The key to monitoring structural health and defect detection of materials is the capacity to detect impact waves and their propagation through materials. A sensor must be extremely flexible and have a complex shape to detect impact waves from a certain type of construction. Complex sensors can be produced using direct ink write (DIW). In this article, the DIW approach is used to create a flexible impact wave propagation sensor (IWPS). Barium titanate (BaTiO3, or BTO), a ferroelectric ceramic material, is dispersed in polydimethylsiloxane (PDMS), which not only increases the flexibility of the 3D-printed sensor but also assures a consistent piezoelectric response across the entire sensor. This study investigated the impact load that caused an impact wave in a flexible sensor and its response to the impact load-generated impact wave. On BTO/PDMS stretchable composites, MWCNT (multi-walled carbon nanotube) based electrodes were printed using the DIW's multi-material printing capability. After contact poling of IWPS, 50wt% of BTO in the PDMS matrix produced a piezoelectric coefficient of 20 pC/N. Applying impact loading at the sensor's center caused an impact wave which eventually vanished as it got further away from the applied impact load's origin. The output voltage from several IWPS nodes was measured in order to characterize the propagation of impact waves. Additionally, the particle-wave velocity of a specific material attached to IWPS was calculated in this study using the voltage response time differences at various sensor locations. The particle-wave velocities of stainless steel (SS) and low-density polyethylene (LDPE) were measured using the specially built IWPS and were found to be 5625 m/s and 2000 m/s, respectively. These values are comparable with their theoretical values.
Selective Laser Sintering (SLS) is a branch of powder bed fusion additive manufacturing (AM) technique in which laser is used as a power source to sinter polymer powder materials. The laser targets the points in space defined by a 3D computer model and binds the material together to create a solid structure. Although thermoplastic materials (PA12, PA6, et) have been successfully demonstrated in SLS, printed 3D objects from these materials exhibit a lack of polymer interchain connection in print direction, resulting in poor mechanical properties and poor fatigue behavior. This deficiency of thermoplastics has encouraged to print high-performance thermosets using SLS. In this research, bismaleimide (BMI) resin thermoset powder was successfully printed using SLS with a two-step melting and post curing process. Dimensional and thermal stability of printed thermosets after curing is proved in this research for the very first time. Almost zero-dimensional change (0.033% increment in length, 0.23% increment in width, and 0.317% decrement in thickness) after curing of SLS printed thermoset part was presented. The thermomechanical property of printed BMI was characterized by dynamic mechanical analysis. Polymer crosslinking mechanism during curing process through FTIR as well as the thermal and mechanical stability of printed thermoset through compression tests have been analyzed in this research. The feasibility study demonstrates the feasibility of using SLS for printing high temperature tehermoset for variety energy and defense related applications.
This paper presents the fabrication, modeling and testing of a metamaterial based passive wireless temperature sensor consisting of an array of closed ring resonators (CRRs) embedded in a dielectric material matrix. A mixture of 70 vol% Boron Nitride (BN) and 30 vol% Barium Titanate (BTO) is used as the dielectric matrix and copper washers are used as CRRs. Conventional powder compression is used for the sensor fabrication. The feasibility of wireless temperature sensing is demonstrated up to 200 C. The resonance frequency of the sensor decreases from 11.93 GHz at room temperature to 11.85 GHz at 200 C, providing a sensitivity of 0.462 MHz/C. The repeatability of temperature sensing tests was carried out to quantify the repeatability. The highest standard deviation observed was 0.012 GHz at 200 C.
Energy harvesting has been gaining significant interest as a potential solution for energizing next generation sensor and energy storage devices. The most widely investigated material for piezoelectric and pyro-electric energy harvesting to date is PZT (Lead Zirconate Titanate), owing to its good piezoelectric and pyro-electric properties. However, Lead is detrimental to human health and to the environment. Hence, alternative materials are required to be investigated for this purpose. In this paper, a lead free material Lithium Niobate (LNB) is reported as a potential material for pyro-electric energy harvesting. Although, it has lower pyro-electric properties than PZT, it has better properties than other lead free alternatives of PZT such as ZnO. In addition, LNB has a high curie point of 1142 °C, which makes it suitable for high temperature environment where other pyro-electric materials are not suitable. Therefore, a single crystal LNB has been investigated as a source of energy harvesting under alternative heating and cooling environment. A commercial 0.2 F super-capacitor was used as the energy storage device.
Development of new materials hold the key to the fundamental progress in energy storage systems such as Li-ion battery, which is widely used in modern technologies because of their high energy density and extended cycle life. Among these materials, porous carbon is of particular interest because it provides high lithiation and excellent cycling capability by shortening the transport length for Li+ ions with large electrode/electrolyte interface. It has also been demonstrated that transition metal oxide nanoparticle can enhance surface electrochemical reactivity and increase the capacity retention capability for higher number of cycles. Here we investigate porous carbon/ceria (CeO2) nanoparticles composites as an anode material. The high redox potential of ceria is expected to provide a higher potential window as well as increase the specific capacity and energy density of the system. Scanning Electron Microscopy (SEM), X-Ray Diffraction (XRD), Transmission Electron Microscopy (TEM) is used for material characterization, while battery analyzer is used for measuring the electrochemical performance of the battery.
Increasing demand for energy storage devices has propelled researchers for developing efficient super-capacitors (SC) with long cycle life and ultrahigh energy density. Carbon-based materials are commonly used as electrode materials for SC. Herein we report a new approach to improve the SC performance utilizing porous carbon /Cerium oxide nanoparticle (PC-CON) hybrid as electrode material synthesized via low temperature hydrothermal method and tetraethyl ammonium tetrafluroborate in acetonitrile as organic electrolyte. Through this approach, charges can be stored not only via electrochemical double layer capacitance (EDLC) from PC but also through pseudo-capacitive effect from CeO2 NPs. The excellent electrode-electrolyte interaction due to the electrochemical properties of the ionic electrolyte provides a better voltage window for the SC. Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM) and X-Ray Diffraction (XRD) measurements were used for the initial characterization of this PC/CeO2 NPs hybrid material system. Electrochemical measurements of SCs was performed using a potentio-galvanostat. It is found that the specific capacitance was improved by 30% using PC-CON system compared with pristine PC system.
Electrochemical super-capacitors have become one of the most important topics in both academia and industry as novel energy storage devices because of their high power density, long life cycles, and high charge/discharge efficiency. Recently, there has been an increasing interest in the development of multifunctional structural energy storage devices such as structural super-capacitors for applications in aerospace, automobiles and portable electronics. These multifunctional structural super-capacitors provide lighter structures combining energy storage and load bearing functionalities. Due to their superior materials properties, carbon fiber composites have been widely used in structural applications for aerospace and automotive industries. Besides, carbon fiber has good electrical conductivity which will provide lower equivalent series resistance; therefore, it can be an excellent candidate for structural energy storage applications. Hence, this paper is focused on performing a pilot study for using nanowire/carbon fiber hybrids as building materials for structural energy storage materials; aiming at enhancing the charge/discharge rate and energy density. This hybrid material combines the high specific surface area of carbon fiber and pseudo-capacitive effect of metal oxide nanowires which were grown hydrothermally in an aligned fashion on carbon fibers. The aligned nanowire array could provide a higher specific surface area that leads to high electrode-electrolyte contact area and fast ion diffusion rates. Scanning Electron Microscopy (SEM) and XRay Diffraction (XRD) measurements were used for the initial characterization of this nanowire/carbon fiber hybrid material system. Electrochemical testing has been performed using a potentio-galvanostat. The results show that gold sputtered nanowire hybrid carbon fiber provides 65.9% better performance than bare carbon fiber cloth as super-capacitor.
Wireless passive temperature sensors are gaining increasing attention due to the ever-growing need of precise monitoring of temperature in high temperature energy conversion systems such as gas turbines and coal-based power plants. Unfortunately, the harsh environment such as high temperature and corrosive atmosphere present in these systems limits current solutions. In order to alleviate these issues, this paper presents the design, simulation, and manufacturing process of a low cost, passive, and wireless temperature sensor that can withstand high temperature and harsh environment. The temperature sensor was designed following the principle of metamaterials by utilizing Closed Ring Resonators (CRR) embedded in a dielectric matrix. The proposed wireless, passive temperature sensor behaves like an LC circuit that has a resonance frequency that depends on temperature. A full wave electromagnetic solver Ansys Ansoft HFSS was used to perform simulations to determine the optimum dimensions and geometry of the sensor unit. The sensor unit was prepared by conventional powder-binder compression method. Commercially available metal washers were used as CRR structures and Barium Titanate (BTO) was used as the dielectric materials. Response of the fabricated sensor at room temperature was analyzed using a pair of horn antenna connected with a network analyzer.
Lithium ion batteries (LIB) have been receiving extensive attention due to the high specific energy density for wide applications such as electronic vehicles, commercial mobile electronics, and military applications. In LIB, graphite
is the most commonly used anode material; however, lithium ion intercalation in graphite is limited, hindering the
battery charge rate and capacity. To overcome this obstacle, nanostructured anode assembly has been extensively
studied to increase the lithium ion diffusion rate. Among these approaches, high specific surface area metal oxide nanowires connecting nanostructured carbon materials accumulation have shown propitious results for enhanced lithium intercalation. Recently, nanowire/graphene hybrids were developed for the enhancement of LIB performance; however, almost all previous efforts employed nanowires on graphene in a random fashion, which
limited lithium ion diffusion rate. Therefore, we demonstrate a new approach by hydrothermally growing uniform
nanowires on graphene aerogel to further improve the performance. This nanowire/graphene aerogel hybrid not only uses the high surface area of the graphene aerogel but also increases the specific surface area for electrodeelectrolyte interaction. Therefore, this new nanowire/graphene aerogel hybrid anode material could enhance the
specific capacity and charge-discharge rate. Scanning Electron Microscopy (SEM) and X-Ray Diffraction (XRD)
are used for materials characterization. Battery Analyzer and Potentio-galvanostat are used for measuring the electrical performance of the battery. The testing results show that nanowire graphene hybrid anode gives significantly improved performance compared to graphene anode.
High energy density capacitors are critically important in advanced electronic devices and electric power systems due to
their reduced weight, size and cost to meet desired applications. Nanocomposites hold strong potential for increased
performance, however, the energy density of most nanocomposites is still low compared to commercial capacitors and
neat polymers. Here, high energy density nanocomposite capacitors are fabricated using surface-functionalized high
aspect ratio barium titanate (BaTiO3) nanowires (NWs) in a poly(vinylidene fluoride-trifluoroethylene-chlorofluoroethylene)
(P(VDF-TrFE-CFE)) matrix. These nanocomposites have 63.5% higher dielectric permittivity
compared to previous nanocomposites with BaTiO3 nanoparticles and also have high breakdown strength. At a 17.5%
volume fraction, the nanocomposites show more than 145.3% increase in energy density above that of the pure P(VDF-TrFE-
CFE) polymer (10.48 J/cm3 compared to 7.21 J/cm3). This value is significant and exceeds those reported for the
conventional polymer-ceramic composites; it is also more than two times larger than high performance commercial
materials. The findings of this research could lead to broad interest due to the potential for fabricating next generation
energy storage devices.
The use of piezoelectric materials has become more popular for a wide range of applications, including structural health
monitoring, power harvesting, vibration sensing and actuation. However, piezoceramic materials are often prone to
breakage and are difficult to apply to curved surfaces when in their monolithic form. One approach to alleviate these
issues is to embed the fragile piezoceramic inclusion into a polymer matrix. The flexible nature of the polymer matrix
protects the ceramic from breaking under mechanical loading and makes the resulting compoistes easier to apply onto
curved structure. However, most developed active ceramic composites have relatively low electroelastic coupling
compared to bulk piezoceramics. There are two main methods to improve the eletroelastic properties of piezoceramic
composites, namely using higher aspect ratio active inclusions and alignment of inclusions in the electric field direction.
In this paper, the dielectric and energy storage property of nanowire composites is significantly enhanced by aligning the
nanowires in the direction of the applied electrical field. PZT nanowires are hydrothermally synthesized and solutioncast
into a polymer matrix, and then aligned using a shear flow based stretching method. The alignment was evaluated
by scanning electron microscopy images and it is shown that the nanowires can be successfully aligned in the PVDF.
The dielectric constant and energy density of the nanocomposites were tested using Agilent E4980A LCR meter and
Sawyer-Tower circuit. This testing result shows that the dielectric constant and energy density of the composites can be
increased by as much as 35.7% and 49.3% by aligning the nanowires in the electric field direction. Piezoceramic
composites with enhanced energy storage property could lead to broader applications when using this type of materials
for polymer based capacitive energy storage.
A piezoelectric based energy harvesting scheme is proposed here which places a capacitor before the load in the
conditioning circuit. It is well known that the impedance between the load and source contributes heavily to the
performance of the energy harvesting system. The additional capacitor provides flexibility in meeting the optimal
impedance value and can be used to expand the bandwidth of the system. A theoretical model of the system is derived
and the response of the system as a function of both resistance and capacitance is studied. The analysis shows that the
energy harvesting performance is dominated by a bifurcation occurring as the electromechanical coupling increases
above a certain value, below this point the addition of an additional capacitor does not increase the performance of the
systems and above the maximum power can be achieved at all point between these two bifurcation frequencies.
Additionally, it has been found that the optimal capacitance is independent of the optimal resistance. Therefore, the
necessary capacitance can be chosen and then the resistance determined to provide optimal energy harvesting at the
desired frequencies. For systems with low coupling the optimal added capacitance is negative (additional power to the
circuit) indicating that a second capacitor should not be used for. For systems with high coupling the optimal
capacitance becomes positive for a range of values inside the bifurcation frequencies and can be used to extend the
bandwidth of the harvesting system. The analysis also demonstrates that the same maximum energy can be harvested at
any frequency; however, outside the two bifurcation frequencies the capacitor must be negative.
Piezoceramic materials have attracted much attention for sensing, actuation, structural health monitoring and energy
harvesting applications in the past two decades due to their excellent coupling between energy in the mechanical and
electrical domains. Among all piezoceramic materials, lead zirconate titanate (PZT) has been the most broadly studied
and implemented, in industrial applications due to its high piezoelectric coupling coefficients. Piezoceramic materials
are most often employed as thin films or monolithic wafers. While there are numerous methods for the synthesis of PZT
films, the sol-gel processing technique is the most widely used due to its low densification temperature, the ease at which
the film can be applied without costly physical deposition equipment and the capability to fabricate both thin and thick
films. However, the piezoelectric properties of PZT sol-gel derived films are substantially lower than those of bulk
materials, which limit the application of sol-gel films. In comparison, single crystal PZT materials have higher
piezoelectric coupling coefficients than polycrystalline materials due to their uniform dipole alignment. This paper will
introduce a novel technique to enhance the piezoelectric properties of PZT sol-gel derived ceramics through the use of
single crystal PbZr0.52Ti0.48O3 microcubes as an inclusion in the PZT sol-gel. The PZT single crystal cubes are
synthesized through a hydrothermal based method and their geometry and crystal structure is characterized through
scanning electron microscopy (SEM) and X-ray diffraction (XRD). A mixture of PZT cubes and sol-gel will then be
sintered to crystallize the sol-gel and obtain full density of the ceramic. XRD and SEM analysis of the cross section of
the final ceramics will be performed and compared to show the crystal structure and microstructure of the samples. The
P-E properties of the samples will be tested using a Sawyer-Tower circuit. Finally, a laser interferometer will be used to
directly measure the piezoelectric strain-coupling coefficient of the PZT sol-gel ceramics with and without PZT cube
inclusions. The results will show that with the integration of PZ0.52T0.48 crystal inclusions the d33 coupling coefficient
will increase more than 200% compared to that of pure PbZr0.52Ti0.48O3 sol-gel.
Piezoelectric fiber composites (PFCs) are a new group of materials recently developed in order to overcome the fragile
nature of monolithic piezoceramics. However, there are some practical limitations associated with these types of
materials, namely the generally separate electrode makes them difficult to embed into composites and when imbedded
the low tensile properties of the material and the abnormal geometry in comparison with traditional reinforcements lead
to stress concentrations reducing the material's strength. To resolve the inadequacies of current PFCs, a novel active
structural fiber (ASF) was developed that can be embedded in a composite material to perform sensing and actuation, in
addition to providing load bearing functionality. The ASF combines the advantages of the high tensile modulus and
strength of the traditional composite reinforcements as well as the sensing and actuation properties of piezoceramic
materials. A micromechanics model based on the double inclusion approach and a finite element model were been
developed to study the effective piezoelectric coupling coefficient of the ASF as well as the ASF lamina. In order to
evaluate the performance of the ASF when embedded in a polymer matrix and validate the model's accuracy, single fiber
lamina have been fabricated and characterized through testing with an atomic force microscope. The results of our
testing demonstrate the accuracy of the model and show that ASF composites could lead to load bearing composites with
electromechanical coupling greater than most pure piezoelectric materials.
Piezoelectric materials offer exceptional sensing and actuation properties however are prone to breakage and
difficult to apply to curved surfaces in their monolithic form. One method of alleviating these issues is through the use
of 0-3 nanocomposites, which are formed by embedding piezoelectric particles into a polymer matrix. This class of
material offers certain advantages over monolithic materials, however has seen little use due to its low coupling. Here
we develop a micromechanics and finite element models to study the electroelastic properties of an active
nanocomposite as a function of the aspect ratio and alignment of the piezoelectric inclusions. Our results show the
aspect ratio is critical to achieving high electromechanical coupling and with an increase from 1 to 10 at 30% volume
fraction of piezoelectric filler the coupling can increase by 60 times and achieve a bulk composite coupling as high as
90% of a pure PZT-7A piezoelectric constituent.
The use of piezoceramic materials for structural sensing and actuation is a fairly well developed practice that has
found use in a wide variety of applications. However, just as advanced composites offer numerous benefits over
traditional engineering materials for structural design, actuators that utilize the active properties of piezoelectric fibers
can improve upon many of the limitations encountered when using monolithic piezoceramic devices. Several new
piezoelectric fiber composites have been developed, however almost all studies have implemented these devices such
that they are surface-bonded patches used for sensing or actuation. This paper will introduce a novel active
piezoelectric structural fiber that can be laid up in a composite material to perform sensing and actuation, in addition to
providing load bearing functionality. The sensing and actuation aspects of this multifunctional material will allow
composites to be designed with numerous embedded functions including, structural health monitoring, power
generation, vibration sensing and control, damping, and shape control through anisotropic actuation. A one dimensional micromechanics model of the piezoelectric fiber will be developed to characterize the feasibility of constructing structural composite lamina with high piezoelectric coupling. The theoretical model will be validated through finite element (FE) modeling in ABAQUS. The results will show that the electromechanical coupling of a fiber reinforced polymer composite incorporating the active structural fiber (ASF) could be more than 70% of the active constituent.
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