Capacitive sensor

A capacitive sensor system for detecting an object. The capacitive sensing system includes a capacitive sensing pad, a conductive discriminating pad, a switch, a capacitance measurement circuit and a controller. The conductive discriminating pad is in proximity to the capacitive sensing pad. The switch includes an input terminal coupled to the discriminating pad. The switch selectively couples the discriminating pad to a voltage potential of the capacitive sensing pad or to a ground potential. The capacitance measurement circuit detects a capacitance value of the capacitive sensing pad. The controller is operable to measure the capacitance value of the capacitive sensing pad when the discriminating pad is coupled to the capacitive sensing pad voltage potential or to the ground potential.

CROSS-REFERENCE TO RELATED APPLICATION

FIELD OF TECHNOLOGY

The present application relates to a capacitive proximity sensor, in particular, capacitive sensors for proximity sensing and discrimination.

BACKGROUND

Existing capacitive sensors have no or limited ability to distinguish between different types of objects or substances.

SUMMARY

According to an embodiment of a capacitive sensing system for detecting an object, the capacitive sensing system includes a capacitive sensing pad, a conductive discriminating pad, a switch, a capacitance measurement circuit and a controller. The conductive discriminating pad is in proximity to the capacitive sensing pad. The switch includes an input terminal coupled to the discriminating pad. The switch selectively couples the discriminating pad to a voltage potential of the capacitive sensing pad or to a ground potential. The capacitance measurement circuit detects a capacitance value of the capacitive sensing pad. The controller is operable to measure the capacitance value of the capacitive sensing pad when the discriminating pad is coupled to the capacitive sensing pad voltage potential or to the ground potential. The capacitive measurements taken provide data about the properties of the object. This data can be used to identify, and/or distinguish between, different objects, materials or liquids.

According to a method of identifying an object or substance, the method includes providing a capacitive sensing pad and n conductive discriminating pads where n≥1, providing a shield driver that provides a voltage potential of the capacitive sensing pad, and providing n switches that each have an input terminal coupled to one of the n discriminating pads and have two switch connection states which selectively couple the input terminal to the capacitive sensing pad voltage potential or to the ground potential, wherein the n switches are operable to provide 2nunique connection states for the n discriminating pads. The method includes placing the object in proximity to the capacitive sensing pad. The method includes measuring up to 2ncapacitance values of the capacitive sensing pad that each correspond to one of the 2nunique connection states for the n discriminating pads. The method includes determining a capacitance value for the object or substance by comparing a first set of the 2ncapacitance values and a second set of the 2ncapacitance values. The method includes identifying the object or substance by comparing the capacitance value to one or more reference capacitance values for reference objects or substances having the same and/or different material properties as the object or sub stance.

According to an embodiment of a method of identifying an object or substance, the method includes providing a capacitive sensing pad and n conductive discriminating pads where n≥1, providing a shield driver that provides a voltage potential of the capacitive sensing pad, and providing n switches that each have an input terminal coupled to one of the n discriminating pads and have two switch connection states which selectively couple the input terminal to the capacitive sensing pad voltage potential or to the ground potential, where the n switches are operable to provide 2nunique connection states for the n discriminating pads. The method includes placing the object or substance in proximity to the capacitive sensing pad. The method includes taking capacitive measurement sets of the object or substance, where each measurement set corresponds to 2ncapacitance values measured using the capacitive sensing pad for the 2nunique connection states for the n discriminating pads. The method includes determining a mathematical relationship between the capacitive measurement sets and known dielectric constants or dipole moments of the object or substance. The method includes identifying the object or substance based on the mathematical relationship and the known dielectric constants or dipole moments of the object or substance.

DETAILED DESCRIPTION

FIG. 1illustrates an embodiment of a system100which includes a sensor measurement system102and a sensing pad unit126. Sensor measurement system102includes a control unit112, a capacitive to digital sensor114, a shield driver116, a single-pole double-throw switch118and a second single-pole double-throw switch122. Sensing pad unit126includes a capacitive sensing pad128, a proximate discriminating pad130, a second proximate discriminating pad132and a shield134. A proximate object or substance136is illustrated in proximity to t sensing pad unit126. The capacitive to digital sensor114is connected via conductive line162to the capacitive sensing pad128, and is connected via conductive line170to the input of the shield driver116. The inputs146and154of the respective switches118and122are controlled by the control unit112. The output of the shield driver116is connected to the shield pad134via conductive line164.

In the illustrated embodiment, control unit112is a micro-controller or micro-controller unit (MCU). In different embodiments, the control unit112and the capacitive to digital sensor114may be separate integrated circuit chips or they may be incorporated into the same integrated circuit chip. Furthermore, in different embodiments, shield driver116and the capacitive to digital sensor114may be separate integrated circuit chips or they may be incorporated into the same integrated circuit chip.

The control unit112uses methods of digital interfacing to control the functioning of the capacitive to digital sensor114. If the control unit112and the capacitive to digital sensor114are separate physical chips then these interface methods can include, but are not limited to, I2C (also known as Inter-Integrated Circuit) and SPI (also known as Serial Peripheral Interface). In the illustrated embodiment, capacitive to digital sensor114is coupled to communication interface140via multiwire conductive lines172. The connection to communication interface140can be I2C (2 wire), SPI (4 wire) or can be another suitable type of connection.

In the illustrated embodiment, the capacitance sensing pad128, the discriminating pads130and132, and shield pad134, are constructed of conductive materials such as metals. By way of example, this can include a printed circuit board, a flex-PCB, copper tape, or conductive cloth, but can also be any other conductive substance.

In the illustrated embodiment, shield driver116is electrically connected to shield pad134via conductive line164, and shield driver116drives shield pad134to the same voltage potential as capacitive sensing pad128. Therefore, there is no electric field between the capacitive sensing pad128and the shield pad134. Consequently, any capacitive effect of a material behind the shield pad134on a capacitance measurement by capacitance to digital sensor114is nullified. In usage, the shield pad134is used to provide directional sensitivity to the capacitive sensing pad128and to limit the capacitive effects of material behind the shield pad134. In the illustrated embodiment, the shield pad134is placed in close proximity to the capacitive sensing pad128, typically a distance of a few tenths of a millimeter up to a few millimeters. In other embodiments, other suitable spacing can be used.

In various embodiments, shield pad134may have a separate physical construction than the capacitive sensing pad128and the discriminating pads130and132, or shield pad134can be within the substrate of capacitive sensing pad128, and discriminating pads130and132, such as with a multilayer printed circuit board.

The size and shape of the capacitive sensing pad128and the discriminating pads130and132will depend on the particular application. For example, if it is necessary that the capacitive sensing pad128be sensitive to distant objects such as a proximate object or substance136that is spaced apart from capacitive sensing pad128by a large distance, then the capacitive sensing pad128should be larger than a capacitive sensing pad128designed for sensitivity to closer objects such as a proximate object or substance136that is spaced apart from capacitive sensing pad128by a distance that is less than the large distance.

In the illustrated embodiment, with regard to the switches118and122, switches118and122may be a solid state type switch. In the illustrated embodiment, switches118and122are controlled via a digital interface from control unit112, and this interface can be an Input/Output (I/O) line set to either a digital high (H) or a digital low (L). In other embodiments, other suitable ways to control switches118and122may be used.

In the illustrated embodiment, the input terminal146of the first switch118is electrically connected to I/O terminal142of the control unit112via conductive line174. The common node148of the first switch118is electrically connected to the first discriminating pad130via conductive line166. One output terminal150of the first switch118is connected to a ground potential at120, and the other output terminal152is connected to the output of the shield driver116via conductive line164. The input terminal154of the second switch122is electrically connected to I/O terminal144of the control unit112via conductive line176. The common node156of the switch122is connected to the second discriminating pad132via conductive line168. One output terminal158of the switch122is connected to a ground potential at124, the other output terminal160is connected to the output of the shield driver116via conductive line164.

The switches118and122are controlled by control unit112and control unit112can set the input terminals146and154of respective switches118and122to the appropriate value of H or L. It is understood that the specifics of this will depend on the chosen implementation of the switches118and122, and that the order of the switching is not important to the method.

If we write in shorthand {X,Y} where X and Y represent the connection state of the first switch118and the second switch122respectively, where the connection state can take the values of either “S” or “G” which representing the state when the first switch118or the second switch122connects respectively the first discriminating pad130or the second discriminating pad132to either the output of the shield driver116via conductive line164(“S”), or to respective ground connections120and124(“G”). Then the possible measurement configurations can be written as: measurement A: {S, S}; measurement B: {G, G}; measurement C: {S, G}; measurement D: {G, S}. At the end of a single measurement cycle, there will be 4 capacitive measurements corresponding to all possible configurations of the discriminating pad connections. The capacitive measurements at the end of the single measurement cycle will be hereafter referred to as a “measurement set” (e.g., capacitive measurement set (A,B,C,D)).

In the illustrated embodiment, switching discriminating pads130and132between respective ground connections120and124and the output of shield driver116via conductive line164results in a change in the electric field lines between the capacitive sensing pad128and the proximate object136, resulting in 4 different capacitive measurements. The degree to which these measurements change will also be dependent on the type of substance or object, its shape, and its distance from the sensing pad unit. Consequently, these measurements may be used to distinguish between and/or identify different objects or substances136, or may be used to determine the properties of the object or substance136.

In the illustrated embodiment, to determine the relationship between the proximate object136and the capacitive measurements, a set of sample measurements for each of a range of objects and substances that are of interest are taken and the sample set of measurement sets analyzed using data analysis techniques. In the illustrated embodiment, the application of one or more methods of Machine Learning or numerical optimization can be used. These methods include, but are not limited to, Neural Networks, Decision Trees and its variants, Nearest Neighbor algorithms, or Linear Discriminant Analysis, evolutionary search, genetic algorithms, high dimensional splines, and linear and non-linear optimization. In other embodiments, visual inspection of the set of sample measurements can be used.

As there may be a non-negligible background capacitance that exists even when there is no proximate object136, for example due to parasitic capacitance in the sensing pad unit126, or to the capacitive effects of the physical installation of the sensor system100, it may be necessary to perform a baseline measurement of this background capacitance for each configuration of the discriminating pads, and then use these values to remove the background reading from further measurements. Consequently there will be 4 baseline values. These baseline values correspond to measurement configurations which are: measurement A: {S, S}; measurement B: {G, G}; measurement C: {S, G}; measurement D: {G, S}. Typical methods of establishing a baseline are to compute the mean or the median of a set of measurements taken in the absence of a proximate object.

FIG. 2illustrates a flow chart of an embodiment of a measurement process. On startup250, the control unit112performs its initialization process252. The capacitive to digital sensor114performs its initialization process254with the measurement parameters set by the control unit112. These parameters are specific to each capacitive sensor but may include parameters like measurement rate, channel number, method of offset, and accuracy. The first switch118and the second switch122are set to state {S,S} at256. A capacitive measurement, A, is made at258. The first switch118and the second switch122are set to state {G,G} at260. A second capacitive measurement, B, is made262. The first switch118and the second switch122are set to state {S,G} at264. A third capacitive measurement, C, is made at266. The first switch118and the second switch122are set to state {G,S} at268. A fourth capacitive measurement, D, is made at270.

If these measurement are part of a data collection process at272, such as to be used as sample data for a Machine Learning analysis, then the data is stored at274for later transfer to a memory device.

If these measurements are part of a baseline process at276, then the baseline is calculated and updated at278. If the baseline is to be removed from the measurement at280, then the baseline is removed at282. If categorization or identification of the object or material is required, or if the computation of material properties is required, then the categorization/computational process is implemented at284. If the process continues at286, then the process returns to the switch process settings at256, otherwise the process halts at288.

FIGS. 3A-3Hillustrate plan or top views of embodiments of a sensing pad unit.FIG. 3Aillustrates a plan view of a symmetrical arrangement, comprising a substantially rectangular capacitive sensing pad300, a first discriminating pad302substantially surrounding the capacitive sensing pad300, a second discriminating pad304substantially surrounding the capacitive sensing pad300and the first discriminating pad302, and a shield pad306underneath the capacitive sensing pad300, first discriminating pad302and second discriminating pad304. In the illustrated embodiment, shield pad306, underneath the capacitive sensing pad300, reduces the sensitivity of capacitance measurements made using the capacitive sensing pad300to capacitance effects caused by material behind the shield pad306.

FIG. 3Billustrates a plan view of a symmetrical arrangement, comprising a polyline of line segments forming a “W” shape that includes a capacitive sensing pad308that includes eight line segments, a first discriminating pad310that includes 18 line segments and substantially surrounding the capacitive pad308, a second discriminating pad312that includes 18 line segments and substantially surrounds the capacitive sensing pad308and the first discriminating pad310, and a shield pad314underneath the capacitive sensing pad308, first discriminating pad310and second discriminating pad312. In other embodiments, capacitive sensing pad308may include of any suitable number of connected line segments or curves.

FIG. 3Cillustrates a plan view of a symmetrical arrangement, comprising a disc shaped capacitive sensing pad316, a first discriminating pad318substantially surrounding the capacitive pad316, a second discriminating pad320substantially surrounding the capacitive sensing pad316and the first discriminating pad318, and a shield pad322underneath the capacitive sensing pad316, first discriminating pad318and second discriminating pad320.

FIG. 3Dillustrates a plan view of a symmetrical arrangement, comprising an arc capacitive sensing pad324, a first discriminating pad326substantially surrounding the capacitive sensing pad324, a second discriminating pad328substantially surrounding the capacitive sensing pad324and the first discriminating pad326, and a shield pad330underneath the capacitive sensing pad324, first discriminating pad326and second discriminating pad328.

FIG. 3Eillustrates a plan view of a grid of four substantially square capacitive sensing pads332,334,336and338, each substantially surrounded by a respective inner discriminating pad340,342,344and346, and a respective outer discriminating pad348,350,352and354, and a shield pad356underneath the capacitive sensing pads332,334,336and338, the inner discriminating pads340,342,344and346and the outer discriminating pads348,350,352and354. The capacitive sensing pad332and its surrounding discriminating pads340and348comprise a first sub unit. The capacitive sensing pad334and its surrounding discriminating pads342and350comprise a second sub unit. The capacitive sensing pad336and its surrounding discriminating pads344and352comprise a third sub unit. The capacitive sensing pad338and its surrounding discriminating pads346and354comprise a fourth sub unit. The grid spacing is tightly packed, whereby the spacing between the individual sub units is less than the size of the sub unit.

FIG. 3Fillustrates a plan view of a grid of four substantially square capacitive sensing pads360,362,364and366, each substantially surrounded by a respective inner discriminating pad368,370,372and374, and a respective outer discriminating pad376,378,380and382, and a shield pad384underneath the capacitive sensing pads360,362,364and366, the inner discriminating pads368,370,372and374and the outer discriminating pads376,378,380and382. The grid of capacitive sensing pads60,362,364and366, are electrically connected together. The grid of inner discriminating pads368,370,372and374are electrically connected together. The grid of outer discriminating pads376,378,380and382are electrically connected together. The capacitive sensing pad360and its surrounding discriminating pads368and376comprise a first sub unit. The capacitive sensing pad362and its surrounding discriminating pads370and378comprise a second sub unit. The capacitive sensing pad364and its surrounding discriminating pads372and380comprise a third sub unit. The capacitive sensing pad366and its surrounding discriminating pads374and382comprise a fourth sub unit. The grid spacing is sparsely packed, whereby the spacing between the individual sub units is greater than the size of the sub units.

In various embodiments, any size or number of grid array sub units can be constructed and the sensing pad units illustrated inFIG. 3EandFIG. 3Fare specific embodiments of 2 by 2 grids of square sensing pad units.

FIG. 3Gillustrates a plan view of a symmetrical arrangement, comprising a substantially rectangular capacitive sensing pad386, a first discriminating pad388substantially surrounding the capacitive sensing pad386, a second discriminating pad390substantially surrounding the capacitive sensing pad386and the first discriminating pad388. There is no shield pad in this embodiment. In the embodiments illustrated inFIGS. 3A-3H, the sensing pad unit can be constructed with or without a shield pad.

FIG. 3Hillustrates a plan view of a symmetrical arrangement, comprising a substantially rectangular capacitive sensing pad392, a first inner discriminating pad393, a second inner discriminating pad394electrically connected to the first inner discriminating pad393via a conductive line402, a first outer discriminating pad395, a second outer discriminating pad396electrically connected to the first outer discriminating pad395via a conductive line404, and a shield pad398underneath the capacitive sensing pad392, the first inner discriminating pad393, the second inner discriminating pad394, the first outer discriminating pad395and the second outer discriminating pad396. In various embodiments, any discriminating pad may comprise multiple line or curve segments which may be physically separated, but which are electrically joined together via conductive lines or traces to comprise a single discriminating pad unit.

In various embodiments of sensing pad units illustrated inFIGS. 3A-3H, the shield pad has a size and shape that is equal to or greater than the capacitive sensing pad, and may be large in extent or area so as to include or be underneath the outermost discriminating pad. In various embodiments of sensing pad units, the separation between the capacitive sensing pad and the shield pad should be less than the smallest dimension of the capacitive sensing pad. For example, inFIG. 3Athe separation between the capacitive sensing pad300and the shield pad306should be less than the width of the capacitive sensing pad300. In various embodiments, the minimum dimension can be a length or width when the capacitive sensing pad has a rectangular shape or can be a diameter when the capacitive sensing pad has a disc or circular shape.

Referring now toFIG. 1, in embodiments of sensing pad unit126, the shield pad may be dispensed with and not used if a substantially symmetrical sensitivity, both forward and behind the capacitive sensing pad328is desired.

In the embodiments illustrated inFIG. 1andFIGS. 3A-3H, a capacitive sensing pad and n conductive discriminating pads where n≥1 can be used. These embodiments include a shield driver that provides a voltage potential of the capacitive sensing pad and n switches that each have an input terminal coupled to one of the n discriminating pads and have two switch connection states which selectively couple the input terminal to the capacitive sensing pad voltage potential or to the ground potential. In these embodiments, the n switches are operable to provide up to 2nunique connection states for the n discriminating pads.FIG. 1illustrates an embodiment where there are n conductive discriminating pads and n=2. The two discriminating pads are illustrated at130and132.FIG. 1further illustrates that for n switches where n=2, the two switches are switch118and switch122.

Referring toFIGS. 3A-3H, it is understood that the number of discriminating pads can be any suitable number n, where n≥1, and that the diagrams inFIG. 3A-3Hillustrate a specific instance of sensing pad units where n=2. Furthermore, the geometric configuration of the pads, e.g. Size, shape, and spatial relationship, will depend upon design purpose of the sensor system, and on the shape and spatial orientation of the objects or substances being interrogated, and upon the space and shape exigencies of the specific physical implementation. The configurations shown inFIGS. 3A-3Hillustrate embodiments of sensing pad units for a number of applications or uses. For example, for use as a seat occupancy sensor, a sensing pad unit for the form ofFIG. 3BorFIG. 3Fmay be found suitable. For use as a level sensor, a sensing pad of the form ofFIG. 3Hmay be suitable. For use as an immersion sensor within a liquid to measure properties of the liquid, a sensing pad of the form ofFIG. 3A,FIG. 3GorFIG. 3Hmay be suitable. For use in object identification for applications such as robotic gripping units, a sensing pad unit of the form inFIG. 3C,FIG. 3DorFIG. 3Emay be suitable. In other embodiments, other suitable physical implementations of sensing pad units may be used.

In various embodiments of switching n switches where each switch connects a corresponding discriminating pad between a ground and a shield potential, the n switches will result in a total of 2nunique combinations of switching states and therefore 2ncapacitive measurements. When n=2, the number of measurements can be 4. If n=3, the number of measurements can be 8. The 2ncapacitive measurements are referred to herein as a measurement set.

It is understood that the user may choose not to set all possible switch state combinations and that the 2nunique states is an upper limit on the number of unique measurements. For example, if n=3, the number of unique measurements may be less than 8, and can be any suitable number of unique measurements such as 7 or 6.

FIG. 4illustrates an embodiment of a system400which includes a sensor measurement system102and a sensing pad unit426. The sensor measurement system102is described with respect toFIG. 1. In the illustrated embodiment, a substance436is placed inside a container438. The sensing pad unit426is immersed in the substance436. In various embodiments, the substance can be a liquid or can be a granular material.

The capacitive to digital sensor114is connected via conductive line462to the capacitive sensing pad428, and is connected via conductive line170to the input of the shield driver116. The inputs146and154of the respective switches118and122are controlled by the control unit112.

In the illustrated embodiment, the capacitance sensing pad428and the discriminating pads430and432, are constructed of conductive materials such as metals. By way of example, this can include a printed circuit board, a flex-PCB, copper tape, or conductive cloth, but can also be any other conductive substance. The size and shape of the capacitive sensing pad428and the discriminating pads430and432will depend on the particular application and geometry as discussed herein. In other embodiments, a shield pad as discussed herein can be used.

The input terminal146of the first switch118is electrically connected to I/O terminal142of the control unit112via conductive line174the common node148of the first switch118is electrically connected to the first discriminating pad430via conductive line466. One output terminal150of the first switch118is connected to a ground potential at120, and the other output terminal152is connected to the output of the shield driver116via conductive line464.

The input terminal154of the second switch122is connected to I/O terminal144of the control unit112via conductive line176. The common node156of the switch122is connected to the second discriminating pad432via conductive line468. One output terminal158of the switch122is connected to a ground potential at124, the other output terminal160is connected to the output of the shield driver116via conductive line464.

The switches118and122are controlled by the control unit112such that when the user wants to make a measurement with the capacitive sensing pad428when one or both of the discriminating pads430and432are connected to the ground potential respectively at120and/or124or to the output of the shield driver116via conductive line464, the control unit112will set the input terminals146and154of respective switches118and122to the appropriate value, either H or L. It is understood that the specifics of this will depend on the chosen implementation of the switches118and122, and that the order of the switching is not important to the method.

If we write in shorthand {X,Y} where X and Y represent the connection state of the first switch118and the second switch122respectively, where the connection state can take the values of either “S” or “G” which representing the state when the first switch118or the second switch122connects respectively the first discriminating pad430or the second discriminating pad432to either the output of the shield driver116via conductive line464(“S”), or to respective ground connections120and124(“G”). Then the possible measurement configurations can be written as: measurement A: {S, S}; measurement B: {G, G}; measurement C: {S, G}; measurement D: {G, S}. At the end of a single measurement cycle, there will be 4 capacitive measurements corresponding to all possible configurations of the discriminating pad connections. The capacitive measurements at the end of the single measurement cycle will be hereafter referred to as a “measurement set” (e.g., capacitive measurement set (A,B,C,D)).

Switching discriminating pads430and432between respective ground connections120and124and the output of shield driver116via conductive line464results in a change in the electric field lines between the capacitive sensing pad428and the surrounding substance436, resulting in 4 different capacitive measurements. The degree to which these measurements change will be dependent on the intrinsic electromagnetic properties of the material.

In the embodiments illustrated herein, the capacitive measurements may be used to determine the intrinsic properties of a substance such as the dipole moment, μ, and the dielectric constant, εr. The dielectric constant is a measure of the energy contained in an electric field in a substance. The dipole moment is a measure of the asymmetry of the electric charge distribution of a molecule. The dielectric constant is a function of varying temperature. The dipole moment remains constant with varying temperature. In order to determine the relationship between the substance properties and the capacitive measurements, in the illustrated embodiment, a set of sample measurement sets are taken using substances that are of interest are taken and that cover the range of properties of interest. The sample measurement sets are analyzed using data analysis techniques. In various embodiments, various methods of numerical modeling and optimization are utilized to derive mathematical relationships between the capacitive measurements and the observed numerical properties. These methods include, but are not limited to, the application of evolutionary search, genetic algorithms, high dimensional splines, and linear and non-linear optimization.

Referring toFIG. 4, there may be a non-negligible background capacitance that exists even when there is no substance436, for example due to parasitic capacitance in the sensing pad unit126, or to the capacitive effects of the physical installation of the sensor system400, and it may be necessary to perform a baseline measurement of this background capacitance for each configuration of the discriminating pads, and then use these values to remove the background reading from further measurements. Consequently there will be 4 baseline values. These baseline values correspond to measurement configurations which are: measurement A: {S, S}; measurement B: {G, G}; measurement C: {S, G}; measurement D: {G, S}. Typical methods of establishing a baseline are to compute the mean or the median of a set of measurements taken in the absence of a proximate object. Consequently, in the illustrated embodiment, there will be 4 baseline values. Typical methods of establishing a baseline are to compute the mean or the median of a set of measurements taken in the absence of a substance436within container438or if the sensing pad unit426is placed away from any nearby objects or materials and or away from container438.

FIG. 5illustrates a flow chart of an embodiment of a measurement process. On550the control unit112performs its initialization process552. The capacitive to digital sensor114performs its initialization process554with the measurement parameters set by the control unit112. These parameters are specific to each capacitive sensor but may include parameters like measurement rate, channel number, method of offset, and accuracy. The first switch118and the second switch122are set to state {S,S} at556. A capacitive measurement, A, is made at558. The first switch118and the second switch122are set to state {G,G} at560. A second capacitive measurement, B, is made at562. The first switch118and the second switch222are set to state {S,G} at564. A third capacitive measurement, C, is made at566. The first switch118and the second switch122are set to state {G,S} at568. A fourth capacitive measurement, D, is made at570.

If these measurement are part of a data collection process at572, such as to be used as sample data for a modeling or optimization analysis, then the data is stored at574for later transfer to a memory device.

If these measurements are part of a baseline process at576then the baseline is calculated and updated at578. If the baseline is to be removed from the measurement at580then the baseline is removed at582. If substance properties or identification of material properties based on measured capacitance, published versus measured dielectric constants or published versus measured dipole moments are required then this process is implemented at584. If the process continues at586then the process returns to the switch process settings at556, otherwise the process halts at580.

FIGS. 6A-6Billustrate scatter plots of embodiments of computed versus known values for a dielectric constant and a dipole moment for several liquid substances.FIG. 6Aillustrates an embodiment of a scatter-plot of computed vs. known dielectric constant for several liquid substances. The horizontal x-axis illustrates known values, obtained from the CRC Handbook of Chemistry and Physics (97th edition, published by CRC Press). The vertical y-axis illustrates values derived from capacitance measurements from the embodiments illustrated inFIG. 4andFIG. 5, with the capacitive sensing pad illustrated inFIG. 3G. The vertical y-axis values are obtained from measuring the dielectric constant as illustrated inFIG. 4andFIG. 5, taking measurement sets as described inFIG. 5for each one of one or more liquid substances, and deriving a mathematical relationship, formula or equation between the measurement sets for the one or more liquid substances and the known dielectric constants for the one or more liquid substances that enables the measurement sets (as inputs to the mathematical relationship) to approximate the known dielectric constants (as outputs of the mathematical equation). In the illustrated embodiment, the mathematical relationship enables mapping of computed dielectric constants to known dielectric constants and allows substances or materials to be identified based on their known dielectric constants.

In the illustrated embodiment, this mathematic relationship between the measurement set and the dielectric constant is a low order non-linear rational polynomial equation derived by taking all of the measured data or a subset of the measured data and using evolutionary search software (e.g., Eureqa; www.nutonian.com. The equation uses as inputs the measured data and provides outputs that approximate the known data as illustrated inFIG. 6Asuch that a linear relationship between the output of the equation and the known dielectric constants can be achieved. This equation enables identification of other materials that are not tested based solely on their known dielectric constants.

In the illustrated embodiment, the dimensions of the capacitive sensing pad428was 6 mm by 12 mm, the width of the first discriminating pad430was 1.5 mm, and the separation between the capacitive sensing pad428and the first discriminating pad430was 1 mm. The width of the second discriminating pad432was 3 mm and the separation between the first discriminating pad430and the second discriminating pad432was 1 mm.

Referring now toFIG. 6Bwhich illustrates an embodiment of a scatter plot of computed vs. known values for the dipole moment for several liquid substances. The horizontal x-axis illustrates known values, obtained from the CRC Handbook of Chemistry and Physics (97th edition, published by CRC Press. The vertical y-axis are values derived from capacitance measurements from the embodiments illustrated inFIG. 4andFIG. 5, with the capacitive sensing pad illustrated inFIG. 3G. The vertical y-axis illustrates values are obtained from measuring the dipole moment as illustrated inFIG. 4andFIG. 5, taking measurement sets as described inFIG. 5for each one of one or more liquid substances, and deriving a mathematical relationship, formula or equation between the measurement sets for the one or more liquid substances and the known dipole moments for the one or more liquid substances that enables the measurement sets (as inputs to the mathematical relationship) to approximate the known dipole moments (as outputs of the mathematical equation). In the illustrated embodiment, the mathematical relationship enables mapping of computed dipole moments to known dipole moments and allows substances or materials to be identified based on their known dipole moments.

In the illustrated embodiment, this mathematic relationship between the measurement set and the dipole moment is a low order non-linear rational polynomial equation derived by taking all of the measured data or a subset of the measured data and using evolutionary search software (e.g., Eureqa; www.nutonian.com). The equation uses as inputs the measured data and provides outputs that approximate the known data as illustrated inFIG. 6Bsuch that a linear relationship between the output of the equation and the known dipole moments can be achieved. This equation enables identification of other materials that are not tested based solely on their known dipole moments.

In the illustrated embodiment, the dimensions of the capacitive sensing pad428was 6 mm by 12 mm, the width of the first discriminating pad430was 1.5 mm and the separation between the capacitive sensing pad428and the first discriminating pad430was 1 mm. The width of the second discriminating pad432was 3 mm and the separation between the first discriminating pad430and the second discriminating pad432was 1 mm. The capacitive measurement sets obtained by the embodiment illustrated inFIG. 4, including four measurements which are a measurement set (A, B, C and D), will depend on the configuration of sensing pad unit426and on the specific geometry of container438.

In the illustrated embodiment, the sensing pad unit436is inside the container438and is immersed in the liquid or substance contained within container438. In other embodiments, sensing pad unit438can be attached to, or near, the inside wall of the container438, or can be attached to, or near, the outside wall of the container438, such that sensing pad unit438is not immersed in the liquid or substance contained within container438.

FIG. 7illustrates an embodiment of a system700which includes a sensor measurement system102and a sensing pad unit726. The sensor measurement system102is described with respect toFIG. 1. In the illustrated embodiment, a substance736is placed inside a container738. The sensing pad unit726is attached to the outside wall of the container738. In various embodiments, the substance can be a liquid or can be a granular material. In the illustrated embodiment, the capacitive to digital sensor114is connected to the capacitive sensing pad726via conductive line762, and is also coupled to the input of the shield driver116via conductive line170. The inputs146and154of the respective switches118and122are controlled by the control unit112. The output of the shield driver116is connected to the shield pad734via conductive line764. In other embodiments, the sensing pad unit726is attached to the inside surface of the container738.

In the illustrated embodiment, the capacitance sensing pad728, the discriminating pads730and732, and shield pad734, are constructed of conductive materials such as metals. By way of example, this can include a printed circuit board, a flex-PCB, copper tape, or conductive cloth, but can also be any other conductive substance. In other embodiments where the sensing pad unit726is immersed in the contents of the container738, the conductive elements of the sensing pad unit726are electrically isolated from the contents of the container738by a suitable non-conductive protective material.

In the illustrated embodiment, shield driver116is electrically connected to shield pad734via conductive line764and shield driver116drives shield pad734to the same voltage potential as capacitive sensing pad728. Therefore, there is no electric field between the capacitive sensing pad728and the shield pad734. Consequently, any capacitive effect of a material behind the shield pad734on a capacitance measurement by capacitance to digital sensor114is nullified. In usage the shield pad734is used to provide directional sensitivity to the capacitive sensing pad728and to limit the capacitive effects of material behind the shield pad734. In the illustrated embodiment, the shield driver116maintains the shield pad734at this voltage potential which is the same voltage potential as capacitive sensing pad728. In the illustrated embodiment, the shield pad734is placed in close proximity to the capacitive sensing pad728, typically a distance of a few tenths of a millimeter up to a few millimeters. In this embodiment, the separation between the capacitive sensing pad728and the shield pad734is less than the overall dimensions of the capacitive sensing pad728. The shield pad734may be a separate physical construction to the capacitive pad728and discriminating pads730and732, but may also be within the substrate of these pads such as with a multilayer printed circuit board. The size and shape of the capacitive sensing pad728and the discriminating pads730and732will depend on the particular application and geometry.

The input terminal146of the first switch118is electrically connected to I/O terminal142of the control unit112via conductive line174. The common node148of the first switch118is electrically connected to the first discriminating pad730via conductive line766. One output terminal150of the first switch118is connected to a ground potential at120, and the other output terminal152is connected to the output of the shield driver116via conductive line764. The input terminal154of the second switch122is connected to I/O terminal144of the control unit112via conductive line176. The common node156of the switch122is connected to the second discriminating pad732via conductive line768. One output terminal158of the switch122is connected to a ground potential at124, the other output terminal160is connected to the output of the shield driver116via conductive line764. The switches118and122are controlled by the control unit112such that when the user wants to make a measurement with the capacitive sensing pad728when either or both of the discriminating pads730and732are connected to the ground potential respectively at120and/or124or to the output of the shield driver116via conductive line764, the control unit112will set the input terminals146and154of respective switches118and122to the appropriate value, H or L. It is understood that the specifics of this will depend on the chosen implementation of the switches118and122, and that the order of the switching is not important to the method.

If we write in shorthand {X,Y} where X and Y represent the connection state of the first switch118and the second switch122respectively, where the connection state can take the values of either “S” or “G” which representing the state when the first switch118or the second switch122connects respectively the first discriminating pad730or the second discriminating pad732to either the output of the shield driver116via conductive line764(“S”), or to respective ground connections120and124(“G”). Then the possible measurement configurations can be written as: measurement A: {S, S}; measurement B: {G, G}; measurement C: {S, G}; measurement D: {G, S}. At the end of a single measurement cycle, there will be 4 capacitive measurements corresponding to all possible configurations of the discriminating pad connections. The capacitive measurements at the end of the single measurement cycle will be hereafter referred to as a “measurement set” (e.g., capacitive measurement set (A,B,C,D)).

Switching discriminating pads730and732between respective ground connections120and124and the output of the shield driver116via conductive line764results in a change in the electric field lines between the capacitive sensing pad728and the surrounding substance736, resulting in 4 different capacitive measurements. The degree to which these measurements change will be dependent on the intrinsic electromagnetic properties of the material which for some properties, such as the dielectric constant, is a function of temperature. The capacitive measurement sets may be used to determine the intrinsic properties such as the dielectric constant, εr, and therefore the temperature, or to directly derive a relationship between the measurement sets and the temperature.

In order to determine the relationship between the level and temperature of the substance and the capacitive measurements, in the illustrated embodiment, a set of sample measurement sets is taken using for each of a range of the substance of interest and that cover the range of volumes and temperatures of interest. These sample sets of measurement sets can be analyzed using data analysis techniques as discussed above with respect toFIGS. 6A and 6B.

A typical method is to apply the any of the various methods of numerical modeling and optimization to derive formulaic relationships between the capacitive measurements and the observed numerical properties. These methods include, but are not limited to, the application of evolutionary search, genetic algorithms, high dimensional splines, and linear and non-linear optimization.

FIGS. 8A-8Billustrate scatter plots of measured versus computed values for temperature and volume of a liquid.FIG. 8Aillustrates a scatter-plot of known and computed temperatures for water in a tank over a range of volumes of approximately 100 ml to 700 ml. In the illustrated embodiments, the capacitive measurement method illustrated inFIG. 5can be used, and the system400illustrated inFIG. 4can be used where the tank is container438, the system700illustrated inFIG. 7can be used where the tank is container738, or the system900illustrated inFIG. 9can be used where the tank is container938. The horizontal x-axis illustrates the sample or measurement number, and the vertical y-axis illustrates temperature.

In the illustrated embodiment, the capacitive sensing pad and discriminating pad unit configuration illustrated inFIG. 3Hwas used to obtain the capacitive measurements. In the illustrated embodiment, the dimensions of the capacitive sensing pad392used was 15 mm by 170 mm, the width of the first inner discriminating pad393and the second inner discriminating pad394was 3 mm, and the separation between either the first inner discriminating pad393or the second inner discriminating pad394and the capacitive sensing pad392was 1 mm. The width of the first outer discriminating pad395and the second outer discriminating pad396was 5 mm, and the separation between first outer discriminating pad395and the first inner discriminating pad393, or between the second outer discriminating pad396and the second inner discriminating pad394was 1 mm. The width is measured in a vertical direction relative to the orientation of the discriminating pad unit configuration illustrated inFIG. 3H.

In the illustrated embodiment, water at a fixed temperature was added to the tank in 100 ml quantities and one or more capacitive measurements sets were obtained for each level of the water in the tank. Referring toFIG. 5, a capacitance measurement set is the four capacitive measurements defined inFIG. 5which are capacitive measurements A at558, B at562, C at566, and D at570, referred to as capacitive measurement set (A,B,C,D. In various embodiments, the capacitive measurements sets (A,B,C,D obtained for each level of the water in the tank can be one, 10, 20 or 100. In other embodiments, any suitable number of capacitive measure sets (A,B,C,D) can be used. In the illustrated embodiment, capacitive measurements sets (A,B,C,D) were obtained for four temperatures which were 2 deg C., 17 deg C., 35 deg C. and 55 deg C. over a range of volumes from 100 ml to 700 ml in 100 ml increments for each temperature.

In order to derive a mathematical relationship between the sensor measurement set and the temperature, a low order non-linear rational polynomial was derived by taking a subset of the measured data and using commercially available evolutionary search software (Eureqa; www.nutonian.com (See also,FIG. 6AandFIG. 6B). The computed values plotted inFIG. 8Aare computed by applying the derived formula to the unused subset of measured data. For water at 35 deg C., the plot has been annotated to show the range of water volume added to the tank in 100 ml quantities where the range illustrated is from 100 ml to 700 ml. The same range of water volume added to the tank in 100 ml quantities from 100 ml to 700 ml applies to the other three temperatures which are 2 deg C., 17 deg C. and 55 deg C.

In the illustrated embodiment, the vertical y-axis values for computed temperature were obtained for each of the four temperatures (2 deg C., 17 deg C., 35 deg C. and 55 deg C.) by measuring or taking a number of capacitive measurement sets (A,B,C,D) as described above and deriving a mathematical relationship, formula or equation between a subset of the number of capacitive measurement sets (A,B,C,D) and the known temperature. In various embodiments, a subset of the number of capacitive measurement sets (A,B,C,D) can be half of the number of capacitive measurement sets (A,B,C,D) such that if the number of capacitive measurement sets (A,B,C,D) is 10 or 20, the subset would be, respectively 5 or 10 measurement results. In other embodiments, the subset of the overall number of capacitive measurement sets (A,B,C,D) used to derive the mathematical relationship, formula or equation can be 10%, 90%, or any other suitable number of the overall number of capacitive measurement sets (A,B,C,D) used to derive the mathematical relationship, formula or equation. In these embodiments, the capacitive measurement sets (A,B,C,D) that were not part of the subset are used to validate the mathematical relationship, formula or equation. In these embodiments, the capacitive measurement sets (A,B,C,D) that were not part of the subset were used to generate the computed temperatures illustrated inFIG. 8Ain order to validate the mathematical relationship, formula or equation. In other embodiments, the entire number of capacitive measurement sets (A,B,C,D) are used to derive a mathematical relationship, formula or equation and a second set of capacitive measurement sets (A,B,C,D) are taken to validate the mathematical relationship, formula or equation.

In the illustrated embodiment, the subset of the number of capacitive measurement sets (A,B,C,D) are used to determine a mathematical relationship, formula or equation that enables the subset of the number of capacitive measurement sets (A,B,C,D), as inputs to the mathematical relationship, formula or equation, to define or approximate the known or measured temperature as an output of the mathematical equation. The capacitive measurement sets (A,B,C,D) that were not part of the subset were used to generate the computed temperatures illustrated inFIG. 8Ain order to validate the mathematical equation. The mathematic relationship is a low order non-linear rational polynomial equation derived by taking all of the measured data or a subset of the measured data and using evolutionary search software (e.g., Eureqa; www.nutonian.com). The equation uses as inputs the capacitive measurement sets and provides outputs that approximate the temperature as illustrated inFIG. 8A.

In the illustrated embodiment, n conductive discriminating pads were used where n=2 in order to obtain the capacitive measurement set (A,B,C,D). In other embodiments, n=1 for a capacitive measurement set (A,B) or n≥3 such as for n=3 to obtain 8 capacitive measurements for a capacitive measurement set (A,B,C,D,E,F,G,H) can be used. In other embodiments, any suitable number of n can be used to obtain the capacitive measurement set.

FIG. 8Billustrates a scatter-plot of measured and computed volumes for water in a tank over a range of volumes of approximately 100 ml to 700 ml and for four temperatures which are 2 deg C., 17 deg C., 35 deg C. and 55 deg C. The embodiments illustrated inFIG. 8Butilize the same capacitive measurement methods and systems used and described with respect toFIG. 8A. The horizontal x-axis illustrates the sample or measurement number for each of the four temperatures, and the vertical y-axis represents a volume of the water in the tank as described with respect toFIG. 8A. The capacitive measurement data set or capacitive measurements sets (A,B,C,D) used for the embodiments described inFIG. 8Bare the same as described above inFIG. 8A. In order to derive a mathematical relationship between the sensor capacitive measurement set and the volume for each of the four temperatures, a low order non-linear rational polynomial was derived by taking a subset of the measured data and using commercially available evolutionary search software (Eureqa; www.nutonian.com) (See also,FIG. 6AandFIG. 6B). The computed values plotted inFIG. 8Bare computed by applying the derived formula to the unused subset of measured data. The temperature for each volume step is shown at the base of the plot. The embodiment illustrated inFIG. 8Bprovides a method to determine a volume and temperature simultaneously for a substance. The substance in the container that the volume and temperature are determined for can be a liquid or a solid particulate.

In the illustrated embodiment, the vertical y-axis values for computed volume were obtained for each of the four temperatures (2 deg C., 17 deg C., 35 deg C. and 55 deg C. by measuring or taking a number of capacitive measurement sets (A,B,C,D) as described above with respect to the description forFIG. 8A, and deriving a mathematical relationship or equation between a subset of the number of capacitive measurement sets (A,B,C,D) and the measured or known volume. In various embodiments, a subset of the number of capacitive measurement sets (A,B,C,D) can be half of the number of capacitive measurement sets (A,B,C,D) such that if the number of capacitive measurement sets (A,B,C,D) is 10 or 20, the subset would be, respectively 5 or 10 measurement results. In other embodiments, the subset of the overall number of capacitive measurement sets (A,B,C,D) used to derive the mathematical relationship, formula or equation can be 10%, 90%, or any other suitable number of the overall number of capacitive measurement sets (A,B,C,D) used to derive the mathematical relationship, formula or equation. In these embodiments, the capacitive measurement sets (A,B,C,D) that were not part of the subset are used to validate the mathematical relationship, formula or equation. In these embodiments, the capacitive measurement sets (A,B,C,D) that were not part of the subset were used to generate the computed temperatures illustrated inFIG. 8Ain order to validate the mathematical relationship, formula or equation. In other embodiments, the entire number of capacitive measurement sets (A,B,C,D) are used to derive a mathematical relationship, formula or equation and a second set of capacitive measurement sets (A,B,C,D) are taken to validate the mathematical relationship, formula or equation.

In the illustrated embodiment, the subset of the number of capacitive measurement sets (A,B,C,D) are used to determine a mathematical relationship, formula or equation that enables the subset of the number of capacitive measurement sets (A,B,C,D), as inputs to the mathematical relationship, formula or equation, to define or approximate the known or measured temperature as an output of the mathematical equation. The capacitive measurement sets (A,B,C,D) that were not part of the subset were used to generate the computed volumes as illustrated inFIG. 8Bin order to validate the mathematical equation. The mathematic relationship is a low order non-linear rational polynomial equation derived by taking all of the measured data or a subset of the measured data and using evolutionary search software (e.g., Eureqa; www.nutonian.com). The equation uses as inputs the capacitive measurement sets and provides outputs that approximate the volume as illustrated inFIG. 8B.

In the illustrated embodiment, n conductive discriminating pads where n=2 were used to obtain the capacitive measurement set (A,B,C,D). In other embodiments, n=1 for a capacitive measurement set (A,B or n≥3 such as for n=3 to obtain 8 capacitive measurements for a capacitive measurement set (A,B,C,D,E,F,G,H). In other embodiments, any suitable number of n can be used to obtain the capacitive measurement set.

In the illustrated embodiments ofFIG. 8AandFIG. 8B, there may be a non-negligible background capacitance that exists even when there is no water in the tank or container, for example due to parasitic capacitance in the sensing pad unit126, or to the capacitive effects of the physical installation of the sensor system100, and it may be necessary to perform a baseline measurement of this background capacitance for each configuration of the discriminating pads, and then use these values to remove the background reading from further measurements. Consequently there will be 4 baseline values. These baseline values correspond to measurement configurations which are: measurement A: {S, S}; measurement B: {G, G}; measurement C: {S, G}; measurement D: {G, S}. Typical methods of establishing a baseline are to compute the mean or the median of a set of measurements taken in the absence of a proximate object.

FIG. 9illustrates an embodiment of a system900which includes a sensor measurement system102and a sensing pad unit926. Sensor measurement system102is described with respect toFIG. 1. In the illustrated embodiment, a substance936is placed inside a container938. The sensing pad unit926is attached to an outside wall of container938. In various embodiments, the substance can be a liquid or can be a granular material. The wall adhesion by viscous fluids and particulates within container938is illustrated as substance adhesion layer940. The bottom of container938is illustrated at942, the level of substance936at the sidewall of container938with respect to the height948of the sidewall is illustrated at944, the bottom of substance adhesion layer940with respect to with respect to the height948of the sidewall of container938is illustrated at944, and the top of substance adhesion layer940with respect to the height948the sidewall of container938is illustrated at946. In the illustrated embodiment, the sensor measurement system102comprises a control unit112, a capacitive to digital sensor114, a shield driver116, a single-pole double-throw switch118, a second single-pole double-throw switch122, and a sensing pad unit926that includes a capacitive sensing pad928, a proximate discriminating pad930, a second proximate discriminating pad932, and a shield934.

In the illustrated embodiment, the capacitance sensing pad928, the discriminating pads930and932, and shield pad934, are constructed of conductive materials such as metals. By way of example, this can include a printed circuit board, a flex-PCB, copper tape, or conductive cloth, but can also be any other conductive substance. In this embodiment, the conductive elements of the sensing pad unit are electrically isolated from the contents of the container936by a suitable non-conductive protective material.

In the illustrated embodiment, shield driver116is electrically connected to shield pad934via conductive line964and shield driver116drives shield pad934to the same voltage potential as capacitive sensing pad928. Therefore, there is no electric field between the capacitive sensing pad928and the shield pad934. Consequently, any capacitive effect of a material behind the shield pad934on a capacitance measurement by capacitance to digital sensor114is nullified. In usage, the shield pad934is used to provide directional sensitivity to the capacitive sensing pad928and to limit the capacitive effects of material behind the shield pad934. In the illustrated embodiment, the shield driver116maintains the shield pad934at this voltage potential which is the same voltage potential as capacitive sensing pad928. In the illustrated embodiment, the shield pad934is placed in close proximity to the capacitive sensing pad928, typically a distance of a few tenths of a millimeter up to a few millimeters. In this embodiment, the separation between the capacitive sensing pad928and the shield pad934is less than the overall dimensions of the capacitive sensing pad928. The shield pad934may be a separate physical construction to the capacitive pad928and discriminating pads930and932, but may also be within the substrate of these pads such as with a multilayer printed circuit board. The size and shape of the capacitive sensing pad928and the discriminating pads930and932will depend on the particular application and geometry.

The input terminal146of the first switch118is electrically connected to I/O terminal142of the control unit112via conductive line174. The common node148of the first switch118is electrically connected to the first discriminating pad930via conductive line966. One output terminal150of the first switch118is connected to a ground potential at120, and the other output terminal152is connected to the output of the shield driver116via conductive line96. The input terminal154of the second switch122is connected to I/O terminal144of the control unit112via conductive line176. The common node156of the switch122is connected to the second discriminating pad932via conductive line968. One output terminal158of the switch122is connected to a ground potential at124, the other output terminal160is connected to the output of the shield driver116via conductive line964. The switches118and122are controlled by the control unit112such that when the user wants to make a measurement with the capacitive sensing pad928when either or both of the discriminating pads930and932are connected to the ground potential respectively at120and/or124or to the output of the shield driver116via conductive line964, the microcontroller will set the input terminals146and154of respective switches118and122to the appropriate value, H or L. It is understood that the specifics of this will depend on the chosen implementation of the switches118and122, and that the order of the switching is not important to the method.

If we write in shorthand {X,Y} where X and Y represent the connection state of the first switch118and the second switch122respectively, and the connection state can take the values “S” or “G”, representing the state when the first switch118or the second switch122connects first discriminating pad930or second discriminating pad932to the output of the shield driver116via conductive line964or to respective ground connections120and124(“G”). Then the possible measurement configurations can be written as: measurement A: {S, S}; measurement B: {G, G}; measurement C: {S, G}; measurement D: {G, S}. At the end of a single measurement cycle, there will be 4 capacitive measurements corresponding to all possible configurations of the discriminating pad connections. The capacitive measurements at the end of the single measurement cycle will be hereafter referred to as a “measurement set” (e.g., capacitive measurement set (A,B,C,D)).

Switching discriminating pads930and932between respective ground connections120and124and the output of the shield driver116via conductive line964results in a change in the electric field lines between the capacitive sensing pad928and the surrounding substance936, resulting in 4 different capacitive measurements. The degree to which these measurements change will be dependent on the intrinsic electromagnetic properties of the material and the shape of the material. The capacitive measurements may be used to determine these properties.

In order to determine the relationship between the level, volume, mass or quantity of the substance936in container938, one or more sample capacitive measurements sets (A,B,C,D) are taken using substance936that cover the range of level, volume, mass or quantity, or of wall adhesion940. These sample capacitive measurement sets can be analyzed using data analysis techniques as discussed above with respect toFIGS. 6A and 6B.

A typical method is to apply the any of the various methods of numerical modeling and optimization to derive formulaic relationships between the capacitive measurements and the observed numerical properties. These methods include, but are not limited to, the application of evolutionary search, genetic algorithms, high dimensional splines, and linear and non-linear optimization.

In the illustrated embodiment, the path of electric field lines within the substance936will be altered by any nearby boundary, such as the boundary between the air and the surface of the substance adhesion layer940. Capacitive measurement sets (A,B,C,D) may be affected by the thickness of the substance adhesion layer940and by the volume of the substance936within the substance adhesion layer940.

FIG. 10illustrates an embodiment of a plot of measured and computed mass for a viscous fluid in a tank. In the illustrated embodiment, viscous fluid is glycerin that is added to and then drained from a tank. In other embodiments, other suitable fluids can be used.

In the illustrated embodiment, the capacitive measurement method illustrated inFIG. 5can be used, and the system900illustrated inFIG. 9can be used where the tank is container938. The sensing pad unit926is attached to an outside wall of container938. The horizontal x-axis illustrates time (in seconds) and the vertical y-axis illustrates the real-time mass and volume of viscous fluid or substance936in the tank or container938. The measured masses were taken from real-time weight measurements of the container938and were taken for each second of time as shown in the x-axis, and volumes calculated assuming a constant density at 20 deg C. of 1.26 gm/cm3. In other embodiments, sensing pad unit926can be attached to the inside surface or the interior surface of container938.

In the illustrated embodiment, computed values were derived from capacitance measurements using system900illustrated inFIG. 9. The capacitive sensing pad and discriminating pad unit configuration illustrated inFIG. 3Hwas used to obtain the capacitive measurements. In the illustrated embodiment, the dimensions of the capacitive sensing pad392used was 15 mm by 170 mm, the width of the first inner discriminating pad393and the second inner discriminating pad394was 3 mm, and the separation between either the first inner discriminating pad393or the second inner discriminating pad394and the capacitive sensing pad392was 1 mm. The width of the first outer discriminating pad395and the second outer discriminating pad396was 5 mm, and the separation between first outer discriminating pad395and the first inner discriminating pad393, or between the second outer discriminating pad396and the second inner discriminating pad394was 1 mm. The width is measured in a vertical direction relative to the orientation of the discriminating pad unit configuration illustrated inFIG. 3H.

In the illustrated embodiment, the viscous fluid or substance936was added to the tank or container936in incremental quantities and one or more capacitive measurements sets were obtained for each mass or volume of substance936in container938. Referring toFIG. 5, a capacitance measurement set is the four capacitive measurements defined inFIG. 5which are capacitive measurements A at558, B at562, C at566and D at570, referred to as capacitive measurement set (A,B,C,D. In various embodiments, the capacitive measurements sets (A,B,C,D) obtained for each mass or volume of substance936in container938can be one, 10, 20 or 100. In other embodiments, any suitable number of capacitive measure sets (A,B,C,D) can be used.

In order to derive a mathematical relationship between the capacitive measurements sets (A,B,C,D and the mass or volume of substance936in container938, a low order non-linear rational polynomial was derived by taking a subset of the measured data and using commercially available evolutionary search software (Eureqa; www.nutonian.com) (See also,FIG. 6AandFIG. 6B). The computed mass and volume plotted inFIG. 10are computed by applying the derived formula to the unused subset of capacitive measurements data. The measured masses and volumes are plotted as points, and the computed masses or volumes are plotted as open circles. The container938had random masses or volumes of glycerin added. Once container938was full, a tap at the base of container938was opened to allow the glycerin to drain out. Two cycles of adding and draining glycerin were performed as illustrated in FIG.10.FIG. 10illustrates adding substance938from zero seconds to 260 seconds at1002, draining substance938from 260 seconds to 425 seconds at1004, adding substance938from 425 seconds to 560 seconds at1006, and draining substance938from 560 seconds to 880 seconds at1008.

Referring toFIG. 9, the increase in mass or volume of substance936per unit increase in height948(e.g., in centimeters of substance936between the bottom942and level944is greater than the increase in mass or volume of substance adhesion layer940per unit increase in height948(e.g., in centimeters between the bottom944and top946because substance936fills the entire volume of container938between level944and bottom942while the substance adhesion layer940between level944and level946does not.

Referring toFIG. 10, the vertical y-axis values for computed mass or volume were obtained by measuring or taking a number of capacitive measurement sets (A,B,C,D) as described above and deriving a mathematical relationship or equation between a subset of the number of capacitive measurement sets (A,B,C,D) and the measured or known mass or volume. In various embodiments, a subset of the number of capacitive measurement sets (A,B,C,D) can be half of the number of capacitive measurement sets (A,B,C,D) such that if the number of capacitive measurement sets (A,B,C,D) is 10 or 20, the subset would be, respectively 5 or 10 measurement results. In other embodiments, the subset of the overall number of capacitive measurement sets (A,B,C,D) used to derive the mathematical relationship, formula or equation can be 10%, 90%, or any other suitable number of the overall number of capacitive measurement sets (A,B,C,D) used to derive the mathematical relationship, formula or equation. In these embodiments, the capacitive measurement sets (A,B,C,D) that were not part of the subset are used to validate the mathematical relationship, formula or equation. In these embodiments, the capacitive measurement sets (A,B,C,D) that were not part of the subset were used to generate the computed mass or volume illustrated inFIG. 10in order to validate the mathematical relationship, formula or equation. In other embodiments, the entire number of capacitive measurement sets (A,B,C,D) are used to derive a mathematical relationship, formula or equation and a second set of capacitive measurement sets (A,B,C,D) are taken to validate the mathematical relationship, formula or equation.

In the illustrated embodiment, the subset of the number of capacitive measurement sets (A,B,C,D) are used to determine a mathematical relationship, formula or equation that enables the subset of the number of capacitive measurement sets (A,B,C,D) as inputs to the mathematical relationship, formula or equation to define or approximate the known or measured mass or volume as an output of the mathematical relationship, formula or equation. The capacitive measurement sets (A,B,C,D that were not part of the subset were used to generate the computed mass or volume illustrated inFIG. 10in order to validate the mathematical relationship, formula or equation. The polynomial equation uses as inputs the capacitive measurement sets and provides outputs that approximate the mass or volume as illustrated inFIG. 10.

In the illustrated embodiment, n conductive discriminating pads were used where n=2 in order to obtain the capacitive measurement set (A,B,C,D). In other embodiments, n=1 for a capacitive measurement set (A,B) or n≥3 such as for n=3 to obtain 8 capacitive measurements for a capacitive measurement set (A,B,C,D,E,F,G,H) can be used. In other embodiments, any suitable number of n can be used to obtain the capacitive measurement set.

FIG. 10illustrates that by using capacitive measurement sets (A,B,C,D) with sensing pad unit926as inputs to the equation as discussed above, a mass and volume of a viscous fluid or particulate illustrated as substance936and including the mass and volume in the viscous layer940can be accurately measured. In various embodiments, the substance936in container938may be a liquid or a solid particulate.

In the illustrated embodiments ofFIG. 10, there may be a non-negligible background capacitance that exists even when there is no water in the tank or container, for example due to parasitic capacitance in the sensing pad unit126, or to the capacitive effects of the physical installation of the sensor system900, and it may be necessary to perform a baseline measurement of this background capacitance for each configuration of the discriminating pads, and then use these values to remove the background reading from further measurements. Consequently there will be 4 baseline values. These baseline values correspond to measurement configurations which are: measurement A: {S, S}; measurement B: {G, G}; measurement C: {S, G}; measurement D: {G, S}. Typical methods of establishing a baseline are to compute the mean or the median of a set of measurements taken in the absence of a proximate object.

FIG. 11illustrates an embodiment of a system1100which includes a sensor measurement system1102and a sensing pad unit1126. Sensor measurement system1102includes a control unit1112, a capacitive to digital sensor1114, a shield driver1116, a single-pole double-throw switch1118. Sensing pad unit1126includes a capacitive sensing pad1128, a proximate discriminating pad1130and a shield1132. A proximate object or substance1136is illustrated in proximity to sensing pad unit1126. The capacitive to digital sensor1114is connected via conductive line1162to the capacitive sensing pad1128, and is connected via conductive line1170to the input of the shield driver1116. The input1146of switch1118is controlled by the control unit1112. The output of the shield driver1116is connected to the shield pad1132via conductive line1164.

In the illustrated embodiment, control unit1112is a micro-controller or micro-controller unit (MCU). In different embodiments, the control unit1112and the capacitive to digital sensor1114may be separate integrated circuit chips or they may be incorporated into the same integrated circuit chip. Furthermore, in different embodiments, shield driver1116and the capacitive to digital sensor1114may be separate integrated circuit chips or they may be incorporated into the same integrated circuit chip.

The control unit1112uses methods of digital interfacing to control the functioning of the capacitive to digital sensor114. If the control unit1112and the capacitive to digital sensor1114are separate physical chips then these interface methods can include, but are not limited to, I2C (also known as Inter-Integrated Circuit) and SPI (also known as Serial Peripheral Interface). In the illustrated embodiment, capacitive to digital sensor1114is coupled to communication interface1140via multiwire conductive lines1172. The connection to communication interface1140can be I2C (2 wire), SPI (4 wire), or can be another suitable type of connection.

In the illustrated embodiment, the capacitance sensing pad1128, the discriminating pad1130and shield pad1132are constructed of conductive materials such as metals. By way of example, this can include a printed circuit board, a flex-PCB, copper tape, or conductive cloth, but can also be any other conductive substance.

In the illustrated embodiment, shield driver1116is electrically connected to shield pad1132via conductive line1164, and shield driver1116drives shield pad1132to the same voltage potential as capacitive sensing pad1128. Therefore, there is no electric field between the capacitive sensing pad1128and the shield pad1132. Consequently, any capacitive effect of a material behind the shield pad1132on a capacitance measurement by capacitance to digital sensor1114is nullified. In usage, the shield pad1132is used to provide directional sensitivity to the capacitive sensing pad1128and to limit the capacitive effects of material behind the shield pad1132. In the illustrated embodiment, the shield pad1132is placed in close proximity to the capacitive sensing pad1128, typically a distance of a few tenths of a millimeter up to a few millimeters. In other embodiments, other suitable spacing can be used.

In various embodiments, shield pad1132may have a separate physical construction than the capacitive sensing pad1128and the discriminating pad1130, or shield pad1132can be within the substrate of capacitive sensing pad1128and discriminating pad1130, such as with a multilayer printed circuit board.

The size and shape of the capacitive sensing pad1128and the discriminating pad1130will depend on the particular application. For example, if it is necessary that the capacitive sensing pad1128be sensitive to distant objects such as a proximate object or substance1136that is spaced apart from capacitive sensing pad1128by a large distance, then the capacitive sensing pad1128should be larger than a capacitive sensing pad1128designed for sensitivity to closer objects such as a proximate object or substance1136that is spaced apart from capacitive sensing pad1128by a distance that is less than the large distance.

In the illustrated embodiment, with regard to the switch1118, switch1118may be a solid state type switch. In the illustrated embodiment, switch1118is controlled via a digital interface from control unit1112, and this interface can be an Input/Output (I/O) line set to either a digital high (H) or a digital low (L). In other embodiments, other suitable ways to control switch1118may be used.

In the illustrated embodiment, the input terminal1146of the first switch1118is electrically connected to I/O terminal1142of the control unit1112via conductive line1174. The common node1148of the first switch1118is electrically connected to the first discriminating pad1130via conductive line1166. One output terminal1150of the first switch1118is connected to a ground potential at1120, and the other output terminal1152is connected to the output of the shield driver1116via conductive line1164.

The switch1118is controlled by control unit1112and control unit1112can set the input terminal1146of switch1118to the appropriate value of H or L. It is understood that the specifics of this will depend on the chosen implementation of the switch1118, and that the order of the switching is not important to the method.

If we write in shorthand {X} where X represents the connection state of the first switch1118, where the connection state can take the values of either “S” or “G” which represents the state when the first switch1118connects the first discriminating pad1130to the output of the shield driver1116via conductive line1164(“S”) or to a ground connection1120(“G”). Then the possible measurement configurations can be written as: measurement A: {S}; measurement B: {G}. At the end of a single measurement cycle, there will be 2 capacitive measurements corresponding to all possible configurations of the discriminating pad connections. The capacitive measurements at the end of the single measurement cycle will be hereafter referred to as a “measurement set” (e.g., capacitive measurement set (A,B)).

In the illustrated embodiment, switching discriminating pad1130between the ground connection1120and the output of shield driver1116via conductive line1164results in a change in the electric field lines between the capacitive sensing pad1128and the proximate object1136, resulting in 2 different capacitive measurements. The degree to which these measurements change will also be dependent on the type of substance or object, its shape, and its distance from the sensing pad unit. Consequently, these measurements may be used to distinguish between and/or identify different objects or substances1136, or may be used to determine the properties of the object or substance1136.

In the illustrated embodiment, to determine the relationship between the proximate object1136and the capacitive measurements, a set of sample measurements for each of a range of objects and substances that are of interest are taken and the sample set of measurement sets analyzed using data analysis techniques. In the illustrated embodiment, the application of one or more methods of Machine Learning or numerical optimization can be used. These methods include, but are not limited to, Neural Networks, Decision Trees and its variants, Nearest Neighbor algorithms, or Linear Discriminant Analysis, evolutionary search, genetic algorithms, high dimensional splines, and linear and non-linear optimization. In other embodiments, visual inspection of the set of sample measurements can be used.

As there may be a non-negligible background capacitance that exists even when there is no proximate object1136, for example due to parasitic capacitance in the sensing pad unit1126, or to the capacitive effects of the physical installation of the sensor system1100, it may be necessary to perform a baseline measurement of this background capacitance for each configuration of the discriminating pads, and then use these values to remove the background reading from further measurements. Consequently there will be 2 baseline values. These baseline values correspond to measurement configurations which are: measurement A: {S}; measurement B: {G}. Typical methods of establishing a baseline are to compute the mean or the median of a set of measurements taken in the absence of a proximate object.

FIG. 12illustrates a flow chart of an embodiment of a measurement process. On startup1250, the control unit1112performs its initialization process1252. The capacitive to digital sensor1114performs its initialization process1254with the measurement parameters set by the control unit1112. These parameters are specific to each capacitive sensor but may include parameters like measurement rate, channel number, method of offset, and accuracy. The first switch1118is set to state {S} at1256. A capacitive measurement, A, is made at1258. The first switch1118is set to state {G} at1260. A second capacitive measurement, B, is made1262.

If these measurement are part of a data collection process at1264, such as to be used as sample data for a Machine Learning analysis, then the data is stored at1266for later transfer to a memory device.

If these measurements are part of a baseline process at1268, then the baseline is calculated and updated at1270. If the baseline is to be removed from the measurement at1272, then the baseline is removed at1274. If categorization or identification of the object or material is required, or if the computation of material properties is required, then the categorization/computational process is implemented at1276. If the process continues at1278, then the process returns to the switch process settings at1256, otherwise the process halts at1280.

FIGS. 13A-13Eillustrate top views of embodiments of a sensing pad unit.FIG. 3Aillustrates a plan view of a substantially rectangular capacitive pad1300with a discriminating pad1302in nearby proximity, and with a shield pad1304underneath. This configuration of capacitive sensing pad1300and discriminating pad1302is asymmetrical. The separation of the discrimination pad and the capacitive sensing pad is generally of the order of, or smaller then, the dimensions of the capacitive sensing pad.

FIG. 13Billustrates a plan view of a symmetrical arrangement, comprising a substantially rectangular capacitive sensing pad1310, a discriminating pad1312substantially surrounding the capacitive pad, and a shield pad1414underneath.

FIG. 13Cillustrates a plan view of a substantially square capacitive pad1320, substantially surrounded by a discriminating pad1322in a symmetrical arrangement and a shield pad1324underneath.

FIG. 13Dillustrates a plan view of an S shaped capacitive sensing pad1330substantially surrounded by a discriminating pad1332in a symmetrical arrangement, and a shield pad1334underneath.

FIG. 13Eillustrates a plan view of a grid of 4 substantially square pads1340,1342,1344, and1346, each surrounded by a discriminating pad1348,1350,1352and1354and a shield pad1356underneath. The capacitive pads are electrically connected together. The discrimination pads are electrically connected together.

In various embodiments of sensing pad units illustrated inFIGS. 13A-13E, the shield pad has a size and shape that is equal to or greater than the capacitive sensing pad, and may be large in extent or area so as to include or be underneath the outermost discriminating pad. In various embodiments of sensing pad units, the separation between the capacitive sensing pad and the shield pad should be less than the smallest dimension of the capacitive sensing pad. For example, inFIG. 13Athe separation between the capacitive sensing pad1300and the shield pad1304should be less than the width of the capacitive sensing pad1300. In various embodiments, the minimum dimension can be a length or width when the capacitive sensing pad has a rectangular shape or can be a diameter when the capacitive sensing pad has a disc or circular shape.

FIG. 14illustrates a plot of embodiments of capacitive measurements A vs (A-B) for a variety of objects and substances. The data points illustrated inFIG. 14were obtained using the capacitive sensing pad1320illustrated inFIG. 13C, the sensor measurement system1102illustrated inFIG. 11, and the measurement method illustrated inFIG. 12. The measurement method illustrated inFIG. 12was used to obtain capacitive measurements sets (A,B). The vertical y-axis illustrates measurement A minus measurement B (e.g., measurement B subtracted from measurement A), and the horizontal x-axis illustrates measurement A. The objects and materials tested were rice, bottles of water of various quantities, aluminum granules, mobile phones of various sizes, books of various sizes, lead granules and wheat. For rice, aluminum granules, lead granules and wheat, the quantities measured were increased in centiliter (cl) units from 4 cl to 40 cl.FIG. 14illustrates a separation between different materials and different object types. The separations depends on the composition, size, shape and quantity of the material/object. Other classes of objects and other materials will occupy other areas in a plot of A vs (A-B).FIG. 14illustrates a separation in an increasing vertical direction of the y-axis between, lead granules (bottom), aluminum granules, rice and wheat (top) based on quantity.FIG. 14further illustrates a separation in an increasing horizontal direction of the x-axis between wheat (first), rice (second), aluminum granules (third) and lead granules (fourth) based on quantity. In the embodiments illustrated herein, these separations enable identification of both the quantity of material and the type of material.

In the illustrated embodiment, the dimensions of the capacitive sensing pad1320was 2 cm on a side, the width of the discriminating pad1322was 5 mm and the and the separation between the capacitive sensing pad1320and the discriminating pad1322was 1 mm. separation between two pads was 1 mm.

In other embodiments, measurements A and B of measurement set (A,B) can be combined in a variety of suitable ways to obtain optimal separation of the desired substances. In various embodiments, values obtained for measurement set (A,B) will depend on the configuration of system1100including the configuration of the sensing pad unit1126, and on the specifics of the proximate object1136, such as, but not limited to, size, shape, temperature and physical form.

FIG. 15illustrates an embodiment of a system1500which includes a sensor measurement system1502and a sensing pad unit1526. Sensor measurement system1502includes a control unit1512, a capacitive to digital sensor1514, a shield driver1516, a single-pole double-throw switch1518and a second single-pole double-throw switch1522. Sensing pad unit1526includes a capacitive sensing pad1528, a proximate discriminating pad1530, a second proximate discriminating pad1532and a shield1534. A proximate object or substance1536is illustrated in proximity to sensing pad unit1526. The capacitive to digital sensor1514is connected via conductive line1562to the capacitive sensing pad1528, and is connected via conductive line1570to the input of the shield driver1516. The inputs1546and1554of the respective switches1518and1522are controlled by the control unit1512. The output of the shield driver1516is connected to the shield pad1534via conductive line1564.

In the illustrated embodiment, control unit1512is a micro-controller or micro-controller unit (MCU). In different embodiments, the control unit1512and the capacitive to digital sensor1514may be separate integrated circuit chips or they may be incorporated into the same integrated circuit chip. Furthermore, in different embodiments, shield driver1516and the capacitive to digital sensor1514may be separate integrated circuit chips or they may be incorporated into the same integrated circuit chip.

The control unit1512uses methods of digital interfacing to control the functioning of the capacitive to digital sensor1514. If the control unit1512and the capacitive to digital sensor1514are separate physical chips then these interface methods can include, but are not limited to, I2C (also known as Inter-Integrated Circuit) and SPI (also known as Serial Peripheral Interface). In the illustrated embodiment, capacitive to digital sensor1514is coupled to communication interface1540via multiwire conductive lines1572. The connection to communication interface1540can be I2C (2 wire), SPI (4 wire) or can be another suitable type of connection.

In the illustrated embodiment, the capacitance sensing pad1528, the discriminating pads1530and1532, and shield pad1534, are constructed of conductive materials such as metals. By way of example, this can include a printed circuit board, a flex-PCB, copper tape, or conductive cloth, but can also be any other conductive substance.

In the illustrated embodiment, shield driver1516is electrically connected to shield pad1534via conductive line1564, and shield driver1516drives shield pad1534to the same voltage potential as capacitive sensing pad1528. Therefore, there is no electric field between the capacitive sensing pad1528and the shield pad1534. Consequently, any capacitive effect of a material behind the shield pad1534on a capacitance measurement by capacitance to digital sensor1514is nullified. In usage, the shield pad1534is used to provide directional sensitivity to the capacitive sensing pad1528and to limit the capacitive effects of material behind the shield pad1534. In the illustrated embodiment, the shield pad1534is placed in close proximity to the capacitive sensing pad1528, typically a distance of a few tenths of a millimeter up to a few millimeters. In other embodiments, other suitable spacing can be used.

In various embodiments, shield pad1534may have a separate physical construction than the capacitive sensing pad1528and the discriminating pads1530and1532, or shield pad1534can be within the substrate of capacitive sensing pad1528, and discriminating pads1530and1532, such as with a multilayer printed circuit board.

The size and shape of the capacitive sensing pad1528and the discriminating pads1530and1532will depend on the particular application. For example, if it is necessary that the capacitive sensing pad1528be sensitive to distant objects such as a proximate object or substance1536that is spaced apart from capacitive sensing pad1528by a large distance, then the capacitive sensing pad1528should be larger than a capacitive sensing pad1528designed for sensitivity to closer objects such as a proximate object or substance1536that is spaced apart from capacitive sensing pad1528by a distance that is less than the large distance.

In the illustrated embodiment, with regard to the switches1518and1522, switches1518and1522may be a solid state type switch. In the illustrated embodiment, switches1518and1522are controlled via a digital interface from control unit1512, and this interface can be an Input/Output (I/O) line set to either a digital high (H) or a digital low (L). In other embodiments, other suitable ways to control switches1518and1522may be used.

In the illustrated embodiment, the input terminal1546of the first switch1518is electrically connected to I/O terminal1542of the control unit1512via conductive line1574. The common node1548of the first switch1518is electrically connected to the first discriminating pad1530via conductive line1566. One output terminal1550of the first switch1518is connected to a ground potential at1520, and the other output terminal1552is connected to the output of the shield driver1516via conductive line1564. The input terminal1554of the second switch1522is electrically connected to I/O terminal1544of the control unit1512via conductive line1576. The common node1556of the switch1522is connected to the second discriminating pad1532via conductive line1568. One output terminal1558of the switch1522is connected to a ground potential at1524, the other output terminal1560is connected to the output of the shield driver1516via conductive line1564.

The switches1518and1522are controlled by control unit1512and control unit1512can set the input terminals1546and1554of respective switches1518and1522to the appropriate value of H or L. It is understood that the specifics of this will depend on the chosen implementation of the switches1518and1522, and that the order of the switching is not important to the method.

If we write in shorthand {X,Y} where X and Y represent the connection state of the first switch1518and the second switch1522respectively, where the connection state can take the values of either “S” or “G” which representing the state when the first switch1518or the second switch1522connects respectively the first discriminating pad1530or the second discriminating pad1532to either the output of the shield driver1516via conductive line1564(“S”), or to respective ground connections1520and1524(“G”). Then the possible measurement configurations can be written as: measurement A: {S, S}; measurement B: {G, G}; measurement C: {S, G}; measurement D: {G, S}. At the end of a single measurement cycle, there will be 4 capacitive measurements corresponding to all possible configurations of the discriminating pad connections. The capacitive measurements at the end of the single measurement cycle will be hereafter referred to as a “measurement set” (e.g., capacitive measurement set (A,B,C,D)).

In the illustrated embodiment, switching discriminating pads1530and1532between respective ground connections1520and1524and the output of shield driver1516via conductive line1564results in a change in the electric field lines between the capacitive sensing pad1528and the proximate object1536, resulting in 4 different capacitive measurements. The degree to which these measurements change will also be dependent on the type of substance or object, its shape, and its distance from the sensing pad unit. Consequently, these measurements may be used to distinguish between and/or identify different objects or substances1536, or may be used to determine the properties of the object or substance1536.

In the illustrated embodiment, to determine the relationship between the proximate object1536and the capacitive measurements, a set of sample measurements for each of a range of objects and substances that are of interest are taken and the sample set of measurement sets analyzed using data analysis techniques. In the illustrated embodiment, the application of one or more methods of Machine Learning or numerical optimization can be used. These methods include, but are not limited to, Neural Networks, Decision Trees and its variants, Nearest Neighbor algorithms, or Linear Discriminant Analysis, evolutionary search, genetic algorithms, high dimensional splines, and linear and non-linear optimization. In other embodiments, visual inspection of the set of sample measurements can be used.

As there may be a non-negligible background capacitance that exists even when there is no proximate object1536, for example due to parasitic capacitance in the sensing pad unit1526, or to the capacitive effects of the physical installation of the sensor system1500, it may be necessary to perform a baseline measurement of this background capacitance for each configuration of the discriminating pads, and then use these values to remove the background reading from further measurements. Consequently there will be 4 baseline values. These baseline values correspond to measurement configurations which are: measurement A: {S, S}; measurement B: {G, G}; measurement C: {S, G}; measurement D: {G, S}. Typical methods of establishing a baseline are to compute the mean or the median of a set of measurements taken in the absence of a proximate object.

FIGS. 16A-16Eillustrate plan or top views of embodiments of a sensing pad unit.FIG. 16Aillustrates a plan view of a substantially rectangular capacitive sensing pad1610, with a substantially rectangular discriminating pad1612in nearby proximity, a second substantially rectangular discriminating pad1614in nearby proximity, and a shield1616underneath. This configuration of capacitive pad and discriminating pad is asymmetrical.

FIG. 16Billustrates a plan view of a symmetrical arrangement, comprising a substantially rectangular capacitive sensing pad1620, a first discriminating pad1622substantially surrounding the capacitive sensing pad1620, a second discriminating pad1624substantially surrounding the capacitive sensing pad1620and the first discriminating pad1622, and a shield pad1626underneath the capacitive sensing pad1620, first discriminating pad1622and second discriminating pad1624. In the illustrated embodiment, shield pad1626, underneath the capacitive sensing pad1620, reduces the sensitivity of capacitance measurements made using the capacitive sensing pad1620to capacitance effects caused by material behind the shield pad306.

FIG. 16Cillustrates a plan view of a symmetrical arrangement, comprising a substantially rectangular capacitive sensing pad1630, a first discriminating pad1632substantially surrounding the capacitive sensing pad1630, a second discriminating pad1634substantially surrounding the capacitive sensing pad1630and the first discriminating pad1632, and a shield pad1636underneath the capacitive sensing pad1630, first discriminating pad1632and second discriminating pad1634. In the illustrated embodiment, shield pad1636, underneath the capacitive sensing pad1630, reduces the sensitivity of capacitance measurements made using the capacitive sensing pad1630to capacitance effects caused by material behind the shield pad1636.

FIG. 16Dillustrates a plan view of an “S” shaped arrangement, comprising an S-shaped capacitive sensing pad1640, a first discriminating pad1642substantially surrounding the capacitive sensing pad1640, a second discriminating pad1644substantially surrounding the capacitive sensing pad1640and the first discriminating pad1642, and a shield pad1646underneath the capacitive sensing pad1640, first discriminating pad1642and second discriminating pad1644. In the illustrated embodiment, shield pad1646, underneath the capacitive sensing pad1640, reduces the sensitivity of capacitance measurements made using the capacitive sensing pad1640to capacitance effects caused by material behind the shield pad1646.

FIG. 16Eillustrates a plan view of a grid of four substantially square capacitive sensing pads1650,1652,1654and1656, each substantially surrounded by a respective inner discriminating pad1658,1660,1662and1664, and a respective outer discriminating pad1666,1668,1670and1672, and a shield pad1674underneath the capacitive sensing pads1650,1652,1654and1656, the inner discriminating pads pad1658,1660,1662and1664and the outer discriminating pads1666,1668,1670and167. The capacitive sensing pad1650and its surrounding discriminating pads1658and1666comprise a first sub unit. The capacitive sensing pad1652and its surrounding discriminating pads1660and1668comprise a second sub unit. The capacitive sensing pad1654and its surrounding discriminating pads1662and1670comprise a third sub unit. The capacitive sensing pad1656and its surrounding discriminating pads1664and1666comprise a fourth sub unit.

FIG. 17illustrates a plot of embodiments of capacitive measurements (A-B) vs (B-C) for a variety of objects and substances. The data points illustrated inFIG. 17were obtained using the capacitive sensing pad1630illustrated inFIG. 16C, the sensor measurement system1502illustrated inFIG. 15, and the measurement method illustrated inFIG. 2. The measurement method illustrated inFIG. 2was used to obtain capacitive measurements sets (A,B,C,D). The vertical y-axis illustrates measurement B minus measurement C (e.g., measurement C subtracted from measurement B), and the horizontal x-axis illustrates measurement A minus measurement B (e.g., measurement B subtracted from measurement A). The objects and materials tested were rice, bottles of water of various quantities, aluminum granules, mobile phone of various size, book of various sizes, lead granules and wheat. For rice, aluminum granules, lead granules and wheat, the quantities measured were increased in centiliter (cl) units from 4 cl to 40 cl.FIG. 17illustrates a separation between different materials and different object types. The separations depends on the composition, size, shape and quantity of the material/object. Other classes of objects and other materials will occupy other areas in a plot of (A-B) vs (B-C). In other embodiments and in plots of other combinations of capacitive measurements such as (A/C) vs (C-D), the form of separation may be different.FIG. 17illustrates a separation in an increasing vertical direction of the y-axis between wheat (bottom), rice, aluminum granules and lead granules (top).FIG. 17further illustrates a separation in an increasing horizontal direction of the x-axis between wheat (first), rice (second), aluminum granules (third) and lead granules (fourth) based on quantity. In the embodiments illustrated herein, these separations enable identification of both the quantity of material and the type of material.

In the illustrated embodiment, the dimensions of the capacitive sensing pad1630was 2 cm on a side, the width of the inner discriminating pad1632was 5 mm, and the separation between the capacitive sensing pad1320and the inner discriminating pad1322was 1 mm. The width of the outer discriminating pad1634was 10 mm, and the separation between inner discriminating pad1322and the outer discriminating pad1634was 1 mm.

In other embodiments, measurements A and B of measurement set (A,B,C,D) can be combined in a variety of suitable ways to obtain optimal separation of the desired substances. In various embodiments, values obtained for measurement set (A,B,C,D) will depend on the configuration of system1300including the configuration of the sensing pad unit1526, and on the specifics of the proximate object1536, such as, but not limited to, size, shape, temperature and physical form.

FIG. 18illustrates an embodiment of a system1800which includes a sensor measurement system1802and a sensing pad unit1826. Sensor measurement system1802includes a control unit1812, a capacitive to digital sensor1814, a shield driver1816, a single-pole double-throw switch1818, a second single-pole double-throw switch1822and a third single-pole double-throw switch1880. Sensing pad unit1826includes a capacitive sensing pad1828, a proximate discriminating pad1830, a second proximate discriminating pad1832, a third proximate discriminating pad1834and a shield1835. A proximate object or substance1836is illustrated in proximity to sensing pad unit1826. The capacitive to digital sensor1814is connected via conductive line1862to the capacitive sensing pad1828, and is connected via conductive line1870to the input of the shield driver1816. The inputs1846,1854and1882of the respective switches1818,1822and1880are controlled by the control unit1812. The output of the shield driver1816is connected to the shield pad1835via conductive line1864.

In the illustrated embodiment, control unit1812is a micro-controller or micro-controller unit (MCU). In different embodiments, the control unit1812and the capacitive to digital sensor1814may be separate integrated circuit chips or they may be incorporated into the same integrated circuit chip. Furthermore, in different embodiments, shield driver1816and the capacitive to digital sensor1814may be separate integrated circuit chips or they may be incorporated into the same integrated circuit chip.

The control unit1812uses methods of digital interfacing to control the functioning of the capacitive to digital sensor1814. If the control unit1812and the capacitive to digital sensor1814are separate physical chips then these interface methods can include, but are not limited to, I2C (also known as Inter-Integrated Circuit) and SPI (also known as Serial Peripheral Interface). In the illustrated embodiment, capacitive to digital sensor1814is coupled to communication interface1840via multiwire conductive lines1872. The connection to communication interface1840can be I2C (2 wire), SPI (4 wire) or can be another suitable type of connection.

In the illustrated embodiment, the capacitance sensing pad1828, the discriminating pads1830,1832and1834, and shield pad1835, are constructed of conductive materials such as metals. By way of example, this can include a printed circuit board, a flex-PCB, copper tape, or conductive cloth, but can also be any other conductive substance.

In the illustrated embodiment, shield driver1816is electrically connected to shield pad1835via conductive line1864, and shield driver1816drives shield pad1835to the same voltage potential as capacitive sensing pad1828. Therefore, there is no electric field between the capacitive sensing pad1828and the shield pad1835. Consequently, any capacitive effect of a material behind the shield pad1835on a capacitance measurement by capacitance to digital sensor1814is nullified. In usage, the shield pad1835is used to provide directional sensitivity to the capacitive sensing pad1828and to limit the capacitive effects of material behind the shield pad1835. In the illustrated embodiment, the shield pad1835is placed in close proximity to the capacitive sensing pad1828, typically a distance of a few tenths of a millimeter up to a few millimeters. In other embodiments, other suitable spacing can be used.

In various embodiments, shield pad1835may have a separate physical construction than the capacitive sensing pad1828and the discriminating pads1830,1832and1834, or shield pad1835can be within the substrate of capacitive sensing pad1828, and discriminating pads1830,1832and1834, such as with a multilayer printed circuit board.

The size and shape of the capacitive sensing pad1828and the discriminating pads1830,1832and1834will depend on the particular application. For example, if it is necessary that the capacitive sensing pad1828be sensitive to distant objects such as a proximate object or substance1836that is spaced apart from capacitive sensing pad1828by a large distance, then the capacitive sensing pad1828should be larger than a capacitive sensing pad1828designed for sensitivity to closer objects such as a proximate object or substance1836that is spaced apart from capacitive sensing pad1828by a distance that is less than the large distance.

In the illustrated embodiment, with regard to the switches1818,1822and1880, switches1818,1822and1880may be a solid state type switch. In the illustrated embodiment, switches1818,1822and1880are controlled via a digital interface from control unit1812, and this interface can be an Input/Output (I/O) line set to either a digital high (H) or a digital low (L). In other embodiments, other suitable ways to control switches1818,1822and1880may be used.

In the illustrated embodiment, the input terminal1846of the first switch1818is electrically connected to I/O terminal1842of the control unit1812via conductive line1874. The common node1848of the first switch1818is electrically connected to the first discriminating pad1830via conductive line1866. One output terminal1850of the first switch1818is connected to a ground potential at1820, and the other output terminal1852is connected to the output of the shield driver1816via conductive line1864. The input terminal1854of the second switch1822is electrically connected to I/O terminal1844of the control unit1812via conductive line1876. The common node1856of the switch1822is connected to the second discriminating pad1832via conductive line1868. One output terminal1858of the switch1822is connected to a ground potential at1824, the other output terminal1860is connected to the output of the shield driver1816via conductive line1864.

The input terminal1882of the third switch1880is electrically connected to I/O terminal1845of the control unit1812via conductive line1876. The common node1884of the third switch1880is connected to the third discriminating pad1834via conductive line1869. One output terminal1888of the third switch1880is connected to a ground potential at1886, the other output terminal1892is connected to the output of the shield driver1816via conductive line1864.

The switches1818,1822and1880are controlled by control unit1812and control unit1812, and control unit1812can set the input terminals1846,1854and1882of respective switches1818,1822and1880, to the appropriate value of H or L. It is understood that the specifics of this will depend on the chosen implementation of the switches1818,1822and1880, and that the order of the switching is not important to the method.

If we write in shorthand {X,Y,Z} where X, Y and Z represent the connection state of the first switch1818, the second switch1822and the third switch1880, respectively, where the connection state can take the values of either “S” or “G” which represent the state when the first switch1818, the second switch1822and the third switch1880connect respectively the first discriminating pad1830, the second discriminating pad1832or the third discriminating pad1834to either the output of the shield driver1816via conductive line1864(“S”), or to respective ground connections1820,1824and1886(“G”). Then the possible measurement configurations can be written as: measurement A: {S, S, S}; measurement B: {G, G, G}; measurement C: {S, G, G}; measurement D: {S, S, G}; measurement E: {S, G, S}; measurement F: {G, S, G}; measurement G: {G, G, S}; measurement H: {G, S, S}. At the end of a single measurement cycle, there will be 8 capacitive measurements corresponding to all possible configurations of the discriminating pad connections. The capacitive measurements at the end of the single measurement cycle will be hereafter referred to as a “measurement set” (e.g., capacitive measurement set (A,B,C,D,E,F,G,H)).

In the illustrated embodiment, switching discriminating pads1830,1832and1834between respective ground connections1820,1824and1886and the output of shield driver1816via conductive line1864results in a change in the electric field lines between the capacitive sensing pad1828and the proximate object1836, resulting in 8 different capacitive measurements. The degree to which these measurements change will also be dependent on the type of substance or object, its shape, and its distance from the sensing pad unit. Consequently, these measurements may be used to distinguish between and/or identify different objects or substances1836, or may be used to determine the properties of the object or substance1836.

In the illustrated embodiment, to determine the relationship between the proximate object1836and the capacitive measurements, a set of sample measurements for each of a range of objects and substances that are of interest are taken and the sample set of measurement sets are analyzed using data analysis techniques. In the illustrated embodiment, the application of one or more methods of Machine Learning or numerical optimization can be used. These methods include, but are not limited to, Neural Networks, Decision Trees and its variants, Nearest Neighbor algorithms, or Linear Discriminant Analysis, evolutionary search, genetic algorithms, high dimensional splines, and linear and non-linear optimization. In other embodiments, visual inspection of the set of sample measurements can be used.

As there may be a non-negligible background capacitance that exists even when there is no proximate object1836, for example due to parasitic capacitance in the sensing pad unit1826, or to the capacitive effects of the physical installation of the sensor system1800, it may be necessary to perform a baseline measurement of this background capacitance for each configuration of the discriminating pads, and then use these values to remove the background reading from further measurements. Consequently there will be 8 baseline values. These baseline values correspond to measurement configurations which are: measurement A: {S, S, S}; measurement B: {G, G, G}; measurement C: {S, G, G}; measurement D: {S, S, G}; measurement E: {S, G, S}; measurement F: {G, S, G}; measurement G: {G, G, S}; measurement H: {G, S, S}. Typical methods of establishing a baseline are to compute the mean or the median of a set of measurements taken in the absence of a proximate object.

FIG. 19illustrates a flow chart of an embodiment of a measurement process. On startup1900, the control unit1812performs its initialization process1902. The capacitive to digital sensor1814performs its initialization process1904with the measurement parameters set by the control unit1812. These parameters are specific to each capacitive sensor but may include parameters like measurement rate, channel number, method of offset, and accuracy. The first switch1818, the second switch1822and the third switch1880are set to state {S,S,S} at1906. A capacitive measurement, A, is made at1908. The first switch1818, the second switch1822and the third switch1880are set to state {G,G,G} at1910. A capacitive measurement, B, is made1912. The first switch1818, the second switch1822and the third switch1880are set to state {S,G,G} at1914. A capacitive measurement, C, is made at1916. The first switch1818, the second switch1822and the third switch1880are set to state {S,S,G} at1918. A capacitive measurement, D, is made at1920. The first switch1818, the second switch1822and the third switch1880are set to state {S,G,S} at1922. A capacitive measurement, E, is made at1924. The first switch1818, the second switch1822and the third switch1880are set to state {G,S,G} at1926. A capacitive measurement, F, is made1928. The first switch1818, the second switch1822and the third switch1880are set to state {G,G,S} at1930. A capacitive measurement, G, is made at1932. The first switch1818, the second switch1822and the third switch1880are set to state {G,S,S} at1934. A capacitive measurement, H, is made at1936.

If these measurement are part of a data collection process at1938, such as to be used as sample data for a Machine Learning analysis, then the data is stored at1940for later transfer to a memory device.

If these measurements are part of a baseline process at1942, then the baseline is calculated and updated at1944. If the baseline is to be removed from the measurement at1946, then the baseline is removed at1948. If categorization or identification of the object or material is required, or if the computation of material properties is required, then the categorization/computational process is implemented at1950. If the process continues at1952, then the process returns to the switch process settings at1906, otherwise the process halts at1954.

FIGS. 20A-20Eillustrate plan or top views of embodiments of a sensing pad unit.FIG. 20Aillustrates a plan view of a substantially rectangular capacitive sensing pad2010, with a substantially rectangular discriminating pad2012in nearby proximity, a second substantially rectangular discriminating pad2014in nearby proximity, a third substantially rectangular discriminating pad2016in nearby proximity, and a shield pad2018underneath. This configuration of capacitive pad and discriminating pad is asymmetrical.

FIG. 20Billustrates a plan view of a symmetrical arrangement, comprising a substantially rectangular capacitive sensing pad2020, a first discriminating pad2022substantially surrounding the capacitive sensing pad2020, a second discriminating pad2024substantially surrounding the capacitive sensing pad2020and the first discriminating pad2022, a third discriminating pad2026substantially surrounding the capacitive sensing pad2020, the first discriminating pad2022and the second discriminating pad2024, and a shield pad2028underneath the capacitive sensing pad2020, the first discriminating pad2022, the second discriminating pad2024and the third discriminating pad2026. In the illustrated embodiment, shield pad2026, underneath the capacitive sensing pad2020, reduces the sensitivity of capacitance measurements made using the capacitive sensing pad2020to capacitance effects caused by material behind the shield pad306.

FIG. 20Cillustrates a plan view of a symmetrical arrangement, comprising a substantially rectangular capacitive sensing pad2030, a first discriminating pad2032substantially surrounding the capacitive sensing pad2030, a second discriminating pad2034substantially surrounding the capacitive sensing pad2030and the first discriminating pad2032, a third discriminating pad2036substantially surrounding the capacitive sensing pad2030, the first discriminating pad2032and the second discriminating pad2034, and a shield pad2038underneath the capacitive sensing pad2030, first discriminating pad2032, second discriminating pad2034and third discriminating pad2036. In the illustrated embodiment, shield pad2038, underneath the capacitive sensing pad2030, reduces the sensitivity of capacitance measurements made using the capacitive sensing pad2030to capacitance effects caused by material behind the shield pad2036.

FIG. 20Dillustrates a plan view of an “S” shaped arrangement, comprising an S-shaped capacitive sensing pad2040, a first discriminating pad2042substantially surrounding the capacitive sensing pad2040, a second discriminating pad2044substantially surrounding the capacitive sensing pad2040and the first discriminating pad2042, a third discriminating pad2046substantially surrounding the capacitive sensing pad2040, the first discriminating pad2042and the second discriminating pad2044, and a shield pad2046underneath the capacitive sensing pad2040, first discriminating pad2042, second discriminating pad2044and third discriminating pad2046. In the illustrated embodiment, shield pad2048, underneath the capacitive sensing pad2040, reduces the sensitivity of capacitance measurements made using the capacitive sensing pad2040to capacitance effects caused by material behind the shield pad2048.

FIG. 20Eillustrates a plan view of a grid of four substantially square capacitive sensing pads2050,2052,2054and2056, each substantially surrounded by a respective first discriminating pad2060,2062,2064and2066, a respective second discriminating pad2070,2072,2074and2076, a respective third discriminating pad2080,2082,2084and2086, and a shield pad2090underneath the capacitive sensing pads2050,2052,2054and2056, the first discriminating pad2060,2062,2064and2066, the second discriminating pad2070,2072,2074and2076, and the respective third discriminating pad2080,2082,2084and2086. The capacitive sensing pad2050and its surrounding discriminating pads2060,2070and2080comprise a first sub unit. The capacitive sensing pad2052and its surrounding discriminating pads2062,2072and2082comprise a second sub unit. The capacitive sensing pad2054and its surrounding discriminating pads2064,2074and2084comprise a third sub unit. The capacitive sensing pad2056and its surrounding discriminating pads2066,2076and2086comprise a fourth sub unit.

FIG. 21illustrates a plot of embodiments of capacitive measurements (G-H) vs (A-D) for a variety of objects and substances. The data points illustrated inFIG. 21were obtained using the capacitive sensing pad unit illustrated inFIG. 16C, the sensor measurement system1802illustrated inFIG. 18, and the measurement method illustrated inFIG. 19. The measurement method illustrated inFIG. 19was used to obtain capacitive measurements sets (A,B,C,D,E,F,G,H). Of these measurement sets, the measurement sets (A,D,G,H) were used forFIG. 21. The vertical y-axis illustrates measurement G minus measurement H (e.g., measurement H subtracted from measurement G), and the horizontal x-axis illustrates measurement A minus measurement D (e.g., measurement D subtracted from measurement A). The objects and materials tested were rice, bottles of water of various quantities, aluminum granules, mobile phones of various quantities, book of various quantities, lead granules and wheat. For rice, aluminum granules, lead granules and wheat, the quantities measured were increased in centiliter (cl) units from 4 cl to 40 cl.FIG. 21illustrates a separation between different materials and different object types. The separations depends on the composition, size, shape and quantity of the material/object. Other classes of objects and other materials will occupy other areas in a plot of (G-H) vs (A-D). In other embodiments and in plots of other combinations of capacitive measurements such as (AB) vs (G/H), the form of separation in the plot may be different.FIG. 21illustrates a separation in an increasing vertical direction of the y-axis between lead granules (bottom), aluminum granules, rice and wheat (top).FIG. 21further illustrates a separation in an increasing horizontal direction of the x-axis between wheat (first), rice (second), aluminum granules (third) and lead granules (fourth) based on quantity. In the embodiments illustrated herein, these separations enable identification of both the quantity of material and the type of material.

In the illustrated embodiment, the dimensions of the capacitive sensing pad2030are 2 cm on a side, the width of the first discriminating pad2032was 5 mm, and the separation between the capacitive sensing pad2030and the first discriminating pad2032was 1 mm. The width of the second discriminating pad2034was 14 mm, and the separation between the first discriminating pad2032and the second discriminating pad2034was 1 mm. The width of the third discriminating pad2036was 14 mm, and the separation between the first discriminating pad2032and the second discriminating pad2034was 1 mm.

In other embodiments, measurements A and B of measurement set (A,B,C,D,E,F,G,H) can be combined in a variety of suitable ways to obtain optimal separation of the desired substances. In various embodiments, values obtained for measurement set (A,B,C,D,E,F,G,H) will depend on the configuration of system1800including the configuration of the sensing pad unit1826, and on the specifics of the proximate object1586, such as, but not limited to, size, shape, temperature and physical form.

With the embodiments and sensing pad unit configurations illustrated herein, the conductive elements of the sensing pad unit are kept electrically isolated from the surrounding environment, including when immersed in, or in contact with, objects or substances. Forms of electrical isolation may include, but are not limited to, a layer of air or a protective non-conductive coating.

With the embodiments and sensing pad unit configurations illustrated herein, the ground connections120and124may be replaced by a fixed voltage reference potential of between 0 volts and V+ where V+ is the digital power supply voltage. In these embodiments, the digital power supply voltage provides power to controller112.

With all embodiments, the ground may be connected to earth.

With all embodiments and sensing pad unit configurations, the shield pad may not be an absolute requirement but usage may depend on whether a symmetric directional sensitivity of the capacitive sensing pad is desired, or limited asymmetry in the directional sensitivity of the capacitive sensing pad is desired.

With all embodiments and sensing pad unit configurations, a ground plane may be added beneath the sensing pad unit.

The advantages of the present invention include, without limitation, the ability to identify, and/or discriminate between, different substances and different objects. These substances may be liquids, or they may be solids, or they may be pourable solids such as granulated or crystalline substances. Objects may be discrete items such as, but not limited to, humans, animals, and items of clothing, mobiles phones, books, newspapers, laptop computers and bottles of liquid. Objects may be parts of other objects such as parts of a human body, for example hands or fingers.

Applications for a discriminating capacitive sensor include, but are not limited to, seat occupancy in cars and public transport, process control, industrial automation, fuel sensors, robotics.

Applications for a capacitive sensor that measures material properties include, but are not limited to, process control, industrial automation, level sensors, purity sensors, temperature sensors and robotics.

In broad embodiment, the present invention is capacitive sensor which has at least one discriminating pad that can be switched between connections to ground and or a shield driver and that can identify and/or discriminate between different objects and substances, and can measure intrinsic electromagnetic properties such as Dielectric Constant and Dipole Moment.