An ionic liquid based strain sensor for large displacement measurement

A robust and low cost ionic liquid based strain sensor is fabricated for high strain measurements in biomedical applications (up to 40 % and higher). A tubular 5 mm long silicone microchannel with an inner diameter of 310 µm and an outer diameter of 650 µm is filled with an ionic liquid. Three ionic liquids have been investigated: 1-butyl-1-methylpyrrolidinium bis (trifluoromethylsulfonyl) imide, ethylammonium nitrate and cholinium ethanoate. When the channel is axially stretched, geometrical deformations change the electrical impedance of the liquid channel. The sensors display a linear response and low hysteresis with an average gauge factors of 1.99 for strains up to 40 %. Additionally, to fix the sensor by surgical stitching to soft biological tissue, a sensor with tube clamps consisting of photopatternable SU-8 epoxy-based resin is proposed.status: publishe

Absolute fiber-optic pressure sensing for high-temperature applications using white light interferometry

Fiber-optic pressure sensors allow rugged high-temperature and ultra-miniature pressure monitoring in harsh environments. However, simple light power based readout suffers from bending losses and light source fluctuations. This paper presents a differential technique based on white light interferometry to alleviate this problem. White light spectroscopic measurements have been performed on absolute Fabry-Pérot pressure sensors fabricated at the tip of multi-mode and single mode optical fibers. Bending loss sensitivity is demonstrated to be reduced with a factor of 79% by using the proposed differential spectroscopic technique. © 2013 IEEE.status: publishe

Miniature absolute optical pressure sensor at a fiber tip for high temperature applications

Fiber optic pressure sensors have attracted considerable attention because of their small size, high sensitivity and immunity to electromagnetic interference. Here, a miniature absolute pressure sensor at the edge of a fiber is presented. Contradictory to earlier pressure sensors with membranes at the fiber tip (in a co-axial configuration), we present a sensor in a cross-axial configuration. It is optimized for aerodynamic pressure measurements in turbomachinery. The sensor is fabricated by thin film deposition techniques and focused ion beam (FIB) microfabrication and uses multilayer Fabry-Perot (FP) interferometry as sensing principle. The reflected power intensity of the prototype is experimentally verified to be 0.77%/bar.status: publishe

An Implantable Intravascular Pressure Sensor for a Ventricular Assist Device

The aim of this study is to investigate the intravascular application of a micro-electro-mechanical system (MEMS) pressure sensor to directly measure the hemodynamic characteristics of a ventricular assist device (VAD). A bio- and hemo-compatible packaging strategy is implemented, based on a ceramic thick film process. A commercial sub-millimeter piezoresistive sensor is attached to an alumina substrate, and a double coating of polydimethylsiloxane (PDMS) and parylene-C is applied. The final size of the packaged device is 2.6 mm by 3.6 mm by 1.8 mm. A prototype electronic circuit for conditioning and read-out of the pressure signal is developed, satisfying the VAD-specific requirements of low power consumption (less than 14.5 mW in continuous mode) and small form factor. The packaged sensor has been submitted to extensive in vitro tests. The device displayed a temperature-independent sensitivity (12 μ V/V/mmHg) and good in vitro stability when exposed to the continuous flow of saline solution (less than 0.05 mmHg/day drift after 50 h). During in vivo validation, the transducer has been successfully used to record the arterial pressure waveform of a female sheep. A small, intravascular sensor to continuously register the blood pressure at the inflow and the outflow of a VAD is developed and successfully validated in vivo

An ionic liquid based strain sensor for large displacements

A novel ionic liquid based strain sensor is fabricated for high strain measurements (up to 10% and higher). A tubular silicone microchannel with a diameter of 310 μm and a length of 5 mm is filled with an ionic liquid (1-Butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide). The final sensor has an outer diameter of 650 μm and a length of 15 mm. When the channel is axially loaded, geometrical deformations change the electrical properties of the liquid channel. 4-point impedance spectroscopy with the integrated circuit AD5933 from Analog Devices and a dedicated galvanostatic front-end is performed to characterize this piezoresistive effect. The highest sensitivity is observed in the frequency range from 10 to 25 kHz, with corresponding gauge factors between 2 and 2.5 for an elongation of 10%.publisher: Elsevier articletitle: An Ionic Liquid Based Strain Sensor for Large Displacements journaltitle: Procedia Engineering articlelink: http://dx.doi.org/10.1016/j.proeng.2014.11.362 content_type: article copyright: Copyright © 2014 Published by Elsevier Ltd.status: publishe

Patterned glass fiber surfaces – Route to interface modification?

Fiber reinforced composites (FRCs) have demonstrated tremendous growth and attention owing to their outstanding mechanical properties such as high strength, specific stiffness, fatigue and toughness, combined with their low density and cost.[1] Recent research has focused much attention towards tailoring the physico-chemical properties of the fiber-matrix interface. It is well known that the interface plays a crucial role in determining the thermo-mechanical and fracture behavior of the composite, thus defining its overall durability. Shear stress transfer between the matrix and reinforcement occurs by a combination of mechanical inter-locking, physical adhesion and chemical bonding.[2] Physical adhesion of a surface is controlled by its surface free energy, which in a composite is associated to the thermodynamic work of adhesion between the fiber and matrix. The present study describes the surface modification of glass fibers by micro patterning and its effects on the physical properties. Among the variety of fibrous reinforcements available, glass fibers have been chosen for this study owing to the balance between thermo-mechanical properties, intrinsic hydrophilicity, and cost. The process of micro patterning is described as follows: as the first step, a thin layer of an hydrophobic photo sensitive resin is coated on the surface of the fibers. When exposed to ultra-violet (UV) light through a photo mask, the resin dissolves, thus rendering a patterned surface exhibiting selective wettability. Surface morphology of patterned fibers has been observed using Scanning Electron Microscopy (SEM). The effect of patterning on dynamic wetting properties of the fiber surface has been studied using Wilhelmy technique. Single fiber fragmentation tests are performed to elucidate the mechanical behavior of such patterned fibers.status: publishe

Fabrication and Characterisation of carbon nanotube composites for strain sensor applications

This paper reports on the fabrication of carbon nanotube (CNT) composites based on poly-dimethylsiloxane (PDMS). Both composites using multiwalled carbon nanotubes (MWCNTs) as well as composites using vertically aligned carbon nano-tubes (VACNTs) as conductive filler elements have been investigated. The MWCNT/PDMS composites show a quasi-linear piezoresistance response with gauge factors between 0.8 and 2.3. The VACNT/PDMS composites behave in a similar way realizing a gauge factor of 1.4. This gauge factor can be explained by only considering the geometrical change of the VACNT/PDMS composites during strain. The dense network of vertically aligned carbon nanotubes limits the contraction or tranver-sal strain during axial strain of the VACNT/PDMS composites. Poisson's ratio drops from 0.45 for pure PDMS to 0.2 for VACNT/PDMS composites. Conclusions about the suitability of these materials for use in MEMS are presentedstatus: publishe

Fabrication of Active Microfluidics on Glass with Semiconductor Grade Material

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