Search results

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.

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.

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.

It is currently difficult to measure temperature and pressure in harsh environments. Such measurements are limited by either the ability of the sensing element or the associated electrical wiring to withstand the operating environment. This is unfortunate as temperature and pressure are important measurands in various engineering structures as they provide critical information on the operating condition of the structure. Hence, there is a need to address this shortcoming. Such a sensor in place would enhance the operating efficiency thereby reducing the pollution burden and its impact on the environment. The purpose of this paper is to present theoretical and preliminary experimental results for a co‐integrated pressure and temperature sensor for harsh environments.

This work describes a co‐integrated pressure‐temperature wireless sensing scheme. The approach presented herein provides the possibility of measuring dynamic pressure and temperature within an enclosed volume using acoustic signals. Resonance tube physics is exploited for the temperature sensing. A microphone is used to obtain the acoustic signal whose frequency is a function of the temperature and the tube geometry.

The dynamic pressure is measured from the calibrated amplitude of the pressure wave signal measured by the microphone. The temperature can be measured through the shift of the standing wave frequency with a resolution of <1°C. The resonance tube can be fabricated using any material that resists harsh environments. The geometry of the tube can be tailored for any specific frequency range, as the application warrants. Also, this provides a means for accurate temperature compensation of pressure sensor data from high temperature environments. A Matlab/Simulink model is developed and presented for the acquisition of acoustic signals through the wall of an enclosed volume. For these applications the standing wave signal transmitted through the enclosure wall becomes a function of the wall material and wall thickness. Preliminary experimental results are presented in which a DC fan is used for generating the dynamic pressure in a varying temperature environment.

The major issue is the separation of the noise from the signal. As various applications yield specific signal noise, the problem needs detailed data to be addressed.

Temperature and dynamic pressure could be recorded/monitored in very harsh environment conditions such as chemical reactors.

This work demonstrates the possibility of employing a co‐integrated acoustic sensing scheme in which both pressure and temperature are measured simultaneously with a sole sensor. The major advantage with acoustic sensing is the wireless transmission of data. This allows for non‐invasive measurement from within enclosed systems. Direct real‐time temperature compensation is possible that does not require any compensation circuitry. Hence, pressure and temperature data may be obtained from caustic operating environments whose access is otherwise not feasible.

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.