Use of a transverse electromagnetic cell for measuring the electrical characteristics of flowing granular materials

Abstract

A device for measuring at least one variable property of a granular material features a transverse electromagnetic (TEM) cell whose interior uniquely includes non-conductive chamber walls that delimit a measurement chamber at a non-tapered mid-region of the TEM cell housing between the two tapered end regions thereof. A center conductor of the TEM cell bisects the measurement chamber, into and from which a granular substance is flowable via inlet and outlet openings of communicative relationship to the measurement chamber. Excitation of the TEM cell generates an electromagnetic wave that is propagated through said granular material flowing through the measurement chamber. Output signal measurements from the TEM cell are used to calculate measurement of at least one variable property of the granular material.

Description

[0001] USE OF A TRANSVERSE ELECTROMAGNETIC CELL FOR MEASURING THE ELECTRICAL CHARACTERISTICS OF FLOWING GRANULAR MATERIALS CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims benefit under 35 U.S.C. 119(e) of U.S. Provisional Application No. 63 / 689,322, filed August 30, 2024, the entirety of which is incorporated herein by reference.

[0003] FIELD OF THE INVENTION

[0004] The present invention relates generally to devices for measuring properties of a substance, and more particularly to devices particularly useful for measuring properties of a flowable granular substance while in a flowing state thereof. BACKGROUND

[0005] Measuring permittivity is important for identifying the properties and composition of materials. For example, the permittivity is related to the moisture content in many materials. When storing agricultural goods, the moisture content and other environmental conditions determine how low it can be safely stored before rotting. The measurement of permittivity is also important for other granular materials, like cement powder. Many devices exist for measuring the permittivity (and thus moisture content) of such materials, but there are very few that can measure the moisture content of flowing granular materials, which would be very useful, for example as part of an industrial process such as loading or unloading a truck or moving cement powder from one storage container to another.

[0006] As permittivity is an electrical property of matter, it needs to me measured by its interaction with electromagnetic (EM) waves. One method of performing this measurement is transmitting a plane wave through the target material and measuring the attenuation and phase shift. This measurement is compared to the theory, as plane waves are well understood and modelled, to extract the permittivity value. Other groups in the past implemented this concept using antennas to transmit and receive the EM waves close to the flowing granular material, and in their calculations, they assume that the waves are planar. This assumption is inaccurate, as the EM fields from such antennas are known to be highly variable close to the antenna, That is, the true EM waves are not well modelled by a plane wave in the near field of antennas. Only far away from the antenna can the fields be properly approximated by a plane wave. Therefore, using antennas for permittivity measurements will have inaccuracies in the modelling, leading to error in the results. Further, the antenna-based approach means that any external change to the electromagnetic environment (i.e. , deploying the sensor in a different location such as a combine or a grain dryer, or at the output of an auger) will lead to changes in the interrogating EM wave. This will make the antenna-based systems unreliable and hard to deploy in many locations without repeated design changes.

[0007] Prior patents concerned with measurement of the permittivity and moisture content of grain using antennas to transmit an EM wave through a grain sample include:

[0008] Stuart Nelson, Samir Trabelsi, Andrzej Kraszewski. “Method for the simultaneous and independent determination of moisture content and density of particulate materials from radio-frequency permittivity measurements.” US Patent 6,147,503. Nov 14, 2000.

[0009] Samir Trabelsi, Stuart Nelson. “Microwave Sensor and Algorithm for Moisture and Density Determination.” US Patent 8,629,681 B1. Jan 14, 2014.

[0010] Amit Vasant Itagi. “Microwave meter and sensor.” Us Patent 10,094,789 B2. Oct 9, 2018.

[0011] In the non-patent literature, Trabelsi’s group at the USDA published many papers on measuring moisture content of agricultural products using microwave transmission from antennas, including:

[0012] Trabelsi, Samir, Andrzej W. Krazsewski, and Stuart 0. Nelson. "New densityindependent calibration function for microwave sensing of moisture content in particulate materials." IEEE Transactions on Instrumentation and Measurement 47.3 (1998): 613-622.

[0013] Trabelsi, Samir, and Stuart 0. Nelson. "Free-space measurement of dielectric properties of cereal grain and oilseed at microwave frequencies." Measurement Science and Technology 14.5 (2003): 589.

[0014] Nelson, Stuart O., Samir Trabelsi, and Micah A. Lewis. "Microwave sensing of moisture content and bulk density in flowing grain and seed." Transactions of the ASABE 59.2 (2016): 429-433.

[0015] Trabelsi, Samir, Micah A. Lewis, and Stuart 0. Nelson. "Density-independent calibration functions for nondestructive moisture sensing in flowing grain." Journal of Microwave Power and Electromagnetic Energy 53.2 (2019): 69-80.

[0016] Among these, the last two were particularly addressed at measuring moisture content of flowing grain.

[0017] In terms of commercially available equipment that actually measures the moisture content of flowing materials, Applicant is aware of the Brock TrueGrain Moisture Sensor System (https: / / www.brockgrain.com / brock-product / truegrain- moisture-sensor-system / ), which is designed be used with their grain dryers, and appears to use an antenna system.

[0018] Another method of calculating permittivity and moisture content is reliant on capacitive sensors, one example of which is the commercially offered solution from Dryer Master Inc. (https: / / www.dryermaster.com / Real-Time-Moisture-Sensors.htrn). These operate on a very different principle of measurement, the accuracy of which has been the subject of concern from some farmers and grain handlers.

[0019] Accordingly, there remains a need for effective means of accurately measuring the permittivity and moisture content of flowing granular substances.

[0020] SUMMARY OF THE INVENTION

[0021] According to a first aspect of the invention, there is provided a device for measuring at least one variable property of a granular material, said device comprising: a transverse electromagnetic (TEM) cell comprising: a metallic housing having terminal ends of opposing and spaced apart relation to one another in an axial direction, and tapered end regions of respectively adjacency to said terminal ends, and comprising first and second metallic sidewall structures of opposing and spaced apart relationship to another in a width direction transverse relation to said axial direction, said two metallic sidewall structures, at the tapered end regions, having an angularly convergent relationship to one another in axially outward directions toward the terminal ends of the metallic housing and each being tapered in height in said axially outward directions; two connectors respectively installed at the two terminal ends of the metallic housing; and a center conductor mounted to the metallic housing in insulated relation thereto in a position residing between said metallic sidewall structures and spanning, connectively, between the two connectors, said center conductor also being tapered in height in said axially outward directions at the tapered end regions of the metallic housing; two non-conductive chamber walls that span between the two metallic sidewall structures in the width direction, in spaced-apart relation to one another in the axial direction, in positions of respective proximity to the tapered end regions of the metallic housing; a measurement chamber that is delimited between the two non- conductive chamber walls and the two metallic sidewall structures, occupies only a nontapered mid-region of the housing between the two tapered end regions thereof, and is bisected by the center conductor; and at least one opening of communicative relation to the measurement chamber to enable admission thereto of the granular material.

[0022] According to a second aspect of the invention, there is provided a device for measuring at least one variable property of a granular material, said device comprising: a transverse electromagnetic (TEM) cell having a measurement chamber delimited between two sidewall structures of the TEM cell at a non-tapered mid-region of the TEM cell that resides between two tapered-end regions thereof at which: sidewall structures of said TEM cell are of angularly convergent relationship to one another in axially outward directions toward opposing ends of the TEM cell; said sidewall structures of said TEM cell are tapered in height in said axially outward directions; and a center conductor of said TEM cell is also tapered in height in said axially outward directions; and at least one of the following: an inlet duct attached to the cell in a position of communicative relationship to the measurement chamber and arranged for introduction thereto of the granular material from a source of said granular material situated upstream of the TEM cell and the inlet duct; and / or an outlet duct attached to the cell in a position of communicative relationship to the measurement chamber and arranged for discharge therefrom of the granular material to a destination situated downstream of the TEM cell and the outlet duct.

[0023] According to a third aspect of the invention, there is provided a method of measuring at least one variable property of a granular material, said method comprising:

[0024] (a) using a transverse electromagnetic (TEM) cell, generating an electromagnetic wave in said TEM cell and propagating said electromagnetic wave through a measurement chamber of said TEM cell during moving flow of said granular material through the measurement chamber and thereby propagating said electromagnetic wave through said moving flow of the granular material.; and

[0025] (b) using output signal measurements from the TEM cell to perform calculated measurement of said at least one variable property of the granular material. DESCRIPTION OF THE DRAWINGS

[0026] Preferred embodiments of the invention will now be described in conjunction with the accompanying drawings in which:

[0027] Figure 1 is a schematic diagram illustrative of well known electromagnetic theory concerning propagation of waves through materials of different characteristic parameters, as introductory explanation to working principles of the present invention.

[0028] Figure 2 is a schematic diagram of a prior art apparatus that uses a plane wave model too measure grain moisture in a static test volume of grain.

[0029] Figures 3A and 3B are prior art plots of the imaginary versus real components of grain permittivity, of which the former plot shows of raw values and the latter plot is normalized by density, and demonstrates a linear relationship.

[0030] Figure 4 is a prior art plot of loss tangent vs moisture content, illustrating increase of the former with increase of the latter

[0031] Figure 5 is a prior art plot of the square root of a final computed parameter, zeta, derived by the prior art technique, illustrating a near linear fit of this parameter when plotted against moisture content.

[0032] Figure 6 is a front elevational view of an inventively configured transverse electromagnetic (TEM) cell of the present invention for novel use in measurement of at least one variable property of a flowing granular material, with a housing sidewall of the TEM cell partially cut away to reveal an internal measurement chamber thereof.

[0033] Figure 7 is a top plan view of the TEM cell of Figure 6.

[0034] Figure 8 is a front elevational view of the TEM cell of Figures 5 and 6 connected to a signal generator and RF measurement device, embodied together in a vector network analyzer (VNA) in this example, to cooperatively form a working measurement apparatus for said measurement of a flowing granular material.

[0035] DETAILED DESCRIPTION

[0036] Background Electromagnetic Theory

[0037] To first provide the reader with useful background to the operating principles of the disclosed invention of the present application, a summary is first given of general knowledge in the technical field of endeavour is given, of which there are many textbook sources, among which selection has been made to reference Microwave Radar and Radiometric Remote Sensing, by lllaby and Long. A starting assumption is to frame the understanding in the context of plane waves (waves whose wavefront is a flat surface). Most of the time, an actual electromagnetic wave is not truly planar, but this assumption is still made as it greatly simplifies the math. Typically, only very far away from radiating sources can one approximate the wavefront as a plane. For this specific case, consideration is made of the setup schematically shown in Figure 1 , in which a wave in free space (air) transmits through a rectangular slab of different material, and then back into air. Each material will have characteristic parameters that describe how waves travel through the material. In this case, assumption is made that the permeability p is constant in all materials, and the complex permittivity £ = s’ - js” describes the wave transmission (j is the complex value V^T). The s in air is equal to (or very close to 1 ), and the goal, in the context of grain moisture measurement, is to recover the s of the grain. In materials other than air, the complex-valued epsilon will depend on the temperature, moisture, material, etc.

[0038] For a single interface of two materials, with material parameters e1and e2, when the incoming wave impinges on a material of different permittivity, some of that wave will reflect, and some of that wave will transmit through the material, depending on the similarity of the material to air. For plane waves at normal incidence, this is described as:

[0039] Reflection coefficient: p

[0040] Transmission coefficient: where the reflection coefficient is the ratio of the reflected electric field to the incident field, and the transmission coefficient is the ratio of the transmitted electric field to the incident electric field.

[0041] However, to build a sensing system for grain moisture, we need to deal with two interfaces (air / grain, then grain / air, see Fig. 1 above). In this case, there will be multiple reflections inside of the center material. When considering the total transmission through the system, and assuming that there is air on either side of the grain bulk (so that the transmission / reflection at all interfaces is the same) the total transmission and reflection is: p + pe~2Y2dPtotal =1 + p2e-2Y2d whereois the wavelength in free space, d is the length of the grain bulk, p is the reflection coefficient from the air / grain interface and y2is the wavenumber in the material to be measured (i.e. grain). To measure the moisture content of grain, the grain’s permittivity must be known. By using the three equations above and measuring either the reflection coefficient or transmission coefficient, it is possible to work back to get y2, and therefore E2. However, the equations for reflection and transmission are non-linear in y2. This means that going from measurements of the reflection / transmission coefficients to permittivity estimates can be extremely sensitive to noise in the measurements (and different methods of finding y2can give different results).

[0042] Regarding the determination of E2from measurements of the reflection and transmission coefficient (p and T), one method to go straight to E2is the Nicolson- Ross-Weir Method [see Nicolson, A. M.; Ross, G. F. (November 1970). "Measurement of the intrinsic properties of materials by time-domain techniques". IEEE Transactions on Instrumentation and Measurement. 19 (4): 377-382] and [Weir, W. B. (January 1974). "Automatic measurement of complex dielectric constant and permeability at microwave frequencies". Proceedings of the IEEE. 62 (1 ): 33-36] that directly goes from measurements of reflection and transmission to permittivity. In attempted implementation of this method by the present inventors, the output was extremely unstable and did not give accurate results. It is believed that when experimental results are taken, the reflection sensitivity is bad, leaving to inaccurate calculations.

[0043] The present inventors instead employed a brute force optimization that only uses the transmission coefficient. Calculation of Ttotai was made using varying real and imaginary components of s2= s’ - js”, and then comparison of the measured transmission (which has an amplitude and phase) to the theoretical solution that matches most closely. To the best of the inventors’ knowledge, prior use of this technique, applied from the perspective of general optimization, rather than attempting to find an exact formulation, has not been made by others. One consideration to be made is that the measurement technique usually doesn’t produce the exact ideal wave expected by the theory, so the experimental measurement is done by subtracting off the measurement with the unknown material (grain) absent from the measurement chamber.

[0044] Once the complex-valued permittivity of the grain (e2) has been measured, the next step is to convert that permittivity to a moisture content. For measuring the moisture content of grain, the most accurate method is to measure a sample of known mass, dry it out in an oven over a set amount of time (e.g. 24 hours at 135 degrees F) to remove the moisture (i.e. to desiccate the grain), and then compare the mass again. This is extremely time and resource intensive, so for more than 100 years, grain handlers have used alternative systems that are ultimately calibrated to the oven-drying method. There are links between the permittivity (which is a purely electromagnetic property) and moisture content (MC), and permittivity is much faster to measure. Grain moisture measurement systems thus use measurements of the bulk permittivity to get to the moisture content. There are decades of work in using permittivity measurements this way, see, e.g., [Stuart Nelson, Dielectric Properties of Agricultural Materials and their Applications, Elsevier, 2015],

[0045] However, for grain, the bulk permittivity is a function of the moisture content, the temperature, and (critically) the density. Temperature compensation is usually done by having a temperature sensor in the grain moisture sensor, then using known measurements of various grain types to compensate the change in bulk permittivity by temperature. Temperature compensation is relatively simple. With respect to density, as the grain is packed more densely, there is more grain (less air) per unit volume, and thus the permittivity goes up. Density is more difficult to compensate for because (a) the permittivity is highly sensitive to the density, and (b) measuring density requires a weight scale, as well as a very accurate volume measurement. The need to accurately know the bulk density of the grain has meant that few, at best, flow-through grain moisture meters has been produced commercially. If the grain is moving, one cannot accurately measure the density.

[0046] To deal with problem of density in grain moisture measurement, there was work done in the late 1990’s and early 2000’s to find a density-independent method to measure the moisture content of grain via electromagnetic measurements. Work from Trabelsi’s group claims that they created a density-independent method to convert permittivity measurements to MC. Some relevant references in this particular area of endeavour are identified as follows: Trabelsi, Samir, Andrzej W. Krazsewski, and Stuart 0. Nelson. "New density-independent calibration function for microwave sensing of moisture content in particulate materials." IEEE Transactions on Instrumentation and Measurement 47.3 (1998): 613-622.

[0047] Kraszewski, A. W., S. Trabelsi, and S. 0. Nelson. "Wheat permittivity measurements in free space." Journal of microwave power and electromagnetic energy 31.3 (1996): 135-141 .

[0048] Nelson, Stuart 0., Samir Trabelsi, and Micah A. Lewis. "Microwave sensing of moisture content and bulk density in flowing grain and seed." Transactions of the ASABE 59.2 (2016): 429-433.

[0049] Trabelsi, Samir, Micah A. Lewis, and Stuart 0. Nelson. "Densityindependent calibration functions for nondestructive moisture sensing in flowing grain." Journal of Microwave Power and Electromagnetic Energy 53.2 (2019): 69-80.

[0050] Stuart Nelson, Samir Trabelsi, Andrzej Kraszewski. “Method for the simultaneous and independent determination of moisture content and density of particulate materials from radio-frequency permittivity measurements.” US Patent 6,147,503. Nov 14, 2000.

[0051] Samir Trabelsi, Stuart Nelson. “Microwave Sensor and Algorithm for Moisture and Density Determination.” US Patent 8,629,681 B1. Jan 14, 2014.

[0052] To collect data in this prior work, two horn antennas were used with a polyethylene sample holder placed between them to hold the grain, as presently shown in Figure 2 hereof. The plane wave model referenced above was used (despite its poor approximation, as remarked upon further below).

[0053] In the above listed series of papers, the authors had their own method of calculating the permittivity of each sample based upon the assumption that the material has a low amount of loss, in contrast to the present inventors’ employed method of going from reflection / transmission measurements to permittivity. Their key observation regarding density independence measurement was that if the real and imaginary component of permittivity are normalized by the density (at least for the frequencies they looked at in the ~11 -18 GHz range), it forms a near linear relationship. This is exemplified in Fig 3 hereof, taken from the 1998 paper cited above. The left plot of Figure 3 is the raw data of s’ and E” which is rather scattered (as density changes for each dot). On the right of the figure, both s’ and E” are normalized by density, and the relationship between s’ and E” becomes linear. Therefore, once the linear parameters are estimated, the density can be estimated based on the measured permittivity data. e"

[0054] To calculate the moisture content, they used the loss tangent, tan 8 = — .

[0055] The loss tangent is commonly used to present the loss how lossy a material. As higher moisture has more water in it, it makes sense that the loss tangent will increase with moisture. It should be noted that tan <5 changes proportional to MC2, which is an empirical observation made by Nelson and Trabelsi. Thus, later a square root of the final parameter was taken, with the resultant data presented in the manner presently shown in Fig. 4 hereof. Considering the loss tangent., it seems to follow the MC2trend, but there is a lot of variation. They claimed this is improved by dividing the loss tangent by the density (and as they estimated the density based on just the permittivity values, this does not require any other measurements). To jump to the end, their reported results comparing their final computed parameter zeta with the MC is presently shown in Fig. 5 hereof. There were a few other steps involved, but the plotted < of Fig. 5 is basically proportional to the loss tangent divided by their estimated density. Performing this calculation on the loss tangent and taking the square root, provided a near-linear fit of the data. At this point, the prior work had achieved a device and method that does measure the moisture content of grain in a stationary state thereof. To measure flowing grain, the method is essentially the same, except as the grain is moving and bouncing around, the density will be lower as there is more space between the kernels. For this reason, the density independence is important. Of the Trabelsi’s group publications cited above, the 2019 publication particularly refers to non-destructive moisture sensing in flowing grain.

[0056] In notable distinction from the present invention, the prior methods documented above for background reference all rely upon two antennas to generate the raw electromagnetic signal to be analyzed.

[0057] The Present Invention

[0058] The present invention notably departs from the prior art in the manner in which the permittivity is measured. Instead of two antennas, a singular Transverse Electromagnetic (TEM) cell is used to generate the electromagnetic wave. In the inventive methodology, the TEM cell generates a Transverse Electric wave, which inside the cell, is a plane wave. The existing methods documented above instead use two antennas to generate the electromagnetic wave. The two-antenna method does not generate a plane wave - the near-field of antennas generate waves very far from the assumptions made about the wave propagation. And these assumptions are key to the accuracy of the final moisture result.

[0059] As will be known to those skilled in the art of electromagnetics, a TEM cell is a metallic chamber with a center conductor and dimensioned such that a plane wave with specific properties propagates through it, which in this case, is a plane wave with known impedance. A TEM cell is a generalization of a coaxial cable. With reference to Figures 6 and 7, initial description is first given of the general construction and geometry of shared by both a conventional TEM cell and the uniquely modified TEM cell employed in the present invention, followed by description of those unique modifications by which the TEM is adapted to its presently intended and inventive purpose.

[0060] The TEM cell 10 features a metallic housing 12 having terminal ends 12A, 12B of opposing and spaced apart relation to one another in an axial direction denoted schematically in the figures by a longitudinal reference axis L. The housing 12 has tapered end regions 14A, 14B of respectively adjacency to said terminal ends 12A, 12B, and a non-tapered mid-region 14C of centrally intervening relationship to the two tapered end regions, which are symmetrically disposed at opposing ends of this nontapered mid-region 14C. The housing 12 features first and second metallic sidewall structures 16A, 16B of opposing and spaced apart relationship to another in a width direction of perpendicularly transverse relation to the axial direction, and denoted schematically in the figures by a transverse reference axis T. The two metallic sidewall structures 16A, 16B, at the tapered end regions 14A, 14B of the housing 12, have an angularly convergent relationship to one another in the widthwise dimension of the cell as they span axially outward toward the terminal ends 12A, 12B of the metallic housing. In contrast, the two metallic sidewall structures 16A, 16B are parallel to one another at the non-tapered mid-region 14C of the housing 12. At the tapered end regions 14A, 14B of housing 12, each of the two metallic sidewall structures is also tapered in height in the axially outward direction. In the illustrated orientation of the TEM cell 10, the height dimension of each metallic sidewall structure 16A, 16B is a vertically measured dimension thereof, and the widthwise convergency of the metallic sidewall structure 16A, 16B at the tapered end regions 14A, 14B of the housing 12 is a horizontal convergency. More generally, the height dimension may be defined as that which is orthogonal to the axial and width directions of the cell, regardless of the orientation in which the TEM cell resides at any given time.

[0061] The two sidewall structures 16A, 16B are of matching shape to one another, and reside in symmetrically mirrored positions and orientations across a longitudinal midplane that longitudinally bisects the TEM cell in parallel relationship to the parallel walls 18A, 18B possessed the two sidewall structures 16A, 16B at the untampered mid-region 14C of the cell. This same longitudinal midplane is occupied by a center conductor 20 of the of the TEM cell 10 that is insulated from the two metallic sidewall structures 16A, 16B and resides parallel to, and midway between, the two parallel walls 18A, 18B of the sidewall structures 16A, 16B of the housing 12 and runs longitudinally from one terminal end 12A of the housing 12 to the other 12B. Like the two sidewall structures 16A, 16B, the center conductor is also tapered in width in the axially outward directions at the tapered end regions 14A, 14B of the metallic housing 12. Two cable connectors 22A, 22B are respectively installed at the two terminal ends of the metallic housing in coupled relationship to the center conductor 20 at respective ends thereof, whereby the center conductor spans longitudinally between, and interconnects, the two cable connectors 22A, 22B.

[0062] Having described the componentry and geometry of the inventive TEM cell 10 that is shared by a conventional TEM cell, attention is now given to the unique modification of the inventive TEM cell 10 for its inventive purpose measuring the permittivity of a flowing granular substance (such as, but not limited to, grain). To the conventional TEM cell structure, there are added two non-conductive chamber walls 24A, 24B that span between the two metallic sidewall structures in the width direction at the parallel walls 18A, 18B of the non-tapered mid-region 14C of the housing 12. The chamber walls 24A, 24B reside in spaced-apart relation to one another in the axial direction, in positions of respective proximity to the two tapered end regions 14A, 14B of the metallic housing 12. The chamber walls 24A, 24B are parallel to one another, and perpendicular to the two parallel walls 18A, 18B of the sidewall structures 16A, 16B. The two parallel walls 18A, 18B of the sidewall structures 16A, 16B and the two chamber walls 24A, 24B thus cooperatively delimit a rectangular sub-compartment of the housing’s interior, which sub-compartment is referred to herein as a measurement chamber 26, as it is this part of the TEM cell through which grain (or other flowable granular material) is passed for measurement of its permittivity, and ultimate deprival of its moisture content therefrom. The two chamber walls 24A, 24B, and the measurement chamber 26 delimited therebetween, are all longitudinally bisected by the center conductor 20 at the longitudinal midplane of the TEM cell 10, which passes longitudinally through the two widthwise chamber walls 24A, 24B.

[0063] The measurement chamber 26is open at two ends thereof of opposing relationship in the same aforementioned directionality (vertical, in the illustrated cell orientation) in which the heights of the sidewall structures 16A, 16B are measured, whereby the opening at one end (the top end 26A, in the illustrated cell orientation) serves as an inlet through which grain (or other granular substance) is admissible to the measurement chamber 26, and the opening at the other opposing end (the bottom end 26B, in the illustrated cell orientation) serves as an outlet from which the admitted grain is evacuable from the measurement chamber 26. By having two such openings for respectively dedicated admission and evacuation of the grain at opposing ends of the measurement chamber, this preferred embodiment is particularly well adapted to measurement of flowing of grain dynamically passing through the measurement chamber, though an otherwise equivalent setup with only one opening could be used for measurement of a static volume of grain. The illustrated orientation of the TEM cell 10 with its measurement chamber of open character at opposing top and bottom ends is one in which the flowing grain passes vertically through the TEM cell, denoting a typical application where the TEM’s is installed at a location in which the grain falls gravitationally through the TEM cell, though other TEM cell orientations reliant on another type of aided grain flow may also be possible.

[0064] In achievement of a fully workable measurement apparatus capable of taking measurements with the inventively modified TEM cell 10, the TEM cell 10 is accompanied by a signal generator 30 by which the center conductor is excitable by an input signal to generate an electromagnetic wave moving axially through the measurement chamber, and a radio-frequency (RF) measurement device 32 operable to measure one or more wave parameters of an output signal outputted from the TEM cell 10 in responsive relation to excitation of the center electrode 20 thereof. In the illustrated example, representative of an experimental prototype of the present invention, the signal generator 30 and RF measurement device 32 are commonly embodied together in a Vector Network Analyzer (VNA), but in other embodiments may instead be embodied using discrete electronic components in a manner that will be understood by those of ordinary skill in the art. The input signal from the signal generator is fed to one of the cable connectors 12A through a microwave transmission line 28A, which particular cable connector 12A and transmission line are therefore referred to as the input connector 12A and input transmission line 28A respectively. The output signal is collected from the other cable connector 12B by another microwave transmission line 28B and fed thereby to the RF measurement device 32 for measurement of the one or more wave parameters of the output signal.

[0065] The RF measurement device 32 is communicatively connected to a data processing device 34 configured to calculate at least one variable property of the grain (or other granular material) from the one or more wave parameters, the at least one variable property most typically being at least the permittivity thereof, from which one or more other variable properties can be derived, which in the grain moisture measurement context includes at least the moisture content of the granular material. Before measurement of any granular material, a background measurement is first taken with the measurement chamber in an empty state void of any granular material, which background measurement is saved in memory of the data processing device 34 for subtraction of this background measurement from each actual test measurement taken in the presence of the granular material being measured, which thereby isolates the output signal change from the TEM cell that is attributable to the presence of the granular material being measured. The resultant measurement derived from such background-correction is compared, by the data processing device, against a stored computer model of the signal change based upon Electromagnetic theory and the dimensions of the measurement chamber, from which the data processing device calculate the permittivity of the granular substance. A singular measurement can be taken of a static sample of the granular material (with the outlet opening of the TEM cell closed off), or continually ongoing measurements can be taken of a moving stream of the granular material continuously flowing through the measurement chamber. The method of converting permittivity to moisture content is publicly available, and well known to those of skill in the art, and need not be described here.

[0066] The data processing device may be any computationally capable device having one or more processors, non-transitory computer readable memory coupled thereto, and executable software embodied in computer readable statements and instructions stored in said non-transitory computer readable memory for execution by the one or more processors to execute the processes described herein. Typically, the data processing device will include, or be connected to, a display device 34A for visible readout of at least one of the one or more calculated material properties of the granular material (e.g. the moisture content thereof, in the illustrated example of Fig. 8) of by any on-site user at the location where the measurement is taken place, but will also log the resultant measurement data for reporting and / or archival purposes, whether locally in the same or another non-transitory computer readable memory of the data processing device, or by transmission over one or more communications networks to one or more remotely situated computing devices, which may collect resultant data from a plurality of the TEM cell measurement apparatuses.

[0067] For energization of the center conductor 20 of the TEM cell 10, the input signal from the signal generator preferably has a frequency between one and twenty gigahertz (GHz), more preferably between three and fourteen GHz, and even more preferably between four and ten GHz. Unless explicitly stated otherwise, each range recited herein is an inclusive of the stated end values of the range.

[0068] The illustrated embodiment of the inventively modified TEM cell 10 in Figures 6 to 8 is representative of a testbench prototype whose chamber walls 24A, 24B project externally beyond the interior bounds of the housing 12, and that incorporate a set of mounting feet 32A, 32B at externally situated bottom ends of the those chamber walls 24A, 24B for bolted or otherwise fastened or affixed attachment to an underlying supportive structure, in this case a benchtop of an experimental lab environment in which the invention was tested. It will be appreciated that in commercial application, the TEM cell 10 may be incorporated into various equipment, machinery and systems involving a moving stream of granular material, and may therefore rely on alternative supportive means of the housing 12. Figure 9 schematically illustrates incorporation of the TEM cell 10 into a mid-stream application, where the inlet opening of the measurement chamber 26 at the top end 26A thereof is fed by an inlet duct 34A and the outlet opening of the measurement chamber 26 at the bottom end 26B thereof feeds into an outlet duct 34B, among which each duct is attached to, or otherwise held in adjacent relationship with, the housing 12 of the TEM cell 14 in aligned relationship with the internal measurement chamber 26 thereof.

[0069] Since various modifications can be made in the invention as herein above described, and many apparently widely different embodiments of same made, it is intended that all matter contained in the accompanying specification shall be interpreted as illustrative only and not in a limiting sense.

Claims

1. CLAIMS:1 . A device for measuring at least one variable property of a granular material, said device comprising: a transverse electromagnetic (TEM) cell comprising: a metallic housing having terminal ends of opposing and spaced apart relation to one another in an axial direction, and tapered end regions of respectively adjacency to said terminal ends, and comprising first and second metallic sidewall structures of opposing and spaced apart relationship to another in a width direction transverse relation to said axial direction, said two metallic sidewall structures, at the tapered end regions, having an angularly convergent relationship to one another in axially outward directions toward the terminal ends of the metallic housing and each being tapered in height in said axially outward directions; two connectors respectively installed at the two terminal ends of the metallic housing; and a center conductor mounted to the metallic housing in insulated relation thereto in a position residing between said metallic sidewall structures and spanning, connectively, between the two connectors, said center conductor also being tapered in height in said axially outward directions at the tapered end regions of the metallic housing; two non-conductive chamber walls that span between the two metallic sidewall structures in the width direction, in spaced-apart relation to one another in the axial direction, in positions of respective proximity to the tapered end regions of the metallic housing; a measurement chamber that is delimited between the two non- conductive chamber walls and the two metallic sidewall structures, occupies only a non-tapered mid-region of the housing between the two tapered end regions thereof, and is bisected by the center conductor; and at least one opening of communicative relation to the measurement chamber to enable admission thereto of the granular material.

2. The apparatus of claim 1 wherein said at least one opening comprises inlet and outlet openings situated across the measurement chamber from one another in a flow direction transverse to both said axial and width directions to enable flow of the granular material through the measurement chamber in said flow direction.

3. The apparatus of claim 1 or 2 wherein the two connectors comprise an input connector connected to a signal generator by which the center conductor is excitable by an input signal to generate an electromagnetic wave moving axially through the measurement chamber.

4. The apparatus of claim 3 in combination with said signal generator, wherein said signal generator is configured to generate said input signal at a frequency measuring between one and twenty gigahertz, inclusive.

5. The apparatus of claim 3 in combination with said signal generator, wherein said signal generator is configured to generate said input signal at a frequency measuring between three and fourteen gigahertz, inclusive.

6. The apparatus of claim 3 in combination with said signal generator, wherein said signal generator is configured to generate said input signal at a frequency measuring between four and ten gigahertz, inclusive.

7. The apparatus of any one of claims 3 to 6 wherein the two connectors further comprise an output connector connected to a radio frequency (RF) measurement device operable to measure one or more wave parameters of an output signal outputted from the output connector in responsive relation to excitation of thecenter electrode, for use in calculation of the variable property of the granular material from said one or more wave parameters.

8. The apparatus of claim 7 wherein said one or more wave parameters comprise magnitude and phase of the output signal.

9. The apparatus of claim 7 or 8 wherein said RF measurement device is communicatively connected to a data processing device configured to calculate said at least one variable property of the granular material from the one or more wave parameters.

10. The apparatus of claim 9 wherein said at least one variable property comprises a permittivity of the granular material.

11. The apparatus of claim 9 or 10 wherein said at least one variable property comprises a moisture content of the granular material.

12. The apparatus of any one of claims 9 to 11 wherein said data processing device is further configured to perform at least one of the following operations:(a) logging of resultant variable property measurement data calculated by said data processing device; and / or(b) displaying of said resultant variable property measurement data on a display device connected to said data processing device.

13. The apparatus of any preceding claim further comprising an inlet duct attached to the TEM cell in a position of communicative relationship to the measurement chamber and arranged for introduction thereto of the granular material from a source of said granular material situated upstream of the TEM cell and the inlet duct.

14. The apparatus of any preceding claim further comprising an outletduct attached to the cell in a position of communicative relationship to the measurement chamber and arranged for discharge therefrom of the granular material to a destination situated downstream of the TEM cell and the outlet duct.

15. A device for measuring at least one variable property of a granular material, said device comprising: a transverse electromagnetic (TEM) cell having a measurement chamber delimited between two sidewall structures of the TEM cell at a non-tapered mid-region of the TEM cell that resides between two tapered-end regions thereof at which: sidewall structures of said TEM cell are of angularly convergent relationship to one another in axially outward directions toward opposing ends of the TEM cell; said sidewall structures of said TEM cell are tapered in height in said axially outward directions; and a center conductor of said TEM cell is also tapered in height in said axially outward directions; and at least one of the following: an inlet duct attached to the cell in a position of communicative relationship to the measurement chamber and arranged for introduction thereto of the granular material from a source of said granular material situated upstream of the TEM cell and the inlet duct; and / or an outlet duct attached to the cell in a position of communicative relationship to the measurement chamber and arranged for discharge therefrom of the granular material to a destination situated downstream of the TEM cell and the outlet duct.

16. The device of claim 15 comprising at least said inlet duct.

17. The device of claim 15 or 16 comprising at least said outlet duct.

18. The device of claim 15 comprising both said inlet duct and said outlet duct.

19. A method of using the device of any preceding claim comprising, during occupation of the measurement chamber by said granular material, exciting the TEM cell to generate an electromagnetic wave therein and thereby propagate said electromagnetic wave through said granular material in the measurement chamber, and using output signal measurements from the TEM cell to perform calculated measurement of said at least one variable property of the granular material.

20. The method of claim 19 comprising exciting the TEM cell during moving flow of said granular material through the measurement chamber and thereby propagating said electromagnetic wave through said moving flow of the granular material.

21. A method of measuring at least one variable property of a granular material, said method comprising:(a) using a transverse electromagnetic (TEM) cell, generating an electromagnetic wave in said TEM cell and propagating said electromagnetic wave through a measurement chamber of said TEM cell during moving flow of said granular material through the measurement chamber and thereby propagating said electromagnetic wave through said moving flow of the granular material.; and(b) using output signal measurements from the TEM cell to perform calculated measurement of said at least one variable property of the granular material.

22. The method of any one of claims 19 to 21 comprising exciting the TEM cell with an input signal having a frequency between one and twenty gigahertz, inclusive.

23. The method of any one of claims 19 to 21 comprising exciting the TEM cell with an input signal having a frequency between three and fourteen gigahertz, inclusive.

24. The apparatus of any one of claims 19 to 21 comprising exciting the TEM cell with an input signal having a frequency between four and ten gigahertz, inclusive.

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