Method and apparatus for performing magnetic field measurements using magneto-optic kerr effect sensors
First Claim
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1. A magneto-optic Kerr effect magnetic field threshold sensor comprising:
- a light source;
a polarizing beamsplitter disposed to intercept incident light provided from said light source, wherein said polarizing beamsplitter provides maximum transmission, along a first direction, of a first polarization vector of said incident light, and substantially reflects, along a second direction, a second polarization vector of said incident light, wherein a relatively small, predetermined component of said second polarization vector, compared to said transmitted first polarization vector, is also transmitted along said first direction, said transmitted second polarization vector being an information-independent second polarization vector component;
a thin-film, magneto-optic Kerr effect magnetic field sensing element, said sensing element comprising a plurality of thin-film layers disposed on a substrate, at least one of said layers being of a reflective metallic ferromagnetic material and having;
an in-plane magnetization orientation;
a well-defined in-plane uniaxial anisotropy;
a predetermined coercive field value; and
a known magneto-optic Kerr effect value, wherein said sensing element is disposed such that an in-plane easy axis of said at least one sensing element ferromagnetic material layer lies in the light plane of incidence, collinear to an external magnetic field to be measured, said at least one sensing element ferromagnetic material layer disposed to intercept light transmitted through said polarizing beamsplitter in said first direction and reflect light that is modified by converting a portion of said first polarization vector to said second polarization vector by an amount determined by the orientation of the magnetization of said at least one sensing element ferromagnetic material layer relative to said incident light, the size of said first polarization vector, and a magneto-optic Kerr effect value, said converted light being an information-containing second polarization vector component;
a highly-reflective mirror disposed to intercept light reflected from said sensing element and to reflect said intercepted light back toward said sensing element for reflection of light, modified by converting a further portion of said first polarization vector to said second polarization vector, back to said polarizing beamsplitter, said converted further portion also contributing to said information-containing second polarization vector component, wherein a remaining portion of said first polarization vector is transmitted through said polarizing beamsplitter in a direction opposite said first direction, and said information-containing second polarization vector component and said information-independent second polarization vector component are reflected in a third direction; and
a detector disposed to intercept said reflected information-containing and information-independent second polarization vector components from said polarizing beamsplitter in said third direction, to mix said information-containing and information-independent second polarization vector components, and to output a mixed output signal having an offset component providing an amplitude which is substantially independent of the external magnetic field, and a signal component dependent on the external magnetic field.
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Abstract
A sensor system includes a magneto-optic Kerr effect magnetic field sensing element and an optical system including a light source, at least one polarizer or polarizing element and a detector disposed about the sensing element. The sensing element is responsive to an external magnetic field. In one embodiment, the optical system and sensing element can be arranged to measure the strength of a magnetic field. In another embodiment the optical system and sensing element can be arranged to measure the rotational speed of rotating members.
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Citations
69 Claims
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1. A magneto-optic Kerr effect magnetic field threshold sensor comprising:
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a light source; a polarizing beamsplitter disposed to intercept incident light provided from said light source, wherein said polarizing beamsplitter provides maximum transmission, along a first direction, of a first polarization vector of said incident light, and substantially reflects, along a second direction, a second polarization vector of said incident light, wherein a relatively small, predetermined component of said second polarization vector, compared to said transmitted first polarization vector, is also transmitted along said first direction, said transmitted second polarization vector being an information-independent second polarization vector component; a thin-film, magneto-optic Kerr effect magnetic field sensing element, said sensing element comprising a plurality of thin-film layers disposed on a substrate, at least one of said layers being of a reflective metallic ferromagnetic material and having;
an in-plane magnetization orientation;
a well-defined in-plane uniaxial anisotropy;
a predetermined coercive field value; and
a known magneto-optic Kerr effect value, wherein said sensing element is disposed such that an in-plane easy axis of said at least one sensing element ferromagnetic material layer lies in the light plane of incidence, collinear to an external magnetic field to be measured, said at least one sensing element ferromagnetic material layer disposed to intercept light transmitted through said polarizing beamsplitter in said first direction and reflect light that is modified by converting a portion of said first polarization vector to said second polarization vector by an amount determined by the orientation of the magnetization of said at least one sensing element ferromagnetic material layer relative to said incident light, the size of said first polarization vector, and a magneto-optic Kerr effect value, said converted light being an information-containing second polarization vector component;a highly-reflective mirror disposed to intercept light reflected from said sensing element and to reflect said intercepted light back toward said sensing element for reflection of light, modified by converting a further portion of said first polarization vector to said second polarization vector, back to said polarizing beamsplitter, said converted further portion also contributing to said information-containing second polarization vector component, wherein a remaining portion of said first polarization vector is transmitted through said polarizing beamsplitter in a direction opposite said first direction, and said information-containing second polarization vector component and said information-independent second polarization vector component are reflected in a third direction; and a detector disposed to intercept said reflected information-containing and information-independent second polarization vector components from said polarizing beamsplitter in said third direction, to mix said information-containing and information-independent second polarization vector components, and to output a mixed output signal having an offset component providing an amplitude which is substantially independent of the external magnetic field, and a signal component dependent on the external magnetic field. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18)
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19. A rotation sensor comprising:
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a rotatable member; at least one permanent magnet coupled to said rotatable member to provide a circumferentially oriented switching magnetic field proximate the member as the member is rotated; a light source; an optical polarizing element disposed to intercept incident light provided by said light source, wherein said optical polarizing element provides maximum transmission, along a first direction, of a first polarization vector of said incident light, and substantially reflects, along a second direction, a second polarization vector of said incident light, wherein a relatively small, predetermined component of said second polarization vector, compared to said transmitted first polarization vector, is also transmitted along said first direction, said transmitted second polarization vector being an information-independent second polarization vector component; a reflective magneto-optic Kerr effect sensing element, said sensing element comprising a reflective metallic ferromagnetic film having;
a well defined in-plane uniaxial anisotropy;
a predetermined coercive field value;
a known magneto-optic Kerr effect constant; and
a predominantly oriented in-plane magnetization vector, said sensing film disposed proximate said rotatable member such that said sensing element is exposed to said switching magnetic field generated by said at least one magnet and oriented such that an in-plane easy axis is oriented both collinear to the switching magnetic field and in the light plane of incidence, said ferromagnetic film disposed to intercept said light provided by transmission through said polarizing beamsplitter, and reflect light modified by converting a portion of said first polarization vector to said second polarization vector by an amount determined by the orientation of the magnetization of said ferromagnetic film relative to said incident light, the size of said first polarization vector, and the magneto-optic Kerr effect value, said converted light being an information-containing component of said second polarization vector;and a detector disposed to intercept light which travels from said sensing element and which is reflected off said optical polarizing element. - View Dependent Claims (20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36)
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37. A magneto-optic Kerr effect magnetic field sensing system comprising:
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a light source; an optical polarizing element disposed to intercept light provided from said light source and to provide maximum transmission of light having a first polarization vector to be transmitted in a first direction and substantially reflects, along a second direction, a second polarization vector of said incident light, wherein a relatively small, predetermined component of said second polarization vector, compared to said transmitted first polarization vector, is also transmitted along said first direction, said transmitted second polarization vector being an information-independent second polarization component; a magneto-optic Kerr effect magnetic field sensing element comprising a reflective thin film comprising at least one metallic ferromagnetic layer having;
known values for effective magnetization and magneto-optic Kerr effect constant; and
a predominantly oriented in-plane magnetization vector region, wherein said sensing film is disposed such that the direction of an external magnetic field to be measured is normal to a plane in which said sensing element is disposed and such that said sensing element intercepts said light transmitted through said optical polarizing element in the first direction and wherein a first portion of the first polarization vector of light intercepted by said sensing element undergoes polarization conversion to said second polarization vector depending upon the value of said magnetic field, the value of said at least one ferromagnetic layer effective magnetization, and the amplitude of said first polarization vector, wherein said first portion comprises said information-containing component of said second polarization vector and said first portion reflects off of said sensing element and returns toward said optical polarizing element, while a second portion of the first polarization vector and said information-independent component of said second polarization vector do not undergo polarization conversion as said second portion and said information-independent component reflects towards said optical polarizing element; anda detector disposed to intercept light comprised of said information-containing component of said second polarization vector and said information-independent component of said second polarization vector which travels from said sensing element and which is reflected off said optical polarizing element. - View Dependent Claims (38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48)
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49. A rotation sensor comprising:
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a rotatable member; at least one permanent magnet coupled to said rotatable member to provide a circumferentially oriented switching magnetic field proximate the member as the member is rotated; a light source; an optical polarizing element disposed to intercept light provided by said light source, wherein said optical polarizing element provides maximum transmission, along a first direction, of a first polarization vector of said light, and substantially reflects, along a second direction, a second polarization vector of said incident light, wherein a relatively small, predetermined component of said second polarization vector, compared to said transmitted first polarization vector, is also transmitted along said first direction, said transmitted second polarization vector being an information-independent second polarization vector component; a reflective magneto-optic Kerr effect sensing element, said sensing element comprising a reflective metallic ferromagnetic film having;
a well defined in-plane uniaxial anisotropy, a predetermined coercive field value;
a known magneto-optic Kerr effect constant; and
a predominantly oriented in-plane magnetization vector, said sensing element disposed proximate said rotatable member such that said sensing element is exposed to said switching magnetic field generated by said at least one magnet and oriented such that an in-plane easy axis is oriented both collinear to the switching magnetic field and in the light plane of incidence, said sensing element of magnetic material further disposed to intercept said light provided by transmission through said polarizing beamsplitter, and reflect light modified by converting a portion of said first polarization vector to said second polarization vector by an amount determined by the orientation of the magnetization of said layer of ferromagnetic material relative to the incident light, the size of said first polarization vector, and said magneto-optic Kerr effect value, said converted light being said information-containing component of said second polarization vector;a detector disposed to intercept light which travels from said sensing element and which is reflected off said optical polarizing element; and a signal generating circuit coupled to said detector for generating a series of signal pulses to indicate a position of said rotating member, wherein said signal generating circuit comprises; a power source; a first amplifier having a first input terminal coupled to said power source wherein said power source is adapted to provide a suppression current to said amplifier and having a second input terminal coupled to a first reference potential; a first resistor having a first terminal coupled to the first input terminal of said first amplifier and having a second terminal coupled to an output terminal of said first amplifier; a capacitor having a first terminal coupled to said output terminal of said first amplifier and having a second terminal; a second amplifier having a first input terminal coupled to the second terminal of said capacitor and having a second input terminal coupled to a second reference potential and having an output terminal; and a second resistor having a first terminal coupled to the first input terminal of said second amplifier and a second terminal coupled to the output terminal of said second amplifier.
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50. A magneto-optic Kerr effect magnetic field threshold sensor comprising:
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a light source; an optical polarizing element disposed to intercept incident light provided from said light source, wherein said optical polarizing element provides maximum transmission, along a first direction, of a first polarization vector of said incident light, and substantially reflects, along a second direction, a second polarization vector of said incident light, wherein a relatively small, predetermined component of said second polarization vector, compared to said transmitted first polarization vector, is also transmitted along said first direction, said transmitted second polarization vector being an information-independent second polarization vector component; a thin-film, magneto-optic Kerr effect magnetic field sensing element, said sensing element comprising a plurality of thin-film layers, at least one of said layers being of a reflective metallic ferromagnetic material and having;
an in-plane magnetization orientation;
a well-defined in-plane uniaxial anisotropy;
a predetermined coercive field value; and
a known magneto-optic Kerr effect constant, wherein said sensing element is disposed such that an in-plane easy axis of said at least one sensing element ferromagnetic material layer lies in the light plane of incidence, collinear to an external magnetic field to be measured, said at least one sensing element ferromagnetic material layer disposed to intercept light transmitted through said optical polarizing element in said first direction and reflect light that is modified by converting a portion of said first polarization vector to said second polarization vector by an amount determined by the orientation of the magnetization of said at least one sensing element ferromagnetic material layer relative to said incident light, the size of said first polarization vector, and a magneto-optic Kerr effect value, said converted light being an information-containing second polarization vector component,wherein said reflected light from said at least one sensing element ferromagnetic material layer returns to said polarizing beamsplitter for transmission of said first polarization vector in a direction opposite said first direction, and for reflection of said information-containing and information-independent second polarization vector components in a third direction; and a detector disposed to intercept said reflected information-containing and information-independent second polarization vector components from said polarizing beamsplitter in said third direction, to mix said information-containing and information-independent second polarization vector components, and to output a mixed output signal having an offset component providing an amplitude which is substantially independent of the external magnetic field, and a signal component dependent on the external magnetic field. - View Dependent Claims (51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62, 63, 64, 65, 66, 67, 68, 69)
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Specification