Frequency Response Of Microcantilevers Research Articles

Characterization of fluid mixtures at high pressures using frequency response of microcantilevers

The frequency response of ferromagnetic nickel microcantilevers immersed in binary mixtures of carbon dioxide (CO2) and nitrogen (N2) at 308K and pressures up to 23MPa was investigated. Experimental data were analyzed using the model developed by Sader for a clamped oscillatory beam immersed in a fluid and a very good agreement between the measured resonant frequencies and quality factors (Q-factors) and the theoretical predictions of the model with cantilever characteristic parameters regressed from experimental data was observed. This suggested that the data could be used to simultaneously measure the density and the viscosity of fluid mixtures over a wide range of pressures. Subsequently, density and viscosity of binary mixtures of CO2 and N2 were determined using N2 as the reference fluid and compared to the predictions of Gerg equation of state and Chung equation, respectively. For the studied fluids with different compositions, the average relative difference between the experimental density values and the values predicted using Gerg equation of state and NIST database ranged from 1.0 to 13%. The average relative difference between the experimental viscosity values and the values obtained using Chung equation and NIST database ranged from 2.4 to 15%. Since the resonant frequency and Q-factor were found to vary with composition at a fixed temperature and pressure, the technique can in principle also be used to measure the composition of a binary mixture at a fixed temperature and pressure. The study represents the first systematic attempt to use microcantilevers for the characterization of high-pressure fluid mixtures and paves the way for devising portable sensors for in-line monitoring of thermophysical properties and composition of fluid mixtures under a wide range of environmental conditions.

Determination of composition of ethanol-CO2 mixtures at high pressures using frequency response of microcantilevers

The measurement of the composition of ethanol-CO2 mixtures at high pressures is important in many applications involving supercritical fluids such as drying of alcogels or release of MEMs. Resonant frequency and quality factor (Q-factor) of microcantilevers immersed in ethanol-CO2 mixtures were measured at a temperature of 308K and pressure range from 8MPa to 22MPa. The measurements were carried out for different mixture compositions ranging from 0.91 to 6.16wt% of ethanol in CO2. At a given pressure and temperature, the resonant frequencies were found to decrease linearly with the increasing ethanol weight percent in the mixture. The sensitivity of the resonant frequency to changes in composition was found to increase with decreasing pressure. The experimental results show that ethanol-CO2 mixture composition can be determined with good accuracy using mainly the measured resonant frequency of microcantilevers.

Determination of viscosity and density of fluids using frequency response of microcantilevers

We report on the simultaneous measurement of density and viscosity of nitrogen in gas and supercritical phases at 308.15K and pressures up to 24MPa. The density and viscosity were extracted from the measured frequency responses of an oscillated microcantilever immersed in N2. To this end, a model of oscillatory motion of immersed cantilevers incorporating the effects of hydrodynamic forces was employed. Using argon as a reference fluid of known density and viscosity, cantilever calibration parameters were obtained from nonlinear regression of cantilever resonant frequencies and quality factors recorded in argon. Subsequently, these calibration parameters were used in the model equations to determine the density and viscosity of nitrogen at the given experimental pressure and temperature. In the studied pressure range, the root-mean-square deviations of the measured density and viscosity of nitrogen from the reference values obtained from NIST database were 2.5% and 5.2%, respectively.

Dynamic Characteristics Measurement of Silicon Micro-Cantilever in Low Temperature Environment

The dynamic testing system for MEMS in low temperature environment has been developed. A thermoelectric cooling refrigerator was utilized to generate the low temperature environment. The base excitation device was established using the piezoelectric ceramic as the driving source. A vacuum chamber was designed to protect the micro-structure from the humid air. Through the base impact excitation, the resonance frequencies are obtained by analyzing the impulse response signals. The frequency response of micro-cantilever was obtained by using both BIST method and laser Doppler vibrometer. The dynamic testing experiments for the silicon micro-cantilever were carried out from -50°C to room temperature. The result shows that the resonance frequency slightly increases with the decreasing temperature. The measurement device is effective to carry out dynamic testing of microstructure from -50°C to room temperature.

Tuning the dynamic behaviour of cantilever MEMS based sensors and actuators

PurposeThis paper seeks to establish an analytical reference model in order to optimize the frequency response of MEMS cantilever structures using cutouts.Design/methodology/approachPresented in this work is a method to tune the frequency response of MEMS cantilevers by using single cutouts of various sizes. From an interpretation of the analytical results, mass and stiffness domains are defined as a function of the cutout position on the cantilever. In this regard, the elastic properties of the MEMS cantilever can be trimmed through mechanical tuning by a single cutout incorporated into the device geometry. The Rayleigh‐Ritz energy method is used for the modeling. Analytical results are compared with FEM and experimental results.FindingsThe eigenvalues are dependent on the position and size of the cutout. Hence, the frequency response of the cantilever can be tuned and optimized through this approach.Research limitations/implicationsMEMS microsystems are sensitive to microfabrication limitations especially at the boundary support of suspended structures such as microcantilevers.Practical implicationsMEMS cantilevers are resistant to low level vibrations due to their low inertia and the elastic properties of the silicon material. For sensor applications these qualities are highly regarded and explored. This analysis will contribute to the performance optimization of atomic force microscope (AFM) probes and micromechanical resonators.Originality/valueA method to tune, with cutouts, the frequency response of microcantilevers is proposed. The data can provide insight into the performance optimization of micromechanical resonators through mass reduction. For industrial applications requiring optimized responses the cutouts can be incorporated into microcantilevers through focused ion beam (FIB) machining or laser drilling, for example.

Frequency Response of Microcantilevers in Viscous Fluids

ABSTRACTThis paper presents a new, general reconstruction algorithm that enables modeling of the experimental resonance spectrum of a prismatic microcantilever in a viscous fluid. A closed-form solution is obtained for the microcantilever frequency response from the equation of motion with fluid damping and internal friction terms, which allows direct calculation of the fluid damping and internal friction damping constants. In principle, the fluid damping constant has a simple relationship to viscosity thus potentially simplifying the process of obtaining viscosity from experimental data. Finally, the model is compared to experimental data.