Measuring and testing – Speed – velocity – or acceleration – Acceleration determination utilizing inertial element
Reexamination Certificate
1999-09-24
2001-11-06
Moller, Richard A. (Department: 2856)
Measuring and testing
Speed, velocity, or acceleration
Acceleration determination utilizing inertial element
C324S207130, C324S209000
Reexamination Certificate
active
06311557
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to methods and apparatus for detecting particular frequencies of vibration, and especially for detecting and selecting particular frequencies of vibration using detection and selection apparatus comprising magnetically-tunable beam members such as cantilevers and very small cantilevers, often called microcantilevers.
BACKGROUND OF THE INVENTION
The resonance frequencies of a beam occur at discrete values based on the geometrical and mechanical properties of the beam and the environment in which it is located. The efficiency of resonance is measured by the quality factor (or Q-factor), where large Q-factors correspond to high efficiency. High-Q beams such as cantilever beams can be used as efficient listening devices for particular frequencies, with much higher sensitivity and specificity for particular acoustic bands of interest in comparison to conventional acoustic transducers. Moreover, microcantilevers, which are only a few hundred microns in length, are also much more simple to produce and could be far smaller in comparison to standard microphone technologies. Unfortunately, as an inevitable consequence of their high specificity, one would need an exorbitant number of fixed-frequency cantilevers to cover a broad frequency spectrum. Because of this simple reason cantilever-based listening devices have not attracted significant attention. Thus, it is desirable to make a high-Q cantilever that use a magnetic method to achieve broad frequency tunability. The resonance frequency of such a cantilever might be changed by varying a magnetic field and thereby varying magnetic attraction or repulsion (hereinafter referred to as magnetic force) acting upon the cantilever. The magnetic field might be produced by a permanent magnet or an electromagnet or combination thereof.
OBJECTS OF THE INVENTION
Accordingly, it is an object of the present invention to provide a new and improved method and apparatus for tuning the resonance frequency of a beam such as a cantilever element, and more specifically to provide a new method and apparatus for tuning the resonance frequency of a beam such as a cantilever element by varying a magnetic field applied to the beam and/or its environment.
Further and other objects of the present invention will become apparent from the description contained herein.
SUMMARY OF THE INVENTION
In accordance with one aspect of the present invention, the foregoing and other objects are achieved by a magnetically-tunable beam for detecting a particular frequency of vibration which comprises: a beam element having an end and a surface, and being fixedly disposed on the end; a stress-sensitive means for controlling stiffness of the beam selected from the group consisting of: a stress sensitive coating having a stiffness that varies with the stress therein affixed on the surface of the beam element and the beam element material having a stiffness that varies with the stress therein; a first ferromagnetic means for exhibiting magnetic polarity from the group consisting of: a ferromagnetic coating disposed on a surface of the beam element and a ferromagnetic property of the beam element material; a second ferromagnetic means for exhibiting magnetic polarity fixedly disposed generally parallel to the first ferromagnetic means and separated from the first ferromagnetic means by a gap formed therebetween; magnetic field means suitably disposed and connected for providing magnetic polarity upon the first ferromagnetic means and the second ferromagnetic means to cause magnetic force between the first ferromagnetic means and the second ferromagnetic means so that magnetic force therebetween causes the beam element to bend, and thus produces a change in stress in the stress-sensitive means and a change in the resonance frequency of the magnetically-tunable beam.
In accordance with a second aspect of the present invention, the foregoing and other objects are achieved by a method for detecting a particular frequency of vibration in an environment, wherein the method comprises the steps of providing a magnetically-tunable beam comprising a beam element having an end and a surface and being fixedly disposed on the end; a stress-sensitive means for controlling stiffness of the beam selected from the group consisting of: a stress sensitive coating having a stiffness that varies with the stress therein affixed on the surface of the beam element and the beam element material having a stiffness that varies with the stress therein; a first ferromagnetic means for exhibiting magnetic polarity selected from the group consisting of: a ferromagnetic coating disposed on a surface of the beam element and a ferromagnetic property of the beam element material; a second ferromagnetic means for exhibiting magnetic polarity fixedly disposed generally parallel to the first ferromagnetic means and separated from the first ferromagnetic means by a gap formed therebetween; and magnetic field means suitably disposed and connected for providing magnetic polarity upon the first ferromagnetic means and the second ferromagnetic means; exposing the beam element to the environment; activating the magnetic field means to cause magnetic force between the first ferromagnetic means and the second ferromagnetic means so that magnetic force therebetween causes the beam element to bend and thus produces a change in stress in the stress-sensitive means and a change in the resonance frequency of the magnetically-tunable beam to permit the magnetically-tunable beam to respond resonantly at the particular frequency; and determining from the resonance response of the magnetically-tunable beam whether the particular frequency of vibration is detected.
In accordance with a third aspect of the present invention, the foregoing and other objects are achieved by a method for selecting a desired frequency of vibration from a mixture of frequencies which comprises the steps of: providing a magnetically-tunable beam comprising a beam element having an end and a surface, and being fixedly disposed on the end; a stress-sensitive means for controlling stiffness of the beam selected from the group consisting of: a stress sensitive coating having a stiffness that varies with the stress therein affixed on the surface of the beam element and the beam element material having a stiffness that varies with the stress therein; a first ferromagnetic means for exhibiting magnetic polarity selected from the group consisting of: a ferromagnetic property disposed on a surface of the beam element and a ferromagnetic property of the beam element material; a second ferromagnetic means for exhibiting magnetic polarity fixedly disposed generally parallel to the first electrical conductor means and separated from the first electrical conductor means by a gap formed therebetween; and magnetic field means suitably disposed and connected for providing magnetic polarity upon the first ferromagnetic means and the second ferromagnetic means; activating the magnetic field means to cause magnetic force between the first ferromagnetic means and the second ferromagnetic means so that magnetic force therebetween causes the beam element to bend and thus produces a change in stress in the stress-sensitive means and a change in the resonance frequency of the magnetically-tunable beam to establish the resonance frequency of the magnetically-tunable beam at the desired frequency; and exposing the magnetically-tunable beam to the mixture of frequencies to excite the magnetically-tunable beam to vibrate at a desired resonance frequency whereby the particular frequency desired is selected out of the mixture of frequencies.
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G. Y. Chen, et al “Adsorption-Induced Surface Stress & Its Effec
Davis J. Kenneth
Thundat Thomas G.
Wachter Eric A.
Marasco Joseph A.
Moller Richard A.
UT-Battelle LLC
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