Measuring and testing – Fluid pressure gauge – Diaphragm
Reexamination Certificate
2000-02-11
2002-05-28
Noori, Max (Department: 2855)
Measuring and testing
Fluid pressure gauge
Diaphragm
C073S722000
Reexamination Certificate
active
06393921
ABSTRACT:
BACKGROUND OF THE INVENTION
In general, the present invention relates to telemetry using sensing elements remotely located from associated pick-up and processing units for the sensing and monitoring of pressure within an environment. More particularly, the invention relates to a unique remote pressure sensing apparatus that incorporates a magnetostrictive element (whether hermetically-sealed within a receptacle) and associated new method of sensing pressure of a fluid environment whether under vacuum or in a liquid, gas, or plasma state. Any of a number of applications is contemplated hereby, for example: biomedical applications (whether in vivo or in vitro) including medical test samples, food quality/inspection, monitoring of water (groundwater, treated water, or wastewater flowing in natural waterways, canals, or pipes), and monitoring manufacturing waste, etc. The new pressure sensing apparatus and method(s) provide information by utilizing, or listening for, the magneto-elastic emissions of one or more magnetostrictive elements (whether the element(s) also has a pre-formed region of ‘local’ hardening). The magneto-elastic listening frequencies of greatest interest are those at the magnetostrictive element's fundamental or harmonic resonant frequency. The pressure sensing apparatus of the invention can operate within a wide range of environments for remote one-time, random, periodic, or continuous/on-going monitoring of a particular fluid environment.
Pressure sensing can be performed according to the invention without requiring sophisticated equipment and the pressure sensor can be installed/positioned and removed with relative ease and without substantial disruption of the test environment. If need be, the sensor may be fabricated as a micro-circuit for use in vitro, in vivo, within small-sized sealed packaging or medical test samples (e.g., a test tube), and so on. As a micro-element, the invention can be used where space is limited and/or it is desired that the tiny sensor be positioned further into the interior of the sample or environment being tested/monitored. And, whether or not built on a larger scale, the novel pressure sensor can be used within buildings, an aircraft, or other open space. As it is well known, pressure, p, of a fluid (whether in liquid, gas, or plasma-form) is a function of the fluid's temperature: The instant invention further includes unique features that can sense and accommodate for environment temperature changes to give accurate pressure readings.
CO-PENDING U.S. PATENT APPLICATIONS ALSO FILED BY ASSIGNEE HEREOF
The assignee hereof filed pending patent applications (1) U.S. Ser. No. 09/223,689 on behalf of applicants common to the instant patent application, on Dec. 30, 1998 entitled “Remote Magneto-elastic Analyte, Viscosity and Temperature Sensing Apparatus and Associated Methods of Sensing”; and (2) U.S. Ser. No. 09/322,403 on behalf of an applicant common to the instant application, on May 28, 1999 entitled “Remote Resonant-Circuit Analyte Sensing Apparatus with Sensing Structure & Associated Method of Sensing”. The invention disclosed in the instant patent application and the inventions disclosed in the pending patent applications U.S. Ser. Nos. 09/223,689 and 09/322,403 were invented by applicants who, at the time of invention, were employed by the assignee hereof.
GENERAL BACKGROUND OF MAGNETOSTRICTION
Simply defined, “magnetostriction” is the phenomena whereby a material will change shape (dimensions) in the presence of an external magnetic field. This effect is brought about by the reordering of the magnetic dipoles within the material. Since the atoms in a magnetostrictive material are not, for all practical purposes, perfectly spherical (they're shaped more like tiny ellipsoids) the reordering of the dipoles causes an elongation (or contraction depending on the mode of reorientation) of the lattice which leads to a macroscopic shape change in the material. There is a “reverse magnetostrictive effect”, called the Villari effect: When an external stress is applied to a magnetostrictive material, a strain develops within the material which induces a surrounding magnetic field. Known magnetostrictive materials include alloys of iron (Fe), cobalt (Co), yttrium (Y), gadolinium (Gd), terbium (TB), dysprosium (Dy), and so on.
The so-called magnetoelastic effect is a phenomenon exhibited by ferromagnetic substances. It refers to the interdependence of the state of magnetization and the amount of mechanical strain present in the material and manifests as magnetostriction, volume change upon magnetization and, inversely, change in the state of magnetization upon application of stress. When a sample of magnetostrictive material is subjected to an applied small time-varying (AC) magnetic field superimposed on a much larger direct-current (DC) magnetic field, the magnetic energy is translated into elastic energy and the sample starts vibrating. The mechanical vibrations are most pronounced as the frequency of the applied AC field gets closer to the characteristic resonant frequency f
0
of the magnetostrictive sample and a voltage peak for emissions radiating from the sample can be registered by a pick-up coil in proximity thereto. This pronounced conversion from magnetic to elastic energy holds true at harmonics of resonant frequency f
0
This condition is known as magnetoelastic resonance. One example of magnetostriction is the “transformer hum” we hear when a transformer core “pulsates” upon the application of a 60 Hz magnetic field—the ‘hum’ is the emission of acoustic energy that generates sound.
It is well known that electric and magnetic fields are fundamentally fields of force that originate from electric charges. Whether a force field may be termed electric, magnetic, or electromagnetic (EM) hinges on the motional state of the electric charges relative to the point at which field observations are made. Electric charges at rest relative to an observation point give rise to an electrostatic (time-independent) field there. The relative motion of the charges provides an additional force field called magnetic. That added field is magnetostatic if the charges are moving at constant velocities relative to the observation point. Accelerated motions, on the other hand, produce both time-varying electric and magnetic fields, or electromagnetic fields. See
Engineering Electromagnetic Fields and Waves,
Carl T. A. Johnk, John Wiley & Sons, 2
nd
Edition (1988). As stated, exposure of a time-varying (sinusoidal/AC) magnetic field will induce a time-varying current in a ferromagnetic sample such that it will emit EM energy. Also, this same piece of ferromagnetic material will emit acoustic and thermal energy due to the changes in size and viscous flexing of the material. An acoustic wave is an elastic, nonelectromagnetic wave with a frequency that may extend into the gigahertz (GHz) range. Acoustic transmission is that transfer of energy in the form of regular mechanical vibration through a medium (as a stress-wave emission). As defined, an ultrasonic wave is an acoustic emission having a frequency generally above 20 KHz (just above human hearing).
The commercially available ‘anti-theft markers’ (also called electronic article surveillance, or EAS, tags) operate by “listening” for acoustic energy emitted in response to an interrogating ac magnetic field, to sense the presence of an EAS marker. Sensormatic, Inc. distributes an EAS tag (dimensions 3.8 cm×1.25 cm×0.04 mm) designed to operate at a fixed frequency of 58 kHz (well beyond the audible range of human hearing). These EAS tags are embedded/incorporated into articles for retail sale. Upon exiting a store, a customer walks through a pair of field coils emitting a 58 kHz magnetic field. If an activated EAS tag is in an article being carried by the customer, the tag will likewise emit a 58 kHz electromagnetic signal that can be detected using a pickup coil, which in turn may set off an audible or visual alarm. More-recently, these tags are being placed in a box-reson
Grimes Craig A.
Kouzoudis Dimitris
Stoyanov Plamen G.
Aw-Musse Abdullahi
Macheledt Bales LLP
Noori Max
University of Kentucky Research Foundation
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