reference oven-drying method. A comparison was also performed between the microwave sensor and the official moisture meter during field testing. Results showed that there was a 2.3% difference in initial kernel moisture content determination and a 0.8% difference in ending kernel moisture content determination between the two. Overall evaluation demonstrated that the accuracy of the microwave moisture sensor and its provision of in-shell kernel moisture content would make it highly effective in the peanut drying process.

Microwave Moisture Sensing of Seedcotton: Part 1: Seedcotton Microwave Material Properties.

Moisture content at harvest is a key parameter that impacts quality and how well the cotton crop can be stored without degrading before processing. It is also a key parameter of interest for harvest time field trials as it can directly influence the quality of the harvested crop as well as skew the results of in-field yield and quality assessments. Microwave sensing of moisture has several unique advantages over lower frequency sensing approaches. The first is that microwaves are insensitive to variations in conductivity, due to presence of salts or minerals. The second advantage is that microwaves can peer deep inside large bulk packaging to assess the internal moisture content without performing a destructive tear down of the package. To help facilitate the development of a microwave moisture sensor for seedcotton; research was performed to determine the basic microwave properties of seedcotton. The research was performed on 110 kg micro-modules, which are of direct interest to research teams for use in ongoing field-based research projects. It should also prove useful for the enhancement of existing and future yield monitor designs. Experimental data was gathered on the basic relations between microwave material properties and seedcotton over the range from 1.0 GHz to 2.5 GHz and is reported on herein. This research is part one of a two-part series that reports on the fundamental microwave properties of seedcotton as moisture and density vary naturally during the course of typical harvesting operations; part two will utilize this data to formulate a prediction algorithm to form the basis for a prototype microwave moisture sensor.

Application of Microwave Moisture Sensor for Determination of Oil Palm Fruit Ripeness

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Microwave Moisture Sensor for Grain and Seed

A low-cost microwave sensor for nondestructive, rapid sensing of moisture content in granular and particulate materials has been built and tested. The sensor operates at a single frequency of 5.8 GHz and uses the principle of free-space transmission for moisture determination from measurement of the dielectric properties of the material. A unified calibration algorithm was used for moisture determination independent of bulk density and independent of the material type. Results for wheat and soybeans show that moisture content can be determined in either material from a single moisture calibration equation with a standard error of calibration of 0.5%. The low price, simplicity of use, and level of accuracy of the proposed sensor can provide an opportunity for widespread integration of microwave sensing technology in numerous industries dealing with granular and particulate materials, including food and agriculture, pharmaceuticals, mining, and construction.

Resonant microwave sensors for instantaneous determination of moisture in foodstuffs

Open microwave resonators are very well suited for online moisture monitoring during the production of foodstuffs. In order to allow for rapid measurements, the required information is derived from the dielectric behaviour of the material. Unlike for example the method of Karl Fischer titration, the dielectric microwave method determines the moisture content indirectly and is thus dependent on density changes. The present paper outlines special features of open resonators for density independent moisture measurement. It is demonstrated, how unfavourable design of the window for coupling out the fringing field of the open resonator leads to non-linear behaviour of the characteristics of resonant frequency and reciprocal quality factor vs density and moisture changes. Several engineered open microwave moisture sensors are presented and discussed. More in detail, a surface sensor, a surface sensor equipped with a small container on top, a self contained hand-held surface moisture sensor and a grooving-probe as well as a multi-hole sensor are shown. The electronics and the signal processing of the sensors are briefly described. Finally experimental moisture measurements and a density independent calibration are given for rolled oats. Moisture measurements on whole kernels of oats, barley and wheat demonstrate the only weak dependence of the microwave moisture measurement approach on the special type of material.

New calibration technique for microwave moisture sensors

A new calibration technique was developed for implementation with microwave moisture sensors. The calibration permittivity function used for this purpose allows computation of moisture content in granular materials with significant differences in shape, dimensions, and composition, independent of bulk density and with temperature compensation. A 3D representation is used to plot the calibration permittivity function as it depends on temperature and moisture content in wheat and corn. For each material, data points form a plane surface. These planes have nearly the same coefficients, which can be utilized for the development of a "universal" calibration method for moisture sensing in natural and manufactured granular materials. Foundations of the method are discussed based on results obtained for wheat and corn over a wide temperature range and at moisture contents of practical interest.

Manufacturers of Radiofrequency and Microwave Moisture Sensors

Manufacturers of Radiofrequency and Microwave Moisture Sensors

On-line Industrial Applications of Microwave Moisture Sensors

On-line Industrial Applications of Microwave Moisture Sensors

Development of a microwave moisture sensor for aggregates

An instantaneous method for measuring the moisture content in an aggregate such as sand is developed using a microwave coaxial cavity resonator with an outer slot antenna. We measure the attenuation of the resonant peak of the cavity resonator, which is related to the moisture content of the aggregate. The resonator is movable so that the moisture can be measured at the several positions in a pile of the aggregate. The standard deviation in the measured moisture content is 0.08%, which is better than our previous result.