Electricity: measuring and testing – Magnetic – Magnetometers
Reexamination Certificate
2002-01-04
2002-08-13
Lefkowitz, Edward (Department: 2862)
Electricity: measuring and testing
Magnetic
Magnetometers
C324S096000, C359S280000
Reexamination Certificate
active
06433543
ABSTRACT:
BACKGROUND OF INVENTION
1. Field of the Invention
This invention relates to fiber optic magnetometers that are smart enough to selectively filter out magnetic fields and variations there of and easily have an a accuracy of less than 1 fT and sensitivities of less than 1 fT/sqrtHz and more particularly to fiber optic magnetic sensors of controllable precision.
2. Prior Art
The prior art is replete with many optical fiber sensors and different variations in Fabry-Perot, Mach-Zehnder modulators or Kerr effect or other optical effect-based magnetic sensors including squid type magnetometer. All of current devices have one or more of the following disadvantages: excessive bulk, slow response, require liquid helium cryogenic temperatures and poor mechanical reliability. Here below we present some typical examples but by no means exhaustive:
It is appropriate to mention some prior art related to the field of the present invention.
U.S. Pat. No. 4,588,947, to Ketchen, issued May 1986 discusses a miniature, fully integrated susceptometer capable of measuring the magnetic properties of very small samples (<10 &mgr;m) is described which is fabricated by thin film lithography on a single chip. The susceptometer is comprised of a dc SQUID including two series wired pick-up loops into which a sample to be measured can be placed. A field coil is provided which includes a separate single turn around each of the SQUID pick-up loops. The SQUID pick-up loops and the surrounding field coil turns are both located over a hole in a superconducting ground plane.
Daalmans in U.S. Pat. No. 4,801,882, issued January 1989 discusses a SQUID magnetometer, which can be fabricated by thin-film technology and used for apparatus for measuring weak magnetic fields. It contains a d-c SQUID with a SQUID loop surrounding the effective area of a coupling hole as well as a superconducting flux transformer with a gradiometer coil and a coupling coil surrounding the coupling hole thereby to achieve an effective inductive coupling of a measuring signal into the SQUID. To this end, the invention provides a separate superconducting surface with the coupling hole, to which the coupling coil and or the SQUID loop is/are assigned.
Hubbell in U.S. Pat. No. 6,005,380, issued December 1999 describes a magnetic field sensor, which can be used as an active antenna is disclosed that is capable of small size, ultra wide band operation, and high efficiency. The sensor includes a multiplicity of magnetic field transducers, e.g., superconducting quantum interference devices (SQUIDs) or Mach-Zehnder modulators that are electrically coupled in a serial array. Dummy SQUIDs may be used about the perimeter of the SQUID array, and electrically coupled to the active SQUIDs for eliminating edge effects that otherwise would occur because of the currents that flow within the SQUIDs. Either a magnetic flux transformer, which collects the magnetic flux and distributes the flux to the transducers or a feedback assembly (bias circuit) or both may be used for increasing the sensitivity and linear dynamic range of the antenna.
Bowman, et. al., in U.S. Pat. No. 3,750,017 issued July 1973 discuss an electromagnetic field measuring device is disclosed having a response which is essentially independent of the physical orientation of the device in the electromagnetic field. Further, the response of the device is essentially independent of the polarization of the field or of the presence of reactive field components or multipath interference. A set of three antennas disposed in a mutually orthogonal relationship with an essentially common center is provided, the antennas being adapted to be placed in an electromagnetic field to be measured. Sensing means, in the form of diodes for example, are associated with each antenna for deriving a signal therefrom. In the preferred embodiment, such antennas may take the form of dipoles, and diodes are contemplated to be connected between the dipole legs. The derived signals so produced are removed from the antennas in a fashion wherein no substantial perturbation of the field to be measured occurs and without substantially affecting the electrical characteristics of the antenna set. In a preferred embodiment, a high-resistance transmission line is provided. Subsequently, the derived and removed signals are combined and processed so as to generate a measurement reading.
Odawara, et. al., in U.S. Pat. No. 5,280,242 issued February 1991, discuss an apparatus for detecting a fine magnetic field comprises a DC SQUID, which detects and converts a magnetic field to an electrical signal. A flux locked looped circuit drives the DC SQUID. The flux locked loop circuit includes an amplifier for amplifying the electrical signal. A phase detector modulates the amplified electrical signal and an integration circuit outputs a voltage signal corresponding to the detected magnetic field. An oscillator coupled to the phase detector supplies a demodulation frequency signal. A modulator including a first voltage-to-current converter and a second voltage-to-current converter is coupled with the integration circuit and the oscillator for supplying a modulation signal to the DC SQUID. The modulator further includes an external input terminal and a feedback modulation change-over circuit for changing an internal feedback signal to an external test signal inputted to the external input terminal. A bias source having a third voltage-to-current converter is coupled to the DC SQUID and supplies a bias signal. The bias source also includes an external input terminal and a change-over circuit for changing an internal bias. signal to an external test signal inputted to the second external input terminal.
Crum, et. al., in U.S. Pat. No. 4,793,355 issued December 1988, discuss a biomagnetometer for measuring magnetic fields produced by the body and an electromagnetic location measurement and recording system for automatically determining the location of the portion of the body from which the magnetic signals are being gathered. The electromagnetic location recording system permits establishing a real time body frame of reference with respect to the biomagnetometer, so that biomagnetic signals can be correlated directly with body location and structure. The electromagnetic location recording system may be operated continuously at radiation wavelengths, which do not interfere with the taking of data, or intermittently with the taking of biomagnetic data, to avoid interference with the measured values of the biomagnetic data. The elements of the electromagnetic location recording system have substantially no residual magnetism when the location recording system is not operating, as the biomagnetic signals are typically so small that even normal residual magnetism might be erroneously recorded as a biomagnetic signal.
Johnson, et. al., in U.S. Pat. No. 5,444,373 issued August 1995, discuss a biomagnetometer comprising an array of biomagnetic sensors, the array comprising a first plurality of magnetic field pickup coils, and a second plurality of detectors, each of which receives a pickup coil output from a pickup coil. There is a third plurality of signal processors, each of which receives an output from a detector, the third plurality of signal processors being fewer in number than the first plurality of pickup coils. The biomagnetometer further includes a selector that selects a subset of pickup coils, equal in number to the third plurality of signal processors, from the first plurality of pickup coils for signal processing by the signal processors. This biomagnetometer permits the placement of a very large array of relatively inexpensive pickup coils adjacent to a subject, and then processing information from subsets of that large array selected to optimize the gathering of data, while maintaining the cost of the signal processing electronics at a more economical level.
Robinson, et. al., in U.S. Pat. No. 4,977,896 issued December 1990, discuss how signals produced by brain activity are measured by each sensor of an array of magnetic and/or elect
Popa Sorin Gabriel
Shahinpoor Mohsen
Sillerud Laurel O.
Le Toan M
Lefkowitz Edward
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