374 research outputs found
Performance of Smart Materials-Based Instrumentation for Force Measurements in Biomedical Applications: A Methodological Review
The introduction of smart materials will become increasingly relevant as biomedical technologies progress. Smart materials sense and respond to external stimuli (e.g., chemical, electrical, mechanical, or magnetic signals) or environmental circumstances (e.g., temperature, illuminance, acidity, or humidity), and provide versatile platforms for studying various biological processes because of the numerous analogies between smart materials and biological systems. Several applications based on this class of materials are being developed using different sensing principles and fabrication technologies. In the biomedical field, force sensors are used to characterize tissues and cells, as feedback to develop smart surgical instruments in order to carry out minimally invasive surgery. In this regard, the present work provides an overview of the recent scientific literature regarding the developments in force measurement methods for biomedical applications involving smart materials. In particular, performance evaluation of the main methods proposed in the literature is reviewed on the basis of their results and applications, focusing on their metrological characteristics, such as measuring range, linearity, and measurement accuracy. Classification of smart materials-based force measurement methods is proposed according to their potential applications, highlighting advantages and disadvantages
Flexible Strain Detection Using Surface Acoustic Waves: Fabrication and Tests
Over the last couple of decades, smart transducers based on piezoelectric materials have been used as sensors in a wide range of structural health monitoring applications. Among them, a Surface Acoustic Wave sensor (SAW) offers an overwhelming advantage over other commercial sensing technologies due to its passive, small size, fast response time, cost-effectiveness, and wireless capabilities. Development of SAW sensors allows investigation of their potential not only for measuring less-time dependent parameters, such as pressure and temperature, but also dynamic parameters like mechanical strains. The objective of this study is to develop a passive flexible SAW sensor with optimized piezoelectric properties that can detect and measure mechanical strains occurred in aerospace structures. This research consists of two phases. First, a flexible thin SAW substrate fabrication using hot-press made of polyvinylidene fluoride (PVDF) as a polymer matrix, with lead zirconate titanate (PZT), calcium copper titanate (CCTO), and carbon nanotubes (CNTs) as micro and nanofillers’ structural, thermal and electrical properties are investigated. Piezoelectric property measurements are carried out for different filler combinations to optimize the suitable materials, examining flexibility and favorable characteristics. Electromechanical properties are enhanced through a noncontact corona poling technique, resulting in effective electrical coupling. Second, the two-port interdigital transducers (IDTs) deposition made of conductive paste onto the fabricated substrate through additive manufacturing is studied. Design parameters of SAW IDTs are optimized using a second-order transmission matrix approach. An RF input signal excites IDTs and generates Rayleigh waves that propagate through the delay line. By analyzing the changes in wave characteristics, such as frequency shift and phase response, the developed passive strain sensor can measure mechanical strains
FORMATION OF CARBON NANOSPRINGS VIA PRECURSOR CONSTRAINED FIBER MICROBUCKLING
Flexible carbon nanosprings and wavy nanofibers can be used in micro and nanoelectromechanical system devices, deployable structures, flexible displays, energy storage, catalysis, nanocomposites and a multitude of other uses. A novel method to produce wavy and helical carbon nanofibers (CNFs) is presented here. The CNFs with controlled geometry were fabricated via pyrolysis of electrospun polyacrylonitrile (PAN) nanofibers as the precursor. The waviness/helicity of nanofibers was achieved by subjecting the precursor nanofibers to constraint buckling inside a thermally shrinking matrix. The much higher tendency of the matrix to shrink, compared to PAN nanofibers, was achieved by controlling the microstructure and crystallinity of the precursors.
The formation of the wavy/helical geometry was explained quantitatively via mechanistic models, by minimizing the total mechanical energy stored in the PAN-matrix system during the matrix shrinkage. Despite its simplicity in considering elastic deformations only, the model provided reasonably quantitative matching with the experiments. Compared to existing methods in generating wavy/helical nanofibers, such as chemical vapor deposition growth methods, our method provides a more controllable geometry which is suitable for large scale production of aligned buckled CNFs
Enabling wearable soft tactile displays with dielectric elastomer actuators
PhDTouch is one of the less exploited sensory channels in human machine
interactions. While the introduction of the tactile feedback would improve the
user experience in several fields, such as training for medical operators,
teleoperation, computer aided design and 3D model exploration, no interfaces
able to mimic accurately and realistically the tactile feeling produced by the
contact with a real soft object are currently available. Devices able to simulate
the contact with soft bodies, such as the human organs, might improve the
experience.
The existing commercially available tactile displays consist of complex
mechanisms that limit their portability. Moreover, no devices are able to provide
tactile stimuli via a soft interface that can also modulate the contact area with the
finger pad, which is required to realistically mimic the contact with soft bodies,
as needed for example in systems aimed at simulating interactions with virtual
biological tissues or in robot-assisted minimally invasive surgery.
The aim of this thesis is to develop such a wearable tactile display based on the
dielectric elastomer actuators (DEAs). DEAs are a class of materials that respond
to an electric field producing a deformation.
In particular, in this thesis, the tactile element consists of a so-called
hydrostatically coupled dielectric elastomer actuator (HC-DEAs). HC-DEAs rely
on an incompressible fluid that hydrostatically couples a DEA-based active part
to a passive part interfaced to the user.
The display was also tested within a closed-loop configuration consisting of a
hand tracking system and a custom made virtual environment. This proof of
concept system allowed for a validation of the abilities of the display.
Mechanical and psychophysical tests were performed in order to assess the
ability of the system to provide tactile stimuli that can be distinguished by the
users.
Also, the miniaturisation of the HC-DEA was investigated for applications in
refreshable Braille displays or arrays of tactile elements for tactile maps
Micro-scale to nano-scale generators for energy harvesting:Self powered piezoelectric, triboelectric and hybrid devices
This comprehensive review focuses on recent advances in energy harvesting of micro-scale and nano-scale generators based on piezoelectric and triboelectric effects. The development of flexible and hybrid devices for a variety of energy harvesting applications are systematically reviewed. A fundamental understanding of the important parameters that determine the performance of piezoelectric, triboelectric and hybrid devices are summarized. Current research directions being explored and the emerging factors to improve harvester functionality and advance progress in achieving high performance and durable energy conversion are provided. Investigations with regard to integrating flexible matrices and optimizing the composition of the piezoelectric and triboelectric materials are examined to enhance device performance and improve cost-effectiveness for the commercial arena. Finally, future research trends, emerging device structures and novel materials in view of imminent developments and harvesting applications are presented.</p
Recent Advances in Energy Harvesting from the Human Body for Biomedical Applications
Energy harvesters serve as continuous and long-lasting sources of energy that can be integrated into wearable and implantable sensors and biomedical devices. This review paper presents the current progress, the challenges, the advantages, the disadvantages and the future trends of energy harvesters which can harvest energy from various sources from the human body. The most used types of energy are chemical; thermal and biomechanical and each group is represented by several nano-generators. Chemical energy can be harvested with a help of microbial and enzymatic biofuel cells, thermal energy is collected via thermal and pyroelectric nano-generators, biomechanical energy can be scavenged with piezoelectric and triboelectric materials, electromagnetic and electrostatic generators and photovoltaic effect allows scavenging of light energy. Their operating principles, power ratings, features, materials, and designs are presented. There are different ways of extracting the maximum energy and current trends and approaches in nanogenerator designs are discussed. The ever-growing interest in this field is linked to a larger role of wearable electronics in the future. Possible directions of future development are outlined; and practical biomedical applications of energy harvesters for glucose sensors, oximeters and pacemakers are presented. Based on the increasingly accumulated literature, there are continuous promising improvements which are anticipated to lead to portable and implantable devices without the requirement for batteries
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