There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality.

Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

I and i

The problem of simultaneously enhancing sensitivity and noise immunity of microcantilevers is investigated. The dependence of deflection and resonant frequency of a microcantilever on its dimensions is studied. A principle to increase deflection and resonant frequency simultaneously is established. Several cantilevers agreeing with this principle are investigated using analytical models and are compared with FEM simulations. Using these results, a cantilever profile that achieves a larger deflection and a larger resonant frequency compared with uniform cantilevers is proposed to be used in sensor elements.

http://iopscience.iop.org/article/10.1088/0022-3727/40/24/009/pdf

Improved cantilever profiles for sensor elements

THEORETICAL ANALYSIS OF LATERALLY VIBRATING MICROCANTILEVER SENSORS IN A VISCOUS LIQUID MEDIUM Russell Cox, B.S., M.S. Marquette University, 2011 Dynamically driven microcantilevers are normally excited into resonance in the out-of-plane flexural mode. The beam’s resonant frequency and quality factor are used to characterize the devices. The devices are well suited for operation in air, but are limited in viscous liquid media due to the increased viscous damping. In order to improve these characteristics, other vibration modes such as the in-plane (or lateral) flexural mode are investigated. In this work, microcantilevers vibrating in the in-plane flexural mode (or lateral direction) in a viscous liquid medium are investigated. The hydrodynamic forces on the microcantilever as a function of both Reynolds number and aspect ratio (thickness over width) are first calculated using a combination of numerical methods and Stokes’ solution. The results allowed for the resonant frequency, quality factor, and mass sensitivity to be investigated as a function of both beam geometry and medium properties. The predicted resonant frequency and quality factor for several different laterally vibrating beams in water are also found to match the trends given by experimentally determined values found in the literature. The results show a significant improvement over those of similar devices vibrating in the out-of-plane flexural mode. The resonant frequency increases by a factor proportional to the inverse of the beam’s aspect ratio. Moreover, the resonant frequency of a laterally vibrating beam shows a smaller decrease when immersed in water (5-10% compared to ~50% for transversely vibrating beams) and, as the viscosity increases, the resonant frequency decreases slower compared to beams excited transversely. The quality factor is found to increase by a factor of 2-4 or higher depending on the medium of operation and the beam geometry. Due to the increased resonant frequency and the decreased effective mass of the beam (compared to beams excited transversely), the estimated mass sensitivity of a laterally excited microcantilever is found to be much larger (up to two orders of magnitude). The improvement in these characteristics is expected to yield much lower limits of detection in liquid-phase bio-chemical sensing applications.

/pdf/theoretical-analysis-of-laterally-vibrating-microcantilever-1b0donixts.pdf

Theoretical analysis of laterally vibrating microcantilever sensors in a viscous liquid medium

This work introduced a half cut stress concentration (HCSC) region on the surface of MEMS piezoresistive cantilever in order to improve the sensitivity of a cantilever sensor based on loading/force effect From the available information, by increasing the stress occurred on the cantilever surface where piezoresistive region place the sensitivity will increase greatly The designs were simulated using ANSYS 90 in order to study the stress distribution and displacement effect Results obtain for solid cantilever and designed cantilever have been compared As expected, stress that occurred was increased and highly concentrated at the HCSC region The cantilever sensitivity also enhances by 4 times This design of cantilever can obviously improve the sensitivity of the surface stress cantilever

Half cut stress concentration (HCSC) region design on MEMS piezoresistive cantilever for sensitivity enhancement

The present invention relates to a micromechanical sensor (1) for detecting a target substante in a liquid or a gas and comprising at least one sensor unit with a capture surface (30) and at least one conducting element (2) of an electrically conducting material with a pair of wires for applying an electrical field over the conducting element. The conducting element comprises at least two divisional units (34) and the conducting element has a larger conductance in one sensor state than in another sensor state due to a change in contact area for electrical conduction between two or more divisional units on deformation from one sensor state to another in response to surface stress arising from a chemical interaction at the capture surface. The conducting element may preferably comprise 2-100 divisional units or even more which divisional units may be systemically arranged or randomly ordered e.g. in a non-conductive dispersant material. In a preferred embodiment, the sensor is used to detect DNA, and the conducting element (2) contains carbon nanowires.

A sensor for use in detection of a target substance in a sample

In this paper, we propose a novel microcantilever for biosensing applications, which we call a segmented cantilever. The aim of this paper is to show that the proposed design minimizes the disadvantages of the currently used micro-cantilevers.

/pdf/novel-cantilever-for-biosensing-applications-4gj0j985tg.pdf

Novel cantilever for biosensing applications

Chemomechanical actuation of a microcantilever beam induced by biomolecular binding such as DNA hybridization and antibody-antigen binding is an important principle useful in biosensing applications. As the magnitude of the forces involved is very small, increasing the sensitivity of the microcantilever beams involved is a priority. In this paper we are considering to achieve this by structural variation of the cantilevers. Merely decreasing the thickness of the microcantilever may improve the sensitivity, but it gives rise to the disadvantages of 'arching' and lesser reliability due to greater probability of defects during fabrication. We consider a 'ribbed' cantilever that eliminates the disadvantages while improving the sensitivity simultaneously. Simulations for validation have been performed using the finite element analysis software ANSYS 8.0. The simulations reveal that a ribbed microcantilever is almost as sensitive as a thin cantilever and has relatively very low arching effect. Simulations also reveal that higher the arching lower is the sensitivity.

Omkar G. Karhade

Papers

Novel cantilever for biosensing applications

Novel cantilever for biosensing applications