Mechatronics Systems Engineering, School of

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Sol-Gel Deposition and Characterization of 1 Vanadium Pentoxide Thin Films with High TCR

Peer reviewed: 
Yes, item is peer reviewed.
Date created: 
2018-07-09
Abstract: 

Vanadium pentoxide thin films have been deposited on quartz substrates via sol-gel synthesis and dip coating. The process was developed to establish a reliable and inexpensive method to produce thin films with a high temperature coefficient of resistance (TCR)for sensing applications. Sol-gel precursor concentration and post-deposition annealing conditions were varied to address their effects on film composition, morphology, structure, resistivity, and TCR response. The resulting thin films were structurally characterized by thin film profilometry, x-ray diffraction, scanning electron microscopy, and Raman spectroscopy. Resistivity and TCR measurements were carried out to determine their efficacy as sensor materials. Both low and high concentration alkoxide sol-gel precursors led to films of pure -V2O5 composition but with characteristically different structural and electrical properties. Low concentration films showed a modest decrease in resistivity and TCR with increasing annealing temperature, consistent with the formation of increasing grain size and the coalescence of largely planar grains with common crystalline orientation. In contrast, films fabricated from higher alkoxide precursor concentration are characterized by a higher density of grains with a larger dispersion in orientation and better-developed grain boundaries, leading to a general increase in resistivity and TCR with annealing temperature. The TCR of the films lied in the range of -3%◦C−1 to -4%◦C−1, comparing favorably with films produced through conventional techniques such as DC magnetron sputtering, chemical vapor deposition, or pulsed laser deposition. Further, their TCR and resistivity characteristics can be controlled through sol gel precursor concentration and post-deposition annealing temperature, indicating that sol-gel deposited vanadium pentoxide films are promising candidates for infrared sensor applications.

Document type: 
Article

Tri-Mode Capacitive Proximity Detection Towards Improved Safety in Industrial Robotics

Peer reviewed: 
Yes, item is peer reviewed.
Date created: 
2018-06-15
Abstract: 

This paper presents a multi-functional capacitive sensor that is developed to improve the worker safety during the industrial human-robot interactions. The sensor is to be mounted on the worker and used to maintain a safe distance between the workers and robots or automotive parts moved by the robots. The response of a capacitive proximity sensor is a function of the distance to an object as well as the dielectric/conductance and geometry properties of the object. This uncertainty can lead to a wrong distance estimation or possibly a missed detection. The presented approach alleviates this issue by implementing three sensing capabilities including distance measurement, motion tracking, and profile recognition in a single platform. The presented sensor employs a capacitive sensing element coupled to reprogrammable interface electronics. The sensing element features a matrix of electrodes that can be reconfigured to various arrangements at run-time by controlling the interface electronics to obtain a more detailed perception of the ambient environment. Quantitative regression models are built to seek out distances while an adaptive classification tool based on support vector machines is employed to recognize the surface profiles. The performance of the sensing modalities has been experimentally assessed. Experimental results are provided to demonstrate that the system is able to detect a metallic object at distances of up to 18 cm with high resolutions, track its motion, and provide an estimate for its shape.

Document type: 
Article
File(s): 

A Wideband, Low-noise Accelerometer Sonar Wave Detection

Peer reviewed: 
Yes, item is peer reviewed.
Date created: 
2018-01
Abstract: 

This paper presents the development of a highperformance micromachined capacitive accelerometer for detection of sonar waves. The device is intended to replace existing hydrophones in towed array sonar systems, and thus, needs to meet stringent performance requirements on noise, bandwidth, and dynamic range, among others. The in-plane, single-axis accelerometer is designed based on a mode-tuning structural platform. A frame was used instead of a solid plate for the proof-mass of the device, allowing us to push undesired vibration modes beyond the operating bandwidth of the device while enabling us to employ a portion of the area for capacitive sensing elements. The designed accelerometer was fabricated on a silicon-on-insulator wafer with 100µm device layer with capacitive gaps of ~2.2µm. The sensitivity of the accelerometer is 4.0V/g with a noise spectral density of better than

Document type: 
Article
File(s): 

A High Performance Piezoelectric Vibration Sensor

Peer reviewed: 
Yes, item is peer reviewed.
Date created: 
2017-07
Abstract: 

We are reporting on the design, fabrication, and characterization of wideband, piezoelectric vibration microsensors. Prototypes were fabricated in a commercial foundry process. The entire thickness of the handle wafer was employed to carve the proof-mass of the device, leading to high sensitivity at a reduced chip area. A thin layer of aluminum nitride was used for sensing the displacements of the proof-mass. A continuous membrane was employed for the device structure in order to push undesired modes to high frequencies. Sensors with different geometries were designed and fabricated. Analytic and finite element analyses were conducted to study device response. A lump element model was developed for the piezoelectric vibration sensor and used for the noise modeling of the complete sensor system. Various performance metrics for the devices were characterized experimentally. Fabricated prototypes exhibited sensitivities as high as 350mV/g with first resonant frequencies of more than 10kHz. These devices are particularly suited for emerging applications in high-frequency vibration sensing.

Document type: 
Article
File(s): 

Conductive Cellulose Composites with Low Percolation Threshold for 3D Printed Electronics

Peer reviewed: 
Yes, item is peer reviewed.
Date created: 
2017-06-12
Abstract: 

We are reporting a 3D printable composite paste having strong thixotropic rheology. The composite has been designed and investigated with highly conductive silver nanowires. The optimized electrical percolation threshold from both simulation and experiment is shown from 0.7 vol. % of silver nanowires which is significantly lower than other composites using conductive nano-materials. Reliable conductivity of 1.19 × 102 S/cm has been achieved from the demonstrated 3D printable composite with 1.9 vol. % loading of silver nanowires. Utilizing the high conductivity of the printable composites, 3D printing of designed battery electrode pastes is demonstrated. Rheology study shows superior printability of the electrode pastes aided by the cellulose's strong thixotropic rheology. The designed anode, electrolyte, and cathode pastes are sequentially printed to form a three-layered lithium battery for the demonstration of a charging profile. This study opens opportunities of 3D printable conductive materials to create printed electronics with the next generation additive manufacturing process.

Document type: 
Article
File(s): 

A High-Performance Piezoelectric Vibration Sensor

Peer reviewed: 
Yes, item is peer reviewed.
Date created: 
2016-12
Abstract: 

We are reporting on the design, fabrication, and characterization of wideband, piezoelectric vibration microsensors. Prototypes were fabricated in a commercial foundry process. The entire thickness of the handle wafer was employed to carve the proof-mass of the device, leading to high sensitivity at a reduced chip area. A thin layer of aluminum nitride was used for sensing the displacements of the proof-mass. A continuous membrane was employed for the device structure in order to push undesired modes to high frequencies. Sensors with different geometries were designed and fabricated. Analytic and finite element analyses were conducted to study device response. A lump element model was developed for the piezoelectric vibration sensor and used for the noise modeling of the complete sensor system. Various performance metrics for the devices were characterized experimentally. Fabricated prototypes exhibited sensitivities as high as 350 mV/g with first resonant frequencies of more than 10 kHz. These devices are particularly suited for emerging applications in high-frequency vibration sensing.

Document type: 
Article
File(s): 

Morphology of Electrospun Poly(ethylene oxide) Ultra-fine Fibres with Incorporated MoO3 Nanoparticles

Peer reviewed: 
Yes, item is peer reviewed.
Date created: 
2016-12
Abstract: 

N-type semiconducting molybdenum trioxide (MoO3) nanoparticles embedded in polyethylene oxide (PEO) polymer ultra-fine fibres were deposited directly onto silicon substrates using an electrospinning technique. The effects of different MoO3/PEO concentrations as well as electrospinning parameters on the fibre morphologies were examined. Experimental results show that embedding nanoparticles and electrospinning onto small areas can be achieved without use of solvents or transfer of the deposited nanostructures. This approach offers a cost effective fabrication method to produce a diverse range of multifunctional materials for many applications including electronics, mechanical enhancement, drug delivery and gas sensing.

Document type: 
Article
File(s): 

Probing Mechanical Properties of Jurkat Cells under the Effect of ART Using Oscillating Optical Tweezers

Peer reviewed: 
Yes, item is peer reviewed.
Date created: 
2015
Abstract: 

Acute lymphoid leukemia is a common type of blood cancer and chemotherapy is the initial treatment of choice. Quantifying the effect of a chemotherapeutic drug at the cellular level plays an important role in the process of the treatment. In this study, an oscillating optical tweezer was employed to characterize the frequency-dependent mechanical properties of Jurkat cells exposed to the chemotherapeutic agent, artesunate (ART). A motion equation for a bead bound to a cell was applied to describe the mechanical characteristics of the cell cytoskeleton. By comparing between the modeling results and experimental results from the optical tweezer, the stiffness and viscosity of the Jurkat cells before and after the ART treatment were obtained. The results demonstrate a weak power-law dependency of cell stiffness with frequency. Furthermore, the stiffness and viscosity were increased after the treatment. Therefore, the cytoskeleton cell stiffness as the well as power-law coefficient can provide a useful insight into the chemo-mechanical relationship of drug treated cancer cells and may serve as another tool for evaluating therapeutic performance quantitatively.

Document type: 
Article
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