News Column

Patent Issued for Conductivity Sensor

July 23, 2014



By a News Reporter-Staff News Editor at Electronics Newsweekly -- According to news reporting originating from Alexandria, Virginia, by VerticalNews journalists, a patent by the inventors Feldkamp, Joseph R. (Appleton, WI); Heller, Jeffrey Robert (Neenah, WI); Laudenslager, Douglas Glen (Firestone, CO), filed on January 30, 2013, was published online on July 8, 2014.

The assignee for this patent, patent number 8773117, is Kimberly-Clark Worldwide, Inc. (Neenah, WI).

Reporters obtained the following quote from the background information supplied by the inventors: "The use of conductivity measurements to analyze various characteristics of specimens such as human tissue specimens and geological specimens has been shown to yield many practical advantages. For example, conductivity measurements have been used to distinguish diseased tissue from healthy tissue. Both conventional electrode and induction coil methods have been used to perform conductivity measurements of various specimens.

"Conventional electrodes for measuring conductivity apply an AC voltage to a specimen of interest. The current traveling through the specimen is measured and the conductivity is computed. In some cases, many electrodes are attached so that imaging of the specimen is made possible in circumstances where conductivity varies spatially through the specimen.

"A disadvantage of conventional electrodes is that it requires direct electrical contact with the specimen of interest. This is particularly true for specimens having a surface that impedes the flow of current through the specimen. For example, the stratum corneum layer of the epidermis may impede the flow of current through a human tissue specimen, leading to variable conductivity measurements. Conventional electrodes may also exhibit electrode polarization, resulting in inaccurate conductivity measurements.

"Induction coil methods and devices for measuring conductivity have used a wide variety of induction coil designs including solenoids or simple loop type coils consisting of a few turns of wire. These coils may probe the specimen at depths allowing interferences from portions of the specimen that distort the conductivity measurement. Many of these devices also involve the use of expensive instrumentation to measure coil related parameters such as complex impedance and use circuitry that permits the induction coil to deviate from resonance as the coil is placed adjacent to a specimen, making measurement of conductivity more difficult.

"Therefore, a need currently exists for an induction coil conductivity sensor that overcomes these deficiencies. An induction coil conductivity sensor that probes a specimen at sufficient depths while avoiding unnecessary interferences from the specimen would be particularly beneficial. Additionally, an induction coil conductivity sensor that drives the sensor circuitry to resonance when the induction coil is placed adjacent to the specimen would also be particularly beneficial."

In addition to obtaining background information on this patent, VerticalNews editors also obtained the inventors' summary information for this patent: "In one aspect of the present invention, a conductivity sensor for measuring the conductivity of a specimen is provided. The conductivity sensor includes an oscillator configured to provide an input signal and a reactive circuit operatively connected to the oscillator. The reactive circuit has an induction coil, a capacitive element and a resistive element connected in parallel. The induction coil is configured to be placed adjacent to the specimen of interest. The conductivity sensor further includes a control circuit for driving the reactive circuit to resonance when the induction coil is placed adjacent to the specimen. The reactive circuit provides an output signal having a parameter indicative of the conductivity of the specimen when the reactive circuit is at resonance. In particular aspects of the present invention, the parameter of the output signal may be the admittance or the impedance of the reactive circuit.

"In a variation of this particular aspect of the present invention, the control circuit drives the reactive circuit to resonance by controlling the oscillator to provide a frequency sweep input signal. The frequency sweep input signal causes the reactive circuit to pass through resonance. The control circuit may include a voltage peak hold circuit and/or current peak hold circuit configured to determine the peak output voltage or peak output current of the reactive circuit. The peak hold circuits may be used to determine the output of the reactive circuit when the reactive circuit passes through resonance.

"In another variation of this particular aspect of the present invention, the control circuit drives the reactive circuit to resonance by using a phase-locked loop circuit configured to tune the reactive circuit to resonance when the induction coil is placed adjacent to the specimen. For instance, the phase-locked loop circuit may tune variable capacitive elements, such as varactor diodes, connected in the reactive circuit in order to drive the reactive circuit to resonance. The phase-locked loop circuit may include a phase comparator configured to determine the phase difference between a voltage output and a current output of the reactive circuit. The phase comparator may be further configured to provide a control signal to a controller such as a digital signal processor representative of a phase difference. The controller may be configured to control the capacitance of the variable capacitive element until the reactive circuit achieves resonance. In a variation of this particular aspect of the present invention, the phase-locked loop circuit may be configured to maintain resonance of the reactive circuit at a fixed input frequency of the input signal.

"In still another variation of this particular aspect of the present invention, the control circuit drives the reactive circuit to resonance by directing the variable capacitive element of the reactive circuit to provide a capacitance sweep through a range of capacitance. The capacitance sweep causes the reactive circuit to pass through resonance. The control circuit may include a voltage peak hold circuit and/or current peak hold circuit configured to determine the peak output voltage or peak output current of the reactive circuit. The peak hold circuits may be used to determine the output of the reactive circuit when the reactive circuit passes through resonance. The reactive circuit may pass through resonance at a fixed input frequency of the input signal.

"In another aspect of the present invention, a conductivity sensor having an induction coil adapted to be placed adjacent to a specimen is provided. The induction coil includes a first conductive element that spirals outward to an external perimeter and a second conductive element operably connected to the first conductive element. The second conductive element spirals inward from the external perimeter staggered relative to the first conductive element.

"In a variation of this particular aspect of the present invention, the induction coil may be located on a circuit board having a first side and an opposing second side. The first conductive element may spiral outward to an external perimeter on the first side of the circuit board and the second conductive element may spiral inward from the external perimeter on the second side of the circuit board. The external perimeter may have an external diameter in the range of about 5 mm to 120 mm, such as about 10 mm to 80 mm, such as about 30 mm to 40 mm, such as about 35 mm, or about 38 mm, or any other diameter or range of diameters therebetween.

"In another variation of this particular aspect of the present invention, the induction coil may have a circular shape, elongated shape, elliptical shape, rectangular shape, triangular shape, hemispherical shape, fructo-hemispherical shape, or any other shape.

"In a further variation of this particular aspect of the present invention, the induction coil may have a surface adapted to match the contours of the specimen. For instance, the induction coil may have a concave surface, a convex surface, or a waved surface designed to match the contours of the specimen.

"In still a further variation of this particular aspect of the present invention, the induction coil may include a protective coating on the induction coil. The protective coating may be an insulating polymer and may have a thickness in the range of about 0.05 mm to 1.2 mm, such as about 0.08 mm to 0.8 mm, such as about 0.1 mm, or about 0.2 mm, or about 0.5 mm to 1.0 mm, or any other thickness or range of thickness therebetween. The protective coating may be composed of a dielectric material having a dielectric constant of less than about 10, such as less than about 5.

"In still a further variation of this particular aspect of the present invention, the conductivity sensor comprises a base unit and a modular induction coil cartridge adapted to engage the base unit. The modular induction coil cartridge is removable from the base unit so that a variety of different modular induction coil cartridges may be used with a single base unit.

"A further aspect of the present invention is directed to a method for measuring the conductivity of a specimen. The method includes oscillating an input signal through a reactive circuit comprising an induction coil, a resistive element, and a capacitive element connected in parallel; placing the induction coil adjacent to the specimen; driving the reactive circuit to resonance; and measuring an output signal of the reactive circuit at resonance. The output signal has a parameter indicative of the conductivity of the specimen.

"In a variation of this particular aspect of the present invention, the step of driving the reactive circuit to resonance includes sweeping the frequency of the input signal so that the reactive circuit passes through resonance. In another variation of this particular aspect of the present invention, the step of driving the reactive circuit to resonance includes tuning the capacitance of the capacitive element until the reactive circuit achieves resonance. In a further variation of this particular aspect of the present invention, the step of driving the reactive circuit to resonance includes sweeping the capacitance of the capacitive element so that the reactive circuit passes through resonance.

"Still a further aspect of the present invention is directed to a conductivity sensor for continuously monitoring the conductivity of a specimen over a period of time. The conductivity sensor includes an induction coil for performing a conductivity measurement, a controller configured to direct the conductivity sensor to perform a series of conductivity measurements comprising a plurality of conductivity measurements taken over a period of time. The conductivity sensor also includes a housing. The housing may be adapted to maintain the conductivity sensor adjacent to the specimen while the series of conductivity measurements is being performed.

"In variations of this particular aspect of the present invention, the conductivity sensor may include a database configured to store the series of conductivity measurements. In particular aspects, the conductivity sensor may include a communications device for communicating the series of conductivity measurements to a remote device. In still other particular aspects, the conductivity sensor may comprise an alert system for triggering an alert when a conductivity measurement of the plurality of conductivity measurements reaches a predetermined threshold.

"In other variations of this particular aspect of the present invention, the housing of the conductivity sensor is adapted to be secured to an extremity of an individual. For example, the conductivity sensor may include a strap to secure the conductivity sensor to the extremity of the individual. In another particular aspect, the conductivity sensor may be secured to an individual by an adhesive material. In still other aspects, the conductivity sensor may be part of a medical sling used to support an extremity of an individual. In still other aspects, the conductivity sensor may be part of a garment or uniform worn by law enforcement or military personnel.

"Still a further aspect of the present disclosure is directed to a platform unit for measuring the conductivity of an individual. The platform unit includes a base unit configured to support an individual standing on the platform unit and an induction coil for performing a conductivity measurement of a foot of the individual standing on the platform unit. The platform unit may include a visual display configured to display the conductivity measurement to the individual. In variations of this particular aspect, the platform unit may comprise a plurality of induction coils for performing a conductivity measurement of a foot of an individual standing on the platform unit.

"These and other features, aspects and advantages of the present invention will become better understood with reference to the following description and appended claims. It is to be understood that different embodiments, as well as different presently preferred embodiments, of the present subject matter may include various combinations or configurations of presently disclosed features, steps, or elements, or their equivalents (including combinations of features, parts, or steps or configurations thereof not expressly shown in the figures or stated in the detailed description of such figures). Additional embodiments of the present subject matter, not necessarily expressed in the summarized section, may include and incorporate various combinations of aspects of features, components, or steps referenced in the summarized objects above, and/or other features, components, or steps as otherwise discussed in this application. Those of ordinary skill in the art will better appreciate the features and aspects of such embodiments, and others, upon review of the remainder of the specification."

For more information, see this patent: Feldkamp, Joseph R.; Heller, Jeffrey Robert; Laudenslager, Douglas Glen. Conductivity Sensor. U.S. Patent Number 8773117, filed January 30, 2013, and published online on July 8, 2014. Patent URL: http://patft.uspto.gov/netacgi/nph-Parser?Sect1=PTO1&Sect2=HITOFF&d=PALL&p=1&u=%2Fnetahtml%2FPTO%2Fsrchnum.htm&r=1&f=G&l=50&s1=8773117.PN.&OS=PN/8773117RS=PN/8773117

Keywords for this news article include: Electronics, Circuit Board, Kimberly-Clark Worldwide Inc.

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Source: Electronics Newsweekly


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