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(Color online) In-plane fundamental flexural resonance of a beam (upper inset) with , , and at for increasing drive amplitudes as measured by the optical reflection technique. The gap between the beam and the side gate is . The measured photodiode current was converted to a beam center displacement by using the data in the lower inset. Here, was obtained by scanning the optical spot along the structure. The center of the beam is located at and the gate at as shown by the shading.
(Color online) (a) Schematic of the PLL. The NEMS resonator is modeled as a two-port electromechanical device. The following components are used: a voltage controlled oscillator (VCO), a radio frequency (rf) mixer, a low-pass filter (LPF), an amplifier, and a frequency counter. (b) PLL output frequency as a function of the VCO carrier frequency in the vicinity of . Locking is observed for . When the gain of the optical transducer-amplifier cascade is lowered by a factor of 10, frequency locking is no longer present (data in gray). The inset shows the fluctuations in while the PLL is locked to . (c) Resonance frequency shift of the NEMS resonator as thermally evaporated gold atoms are absorbed on its surface. The mass is determined from separate quartz crystal and NEMS surface area measurements. The inset shows the experimental geometry.
(Color online) Results from the analysis of PLL operation. (a) vs at different loop gains . For small , . Frequency locking is observed beyond a critical gain value . For these values, is a multivalued function of . The lock range (inset) increases with increasing . (b) Frequency flow as a function of . Locking is observed for .
Experimentally determined parameters used in the simulations.
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