Journal of the Acoustical Society of America, Sep 1, 2018
Design, fabrication, and performance of large size and high power-density encapsulated thermoacou... more Design, fabrication, and performance of large size and high power-density encapsulated thermoacoustic sound projectors driven by short pulses will be presented. The analysis of enhanced energy conversion efficiency using proper signal processing and low-dimensional thermodynamics will be given. [Work supported by the Office of Naval Research and Army Research Office.]
ABSTRACT A passive matrix electrochromic display (ECD) working in transparent or reflective mode ... more ABSTRACT A passive matrix electrochromic display (ECD) working in transparent or reflective mode is described. In this paper, we report the main reasons of image diffusion and cross-talk in passive matrix ECD and initial computer simulation results of the 7×7 matrix display. These suggest that the insulation of electrolyte under each pixel and threshold (nonlinearity) of coloration current can in practice completely eliminate the image diffusion and cross-talk. The matrix addressed ECD based on solid polymer electrolyte and two complementary electrodes, (WO3+0.1TiO2, TiO2–0.25CeO2), in which all pixels were insulated by negative photoresist material was elaborated. An additional protected thin film (0.2Li2O–0.2CeO2–0.6SiO2) deposited on working electrode was used to provide the enhanced threshold effect. The ECD exhibited excellent memory effect and substantially free from image diffusion and cross talk effects.
The WO3-x –0.1TiO2-y thin films prepared by the sol–gel route exhibit increased lifetime and stab... more The WO3-x –0.1TiO2-y thin films prepared by the sol–gel route exhibit increased lifetime and stability. A sol–gel solution mixed with nanoscopic silicon oxide particles (40 nm, 200 nm) was spin-coated onto an indium tin oxide (ITO)-covered glass substrate followed by further surface development by chemical etching. A significantly faster response time of the electrochromic cell due to the increase of the surface area of the WO3/electrolyte interface and enhancement of the lithium ion diffusion rate have been obtained. The coloration efficiency was found to be much higher in the areas surrounding incorporated nanoscale particles.
... additional protected thin film (0.2Li 2 O0.2CeO 2 0.6SiO 2 ) deposited on working ... 6]. T... more ... additional protected thin film (0.2Li 2 O0.2CeO 2 0.6SiO 2 ) deposited on working ... 6]. The peroxotitanic acid was obtained by the same method via the dissolution of titanium powder in ... alcohol and can be coated on various substrates by spin-coating, dip-coating or spray of its ...
Silver vanadium oxide (SVO) and V2O5 nanowires have been hydrothermally synthesized. The as-made ... more Silver vanadium oxide (SVO) and V2O5 nanowires have been hydrothermally synthesized. The as-made nanowires are over 30 microm long and 10-20 nm in diameter. The nanowires have a layered structure with a d-spacing of 1.07 nm. The nanowires can be fabricated into free-standing and flexible sheets by suction filtration. The electrical conductivity of the SVO nanowires is 0.5 S/cm, compared to 0.08 S/cm for the V2O5 nanowires. The Li ion diffusion coefficient in the SVO nanowires was 7 times higher than that in the V2O5 nanowires. An electrochromic device was fabricated from the SVO nanowires that displayed a color-switching time of 0.2 s from the bleached state (green) to the colored state (red-brown) and 60% transmittance contrast.
Journal of the Acoustical Society of America, Oct 1, 2017
Advances in thermophone transduction from the perspective of novel nanostructured materials, devi... more Advances in thermophone transduction from the perspective of novel nanostructured materials, device design, and signal processing will be presented. The comparison of studied 2D and 3D networks of nanostructured materials with aerogel structures will be given. The energy conversion efficiency of encapsulated thermoacoustic devices excited by short pulses with varying duty cycle, shape of pulse, and carrier signal frequency will be analyzed for a variety of fabricated devices. I will provide an extensive experimental study of pulse excitation in different thermodynamic regimes for freestanding carbon nanotube sheets with varying thermal inertias (single-wall, multi-wall with varying diameters, and number of superimposed sheets) in vacuum and in air. The experimental observations are rationalized within a basic theoretical framework. The acoustical and geometrical parameters providing further increase in efficiency and transduction performance for open and closed resonant systems will be discussed. [Research supported by ONR, Grant No.: N00014-17-1-2521.]
Journal of the Acoustical Society of America, Oct 1, 2017
Thermo-acoustic (TA) sound generation (thermophone) is a non-resonant technique where electrical ... more Thermo-acoustic (TA) sound generation (thermophone) is a non-resonant technique where electrical energy is converted to sound waves through Joule heating of a resistor (TA heat source) without any mechanical vibration, thus allowing for a wideband operation. It is clear that the material and the structure of the resistor play an important role on the performance of the thermophone. Recently, thermophone transducers fabricated from nanoscale materials hold the promise of a new transducer technology. Transducers made from these nanomaterials operate over a broad frequency range and can be designed to be lighter and thinner than competing technologies. Here, we report the TA heat source using nanocarbon foams. Nanocarbon foams are carbon nanotubes (CNTs) based all carbon porous materials. They have a hierarchically porous structure and the pore size and porosity can be tuned easily during the fabrication process. The foams consist of highly porous conductive CNT networks. They are freestanding, flexible, and mechanically robust in various environments. It is demonstrated that the foams can be used as elastically compressible, flexible TA heat source. The detailed fabrication process, the morphology of the foams, their thermal and electrical properties, and their performance as thermophone transducers will be presented.
Cobalt nanoparticles with high quality crystal structure and spin polarization support an excelle... more Cobalt nanoparticles with high quality crystal structure and spin polarization support an excellent plasmon resonance at about 275 nm, which is comparable with gold nanoparticles. The quality of plasmon resonance is highly correlated with the superparamagnetic response of the isolated nanoparticles and disappeared in the aggregates. The fluorescence enhancement of about 3×103 for surfactant molecules is demonstrated.
The temperature dependences of the specific heat and the thermal conductivity of crystalline supe... more The temperature dependences of the specific heat and the thermal conductivity of crystalline superionic conductors LnF3 (Ln = La, Ce, Pr), Li2B4O7 and α-LiIO3 in the superionic phase have been investigated experimentally. The specific heat C p and the thermal conductivity K are observed to increase monotonically over a wide range of temperatures above the Debye temperature ΘD. This increase is attributed to the relaxational interaction of high-frequency phonons with two-level systems.
We observed very pronounced polarization of light emitted by highly aligned free-standing multiwa... more We observed very pronounced polarization of light emitted by highly aligned free-standing multiwall carbon nanotube (MWNT) sheet in axial direction which is turned to the perpendicular polarization when a number of layers are increased. The radiation spectrum of resistively heated MWNT sheet closely follows to the Plank's blackbody radiation distribution. The obtained polarization features can be described by a classical
Journal of the Acoustical Society of America, Sep 1, 2018
Design, fabrication, and performance of large size and high power-density encapsulated thermoacou... more Design, fabrication, and performance of large size and high power-density encapsulated thermoacoustic sound projectors driven by short pulses will be presented. The analysis of enhanced energy conversion efficiency using proper signal processing and low-dimensional thermodynamics will be given. [Work supported by the Office of Naval Research and Army Research Office.]
ABSTRACT A passive matrix electrochromic display (ECD) working in transparent or reflective mode ... more ABSTRACT A passive matrix electrochromic display (ECD) working in transparent or reflective mode is described. In this paper, we report the main reasons of image diffusion and cross-talk in passive matrix ECD and initial computer simulation results of the 7×7 matrix display. These suggest that the insulation of electrolyte under each pixel and threshold (nonlinearity) of coloration current can in practice completely eliminate the image diffusion and cross-talk. The matrix addressed ECD based on solid polymer electrolyte and two complementary electrodes, (WO3+0.1TiO2, TiO2–0.25CeO2), in which all pixels were insulated by negative photoresist material was elaborated. An additional protected thin film (0.2Li2O–0.2CeO2–0.6SiO2) deposited on working electrode was used to provide the enhanced threshold effect. The ECD exhibited excellent memory effect and substantially free from image diffusion and cross talk effects.
The WO3-x –0.1TiO2-y thin films prepared by the sol–gel route exhibit increased lifetime and stab... more The WO3-x –0.1TiO2-y thin films prepared by the sol–gel route exhibit increased lifetime and stability. A sol–gel solution mixed with nanoscopic silicon oxide particles (40 nm, 200 nm) was spin-coated onto an indium tin oxide (ITO)-covered glass substrate followed by further surface development by chemical etching. A significantly faster response time of the electrochromic cell due to the increase of the surface area of the WO3/electrolyte interface and enhancement of the lithium ion diffusion rate have been obtained. The coloration efficiency was found to be much higher in the areas surrounding incorporated nanoscale particles.
... additional protected thin film (0.2Li 2 O0.2CeO 2 0.6SiO 2 ) deposited on working ... 6]. T... more ... additional protected thin film (0.2Li 2 O0.2CeO 2 0.6SiO 2 ) deposited on working ... 6]. The peroxotitanic acid was obtained by the same method via the dissolution of titanium powder in ... alcohol and can be coated on various substrates by spin-coating, dip-coating or spray of its ...
Silver vanadium oxide (SVO) and V2O5 nanowires have been hydrothermally synthesized. The as-made ... more Silver vanadium oxide (SVO) and V2O5 nanowires have been hydrothermally synthesized. The as-made nanowires are over 30 microm long and 10-20 nm in diameter. The nanowires have a layered structure with a d-spacing of 1.07 nm. The nanowires can be fabricated into free-standing and flexible sheets by suction filtration. The electrical conductivity of the SVO nanowires is 0.5 S/cm, compared to 0.08 S/cm for the V2O5 nanowires. The Li ion diffusion coefficient in the SVO nanowires was 7 times higher than that in the V2O5 nanowires. An electrochromic device was fabricated from the SVO nanowires that displayed a color-switching time of 0.2 s from the bleached state (green) to the colored state (red-brown) and 60% transmittance contrast.
Journal of the Acoustical Society of America, Oct 1, 2017
Advances in thermophone transduction from the perspective of novel nanostructured materials, devi... more Advances in thermophone transduction from the perspective of novel nanostructured materials, device design, and signal processing will be presented. The comparison of studied 2D and 3D networks of nanostructured materials with aerogel structures will be given. The energy conversion efficiency of encapsulated thermoacoustic devices excited by short pulses with varying duty cycle, shape of pulse, and carrier signal frequency will be analyzed for a variety of fabricated devices. I will provide an extensive experimental study of pulse excitation in different thermodynamic regimes for freestanding carbon nanotube sheets with varying thermal inertias (single-wall, multi-wall with varying diameters, and number of superimposed sheets) in vacuum and in air. The experimental observations are rationalized within a basic theoretical framework. The acoustical and geometrical parameters providing further increase in efficiency and transduction performance for open and closed resonant systems will be discussed. [Research supported by ONR, Grant No.: N00014-17-1-2521.]
Journal of the Acoustical Society of America, Oct 1, 2017
Thermo-acoustic (TA) sound generation (thermophone) is a non-resonant technique where electrical ... more Thermo-acoustic (TA) sound generation (thermophone) is a non-resonant technique where electrical energy is converted to sound waves through Joule heating of a resistor (TA heat source) without any mechanical vibration, thus allowing for a wideband operation. It is clear that the material and the structure of the resistor play an important role on the performance of the thermophone. Recently, thermophone transducers fabricated from nanoscale materials hold the promise of a new transducer technology. Transducers made from these nanomaterials operate over a broad frequency range and can be designed to be lighter and thinner than competing technologies. Here, we report the TA heat source using nanocarbon foams. Nanocarbon foams are carbon nanotubes (CNTs) based all carbon porous materials. They have a hierarchically porous structure and the pore size and porosity can be tuned easily during the fabrication process. The foams consist of highly porous conductive CNT networks. They are freestanding, flexible, and mechanically robust in various environments. It is demonstrated that the foams can be used as elastically compressible, flexible TA heat source. The detailed fabrication process, the morphology of the foams, their thermal and electrical properties, and their performance as thermophone transducers will be presented.
Cobalt nanoparticles with high quality crystal structure and spin polarization support an excelle... more Cobalt nanoparticles with high quality crystal structure and spin polarization support an excellent plasmon resonance at about 275 nm, which is comparable with gold nanoparticles. The quality of plasmon resonance is highly correlated with the superparamagnetic response of the isolated nanoparticles and disappeared in the aggregates. The fluorescence enhancement of about 3×103 for surfactant molecules is demonstrated.
The temperature dependences of the specific heat and the thermal conductivity of crystalline supe... more The temperature dependences of the specific heat and the thermal conductivity of crystalline superionic conductors LnF3 (Ln = La, Ce, Pr), Li2B4O7 and α-LiIO3 in the superionic phase have been investigated experimentally. The specific heat C p and the thermal conductivity K are observed to increase monotonically over a wide range of temperatures above the Debye temperature ΘD. This increase is attributed to the relaxational interaction of high-frequency phonons with two-level systems.
We observed very pronounced polarization of light emitted by highly aligned free-standing multiwa... more We observed very pronounced polarization of light emitted by highly aligned free-standing multiwall carbon nanotube (MWNT) sheet in axial direction which is turned to the perpendicular polarization when a number of layers are increased. The radiation spectrum of resistively heated MWNT sheet closely follows to the Plank's blackbody radiation distribution. The obtained polarization features can be described by a classical
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