Patent Application
20210223336
Newly developed technologies for measuring magnetic fields have yielded devices and systems that are small, inherently inexpensive, operable at room temperature, and capable of reasonable sensitivity for magnetic field detection. One example of such technologies is the giant magnetoresistive (GMR) sensor, which can be useful in reading information stored on computer hard drives. However, despite widespread efforts, the sensitivity of even the latest technologies has proven inadequate for applications requiring high sensitivity in detecting magnetic fields, such as is required for clinical diagnostic devices. One specific clinical application in which the sensitivity of current technologies falls short is the monitoring of human heart function, for example, from outside the chest wall.
A major obstacle to achieving magnetic field measurement sensitivities is the effect of low-frequency l/f resistive noise produced by magnetic field sensors, such as GMR and tunneling magnetoresistance (TMR) sensors. In clinical applications, high sensitivity magnetic field detection is critical. For example, the magnetic field produced by the heart's electrical function is approximately one million times less than the Earth's magnetic field. The magnetic fields produced by the heart have low frequencies, frequencies that are in the same frequency range as the relatively strong l/f noise. One proposed solution is to shift the low-frequency cardiac fields to higher frequencies where the noise can be several orders of magnitude less. The basic phenomenon used to shift the frequency of a signal is well known and is used in many applications. When the strength of one sinusoidal signal is modulated by a second sinusoidal frequency, the resulting signal comprises of two sinusoidal signals, one with frequency given by the sum of the two initial frequencies and the other given by the difference of the two initial frequencies. Modulating one signal with another is effectively multiplying the two. Mathematically, multiplying two dissimilar sinusoids results in the sum and difference frequencies.
Microelectromechanical systems (MEMS) devices have been developed to shift the frequency of magnetic fields of interest in the vicinity of a magnetic field sensor, thus moving the signal of a magnetic field of interest from a low frequency where sensor noise may affect sensitivity of detection to a higher frequency where there exists significantly less sensor noise. MEMS devices can modulate the strength of the magnetic field by physically moving or flexing magnetic flux concentrators or flux guides placed within the magnetic field in proximity to the sensor, thereby deflecting or guiding the magnetic field near the sensor and altering the field strength detected by the sensor as a function of time. For example, some MEMS-based magnetic field sensing devices function by driving the outer ends of movable flux concentrator flaps up and down using electrostatics, which causes the inner ends of the flux concentrators to be repetitively moved closer to and then further away from a TMR sensor as the flux concentrators are driven up and down by the electrostatics, thus modulating the magnetic field detected or “seen” by the sensor.
In some cases, MEMS-based magnetic field sensing devices operate by moving a magnetic flux guide close to and parallel to a sensor and then moving the flux guide away from the sensor. When the flux guide is brought near to the sensor, the magnetic flux preferentially travels through the low-resistance flux guide and not the sensor. When the flux guide is moved away from the sensor, the sensor “sees” more magnetic flux. In some cases, only a portion of the flux guide is moved toward and away from the sensor, contacting stationary portions of the flux guide on either side of the sensor when the movable flux guide is brought near to the sensor, thus providing a continuous magnetic flux path when the movable flux guide is moved into contact with the stationary flux guide portions.
Unfortunately, existing methods of modulating a magnetic field seen by a sensor have low efficiency and have not been shown to significantly improve sensor sensitivity. Further, the complexity of fabricating a sensor system that relies on mechanically moving a portion of the magnetic detection apparatus, as is the case in MEMS-based systems, also renders such devices exceedingly difficult to manufacture and draws into question their utility in applications requiring high sensitivity. Therefore, there are needs for improved magnetic field sensors and sensor systems that address these drawbacks.
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Systems, devices, and methods for measuring magnetic fields are provided herein. The embodiments of the disclosure can address at least some of the above limitations and deficiencies.
In various aspects, a system for detecting a magnetic field comprises a magnetic field sensor; and one or more current-driven flux modulators (CDFMs), each CDFM comprising a magnetically soft material; and one or more current sources electrically coupled to the one or more of CDFMs. In some embodiments, a magnetic permeability of the magnetically soft material decreases when electrical current is applied to the CDFM. In some embodiments, a direction of sensitivity of the magnetic field sensor is oriented at an angle of zero relative to a longitudinal axis of the one or more CDFMs defined by a proximal end and a distal end of the CDFMs. In some embodiments, a direction of sensitivity of the magnetic field sensor is oriented at a non-zero angle relative to a longitudinal axis of one or more CDFMs defined by a proximal end and a distal end of the CDFM. In some embodiments, a proximal end of the one or more CDFMs is positioned proximal to the magnetic field sensor. In some embodiments, at least one CDFM of the one or more CDFMs comprises a microwire. In some embodiments, a first current source of the one or more current sources provides a first electrical drive current having a first repetitive electrical drive current pattern. In some embodiments, the first repetitive electrical drive current pattern comprises an oscillatory waveform. In some embodiments, the oscillatory waveform comprises a frequency greater than a frequency of a magnetic field signal of interest. In some embodiments, a second current source of the one or more current sources is configured to provide a second repetitive electrical drive current having a different frequency than a frequency of the first repetitive electrical drive current. In some embodiments, the system is configured to apply the first repetitive electrical drive current to a first CDFM and the second repetitive electrical drive current to a second CDFM, wherein a longitudinal axis of the first CDFM and a longitudinal axis of the second CDFM are oriented at a non-zero angle with respect to one another. In some embodiments, the magnetic field sensor comprises a magnetoresistive sensor. In some embodiments, the magnetoresistive sensor is a giant magnetoresistive sensor or a tunneling magnetoresistive sensor. In some embodiments, the magnetic field sensor comprises a giant magnetoimpedance sensor. In some embodiments, the magnetic field sensor comprises a coil comprising an electrically conductive material and a core comprising a magnetically soft material, wherein the coil is disposed at least partially around the core. In some embodiments, the system is configured to detect the magnetic field based on an electrical current or voltage in the coil.
In various aspects, a device for controlling the flow of magnetic flux from a first location to a second location comprises: an elongate flux modulator comprising a first electrical connection point at a first end of the elongate flux modulator and a second electrical connection point at a second end of the elongate flux modulator, wherein the first and second electrical connection points are couplable to an electrical current source, wherein the elongate flux modulator comprises a magnetically soft material and wherein the magnetically soft material changes magnetic permeability upon the application of an electrical current. In some embodiments, the second location comprises a magnetic field sensor. In some embodiments, the magnetic permeability of the magnetically soft material decreases upon application of the electrical current. In some embodiments, the magnetic permeability of the magnetically soft material increases upon removal of an electrical current applied to the magnetically soft material.
In various aspects, a method of detecting a magnetic field comprises: providing a magnetic field sensor within a magnetic field; providing one or more current-driven flux modulators (CDFMs) proximal to the magnetic field sensor, each CDFM of the one or more CDFMs comprising a magnetically permeable material; applying one or more electrical drive currents to the one or more CDFMs; and detecting the magnetic field with the magnetic field sensor. In some embodiments, applying one or more electrical drive currents changes the magnetic permeability of the one or more CDFMs. In some embodiments, applying the one or more electrical drive currents decreases the magnetic permeability of the one or more CDFMs. In some embodiments, the electrical drive current comprises an oscillatory waveform. In some embodiments, the one or more electrical drive currents comprises an oscillation frequency greater than a frequency of the magnetic field prior to applying the one or more electrical drive currents to the one or more CDFMs. In some embodiments, a proximal end of the one or more CDFMs is positioned proximal to the magnetic field sensor. In some embodiments, the method further comprises filtering a signal obtained by detecting the magnetic field. In some embodiments, the filtering comprises applying a high pass filter to the signal. In some embodiments, the one or more electrical drive currents comprises a plurality of electrical drive currents and wherein a first electrical drive current of the plurality of electrical drive currents comprises a repetitive drive current pattern with a different frequency than a frequency of a second electrical drive current of the plurality of electrical drive currents. In some embodiments, the first electrical drive current is applied to a first CDFM and a second electrical drive current is applied to a second CDFM, wherein a longitudinal axis of the first CDFM and a longitudinal axis of the second CDFM are oriented at a non-zero angle with respect to one another. In some embodiments, the magnetic field sensor comprises a magnetoresistive sensor. In some embodiments, the magnetic field sensor comprises a giant magnetoresistive sensor or a tunneling magnetoresistive sensor. In some embodiments, the magnetic field sensor comprises a giant magnetoimpedance sensor. In some embodiments, the CDFM comprises a microwire. In some embodiments, the magnetic field sensor comprises a coil comprising an electrically conductive material and a core comprising a magnetically soft material, wherein the coil is disposed at least partially around the core. In some embodiments, the method further comprises detecting the magnetic field by detecting an electrical current or voltage in the coil.
Not necessarily all such aspects or advantages are achieved by any particular embodiment. Thus, various embodiments may be carried out in a manner that achieves or optimizes one advantage or group of advantages taught herein without necessarily achieving other aspects or advantages as may also be taught or suggested herein.
All publications, patents, and patent applications mentioned in this specification are herein incorporated by reference to the same extent as if each individual publication, patent, or patent application was specifically and individually indicated to be incorporated by reference.
The novel features of the present disclosure are set forth with particularity in the appended claims. A better understanding of the features and advantages of the present disclosure will be obtained by reference to the following detailed description that sets forth illustrative embodiments, in which the principles of the present disclosure are utilized, and the accompanying drawings of which:
Described herein are devices, systems, and methods for the detection of magnetic fields and for obtaining improved sensitivity in the measurement or detection magnetic fields. A major challenge to existing magnetic field sensors is that they can produce far more noise in the low-frequency ranges than in high frequencies. Much of this low-frequency noise can be low-frequency l/f noise, an electromagnetic noise primarily affecting the low end of the frequency range and occurring in most electronic devices, sometimes referred to as “pink noise.” The l/f noise can present a major challenge in applications requiring sensitive measurement of magnetic signals in a low frequency band, such as biological signals (e.g., magnetic fields created during cardiac function).
As presented herein, the effects of electromagnetic noise (e.g., l/f noise) can be greatly reduced and the sensitivity of a magnetic field sensor system (e.g., a magnetic field detection system) greatly increased by modulating (e.g., shifting) the apparent frequency of a magnetic field, as detected (or “seen”) by a magnetic sensor. In particular, the sensitivity of a magnetic field sensor can be improved by modulating an electrical current in a magnetically conductive material (e.g., a magnetic flux conductor, such as a magnetic flux guide) positioned in the vicinity of the sensor. Modulation of an electrical current in a magnetically conductive material positioned in the vicinity of a magnetic field sensor can modulate the amplitude of the magnetic field near the magnetic field sensor, thus altering the frequency of the field of interest, as detected (or “seen”) by the magnetic field sensor and effectively shifting the frequency of a magnetic field signal of interest (e.g., from low frequency to a higher frequency) from the perspective of the magnetic field sensor. Without wishing to be bound by theory, this can occur as the result of temporal modulation of the magnetic permeability of the magnetically conductive material through which the temporally modulated current flows, which can directly affect the degree to which the magnetically conductive material allows or disallows magnetic flux through the material (e.g., and through or across the magnetic field sensor).
By modulating a current within the magnetically conductive material, it is not necessary to physically move a portion of the magnetic field sensor system (e.g., using mechanically driven modulators) to shift the frequency of the field, in many embodiments. This can simplify the design and manufacture of the system. For example, in many cases, no additional space or clearance is needed for physical oscillation of components. In contrast to existing (e.g., mechanically driven modulator) systems, mechanical fatigue of components may not be a concern in the systems presented herein. Furthermore, fabrication and assembly of the components of a current-mediated magnetic field modulator (e.g., as described herein) can be simpler than in systems requiring mechanically-driven modulators, such as MEMS-based systems. Mechanical resonances that may arise from mechanically driven modulators may not be a concern in systems that rely on current-mediated magnetic field modulation, as described herein. Importantly, current-mediated magnetic field modulation can be used to produce a wider range of magnetic frequency shifts and can shift magnetic fields to higher frequencies than existing technologies, such as those relying on mechanically-driven modulators. Current-mediated magnetic field modulation can also be tuned and adjusted more easily than systems reliant on mechanically-driven modulators. For example, a new input current pattern can easily be implemented in current-mediated magnetic field modulation systems to change the frequency shift applied to the magnetic field of interest, allowing facile adjustments between or during magnetic field measurements, for example, to adjust for dynamic changes in environmental noise.
After a magnetic field (e.g., a modulated magnetic field) is detected, for example by a magnetic field sensor, the detected magnetic field signals can be shifted back to their original frequencies. In many cases, the detected magnetic field signals can be shifted back to their original frequencies in silico, for example, using a computer processor and computer program stored thereupon to process the detected magnetic field signal. In some cases, a detected magnetic field signal can be filtered, e.g., via incorporation of solid state electronic architecture into the magnetic field sensor system and/or software-based computer signal processing.
A magnetic field sensor system can comprise a sensor, for instance a magnetoresistive sensor capable of detecting magnetic fields (e.g., a magnetic field sensor). In some cases, a magnetoresistive sensor can be a tunnel magnetoresistive sensor (TMR). In some cases, a magnetoresistive sensor can be a giant magnetoresistive (GMR) sensor. In some embodiments, a sensor of a magnetic field sensor system can be not a magnetoresistive sensor. For instance, a sensor of a magnetic field sensor system can be a giant magnetoimpedance (GMI) sensor. In some embodiments, additional or alternative sensor technologies can be used in magnetic field sensor systems presented herein.
A magnetic field sensor system can comprise one or more magnetic flux paths. A flux path can comprise one or more of a current-driven flux modulator (CDFM), a flux guide, or a flux concentrator. In many cases, a CDFM can be used to modulate a magnetic flux detected by a sensor of a magnetic field sensor system (e.g., by driving a temporally dynamic current pattern through the CDFM, for instance, to vary magnetic permeability in the CDFM). A magnetic field sensor system comprising a CDFM can achieve higher magnetic field modulation efficiency than existing technologies (e.g., by modulating a magnetic flux of a magnetic field signal of interest at a high frequency, which can separate the signal of interest from environmental magnetic noise). For example, a magnetic field sensor system comprising one or more CDFMs can have a much higher ratio of magnetic flux conduction to non-conduction compared to prior art methods. In many cases, positioning a magnetic flux path in close proximity to a magnetic field sensor can aid in guiding or concentrating magnetic fields of interest in one or more desired directions. A magnetic flux path can be oriented such that a magnetic field is guided through the magnetic flux path and toward a magnetic field sensor of a magnetic field sensor system. For instance, a magnetic flux path comprising a microwire can be oriented such that one end of the microwire is pointed toward the magnetic field sensor. In some cases, a magnetic flux path comprises a microwire. A magnetic flux path can comprise a magnetically soft material. In many cases, a magnetic flux path has a high magnetic permeability. In some cases, a magnetic flux path can have a magnetic permeability of from 0.00001 Henries/meter (H/m) to 1.5 H/m. In some embodiments, a material comprising at least a portion of a magnetic flux path can have a magnetic permeability of from 0.01 H/m to 1.5 H/m. In some embodiments, a material comprising at least a portion of a magnetic flux path can have a magnetic permeability of from 0.01 H/m to 0.05 H/m, 0.01 H/m to 0.1 H/m, 0.01 H/m to 0.25 H/m, 0.01 H/m to 0.5 H/m, 0.01 H/m to 0.75 H/m, 0.01 H/m to 1 H/m, 0.01 H/m to 1.25 H/m, 0.01 H/m to 1.5 H/m, 0.05 H/m to 0.1 H/m, 0.05 H/m to 0.25 H/m, 0.05 H/m to 0.5 H/m, 0.05 H/m to 0.75 H/m, 0.05 H/m to 1 H/m, 0.05 H/m to 1.25 H/m, 0.05 H/m to 1.5 H/m, 0.1 H/m to 0.25 H/m, 0.1 H/m to 0.5 H/m, 0.1 H/m to 0.75 H/m, 0.1 H/m to 1 H/m, 0.1 H/m to 1.25 H/m, 0.1 H/m to 1.5 H/m, 0.25 H/m to 0.5 H/m, 0.25 H/m to 0.75 H/m, 0.25 H/m to 1 H/m, 0.25 H/m to 1.25 H/m, 0.25 H/m to 1.5 H/m, 0.5 H/m to 0.75 H/m, 0.5 H/m to 1 H/m, 0.5 H/m to 1.25 H/m, 0.5 H/m to 1.5 H/m, 0.75 H/m to 1 H/m, 0.75 H/m to 1.25 H/m, 0.75 H/m to 1.5 H/m, 1 H/m to 1.25 H/m, 1 H/m to 1.5 H/m, or 1.25 H/m to 1.5 H/m. In some embodiments, a material comprising at least a portion of a magnetic flux path can have a magnetic permeability of from 0.01 H/m, 0.05 H/m, 0.1 H/m, 0.25 H/m, 0.5 H/m, 0.75 H/m, 1 H/m, 1.25 H/m, or 1.5 H/m. In some embodiments, a material comprising at least a portion of a magnetic flux path can have a magnetic permeability of from at least 0.01 H/m, 0.05 H/m, 0.1 H/m, 0.25 H/m, 0.5 H/m, 0.75 H/m, 1 H/m, 1.25 H/m, or 1.5 H/m. In some embodiments, a material comprising at least a portion of a magnetic flux path can have a magnetic permeability of from at most 0.01 H/m, 0.05 H/m, 0.1 H/m, 0.25 H/m, 0.5 H/m, 0.75 H/m, 1 H/m, 1.25 H/m, or 1.5 H/m. A magnetically soft material of a magnetic flux path (e.g., a CDFM) can be an alloy. For instance, a portion of a magnetic flux path (e.g., a CDFM) can comprise one or more magnetically soft alloys selected from iron-silicon alloys, cobalt-iron alloys, nickel-iron alloys, and soft ferrites. In many cases, a portion of a magnetic flux path can also be electrically conductive. In many cases, a portion of a magnetic flux path can comprise a magnetically soft material that experiences a change in magnetic permeability when a current is passed through the material. In some cases, a portion of a magnetic flux path can comprise cobalt, nickel, iron, ferrite, steel, molybdenum, zinc, Metglas Permalloy, MuMETAL®, NANOPERM®, or a combination thereof. A magnetic field sensor system can comprise a plurality of magnetic flux paths. For instance, a magnetic field sensor can comprise 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, from 13 to 20, from 20 to 30, from 30 to 40, from 40 to 50, or more than 50 magnetic flux paths. A magnetic flux path of a magnetic field sensor system, such as one or more CDFM(s) of the magnetic field sensor system can be constructed on a printed circuit board or other base with strip-lines or by using alternative techniques known in the art.
A CDFM can comprise a microwire. In many cases, a CDFM can comprise a magnetically soft material that experiences a change in magnetic permeability when a current is passed through the material. In some embodiments, a CDFM can comprise a material having high permeability. High permeability can aid in a material's ability to guide magnetic flux toward a sensor. In some embodiments, a material useful in a CDFM can have a permeability of from 0.00001 H/m to 1.5 H/m. In some embodiments, a material useful in a CDFM can have a permeability of from 0.01 H/m to 0.1 H/m, 0.01 H/m to 0.25 H/m, 0.01 H/m to 0.5 H/m, 0.01 H/m to 0.75 H/m, 0.01 H/m to 1.0 H/m, 0.01 H/m to 1.25 H/m, 0.01 H/m to 1.5 H/m, 0.1 H/m to 0.5 H/m, 0.1 H/m to 0.75 H/m, 0.1 H/m to 1.0 H/m, 0.1 H/m to 1.25 H/m, 0.1 H/m to 1.5 H/m, 0.5 H/m to 1.0 H/m, 0.5 H/m to 1.25 H/m, 0.5 H/m to 1.5 H/m, 0.75 H/m to 1.25 H/m, 0.75 H/m to 1.5 H/m, or 1.0 H/m to 1.5 H/m. In some embodiments, a material useful in a CDFM can have a permeability of from 0.00001 H/m, 0.0001 H/m, 0.001 H/m, 0.01 H/m, 0.1 H/m, or 1 H/m. In some embodiments, a material useful in a CDFM can have a permeability of from at least 0.00001 H/m, 0.0001 H/m, 0.001 H/m, 0.01 H/m, 0.1 H/m, or 1 H/m. In some embodiments, a material useful in a CDFM can have a permeability of from at most 0.00001 H/m, 0.0001 H/m, 0.001 H/m, 0.01 H/m, 0.1 H/m, or 1 H/m.
In some cases, a CDFM can comprise cobalt, nickel, iron, ferrite, steel, molybdenum, zinc, Metglas®, Permalloy, MuMETAL®, NANOPERM®, or a combination thereof. A CDFM can comprise a magnetically soft material. In many cases, a magnetically soft material of a CDFM can be an alloy. For instance, a CDFM can comprise one or more magnetically soft alloys selected from iron-silicon alloys, cobalt-iron alloys, nickel-iron alloys, and soft ferrites. In many cases, a CDFM can also be electrically conductive. In some cases, a CDFM can comprise a non-conductive material having high magnetic permeability, such as ferrite. For example, a CDFM can comprise a non-conductive material with high magnetic permeability, e.g., in order to electrically isolate the current-modulated portion(s) of the CDFM from a sensor of the magnetic field sensor system. In some cases, such non-conductive but highly permeable materials can aid in design of the magnetic field sensor system, as a non-conductive end cap on the CDFM that allows magnetic flux to pass through can allow the CDFM to be positioned extremely close to the sensor without allowing an electrically conductive bridge. Minimizing the distance between the CDFM and the sensor can aid in optimizing transmission of a magnetic field of interest to the sensor.
The physical arrangement of one or more components of a magnetic field sensor system can affect the sensitivity of system for detecting a magnetic field of interest. The positioning of one or more CDFMs relative to a sensor and a magnetic field of interest can be leveraged to increase the sensitivity of the system, for example, as described in the system configurations discussed below. In many embodiments, a device or system disclosed herein can control the flow of magnetic flux from a first location to a second location, for example, from a distal end of a CDFM to a second location, such as a proximal end of the CDFM or the location of a sensor. In some cases, a first (e.g., axially aligned) CDFM 12 can be positioned “upstream” in the magnetic field relative to sensor 11, e.g., wherein a magnetic field passes through the CDFM before passing through the sensor. In some cases, a second (e.g., axially aligned) CDFM 13 can be positioned “downstream” in the magnetic field relative to sensor 11 (e.g., wherein a magnetic field passes through the CDFM after it passes through the sensor), for example, to steady and further establish the magnetic flux through the sensor (e.g., when no current is driven through the CDFM). In some cases, for instance in “axial” configurations or “non-axial” configurations, a first end (e.g., proximal end) of a CDFM can be oriented proximal to a sensor relative to a second end (e.g., distal end) of the CDFM. In some cases, a second end (e.g., a distal end) of a CDFM can be oriented distal to a sensor relative to a first end (e.g., proximal end) the CDFM. While several examples and figures described herein illustrate systems having two or four CDFMs, it is contemplated that a system can comprise any number of CDFMs (e.g., with any number of CDFMs positioned in-line with one another or with one or more of the CDFMs oriented parallel to or at an angle to one or more of the other CDFMs). In some cases, a magnetic field sensor system can comprise 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 10-15, 15-20, 20-30, 30-50, or more than 50 CDFMs. It may be beneficial for the CDFM to consist of an even number (e.g., two or four) microwires with the current being driven in opposite directions at a given time in any two CDFM microwires in close proximity to one another. In some cases, such configurations can minimize components of magnetic field(s) generated by the microwires.
A magnetic field sensor system having an “axial” configuration in accordance with various embodiments is shown in
A magnetic field sensor system can comprise one or more current source(s) and electrically conductive leads electrically joining the one or more current source(s) to one or more of the CDFMs of the magnetic field sensor system. The current source and electrical connections (e.g., to CDFM 12 and CDFM 13) are not shown in
In some cases, a current source can be used or programmed to drive one or more CDFMs with an electrical current having a specific pattern. For instance, a current source can drive a CDFM with a current, or “drive-current” (e.g., an electrical drive current), e.g., having a constant amplitude or a temporally modulated (e.g., sinusoidal) amplitude. In some cases, an electrical drive current can be repetitive, for example, wherein all or a portion of the waveform repeats over time. In some cases, a drive current having a constant amplitude (e.g., by applying a constant voltage to a first and second electrical connection of a CDFM) can be repeatedly applied and removed from a CDFM, for example, in order to drive the CDFM with a current having a square wave pattern. In some cases, a drive current may reverse direction over time (e.g., repeatedly), for instance, as is the case in some sinusoidal or square wave drive currents. Plot 16 of
Plot 17 of
It can be seen from plot 17 that the aggregate magnetic field “seen” by sensor 11 may have two components, one alternating, or AC, and the other static, or DC. The trace 17 shows five or six cycles of a square wave, or AC component, indicated by 18. The AC component is added to a DC component indicated by 19.
A magnetic field sensor system can comprise one or more flux concentrators. In some cases, a magnetic field sensor system can comprise a plurality of flux concentrators. Flux concentrators can aid in increasing the flux observed by a sensor of a magnetic field sensor system (e.g., as shown in
A magnetic field sensor system can comprise one or more flux guides (e.g., flux guide 24 or flux guide 25, as shown in
It can be advantageous to select and position (e.g., place or orient relative to other components) the components of a magnetic field sensor system to minimize any potential impact of un-modulated magnetic flux (e.g., magnetic field signals other than those of interest, for example, resulting from environmental sources). For example, a magnetic field sensor system comprising a GMI type sensor can be assembled using a shorter GMI microwire than usual to limit the impact of un-modulated magnetic flux. Electromagnetic shielding can also be selectively applied to a magnetic field sensor in order to reduce the impact of environmental and other un-modulated magnetic fields on the sensor's measurements. In some cases, the impact of un-modulated magnetic fields on sensor readings can be evaluated by determining detectable magnetic field strengths when the CDFM(s) of a magnetic field sensor system are not conducting flux (e.g., when permeability in the CDFM(s) is low). Such a technique can be useful in evaluating modulation efficiency and in designing magnetic field sensor system composition and spatial layout, as it can provide a baseline magnetic field reading for comparison and/or optimization.
In some cases, it can be advantageous to electrically couple the drive-current of two or more CDFMs. In some embodiments, two or more CDFMs can be electrically coupled across a magnetic field sensor, for example, to simplify delivery of current to the CDFMs and/or to synchronize current in a plurality of CDFMs. To reduce the chance of generating a magnetic field detectable to the magnetic field sensor, an electrically conductive material that does not produce a magnetic field that can be seen by the sensor when driven with current (e.g., copper tubing, in which very little magnetic field is produced, even when it is conducting current.) can be used to connect two or more CDFMs across the sensor. It can also be advantageous to electrically insulate the CDFM(s) from the sensor(s) (and, in some cases, from one another). In some cases, for example, wherein the sensor comprises a microwire (e.g., a GMI sensor), the microwires can be placed end-to-end (or side-by-side) with a thin electrically insulating film between them.
In many cases, a magnetic field sensor (e.g., sensor 11) can detect at least a portion of an applied magnetic field B, for instance, regardless of the action of the CDFMs. In some cases, CDFMs may still conduct some flux even when the drive-current is flowing (e.g., when magnetic permeability in the CDFM is low). In some cases, the magnetic field sensor may see a portion of the magnetic field B that is not modified (e.g., un-modulated) by the action of the CDFMs. However, when the drive-currents are not flowing, the CDFMs and, optionally, flux concentrators of the system can allow more magnetic flux to reach the magnetic field sensor. Thus, in many cases, a magnetic field sensor of a magnetic field sensor system can detect a (e.g., un-modulated) magnetic field present while a drive-current is applied to a CDFM in addition to a (e.g., modulated) magnetic field conducted to the sensor by the CDFM(s) and optional flux guide(s) and flux concentrator(s) at the same time. Accordingly, the aggregate magnetic field signal detected by a magnetic field sensor can comprise both a low-frequency (e.g., un-modulated) magnetic field signal component and high-frequency (e.g., modulated) magnetic field signal component. Using the methods, systems, and devices described herein, a magnetic field signal of interest (e.g., which may be modulated to a high frequency using CDFMs) can be separated from low-frequency noise generated by environmental sources, such as the magnetic field sensor itself, which remains at low frequencies during operation of the magnetic field sensor system.
An aggregate magnetic field signal (e.g., comprising a low-frequency component and/or a high-frequency component) can be filtered. For example, an aggregate magnetic field signal can be filtered either before the detected magnetic field signal is returned from a sensor to a computer or display for user presentation or computer memory storage (e.g., using solid state electrical filtering architectures) or after the detected magnetic field signal is returned to a computer or display for user presentation or computer memory storage (e.g., using post-processing software). In some cases, a high-pass filter (e.g., comprising solid state electrical components or software based signal filtering) can be used to filter (e.g., reduce or eliminate) low-frequency noise from the magnetic signal. In some cases, digital filtering (for example, using computer software) can be applied after a magnetic signal has been Fourier transformed to a frequency-domain signal. In some cases, digital filtering can be applied to the signal in the time domain.
High-frequency components of a detected magnetic field signal can be ‘de-modulated’ in several ways. For instance, a high-frequency magnetic field signal can be rectified and filtered (e.g., using a low-pass filter. Because the exact frequency and phase of the modulation of the magnetic field signal of interest is known (e.g., because the frequency modulation can be based on the frequency modulation of the drive current applied to the CDFMs), phase-coherent de-modulation techniques may be used to isolate magnetic field signal(s) of interest modulated prior to detection by current modulation of CDFMs in the system used to acquire the magnetic field signal(s). Other methods of obtaining the desired (e.g., frequency based) information from the signal may be used. Examples of such signal processing methods can incorporate techniques known in the literature. It is also contemplated that a first magnetic field signal of interest can be separated from a second magnetic field signal of interest (e.g., where the second magnetic field signal of interest is in a direction perpendicular to that of the first magnetic field signal of interest) by modulating two sets of CDFMs (e.g., wherein the first set of CDFMs is configured similar to the system shown in FIG.3 and the second set of CDFMs is oriented perpendicularly to the first set of CDFMs) using drive currents having different frequencies in each of the two sets of CDFMs.
A mentioned above, certain architectures of magnetic field sensor systems can be limited in that the magnetic field sensor may report or “see” a portion of an applied magnetic field B even when the CDFMs are not conducting magnetic flux (e.g., when current is driven through the CDFMs to reduce magnetic permeability of the CDFMs). As show in
Flux guides such as flux guide 24 and flux guide 25 can be added to improve the flux linkage between the CDFMs and the sensor. Optional flux concentrators (e.g., flux concentrator 26 and flux concentrator 27) are also shown. CDFM(s) of the system (e.g., CDFM 22 and CDFM 23) can be oriented (e.g., bent, tilted, or turned) in toward center-line 28 in order to reduce the net vertical-component of the field reported by the sensor.
A signal obtained from a magnetic field sensor system comprising the configuration shown in
The sensor in the
With four CDFMs, two at each end of the sensor and at or near right angles to the direction of highest sensitivity of the sensor (e.g., indicated with an arrow in
Plot 38 of
As with the other configurations described herein, the CDFMs can be curved or tilted in toward the center line 311 or otherwise arranged in order to minimize the signal from the field component in the sensor's original direction of sensitivity.
With well-matched CDFMs, the field seen by the sensor may have no low-frequency component and the peak-to-peak strength of the modulated field may be equal to twice the peak-to-peak strength of the field obtained by the previous crossed-sensor or coaxial configurations. In some cases, e.g., when the CDFMs are well matched, the strength of the un-modulated low-frequency field may be vanishingly small. Thus, the modulation efficiency may be as high as 300%, depending on the efficiency of the CDFMs. In some embodiments, magnetic field modulation efficiency can be 20 percent to 300 percent. In some embodiments, magnetic field modulation efficiency can be 20 percent to 50 percent, 20 percent to 75 percent, 20 percent to 100 percent, 20 percent to 125 percent, 20 percent to 150 percent, 20 percent to 175 percent, 20 percent to 200 percent, 20 percent to 250 percent, 20 percent to 300 percent, 50 percent to 75 percent, 50 percent to 100 percent, 50 percent to 125 percent, 50 percent to 150 percent, 50 percent to 175 percent, 50 percent to 200 percent, 50 percent to 250 percent, 50 percent to 300 percent, 75 percent to 100 percent, 75 percent to 125 percent, 75 percent to 150 percent, 75 percent to 175 percent, 75 percent to 200 percent, 75 percent to 250 percent, 75 percent to 300 percent, 100 percent to 125 percent, 100 percent to 150 percent, 100 percent to 175 percent, 100 percent to 200 percent, 100 percent to 250 percent, 100 percent to 300 percent, 125 percent to 150 percent, 125 percent to 175 percent, 125 percent to 200 percent, 125 percent to 250 percent, 125 percent to 300 percent, 150 percent to 175 percent, 150 percent to 200 percent, 150 percent to 250 percent, 150 percent to 300 percent, 175 percent to 200 percent, 175 percent to 250 percent, 175 percent to 300 percent, 200 percent to 250 percent, 200 percent to 300 percent, or 250 percent to 300 percent. In some embodiments, magnetic field modulation efficiency can be 20 percent, 50 percent, 75 percent, 100 percent, 125 percent, 150 percent, 175 percent, 200 percent, 250 percent, or 300 percent. In some embodiments, magnetic field modulation efficiency can be at least 20 percent, 50 percent, 75 percent, 100 percent, 125 percent, 150 percent, 175 percent, 200 percent, 250 percent, or 300 percent. In some embodiments, magnetic field modulation efficiency can be at most 20 percent, 50 percent, 75 percent, 100 percent, 125 percent, 150 percent, 175 percent, 200 percent, 250 percent, or 300 percent. Modulation efficiency may be determined as the percentage of the original magnetic signal that is shifted to a different (e.g., higher) frequency.
The two CDFMs on either side of the sensor 41 (e.g., CDFM 42 and 44 and/or CDFMs 43 and 45) can be disposed within in open-ended tubes or boxes comprising an electrically conductive material. As one microwire in the tube conducts current, the flux it ejects may increase the flux in the other microwire, which may increase the performance of the system.
One benefit of bipolar field modulation is that by subtracting the ‘negative’ signal from the ‘positive’ signal, the result is a signal twice as strong with several unwanted signal components cancelling each other. A non-zero or drifting baseline, for example, may be normalized and removed from the difference signal.
In some cases, the sensor can be replaced with a coil of wire, optionally, surrounding a piece of magnetic material, herein denoted as a ‘core’. For example, the above sensor configurations can be modified by replacing the magnetic field sensor with a coil of wire (e.g., coil 51 shown in
Signals 61 and 63 can have similar shapes as signals described in U.S. Patent Publication No. US 2020/0256930 A1 and PCT Patent Publication No. WO2020167551A1, which are incorporated herein in its entirety and for all purposes, for current-sensing GMI sensors. The signal can rapidly increase when the drive-current turns on and then decays exponentially with time. In some cases, the signal can then rapidly increase again, but with the opposite polarity, e.g., when the drive-current turns off. Note that the current pulse 62 can create a positive-going signal and current pulse 64 can create a similar but negative-going signal. When the CDFM sensor was rotated so that the Earth's field was in the other direction, the polarity of both signals reversed. The results presented in
In some cases, a magnetic field sensor system can detect a magnetic field in a plurality of directions simultaneously. In some cases, a magnetic field sensor system can comprise a muti-axis sensor. In some cases, a magnetic field sensor system can comprise a plurality of co-axial (or substantially parallel) CDFMs and one or more additional CDFMs disposed at an angle to the plurality of co-axial or substantially parallel CDFMs. In some cases, such a sensor configuration may be referred to as a multi-axis sensor. In some cases, the one or more additional CDFMs can be disposed at a non-zero angle (e.g., an angle from 15 degrees to 165 degrees or from 45 degrees to 90 degrees) relative to one or more of the pluralities of co-axial or substantially parallel CDFMs. For example, a first and second CDFM can be oriented such that a longitudinal axis of the first CDFM (e.g., which can run from a proximal end of the CDFM to a proximal end of the CDFM, for instance, through a center point of the CDFM) can be at a non-zero angle relative to a longitudinal axis of a second CDFM) is at a non-zero angle relative to a longitudinal axis of the second CDFM. In some cases, a first and second CDFM can be oriented such that a longitudinal axis of the first CDFM is at an angle of zero (e.g., axially in-line or parallel) relative to a longitudinal axis of the second CDFM. By adding additional and similar CDFMs in a different direction, such as in a direction perpendicular to the page in
Various drive current patterns can be used to modulate the electrical current within a component of a magnetic field sensor system. An amplitude and/or frequency of a drive current pattern can correlate to the amplitude and/or frequency with which a magnetic field is modulated.
For instance, a drive current pattern (e.g., a periodic or oscillatory drive current pattern) with a higher maximum amplitude (and, in some cases, a lower minimum amplitude) may evoke a modulated magnetic field with a greater dynamic range and/or with more rapid falloff and/or rises in magnetic flux. In many cases, the frequency of oscillation or reversal of a drive current in a magnetically conductive component of a magnetic field sensor system can determine, at least in part, the frequency of a modulated magnetic field.
In a multi-axis sensor, each magnetic field signal of two or more detected magnetic field signals, e.g., which have been detected in a respective direction of the two or more axial directions using one or more set of CDFMs oriented in each of the respective directions, can be acquired separately by time sharing the drive-currents (e.g., temporally separating the application of drive current to a CDFM or set of CDFMs oriented in each direction). Alternatively or additionally, the two magnetic field signals detected in each different direction can be distinguished from one other by driving CDFM(s) in each different direction with drive current patterns having different drive frequencies (e.g., and separately processing the signals from those frequency bands after raw magnetic field data acquisition with the sensor(s)).
The electrical drive-current in a CDFM and the electrically conductive components connected to it can produce magnetic fields that may affect the field seen by the sensor. These fields from a CDFM could potentially affect the data pertaining to a magnetic field of interest since the drive-current may be flowing when the measurement is being performed. The impact of additional magnetic fields on magnetic field sensor readings can be minimized through careful design and placement of conductors (e.g., CDFMs, flux guides, and/or flux concentrators). For example, positioning leads for delivering a drive current to the CDFMs in close proximity to one another (e.g., evaluated at the point of coupling with the CDFMs) minimizes field generation. In some cases, selecting a drive-current to minimize the production of stray fields during application to a CDFM can help to minimize the effect of such stray fields on magnetic field sensor readings. Alternatively or additionally, passive electromagnetic shielding (e.g., comprising an open-ended conductor disposed around the CDFMs) can be used to minimize the impact of additional magnetic fields produced by CDFMs on the sensor(s).
A CDFM can be incorporated into the end of a coaxial cable (e.g., a small-diameter semi-rigid coaxial cable). In some embodiments, a coaxial CDFM can be configured shown in
The term “microwire” can include cross-sectional shapes other than wires with small-diameters and round cross sections. In some cases, the microwire can comprise material that changes its magnetic permeability when carrying an electrical current. A discussion of microwire that changes permeability when carrying an electrical current is described in U.S. Patent Publication No. US 2020/0256930 A1 and PCT Patent Publication No. WO2020167551A1, which are incorporated herein in its entirety and for all purposes.
Multiple parallel microwires can be used instead of a single microwire as shown in the drawings. This may have benefits, including increasing the flux carrying capacity and thus increasing the strength of the applied field that the microwire (e.g., CDFM microwire) can handle.
A drive-current can be applied to components of magnetic field sensor systems (e.g., CDFMs) in pulses that are short relative to the time between them, for example, to reduce the rate of energy deposition, as microwires may have a high electrical resistivity so that the current used to reduce their permeability may deposit a significant amount of heat. Also, the microwires may have a small cross-sectional area so that a small amount of deposited heat causes a significant temperature rise. A heat-sink compound or structure or other means and methods of heat removal can be employed, e.g., to conduct heat away from current-driven microwires. Optionally, microwires with higher electrical conductivity can be employed to reduce heating of the microwires caused by drive currents.
Ideally, a CDFM microwire can have high permeability when the drive current is zero and low permeability when the drive current is applied to the CDFM.
The present disclosure provides embodiments of devices, systems, and methods useful for measuring and assessing cardiac function and health. A major advantage of the magnetic field sensor systems provided herein is that magnetic field detection can be performed exterior to the chest cavity (e.g., noninvasively and without the application of electrical leads to the skin surface).
One of skill in the art will appreciate that the devices and methods disclosed herein may be used in other technological fields for measuring magnetic fields, including but not limited to agriculture, industrial applications, national defense, biology, medicine, aerospace, interplanetary research, videogames, geological survey, telecommunications, determining magnetic fields and/or electrical fields in electrical networks and systems, and reading information on computer media (e.g., information stored on computer hard drives).
As used herein in the specification and claims, including as used in the examples and unless otherwise expressly specified, all numbers may be read as if prefaced by the word “about” or “approximately,” even if the term does not expressly appear. The phrase “about” or “approximately” may be used when describing magnitude and/or position to indicate that the value and/or position described is within a reasonable expected range of values and/or positions. For example, a numeric value may have a value that is +/−0.1% of the stated value (or range of values), +/−1% of the stated value (or range of values), +/−2% of the stated value (or range of values), +/−5% of the stated value (or range of values), +/−10% of the stated value (or range of values), etc. Any numerical values given herein should also be understood to include about or approximately that value, unless the context indicates otherwise. For example, if the value “10” is disclosed, then “about 10” is also disclosed. Any numerical range recited herein is intended to include all sub-ranges subsumed therein. It is also understood that when a value is disclosed that “less than or equal to” the value, “greater than or equal to the value” and possible ranges between values are also disclosed, as appropriately understood by the skilled artisan. For example, if the value “X” is disclosed the “less than or equal to X” as well as “greater than or equal to X” (e.g., where X is a numerical value) is also disclosed. It is also understood that the throughout the application, data is provided in a number of different formats, and that this data, represents endpoints and starting points, and ranges for any combination of the data points. For example, if a particular data point “10” and a particular data point “15” are disclosed, it is understood that greater than, greater than or equal to, less than, less than or equal to, and equal to 10 and 15 are considered disclosed as well as between 10 and 15. It is also understood that each unit between two particular units are also disclosed. For example, if 10 and 15 are disclosed, then 11, 12, 13, and 14 are also disclosed.
Although the terms “first” and “second” may be used herein to describe various features/elements (including steps), these features/elements should not be limited by these terms, unless the context indicates otherwise. These terms may be used to distinguish one feature/element from another feature/element. Thus, a first feature/element discussed herein could be termed a second feature/element, and similarly, a second feature/element discussed herein could be termed a first feature/element without departing from the teachings of the present invention.
When used in the following claims, the terms “comprise”, “include”, “have” and their conjugates mean “including but not limited to.” Throughout this specification and the claims which follow, unless the context requires otherwise, the word “comprise”, and variations such as “comprises” and “comprising” means various components can be co-jointly employed in the methods and articles (e.g., compositions and apparatuses including device and methods). For example, the term “comprising” will be understood to imply the inclusion of any stated elements or steps but not the exclusion of any other elements or steps.
While preferred embodiments of the present invention have been shown and described herein, it will be obvious to those skilled in the art that such embodiments are provided by way of example only. Numerous variations, changes, and substitutions will now occur to those skilled in the art without departing from the invention. It should be understood that various alternatives to the embodiments of the invention described herein may be employed in practicing the invention. It is intended that the following claims define the scope of the invention and that methods and structures within the scope of these claims and their equivalents be covered thereby. For purposes of comparing various embodiments, certain aspects and advantages of these embodiments are described. Not necessarily all such aspects or advantages are achieved by any particular embodiment. Thus, for example, various embodiments may be carried out in a manner that achieves or optimizes one advantage or group of advantages as taught herein without necessarily achieving other aspects or advantages as may also be taught or suggested herein.
This application claims the benefit of U.S. Provisional Application Nos. 62/963,877, filed Jan. 21, 2020, which application is incorporated herein by reference in its entirety.
| Number | Date | Country | |
|---|---|---|---|
| 62963877 | Jan 2020 | US |
