Microcantilever Systems Research Articles

Identification and evaluation of cracks in electrostatically actuated resonant gas sensors using Harris Hawk / Nelder Mead and perturbation methods

In this paper we study the static deflection, natural frequency, primary resonance of an electrostatically actuated cracked gas sensor. Besides, a novel hybrid metaheuristic algorithm is proposed to detect the location and depth of possible crack on the microcantilever systems. The gas sensor configuration consists of a microcantilever with a rigid plate attached to its end. The nonlinear effects of the electrostatic force and fringing field are taken into account in the mathematical model. The crack is represented by a rotational spring. In the first part, the effect of crack on the static and dynamic pull-in instability are studied. The equations of motion are solved by the application of the perturbation methods. Next, an inverse problem is formulated to predict the location and depth of the crack in the gas sensor. For that purpose, the weighted squared difference of the analytical and predicted frequency response is considered as the objective function. The location and depth of the crack in the microsystem are determined using the hybrid Harris Hawk and Nelder Mead optimization algorithms. The accuracy and efficiency of the proposed algorithm are compared with the HHO, DA, GOA, and WOA algorithms. Taguchi design of experiments method is used in order to tune the parameters of optimization algorithms systematically. It is shown that the proposed algorithm can predict the exact location and depth of the open-edge crack on an electrostatically actuated microbeam with proof mass.

Microfluidic microcantilever as a sensitive platform to measure evaporation rate of picoliters of ethanol

Resonating microfluidic cantilevers are used for a broad range of biochemical sensing applications where a shift in the resonance frequency is used to detect minute changes in the cantilever mass. These multifunctional microfluidic microcantilevers open up opportunities for new ultrasensitive biochemical sensors wherein the target species in a carrier fluid bind to the inner functionalized walls of microfluidic channel, thereby changing the mass and hence the resonance frequency of the system for detection. In this paper, we develop computational models that predict the change in the resonance frequency as a function of change in mass for this hollow microcantilever system. We present computational models to simulate this process and validate the models using experimental data based on the evaporation of ethenol, a commonly available volatile compound. Specifically, a computational approach is presented in two variants; a one-dimensional structural beam element model, and a three-dimensional finite element model. The numerically predicted increase in the resonance frequencies due to a decrease in ethanol mass correlates well with experimental data. The models enable the determination of proof-of-concept and the rational design of novel resonant-based microfluidic microcantilever systems.

Flow force augmented 3D suspended polymeric microfluidic (SPMF3 ) platform.

Detection and study of bioelements using microfluidic systems has been of great interest in the biodiagnostics field. Microcantilevers are the most used systems in biodetection due to their implementation simplicity which have been used for a wide variety of applications ranging from cellular to molecular diagnosis. However, increasing further the sensitivity of the microcantilever systems have a great effect on the cantilever based sensing for chemical and bio applications. In order to improve further the performance of microcantilevers, a flow force augmented 3D suspended microchannel is proposed using which microparticles can be conveyed through a microchannel inside the microcantilever to the detection area. This innovative microchannel design addresses the low sensitivity issue by increasing its sensitivity up to 5 times than the earlier reported similar microsystems. Moreover, fabricating this microsystem out of Polydimethylsiloxane (PDMS) would eliminate external exciter dependency in many detection applications such as biodiagnostics. In this study, the designed microsystem has been analyzed theoretically, simulated and tested. Moreover, the microsystem has been fabricated and tested under different conditions, the results of which have been compared with simulation results. Finally, its innovative fabrication process and issues are reported and discussed.

Modeling and Measurement of Geometrically Nonlinear Damping in a Microcantilever–Nanotube System

Nonlinear mechanical systems promise broadband resonance and instantaneous hysteretic switching that can be used for high sensitivity sensing. However, to introduce nonlinear resonances in widely used microcantilever systems, such as AFM probes, requires driving the cantilever to an amplitude that is too large for any practical applications. We introduce a novel design for a microcantilever with a strong nonlinearity at small cantilever oscillation amplitude arising from the geometrical integration of a single BN nanotube. The dynamics of the system was modeled theoretically and confirmed experimentally. The system, besides providing a practical design of a nonlinear microcantilever-based probe, demonstrates also an effective method of studying the nonlinear damping properties of the attached nanotube. Beyond the typical linear mechanical damping, the nonlinear damping contribution from the attached nanotube was found to be essential for understanding the dynamical behavior of the designed system. Experimental results obtained through laser microvibrometry validated the developed model incorporating the nonlinear damping contribution.

Resonant actuation of microcantilever by pulse wave of one-nth the resonant frequency

We achieve the resonant actuation of a microcantilever by using a pulse wave of one-nth the microcantilever resonant frequency. Our studies on the relationship between pulse duration and microcantilever resonant amplitude reveal that the most effective actuation can be acquired when the pulse duration is odd multiples of the half period of microcantilever resonant oscillation. This actuation method is generally applicable and may find applications in ultrahigh frequency actuation of microcantilever or similar resonant systems for high sensitivity detection.

Energy dissipation in microfluidic beam resonators

The fluid–structure interaction of resonating microcantilevers immersed in fluid has been widely studied and is a cornerstone in nanomechanical sensor development. In many applications, fluid damping imposes severe limitations by strongly degrading the signal-to-noise ratio of measurements. Recently, Burget al. (Nature, vol. 446, 2007, pp. 1066–1069) proposed an alternative type of microcantilever device whereby a microfluidic channel was embedded inside the cantilever with vacuum outside. Remarkably, it was observed that energy dissipation in these systems was almost identical when air or liquid was passed through the channel and was 4 orders of magnitude lower than that in conventional microcantilever systems. Here, we study the fluid dynamics of these devices and present a rigorous theoretical model corroborated by experimental measurements to explain these observations. In so doing, we elucidate the dominant physical mechanisms giving rise to the unique features of these devices. Significantly, it is found that energy dissipation is not a monotonic function of fluid viscosity, but exhibits oscillatory behaviour, as fluid viscosity is increased/decreased. In the regime of low viscosity, inertia dominates the fluid motion inside the cantilever, resulting in thin viscous boundary layers – this leads to an increase in energy dissipation with increasing viscosity. In the high-viscosity regime, the boundary layers on all surfaces merge, leading to a decrease in dissipation with increasing viscosity. Effects of fluid compressibility also become significant in this latter regime and lead to rich flow behaviour. A direct consequence of these findings is that miniaturization does not necessarily result in degradation in the quality factor, which may indeed be enhanced. This highly desirable feature is unprecedented in current nanomechanical devices and permits direct miniaturization to enhance sensitivity to environmental changes, such as mass variations, in liquid.

Low-Noise Chemical Detection with a Piezoresistive Microcantilever Array

Piezoresistive microcantilever systems are well suited for chemical sensing with low detection limits. A major hurdle in the realization of such systems is measurement noise associated with DC piezoresistance measurements. A piezoresistive microcantilever array has been fabricated and phase sensitive detection methods are used for realization of a low detection limit piezoresistive cantilever array. Reference cantilevers in the array can act as thermomechanical or chemical references to aid in lowering the detection limits.

A review of atomic force microscopy imaging systems: application to molecular metrology and biological sciences

The atomic force microscope (AFM) system has evolved into a useful tool for direct measurements of micro-structural parameters and unraveling the intermolecular forces at nanoscale level with atomic-resolution characterization. Typically, these micro-cantilever systems are operated in three open-loop modes; non-contact mode, contact mode, and tapping mode. In order to probe electric, magnetic, and/or atomic forces of a selected sample, the non-contact mode is utilized by moving the cantilever slightly away from the sample surface and oscillating the cantilever at or near its natural resonance frequency. Alternatively, the contact mode acquires sample attributes by monitoring interaction forces while the cantilever tip remains in contact with the target sample. The tapping mode of operation combines qualities of both the contact and non-contact modes by gleaning sample data and oscillating the cantilever tip at or near its natural resonance frequency while allowing the cantilever tip to impact the target sample for a minimal amount of time. Recent research on AFM systems has focused on many manufacturing and metrology processes at molecular levels due to its tremendous surface microscopic capabilities. This paper provides a review of such recent developments in AFM imaging system with emphasis on operational modes, micro-cantilever dynamic modeling and control. Due to the important contributions of AFM systems to metrology and biological sciences, this study also provides a comprehensive review of recent applications of different AFM systems in these two important areas.

A fractal analysis of analyte–receptor binding and dissociation kinetics in microcantilever biosensors

A fractal analysis of a confirmative nature only is presented for the binding and dissociation (where ever it is applicable) for (a) CrO 4 2− in solution to a SAM-coated microcantilever surface [8], and (b) for two hybridization reactions occurring on microcantilever surfaces [1,28]. Data taken from these references may be modeled by using a single- or a dual-fractal analysis. Relationships are presented for the binding rate coefficient as a function of the fractal dimension and for the analyte concentration in solution. The binding and the dissociation rate coefficients are very sensitive to the degree of heterogeneity that exists on the microcantilever surface. For the reactions analyzed the binding and dissociation rate coefficients increase with an increase in the degree of heterogeneity on the microcantilever surface. For one of the hybridization reactions analyzed [28] the binding rate coefficient increases with the number of bases (25- and 9-mer) present in the oligomer (analyte) in solution. The analysis should assist in placing the analyte–receptor reactions occurring on microcantilever systems on a kinetic basis.