Electricity: measuring and testing – Magnetic – Magnetometers
Reexamination Certificate
1998-08-20
2001-07-03
Strecker, Gerard R. (Department: 2862)
Electricity: measuring and testing
Magnetic
Magnetometers
C324S202000, C324S260000, C336S092000
Reexamination Certificate
active
06255815
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to measuring devices and more specifically to a portable device for measuring magnetic field strength.
Therapeutic magnetic stimulation of human nerve tissue has significant advantages over traditional direct electrical stimulation. Electrical stimulation requires that an electrically conductive gel or buffer solution be applied between the electrodes supplying current and the surface of the skin of the patient. Long term excitation of the nerves is often accompanied by skin irritation caused by current concentration at the electrode/skin interface.
By contrast, magnetic stimulation does not even require direct contact with the patient, because magnetic stimulation causes current to be induced in the target tissues. Rapidly changing magnetic fields induce electric fields in biological tissue; when properly oriented and of the correct magnitude, the magnetically induced electric field transfers charge directly into the nerve tissue. When the localized membrane potential inside the nerve rises to a certain level, the nerve “fires.” An excellent device and method for the implementation of magnetic stimulation of nerve tissue is described in U.S. Pat. No. 5,725,471, entitled “Magnetic Nerve Stimulator for Exciting Peripheral Nerves” to Davey et al. (the same Davey as is the inventor of the present invention), the teachings of which are incorporated by reference herein.
While magnetic stimulation is safer and easier to administer than direct electrical stimulation, it is important that the stimulator device maintain the proper magnetic field strength. If the magnetic field strength is too low, the charge induced in the target nerves will be too low and the nerves will be understimulated. However, if the magnetic field generated by the device is too strong, then the charge induced in the target nerves will be too high and injury may result.
SUMMARY OF THE INVENTION
Accordingly, it is an object of the invention to enable a medical practitioner or field technician to determine quickly and accurately the field strength of the magnetic field generated by a magnetic nerve stimulator and to insure that the field is within the range set by the manufacturer as appropriate for its intended use.
It is another object of the invention to provide a device for accurately measuring magnetic field strengths.
It is another object of the invention to provide a device for measuring magnetic field strengths that is easy to use.
The above and other objects are fulfilled by the invention which includes a magnetic field calibration device, having a coil of wire and conductive connectors attached to the coil of wire. The coil is disposed in the interior of a housing, and a locator window is formed in the housing in a position internal to the coil; that is, the coil circumscribes or substantially surrounds the locator window. The housing is preferably substantially planar and the locator window includes a hole formed all the way through the housing extending from a first primary side of the housing to an opposite second primary side of the housing. The locator window may preferably include an at least partially light transmissible section of housing formed on the first primary side and another at least partially light transmissible section of housing formed on the second primary side. Preferably, these sections of housing are clear and allow the user to see through the device via the locator window. The locator window allows the user to position the device properly with respect to the source of the magnetic field, thereby increasing the accuracy with which the device may be employed.
The coil preferably includes approximately 4-5 turns of wire. The conductor pads attached to the coil are attachable to a voltmeter, ammeter, or oscilloscope, so that the current induced in the coils by the magnetic field is detectable and measurable. The strength of the magnetic field is proportional to the current induced in the coil; thus, if one measures the current induced in the coil, one can readily determine the strength of the magnetic field. The conductor pads may be predominantly flat so that clip leads may be attached to them for connecting the coil to an oscilloscope or voltmeter/ammeter, or the conductor pads may be male terminals (i.e., prong-like) attachable to mating female terminals of the voltmeter or oscilloscope.
The invention also includes a magnetic field calibration device, having a coil of wire and a built-in voltmeter or ammeter, attached to the coil of wire, for reading voltage/current induced in the coil when the device is placed in a magnetic field. The coil and the voltmeter are disposed in the interior of the housing, and the voltmeter preferably includes a display formed on an outer surface of the housing. Preferably, the voltmeter determines the current induced in the coil and the display indicates a value of magnetic field strength corresponding to the magnetic field which the device is measuring. More preferably, a microprocessor is disposed in the interior of the housing and connected to the display and the coil which converts a value of voltage induced in the coil into a value of magnetic field strength; the microprocessor transmits the value of magnetic field strength to the display. The microprocessor may need to be shielded from the effects of the magnetic field being measured. This embodiment also includes the locator window to enable quick and accurate placement of the device on the magnetic nerve stimulator device.
REFERENCES:
patent: 1241963 (1917-10-01), Grove
patent: 2103179 (1937-12-01), Rennau
patent: 2542057 (1951-02-01), Relis
patent: 2802182 (1957-08-01), Godshalk et al.
patent: 3836848 (1974-09-01), Blevins
patent: 3979566 (1976-09-01), Willy
patent: 5017877 (1991-05-01), Haus, Jr.
patent: 5432437 (1995-07-01), Turner
patent: 5434500 (1995-07-01), Hauck et al.
patent: 2352305 (1977-12-01), None
Levisohn, Lerner, Berge & Langsam
Neotonus, Inc.
Strecker Gerard R.
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