Mechatronics Systems Engineering, School of

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Endoscopic Optical Imaging Technologies and Devices for Medical Purposes: State of the Art

Peer reviewed: 
Yes, item is peer reviewed.
Date created: 
2020-09-29
Abstract: 

The growth and development of optical components and, in particular, the miniaturization of micro-electro-mechanical systems (MEMSs), has motivated and enabled researchers to design smaller and smaller endoscopes. The overarching goal of this work has been to image smaller previously inaccessible luminal organs in real time, at high resolution, in a minimally invasive manner that does not compromise the comfort of the subject, nor introduce additional risk. Thus, an initial diagnosis can be made, or a small precancerous lesion may be detected, in a small-diameter luminal organ that would not have otherwise been possible. Continuous advancement in the field has enabled a wide range of optical scanners. Different scanning techniques, working principles, and the applications of endoscopic scanners are summarized in this review.

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Article
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Material Properties and Structure of Natural Graphite Sheet

Peer reviewed: 
Yes, item is peer reviewed.
Date created: 
2020-10-29
Abstract: 

Natural graphite sheet (NGS) is compressible, porous, electrically and thermally conductive material that shows a potential to be used in fuel cells, fow batteries, electronics cooling systems, supercapacitors, adsorption air conditioning, and heat exchangers. We report the results of an extensive material characterization study that focuses on thermal conductivity, thermal difusivity, electrical conductivity, coefcient of thermal expansion (CTE), compression strain, and emissivity. All the properties are density-dependent and highly anisotropic. Increasing the compression from 100 to 1080 kPa causes the through-plane thermal and electrical conductivities to increase by up to 116% and 263%, respectively. The properties are independent of the sheet thickness. Thermal and electrical contact resistance between stacked NGS is negligible at pressures 100 to 1080 kPa. In the in-plane direction, NGS follows the Wiedemann-Franz law with Lorenz number 6.6 × 10−6 W  K−2. The in-plane CTE is low and negative (shrinkage with increasing temperature), while the through-plane CTE is high, increases with density, and reaches 33 × 10−6 K−1. Microscope images are used to study the structure and relate it to material properties. An easy-to-use graphical summary of the forming process and NGS properties are provided in Appendices A and B.

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Article
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Electrostatic Twisting of Core-Shell Nanofibers for Strain Sensing Applications

Peer reviewed: 
Yes, item is peer reviewed.
Date created: 
2020-09-18
Abstract: 

Stretchable strain sensors are increasingly needed in emerging fields of wearable electronics and smart textiles for applications ranging from human motion detection to health monitoring. Nanofibers made from conductive materials or composites of polymers and conductive nanoparticles exhibit strong sensitivities but are difficult to utilize due to their small dimensions. Herein, we report on a technique for producing core-shell nanofibers and in-situ twisting of them to each other using a rotating electric field. The process produces sensitive threads that can be handled easily and used, for instance, in smart textile applications. The core-shell nanofibers utilized poly(vinylidene fluoride) as the structural polymer and multiwalled carbon nanotubes were used to make the core electrically conductive. The structure of nanofibers was studied through a set of analytical methods. The fibers exhibit strong piezoresistive responses and can be utilized in various strain sensing applications. Mechanical properties of fabricated submicron fiber yarns are compared with non-twisted fibers and improvement of their stretchability has been demonstrated. Furthermore, the sensitivity of fiber threads to different directions of stretching depended on the way of their knitting into fabric has been compared.

Document type: 
Article

Compressive Mechanical Characterization of Non-Human Primate Spinal Cord White Matter

Peer reviewed: 
Yes, item is peer reviewed.
Date created: 
2018-07-01
Abstract: 

The goal of developing computational models of spinal cord injury (SCI) is to better understand the human injury condition. However, finite element models of human SCI have used rodent spinal cord tissue properties due to a lack of experimental data. Central nervous system tissues in non human primates (NHP) closely resemble that of humans and therefore, it is expected that material constitutive models obtained from NHPs will increase the fidelity and the accuracy of human SCI models. Human SCI most often results from compressive loading and spinal cord white matter properties affect FE predicted patterns of injury; therefore, the objectives of this study were to characterize the unconfined compressive response of NHP spinal cord white matter and present an experimentally derived, finite element tractable constitutive model for the tissue. Cervical spinal cords were harvested from nine male adult NHPs (Macaca mulatta). White matter biopsy samples (3 mm in diameter) were taken from both lateral columns of the spinal cord and were divided into four strain rate groups for unconfined dynamic compression and stress relaxation (post-mortem <1-hour). The NHP spinal cord white matter compressive response was sensitive to strain rate and showed substantial stress relaxation confirming the viscoelastic behavior of the material. An Ogden 1st order model best captured the non-linear behavior of NHP white matter in a quasi-linear viscoelastic material model with 4-term Prony series. This study is the first to characterize NHP spinal cord white matter at high (>10/sec) strain rates typical of traumatic injury. The finite element derived material constitutive model of this study will increase the fidelity of SCI computational models and provide important insights for transferring pre-clinical findings to clinical treatments.

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Article
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Buck-Plus-Unfolder as the Superior Active Power Decoupling Solution for 400 Vdc/kW-Level Applications

Peer reviewed: 
Yes, item is peer reviewed.
Date created: 
2020-07-21
Abstract: 

In single-phase ac/dc applications where reliability and/or power-density are critical, active power decoupling (APD) circuits can be employed to reduce the required capacitance on the dc-link. Various APD circuits have been proposed so far, all with their advantages and disadvantages. However, many confusions still exist in the literature on this topic which is mainly attributed to a lack of unified and comprehensive assessment criteria. In this paper, first the decisive criteria for a modern APD circuit are established, and the buck APD is identified as the current state-of-the-art, based on them. Then the buck-plus-unfolder topology with triangular current mode (TCM) modulation is proposed as an improvement, and a simple, yet solid foundation is introduced to choose the superior decoupling solution at different specifications. The operation equations for the APD with TCM modulation are derived next, and the operation of the proposed solution is demonstrated using a hardware prototype.

Document type: 
Article
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Buck-Plus-Unfolder as the Superior Active Power Decoupling Solution for 400 Vdc/kW-Level Applications

Peer reviewed: 
Yes, item is peer reviewed.
Date created: 
2020-07-21
Abstract: 

In single-phase ac/dc applications where reliability and/or power-density are critical, active power decoupling (APD) circuits can be employed to reduce the required capacitance on the dc-link. Various APD circuits have been proposed so far, all with their advantages and disadvantages. However, many confusions still exist in the literature on this topic which is mainly attributed to a lack of unified and comprehensive assessment criteria. In this paper, first the decisive criteria for a modern APD circuit are established, and the buck APD is identified as the current state-of-the-art, based on them. Then the buck-plus-unfolder topology with triangular current mode (TCM) modulation is proposed as an improvement, and a simple, yet solid foundation is introduced to choose the superior decoupling solution at different specifications. The operation equations for the APD with TCM modulation are derived next, and the operation of the proposed solution is demonstrated using a hardware prototype.

Document type: 
Article
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Highly-doped SiC Resonator with Ultra-Large Tuning Frequency Range by Joule Heating Effect

Peer reviewed: 
Yes, item is peer reviewed.
Date created: 
2020-06-27
Abstract: 

Tuning the natural frequency of a resonator is an innovative approach for the implementation of mechanical resonators in a broad range of fields such as timing applications, filters or sensors. The conventional electrothermal technique is not favorable towards large tuning range because of its reliance on metallic heating elements. The use of metallic heaters could limit the tuning capability due to the mismatch in thermal expansion coefficients of materials forming the resonator. To solve this drawback, herein, the design, fabrication, and testing of a highly-doped SiC bridge resonator that excludes the use of metallic material as a heating element has been proposed. Instead, free-standing SiC structure functions as the mechanical resonant component as well as the heating element. Through the use of the Joule heating effect, a frequency tuning capability of almost ∆f/fo ≈ 80% has been demonstrated. The proposed device also exhibited a wide operating frequency range from 72.3 kHz to 14.5 kHz. Our SiC device enables the development of highly sensitive resonant-based sensors, especially in harsh environments.

Document type: 
Article

A Micromachined Vector Light Sensor

Peer reviewed: 
Yes, item is peer reviewed.
Date created: 
2020-05-24
Abstract: 

We report the design, fabrication, and performance characteristics of a novel microfabricated light sensor designed to determine the intensity and direction of an incident light source. The device structure comprises several light sensors that are integrated onto a pyramid base. The direction to the light source is estimated using the ratios of the signals from the lights sensors that are facing different directions. We demonstrate that this “vector light sensor”, is capable of measuring both the intensity and the direction of light from a source. The three-dimensional structure of the sensor is created based on well-known silicon microfabrication techniques and uses photodiodes for the detection of visible light. The signals from the photodiodes were read and processed based on a simple algorithm to experimentally verify the device performance. In addition to the direction, the distance to a light source may be estimated by simple triangulation of data from two vector light sensors. The small size and low power consumption of the individual sensors make them suitable for applications where passive distance and direction estimation is required. Furthermore, it is envisioned that arrayed sensors can directly provide light-field information in a plane.

Document type: 
Article

Self-Powered Monolithic Accelerometer Using a Photonic Gate

Peer reviewed: 
Yes, item is peer reviewed.
Date created: 
2020-07-02
Abstract: 

Harvesting sustainable energy resources from surrounding environments to power small electronic devices and systems has attracted massive research attention. Herein, we develop a novel technology to harvest light energy to self-power and simultaneously sense mechanical acceleration in a monolithic structure. When the photonic gate is illuminated the operation mode of the device changes from conventional mode to light harvesting and self-powered operation. The light illumination provides a gradient of majority carrier concentration on the top semiconductor layer, generating a lateral photovoltage, which is the output voltage of the sensor. Under acceleration, the mechanical inertial force induces stress in the sensor material leading to the change of mobility of the charge carriers, which shifts their diffusion rate, and hence changes the gradient of the majority carriers and the lateral photovoltage. The sensitivity at 480 lx light illumination was measured to be 107 , while it was approximately 30  under the ambient light illumination without any electrical power source. In addition, the acceleration sensitivity is tunable by controlling parameters of the photonic gate such as light power, light spot position and light wavelength. The integration of sensing and powering functions into a monolithic platform proposed in this work eliminates the requirement of external power sources and offers potential solutions for wireless, independent, remote, and battery-free sensing devices and systems.

Document type: 
Article

Using Inclusive Language in the Applied-Science Academic Environments

Author: 
Peer reviewed: 
Yes, item is peer reviewed.
Date created: 
2020-07-03
Abstract: 

Language is not neutral or used in a vacuum; language is one of the most powerful tools we have as humans that incorporates personal assumptions, social norms, and cultural ideologies. It is therefore important to consider language critically and to watch for biases in usage. Language reflects the world it is used in, but it is also active in maintaining or redesigning that world. It can be a tool of discrimination or of empowerment. We can use it to foster discrimination, unintentionally or otherwise, or we can use it to help make a fairer world [1]. Words have the power to affect our personhood, our identity, our attitudes, and our images about others. The power of language to affect our identity and behaviour was realized by oppressed groups in the 20th Century. Language is an important part of socialization - it plays a crucial part in the process whereby people learn the behaviours and values of a particular group or culture [2]. Historically, language has left many out. Individuals and groups have been marginalized and discriminated against because of their culture, race, ethnicity, gender, sexual orientation, age, disability, socioeconomic status, appearance, and more. Inclusive language seeks to treat all people with respect, dignity, and impartiality. It is constructed to bring everyone into the group and exclude no one. It is suggested that the basis of communication is not what is said, but how the words are heard. Language framed by derogatory names and symbols can have implications for people and their life experiences [3]. Making changes to use more inclusive language offers us a chance to grow and become better communicators who care for those we are communicating with [4]. This short article is meant to review the concept of political correctness and inclusive language and raise awareness for students and teachers to discriminatory terms that can be easily replaced with clearer and less-offensive alternatives. This topic has been vastly discussed in social sciences and a great number of theories and articles have shed light on the importance of this topic. The goal of this paper is to communicate these ideas to a larger audience including educators in applied sciences including Science, Technology, Engineering and Math (STEM). 

Document type: 
Article
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