1,929 research outputs found

    SU-8 Guiding Layer for Love Wave Devices

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    SU-8 is a technologically important photoresist used extensively for the fabrication of microfluidics and MEMS, allowing high aspect ratio structures to be produced. In this work we report the use of SU-8 as a Love wave sensor guiding layer which allows the possibility of integrating a guiding layer with flow cell during fabrication. Devices were fabricated on ST-cut quartz substrates with a single-single finger design such that a surface skimming bulk wave (SSBW) at 97.4 MHz was excited. SU-8 polymer layers were successively built up by spin coating and spectra recorded at each stage; showing a frequency decrease with increasing guiding layer thickness. The insertion loss and frequency dependence as a function of guiding layer thickness was investigated over the first Love wave mode. Mass loading sensitivity of the resultant Love wave devices was investigated by deposition of multiple gold layers. Liquid sensing using these devices was also demonstrated; water-glycerol mixtures were used to demonstrate sensing of density-viscosity and the physical adsorption and removal of protein was also assessed using albumin and fibrinogen as model proteins

    Acoustic Wave Based MEMS Devices, Development and Applications

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    Acoustic waves based MEMS devices offer a promising technology platform for a wide range of applications due to their high sensitivity and the capability to operate wirelessly. These devices utilize acoustic waves propagating through or on the surface of a piezoelectric material. An acoustic wave device typically consists of two layers, metal transducers on top of piezoelectric substrate or thin films. The piezoelectric material has inherent capabilities of generating acoustic waves related to the input electrical sinusoidal signals placed on the transducers. Using this characteristic, different transducer designs can be placed on top of the piezoelectric material to create acoustic wave based filters, resonators or sensors. Historically, acoustic wave devices have been and are still widely used in telecommunications industry, primarily in mobile cell phones and base stations. Surface Acoustic Wave (SAW) devices are capable of performing powerful signal processing and have been successfully functioning as filters, resonators and duplexers for the past 60 years. Although SAW devices are technological mature and have served the telecommunication industry for several decades, these devices are typically fabricated on piezoelectric substrates and are packaged as discrete components. Considering the wide flexibility and capabilities of the SAW device to form filters, resonators there has been motivation to integrate such devices on silicon substrates as demonstrated in (Nordin et al., 2007; M. J. Vellekoop et al., 1987; Visser et al., 1989). One such example is illustrated in (Nordin et al., 2007) where a CMOS SAW resonator was fabricated using 0.6 m AMIs CMOS technology process with additional MEMS post-processing. The traditional SAW structure of having the piezoelectric at the bottom was inverted. Instead, the IDTs were cleverly manufactured using standard complementary-metal-oxide-semiconductor (CMOS) process and the piezoelectric layer was placed on the top. Active circuitry can be placed adjacent to the CMOS resonator and can be connected using the integrated metal layers. A SAW device can also be designed to have a long propagation path between the input and output transducer. The propagating acoustic waves will then be very sensitive to ambient changes, allowing the device to act as a sensor. Any variations to the characteristics of the propagation path affect the velocity or amplitude of the wave. Important application for acoustic wave devices as sensors include torque and tire pressure sensors (Cullen et al., 1980; Cullen et al., 1975; Pohl et al., 1997), gas sensors (Levit et al., 2002; Nakamoto et al., 1996; Staples, 1999; Wohltjen et al., 1979), biosensors for medical applications (Andle et al., 1995; Ballantine et al., 1996; Cavic et al., 1999; Janshoff et al., 2000), and industrial and commercial applications (vapor, humidity, temperature, and mass sensors) (Bowers et al., 1991; Cheeke et al., 1996; Smith, 2001; N. J. Vellekoop et al., 1999; Vetelino et al., 1996; Weld et al., 1999). In recent years, the interest in the development of highly sensitive acoustic wave devices as biosensor platforms has grown. For biological applications the acoustic wave device is integrated in a microfluidic system and the sensing area is coated with a biospecific layer. When a bioanalyte interacts with this sensing layer, physical, chemical, and/or biochemical changes are produced. Typically, mass and viscosity changes of the biospecific layer can be detected by analyzing changes in the acoustic wave properties such as velocity, attenuation and resonant frequency of the sensor. An important advantage of the acoustic wave biosensors is simple electronic readout that characterizes these sensors. The measurement of the resonant frequency or time delay can be performed with high degree of precision using conventional electronics. This chapter is focused on two important applications of the acoustic-wave based MEMS devices; (1) biosensors and (2) telecommunications. For biological applications these devices are integrated in a microfluidic system and the sensing area is coated with a biospecific layer. When a bioanalyte interacts with this sensing layer, physical, chemical, and/or biochemical changes are produced. Typically, mass and viscosity changes of the biospecific layer can be detected by analyzing changes in the acoustic wave properties such as velocity, attenuation and resonant frequency of the sensor. An important advantage of the acoustic wave biosensors is simple electronic readout that characterizes these sensors. The measurement of the resonant frequency and time delay can be performed with high degree of precision using conventional electronics. Only few types of acoustic wave devices could be integrated in microfluidic systems without significant degradation of the quality factor. The acoustic wave based MEMS devices reported in the literature as biosensors are film bulk acoustic wave resonators (FBAR) and surface acoustic waves (SAW) resonators and SAW delay lines. Different approaches to the realization of FBARs and SAW resonators and SAW delay lines used for various biochemical applications are presented. Next, acoustic wave MEMS devices used in telecommunications applications are presented. Telecommunication devices have different requirements compared to sensors, where acoustic wave devices operating as a filter or resonator are expected to operate at high frequencies (GHz), have high quality factors and low insertion losses. Traditionally, SAW devices have been widely used in the telecommunications industry, however with advancement in lithographic techniques, FBARs are rapidly gaining popularity. FBARs have the advantage of meeting the stringent requirement of telecommunication industry of having Qs in the 10,000 range and silicon compatibility

    Unconventional Uses of Cantilevers for Chemical Sensing in Gas and Liquid Environments

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    Microcantilevers used as (bio)chemical sensors are usually coated with a chemically sensitive layer. The coated devices operate either in a static bending regime or in a dynamic flexural mode. While the coated devices operate generally well in both the static and dynamic mode, they do suffer from certain shortcomings depending on the medium of operation and the application, including lack of selectivity and of reversibility of the sensitive coating and a reduced quality factor due to the surrounding medium. In particular, the performance of microcantilevers excited in their standard out-of-plane dynamic mode drastically decreases in viscous liquid media. Moreover, the responses of coated cantilevers operating in the static bending mode are often difficult to interpret. To resolve those performance issues, unconventional uses of microcantilever are reviewed in this paper, which consist of the use of the dynamic mode without sensitive coating, the use of in-plane (flexural and longitudinal) vibration modes in liquid media, and fully accounting for the viscoelastic effects of the coatings in the static mode of operation. The advantages and drawbacks of these unconventional uses of microcantilevers for chemical sensing in gas and liquid environments are discussed

    Microfabricated liquid density sensors using polyimide-guided surface acoustic waves

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    The simultaneous measurements of liquid density and refractive index on the same liquid sample are desirable. This thesis investigates the development of a micro- fabricated liquid density sensor that can be integrated into existing refractometers. A discussion of density sensing techniques and review of suitable sensors is given, leading to the choice of a Love mode surface acoustic wave (SAW) device. Love modes are formed by focussing the acoustic energy in a thin waveguide layer on a surface acoustic wave device. The horizontal-shear wave motion reduces attenuation in liquid environments, and the high surface energy density theoretically gives the highest sensitivity of all SAW devices. This study follows the development of a Love mode liquid density sensor using a polyimide waveguide layer. The novel use of polyimide offers simple and cheap fabrication, and theoretically gives a very high sensitivity to surface loading due to its low acoustic velocity. Love mode devices were fabricated with different polyimide waveguide thicknesses. The optimum thickness for a compromise between low loss and high sensitivity was 0.90 - 1.0 μm. These devices exhibited a linear shift in frequency with the liquid density-viscosity product for low viscosities. The response was smaller for high viscosities due to non-Newtonian liquid behaviour. Dual delay-line structures with a smooth 'reference' and corrugated 'sense' delay- lines were used to trap the liquid and separate the density from the density-viscosity product. A sensitivity up to 0.13 μgcm(^-3)Hz(^-1) was obtained. This is the highest density sensitivity obtained from an acoustic mode sensor. Experimental results show a zero temperature coefficient of frequency is possible using polyimide waveguides. These are the first Love mode devices that demonstrate temperature independence, highlighting the importance of polyimide as a new waveguide material

    The Design of Digital Liquid Density Meter Based on Arduino

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    A measure of liquid thickness is needed to make a dough or formula for medicinal syrup. The tools to measure the thickness available in the market are analog that is less accurate and precision. To overcome these problems, digital density measuring devices are needed. The limitation of the digital density meter, especially liquid, urges the author to carry out further research on the digitization of this measuring instrument. This research aims to make a digital density meter for liquid matter with a high level of measurement accuracy, as the reference measurement study for liquid density in digital form. The instrument was designed using the load cell method as the main sensor. It was also equipped with a DS18B20 water-resistant temperature sensor to measure the temperature of the liquid. The data were analyzed to obtain the accuracy and error of the liquid density measurement from the density meter. The liquid samples used for research were Pertamax, solar, and water. Sample accuracy and error measurement results were 99.83 percent and 0.17 percent respectively for Pertamax, 99.63 percent and 0.37 percent for solar and 99.46 percent and 0.54 percent for water. The measured density value was finally shown on the 16x2 LCD

    Unconventional Uses of Microcantilevers as Chemical Sensors in Gas and Liquid Media

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    The use of microcantilevers as (bio)chemical sensors usually involves the application of a chemically sensitive layer. The coated device operates either in a static bending regime or in a dynamic flexural mode. While some of these coated devices may be operated successfully in both the static and the dynamic modes, others may suffer from certain shortcomings depending on the type of coating, the medium of operation and the sensing application. Such shortcomings include lack of selectivity and reversibility of the sensitive coating and a reduced quality factor due to the surrounding medium. In particular, the performance of microcantilevers excited in their standard out-of-plane dynamic mode drastically decreases in viscous liquid media. Moreover, the responses of coated cantilevers operating in the static bending mode are often difficult to interpret. To resolve these performance issues, the following emerging unconventional uses of microcantilevers are reviewed in this paper: (1) dynamic-mode operation without using a sensitive coating, (2) the use of in-plane vibration modes (both flexural and longitudinal) in liquid media, and (3) incorporation of viscoelastic effects in the coatings in the static mode of operation. The advantages and drawbacks of these atypical uses of microcantilevers for chemical sensing in gas and liquid environments are discussed
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