"Other known methods of using nanomechanical and micromechanical oscillators achieve improved stability by exciting large oscillation amplitudes to minimize effects of thermal and ambient noise. However, these known nanomechanical and micromechanical oscillators become nonlinear at large oscillations and the resonance behavior cannot be analyzed using known methods and instruments for linear resonators. In particular, mass loading of nanomechanical and micromechanical oscillators cannot be determined by fitting a resonance curve of the oscillator to a Lorentzian curve or by measuring an output frequency of a self-oscillating circuitry based on a phased-locked loop."
In addition to the background information obtained for this patent, VerticalNews journalists also obtained the inventors' summary information for this patent: "The present invention is directed to a system for ultrasensitive mass and/or force detection that includes nanoscale and/or microscale mechanical oscillators which are driven to oscillate in a nonlinear regime. By driving the nanoscale and/or microscale mechanical oscillators to oscillate in the nonlinear regime, limitations of previously known resonating nanoscale and microscale structures, such as noise and difficulties with measurements, can be minimized.
"According to an embodiment of this invention, the system for ultrasensitive mass and force detection includes a piezoelectric base with at least one cantilever resonator etched into the piezoelectric base. The cantilever resonator is etched into the piezoelectric base such that the cantilever resonator includes a fixed or clamped end attached to the piezoelectric base and a free end extending away from the piezoelectric base. In an alternative embodiment, the cantilever resonator can be formed by any known method including a top-down process such as bulk or surface micromachining or by mounting a separate cantilever resonator to the piezoelectric base.
"The cantilever resonator is preferably a nonlinear resonator with nonlinear elasticity that is operated in a mode that includes both a quadratic term and a cubic term. The cubic term arises from stiffening or softening of a material of the cantilever resonator as a degree of deformation increases. However, material properties alone do not give rise to the quadratic term. In an embodiment of this invention, the cantilever resonator includes an asymmetrical geometrical design providing the quadratic term. In a preferred embodiment, the cantilever resonator includes a pre-stressed cantilever with an out-of-plane deformation.
"In an embodiment of this invention, the cantilever resonator is driven to oscillate with a frequency and an amplitude by a transducer connected to the piezoelectric base. In an alternative embodiment, the transducer and the piezoelectric base are combined into a single element as a piezoelectric transducer. The transducer is preferably in communication with a digital programmable generator. The digital programmable generator instructs the transducer to excite the cantilever resonator to oscillate over a frequency range. In a preferred embodiment, the cantilever resonator is driven into the nonlinear regime with oscillation amplitudes greater than 5% of a length of the cantilever resonator. In a preferred embodiment, the cantilever resonator can also function as a mechanical demodulator converting the amplitude into a measurable DC signal.
"The system of this invention preferably detects a bifurcation point while the cantilever resonator is excited with the digital programmable generator. The bifurcation point is a frequency at which the oscillation amplitude of the cantilever resonator collapses. In an initial state, without an external stimulus such as mass and/or force, the cantilever resonator will reach its bifurcation point at an initial frequency. As mass and/or force is introduced to the cantilever resonator, the bifurcation point of the cantilever resonator shifts along a frequency axis in proportion to added mass and/or force. In operation, the cantilever resonator is driven with the digital programmable generator programmed to sweep a frequency range in a vicinity of the bifurcation point. By using the digital programmable generator, no direct measurement of frequency or any AC signal is required, a time at which the oscillation amplitude collapses defines the bifurcation frequency according to the digital programmable generator.
"The system of this invention preferably includes a subsystem to detect the amplitude collapse, the bifurcation point. In an embodiment of this invention, the subsystem to detect amplitude collapse includes a laser positioned over and at an angle to the cantilever resonator such that a laser beam from the laser reflects off the cantilever resonator and projects a laser spot onto a screen. In operation, the cantilever resonator is driven to oscillate at amplitudes of up to several tens of micrometers, sufficient to deflect the laser beam by an angle of tens of degrees. In an embodiment of this invention, the screen is positioned 10 cm from the cantilever resonator which corresponds to approximately a 2 cm span of the laser spot projected onto the screen. The digital programmable generator is programmed to make a continuously repeated linear frequency sweep in a range surrounding and including the bifurcation point. When the frequency reaches the bifurcation point, a sharp drop in the oscillation amplitude is observed and detected with a spot photodetector. By continuously repeating frequency sweeps, the frequency at which bifurcation occurs as a function of time may be monitored with accuracy better than 50 mHz for a structure resonating at approximately 140 kHz. This corresponds to relative accuracy of 3.5.times.10.sup.-7, an unprecedented value for linear oscillators with similar parameters. Using this approach and an experimental setup that does not require complex electronic components, detection of femtogram level mass changes is possible, a level of performance previously achievable only with much smaller resonators that are very difficult to utilize in a practical device."
URL and more information on this patent, see: Datskos,
Keywords for this news article include:
Our reports deliver fact-based news of research and discoveries from around the world. Copyright 2013, NewsRx LLC
Most Popular Stories
- 15 Myths That Could Ruin Your Hispanic Ad Campaign
- Bitcoin Clones Lurch Onto Financial Scene
- General Motors Names Mary Barra as First Female CEO
- AIG to Create 230 Jobs in Charlotte
- Clinton to Keynote Annual Simmons Leadership Conference
- How Bitcoin and Other Cryptocurrencies Work
- Californians Want to Legalize Marijuana
- Pacific Trade Pact Delay Hinders U.S. Pivot to Asia
- Budget Deal Sets Off Grumbles in Both Houses
- Russia Says Nyet to Canada North Pole Claim