Search results

To predict the influence of inherent microfabrication and operating environmental influences on the performance of capacitive type sensors and actuators so that one can tune the performance and carry out more realistic designs.

When the sensors and actuators are micromachined or microfabricated, they are subjected to special problems that are characteristic to microdimensions. The important concerns are the influence of microfabrication process on the material properties and influence of operating environment on the system behavior. Hence, this paper proposed a way of quantifying and modeling the influence of inherent limitations of microfabrication and operating environment for the better design of micromachined capacitive type sensors and actuators. The methodology applies the modeling the variation of the elastic property of the system due to above influences through elastic stiffening and weakening concepts. The approach includes the application of boundary conditioning concept through Rayleigh energy method.

The microfabrication process and electrostatic field can alter significantly both static and dynamic behavior of the device. The performance of the device could also be tuned through these influences.

As the displacement of the sensors is expected to be small, linear approach is applied. The sensitivity, output range, operating limits and natural frequencies of the sensor can be easily controlled by varying the process and operating environmental influences.

Improved and more realistic design of microfabricated capacitive type sensors and actuators for many applications, such as, pressure sensors, microphones, microspeakers, etc.

A simple and easy way of modeling and quantifying the influence of process and operating environment was proposed for the betterment of design. The proposed design method can be applied for any micromachined or microfabricated capacitive type sensors and actuators so that varying sensitivities, output ranges and natural frequencies could be obtained. Over the last few years, newly emerging micro‐electro‐mechanical‐systems (MEMS) technology and micro‐fabrication techniques have gained popularity and importance in the miniaturization of a variety of sensors and actuators. The proposed technique is very useful in making the field of MEMS more matured as it attempts to model the problems that are unique to MEMS environment.

The purpose of this paper is to demonstrate the simplicity and versatility of micro‐cantilever based sensors and to present the influence of added mass and stress on the frequency response of the sensor in order to determine the most suitable sensing domain for a given application.

The frequency response of micro‐cantilevers depends not only on the applied mass and surface stress, but also on the mass position. An interpretation of the theoretical frequency results of the 1st and 2nd natural frequencies, for added mass, identifies a nodal point for the 2nd natural frequency which demonstrates mass invariance. Hence, at this nodal point, the frequency response remains constant regardless of mass and may be used for identifying purely induced surface stress influences on the micro‐cantilever's dynamic response. The Rayleigh‐Ritz energy method is used for the theoretical analysis. Theoretical results are compared with experimental results.

A graph of the 2nd natural frequency of micro‐cantilevers with added mass demonstrates the variability of the frequency with mass position on the micro‐cantilever. Of particular interest is the nodal point at which mass independence is revealed. This nodal point may be exploited to investigate purely stress‐related influences on the dynamic characteristics of micro‐cantilever sensors, thereby eliminating such effects as reactant evaporation from the micro‐cantilever sensor surface. In this regard, the nodal point of the 2nd natural frequency response is used to decouple mass‐stress influences.

Owing to the micro‐scale size of the micro‐cantilevers, it may not be possible to apply mass or stress directly at the nodal point and to concentrate its influence there. Hence, a certain amount of influence due to mass‐stress coupling may remain in the frequency responses observed.

Silicon micro‐cantilevers can be easily shaped and sensitized to a variety of influences. These qualities are highly regarded for sensor applications. The work presented herein, contributes to the optimization of micro‐cantilever sensors' dynamic response as a function of mass and surface stress influences. The main criterion for choosing one or the other is based on the time for the surface reaction to take place between the sensing material and the target material. The results presented contribute to the performance optimization of micro‐cantilever based medical and bio‐sensors.

Surface stress effects are generally of much smaller magnitude than mass influences; hence, through an investigation of the stress effects at the nodal point of the 2nd natural frequency it is possible to eliminate the mass influence completely. At this position mass and stress influences are decoupled and the sensor response can be uniquely quantified as a function of the applied stress. This is important for bio‐medical and health monitoring applications in which changes to the applied mass or surface stress on a micro‐cantilever sensor, may be readily observed through changes to the natural frequency response of the micro‐cantilever.

This paper seeks to establish an analytical reference model in order to optimize the frequency response of MEMS cantilever structures using cutouts.

Presented 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.

The 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.

MEMS microsystems are sensitive to microfabrication limitations especially at the boundary support of suspended structures such as microcantilevers.

MEMS 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.

A 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.

This paper proposes to examine a simple and cost‐effective method of integrating a reflector surface with a silicon‐based microfluidic channel for enhanced biosensing through the method of fluorescence in a microfluidics and nanofluidics‐based lab‐on‐a‐chip device.

Herein, the reflector is integrated with silicon‐based microfluidic channels and fluorescence measurements were carried out using alexafluor 647 particles. Two types of microfluidic channel surfaces were used, with and without reflector integration, for the experiments.

The experimental results prove that the proposed technique of partial reflector integration within microfluidic or nanofluidic channel surfaces is highly suitable for fluorescence‐based detection of single molecules and low concentration fluorophore‐tagged receptors.

It is believed that this is a novel work of integrating a reflector with a microfluidic channel surface for fluorescence‐based biodetection. This method will be very useful for fluorescence‐based biosensors in detecting low concentration fluorophores and single molecules.

To establish an accurate and sensitive method to characterize the moisture content of a particular environment.

This paper proposes a relatively simple humidity sensor design consisting of electrodes on a suitable substrate coated with a polyimide material. The changes in relative humidity are denoted by a corresponding change in the polyimide material's electrical resistance profile. The design proposed in this work can be microfabricated and integrated with electronic circuitry. This sensor can be fabricated on alumina or silicon substrates. The electrode material can be made up of nickel, gold or aluminum and the thickness of the electrodes ranges typically between 0.2 and 0.3 μm. The sensor consists of an active sensing layer on top of a set of electrodes. The design of the electrodes can be configured for both resistive and capacitive sensing.

The polyimide material's ohmic resistance changes significantly with humidity variations. Changes in resistance as large as 4‐6 orders of magnitude are attainable over the entire operational humidity range.

As the sensitivity varies non‐linearly with the humidity, the measurement has to be carried out over a very wide range in order to calibrate the sensor. The sensitivity and output range of the sensor can be easily controlled by changing the electrode spacing or geometry.

The control of humidity is important in many applications ranging from bio‐medical to space exploration.

A simple, easy to fabricate and measure, and low cost resistive‐type humidity sensor was developed. The realized sensor is suitable for integrating with microfabrication. Hence, multiple sensors of varying sensitivities and output ranges could be integrated on the same chip. Over the last few years, newly emerging micro‐electro‐mechanical‐systems technology and micro‐fabrication techniques have gained popularity and importance in the miniaturization of a variety of sensors and actuators.