Electricity: measuring and testing – Particle precession resonance – Using a magnetometer
Reexamination Certificate
2001-05-17
2002-12-17
Arana, Louis (Department: 2862)
Electricity: measuring and testing
Particle precession resonance
Using a magnetometer
C324S322000
Reexamination Certificate
active
06496005
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention is directed to a magnetometer for, among other things, measuring a magnetic field associated with nuclear magnetic spins or electron spins.
2. Description of the Prior Art
With known nuclear magnetic spin or electron spin magnetometers for measuring a magnetic field with a specimen of a material that produces nuclear magnetic resonance or electron spin resonance and whose resonant frequency is a measure for a magnetic flux density of the magnetic field to be measured, the specimen is employed as a frequency-selective absorber or as a linear component. To that end, the known nuclear magnetic spin or electron spin magnetometers have a transmission device for radiating a transmission signal into the specimen with a controllable transmission frequency. The transmission frequency is regulated by a regulating device so that it is continually re-adjusted to the resonant frequency, which changes dependent on the magnetic flux density given a temporally varying magnetic field. As a result, the transmission frequency is equal to or nearly equal to the resonant frequency at every point in time. This results in the resonant frequency of interest being difficult to detect with the isofrequency transmission frequency as a consequence of the noise signals that are thereby introduced. This, further, requires that the control device be designed with a comparatively small bandwidth, so that narrow limits are placed on the tracking speed of the resonant frequency in the case of magnetic fields that change rapidly over time.
SUMMARY OF THE INVENTION
An object of the present invention is to provide an improved nuclear magnetic spin or electron spin magnetometer that, among other things, alleviates the aforementioned disadvantages.
This object is inventively achieved by a nuclear magnetic spin or electron spin magnetometer for, among other things, measuring a magnetic field which is adopted to receive a specimen of a material that produces nuclear magnetic resonance or electron spin resonance having a resonant frequency that is dependent on a magnetic flux density of the magnetic field to be measured, and having a transmission device for emitting a transmission signal into the specimen with at least one prescribable transmission frequency that has a frequency spacing from the resonant frequency, and a reception device for receiving a mixed signal with mixed frequencies containing the resonant frequency and the transmission frequency and for filtering out the resonant frequency from at least one of the mixed frequencies as a criterion (indicator) for the magnetic flux density.
A spin resonance of the specimen is thereby used as a non-linear component. The essentially fixed transmission frequency thus can be prescribed such that the utilized mixed frequency of the mixed signal can be filtered out by a broadband filter having a short transit time. A signal oscillating at the resonant frequency that represents an indicator or identifier for the magnetic flux density to be measured can be ultimately acquired by a following mixing of the filtered mixed signal with a signal oscillating with the transmission frequency. Among other things, magnetic fields that change arbitrarily fast in time thus can also be measured. A re-adjustment of the transmission frequency is not necessary, and therefore a control device for such re-adjustment is not necessary.
In an embodiment, the reception device has a counter with which cycles of a signal that oscillates at the resonant frequency can be counted, and the counter is fashioned to emit a counter reading that is one indicator for the electrical charge of a current that corresponds to the magnetic field to be measured. When the specimen of the magnetometer is arranged within an electrical coil in which this current flows, a current-time integral of the current can be directly measured and is available as a digital quantity as the counter reading emitted by the counter.
In another embodiment, the transmission device has a phase shifter for generating at least a 180° phase shift of the transmission signal. This 180° phase shift can thereby be generated either following a prescribable time duration or dependent on the amplitude of the mixed signal. As a result, the signal amplitude of the mixed signal, that decreases overtime, is maintained at a relatively high level by re-exciting the spins in the specimen, so that a consistently high signal-to-noise ration can be achieved. In particular, the generation of 180° phase shifts dependent on the amplitude of the mixed signal has the advantage that changes in the T
2
decay time of the specimen—due, for example, to field inhomogeneities of the magnetic field to be measured—can be dynamically adapted.
In a further embodiment, the transmission device is fashioned such that a magnetization amplitude of the transmission signal is smaller by a factor of approximately 10
−3
than the magnetic flux density to be measured. As a result, influence of the magnetization amplitude on the resonant frequency is negligible, so that it is not necessary to make a correction by a frequency component corresponding to the magnetization amplitude to be subsequently implemented for the resonant frequency that has been filtered out.
In another embodiment, the nuclear magnetic spin or electron spin magnetometer has a magnetic field generator for generating a static magnetic field the pre-polarizes the specimen. As a result, a magnetic flux density with a value of zero can be unambiguously identified and detected with the magnetometer.
REFERENCES:
patent: 2772391 (1956-11-01), Mackey
patent: 5404103 (1995-04-01), Duret
patent: 5530348 (1996-06-01), Heflinger
“An Automatic Tracking Nuclear Magnetic Resonance Gaussmeter,” Lue, Nuclear Instruments And Methods, vol. 147 (1977), pp. 595-598.
“Kernspin-Tomographie für die Medizinische Diagnostik,” Bösiger (1985), Chapter 2.4, pp. 16-20.
Arana Louis
Schiff & Hardin & Waite
Siemens Aktiengesellschaft
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