Simultaneous High Speed Research Articles

Simultaneous plane-wave and ultra high-speed imaging of acoustic droplet vaporization

Super-heated sub-micrometre perfluorocarbon droplets have been shown to offer advantages over microbubbles for ultrasound localization microscopy (ULM). These include better penetration of the microcirculation and enabling higher frame rates using methods such as acoustic wave sparsely activated localization microscopy (AWSALM). The variability of droplet behaviour has however been found to be substantially higher than that of microbubbles and this poses challenges for ULM image construction. The aim of this study was to use simultaneous high speed optical and acoustic imaging to capture the droplet vaporisation process and subsequent bubble dynamics. Droplets composed of octofluoropropane and decafluorobutane were injected into a polyethylene tube submerged in a 37 °C water bath and located at the focus of an ultrasound probe and microscope objective. Optical images were captured at 10 Mfps of the droplet response to ultrasound pulses of varying lengths and amplitude. The results indicate that the number of activated droplets is impacted by increasing either the ultrasound pressure or number of half-cycles as well as by the preceding activation ultrasound pulses; and that different droplet sub-populations can be activated by varying pulse parameters. These data indicate the potential for optimising droplet activation of ULM applications.

Impact of volume and rate of milk delivery on coordination of respiration and swallowing in infant pigs.

The coordination of respiration and swallowing is a life-critical function in infants. Varying volume and rate of milk delivery changes swallowing frequency and bolus volume but any impact on swallow-respiration coordination is unknown. Five infant pigs were filmed with simultaneous high speed videofluoroscopy and plethysmography while feeding from an automatic system delivering milk across a range of volumes and frequencies. Swallow inspiration delay, respiratory cycle duration, and distribution of inspiratory and expiratory swallows were calculated. At constant volume, there were more inspiratory phase swallows when frequency increased. At high constant frequency, increasing volume changed swallow-respiration coordination patterns, with increased occurrence of inspiratory phase swallows. Respiratory cycle duration did not change in response to changes in oral milk delivery. These results suggest that the observed pattern of expiratory swallowing in infants is achieved primarily by regulation of milk intake, not modulation of respiratory patterns by oral sensation.

Comparison of pulsatile flow dynamics before and after endovascular intervention in 3D-printed patient-specific internal carotid artery aneurysm models using 1000 fps photon-counting detectors for Simultaneous Biplane High Speed Angiography (SB-HSA).

A significant challenge regarding the treatment of aneurysms is the variability in morphology and analysis of abnormal flow. With conventional DSA, low frame rates limit the flow information available to clinicians at the time of the vascular intervention. With 1000 fps High-Speed Angiography (HSA), high frame rates enable flow details to be better resolved for endovascular interventional guidance. The purpose of this work is to demonstrate how 1000 fps biplane-HSA can be used to differentiate flow features, such as vortex formation and endoleaks, amongst patient-specific internal carotid artery aneurysm phantoms pre- and post-endovascular intervention using an in-vitro flow setup. The aneurysm phantoms were attached to a flow loop configured to a carotid waveform, with automated injections of contrast media. Simultaneous Biplane High-Speed Angiographic (SB- HSA) acquisitions were obtained at 1000 fps using two photon-counting detectors with the respective aneurysm and inflow/ outflow vasculature in the FOV. After x-rays were turned on, the detector acquisitions occurred simultaneously, during which iodine contrast was injected at a continuous rate. A pipeline stent was then deployed to divert flow from the aneurysm, and image sequences were once again acquired using the same parameters. Optical Flow, an algorithm that calculates velocity based on spatial-temporal intensity changes between pixels, was used to derive velocity distributions from HSA image sequences. Both the image sequences and velocity distributions indicate detailed changes in flow features amongst the aneurysms before and after deployment of the interventional device. SB-HSA can provide detailed flow analysis, including streamline and velocity changes, which may be beneficial for interventional guidance.

Modular pulse synthesizer for transcranial magnetic stimulation with fully adjustable pulse shape and sequence

The temporal shape of a pulse in transcranial magnetic stimulation (TMS) influences which neuron populations are activated preferentially as well as the strength and even direction of neuromodulation effects. Furthermore, various pulse shapes differ in their efficiency, coil heating, sensory perception, and clicking sound. However, the available TMS pulse shape repertoire is still very limited to a few biphasic, monophasic, and polyphasic pulses with sinusoidal or near-rectangular shapes. Monophasic pulses, though found to be more selective and stronger in neuromodulation, are generated inefficiently and therefore only available in simple low-frequency repetitive protocols. Despite a strong interest to exploit the temporal effects of TMS pulse shapes and pulse sequences, waveform control is relatively inflexible and only possible parametrically within certain limits. Previously proposed approaches for flexible pulse shape control, such as through power electronic inverters, have significant limitations: The semiconductor switches can fail under the immense electrical stress associated with free pulse shaping, and most conventional power inverter topologies are incapable of generating smooth electric fields or existing pulse shapes. Leveraging intensive preliminary work on modular power electronics, we present a modular pulse synthesizer (MPS) technology that can, for the first time, flexibly generate high-power TMS pulses (one-side peak ∼4000 V, ∼8000 A) with user-defined electric field shape as well as rapid sequences of pulses with high output quality. The circuit topology breaks the problem of simultaneous high power and switching speed into smaller, manageable portions, distributed across several identical modules. In consequence, the MPS TMS techology can use semiconductor devices with voltage and current ratings lower than the overall pulse voltage and distribute the overall switching of several hundred kilohertz among multiple transistors. MPS TMS can synthesize practically any pulse shape, including conventional ones, with fine quantization of the induced electric field (⩽17% granularity without modulation and ∼300 kHz bandwidth). Moreover, the technology allows optional symmetric differential coil driving so that the average electric potential of the coil, in contrast to conventional TMS devices, stays constant to prevent capacitive artifacts in sensitive recording amplifiers, such as electroencephalography. MPS TMS can enable the optimization of stimulation paradigms for more sophisticated probing of brain function as well as stronger and more selective neuromodulation, further expanding the parameter space available to users.

Dynamic Microwave Imaging of the Cardiovascular System Using Ultra-Wideband Radar-on-Chip Devices.

Microwave imaging has been investigated for medical applications such as stroke and breast imaging. Current systems typically rely on bench-top equipment to scan at a variety of antenna positions. For dynamic imaging of moving structures, such as the cardiovascular system, much higher imaging speeds are required than what has thus far been reported. Recent innovations in radar-on-chip technology allow for simultaneous high speed data collection at multiple antenna positions at a fraction of the cost of conventional microwave equipment, in a small and potentially portable system. The objective of the current work is to provide proof of concept of dynamic microwave imaging in the body, using radar-on-chip technology. Arrays of body-coupled antennas were used with nine simultaneously operated coherent ultra-wideband radar chips. Data were collected from the chest and thigh of a volunteer, with the objective of imaging the femoral artery and beating heart. In addition, data were collected from a phantom to validate system performance. Video data were constructed using beamforming. The location of the femoral artery could successfully be resolved, and a distinct arterial pulse wave was discernable. Cardiac activity was imaged at locations corresponding to the heart, but image quality was insufficient to identify individual anatomical structures. Static and differential imaging of the femur bone proved unsuccessful. Using radar chip technology and an imaging approach, cardiovascular activity was detected in the body, demonstrating first steps towards biomedical dynamic microwave imaging. The current portable and modular system design was found unsuitable for static in-body imaging. This first proof of concept demonstrates that radar-on-chip could enable cardiovascular imaging in a low-cost, small and portable system. Such a system could make medical imaging more accessible, particularly in ambulatory or long-term monitoring settings.

Combining multiple fluorescence imaging techniques in biology: when one microscope is not enough.

While fluorescence microscopy has proven to be an exceedingly useful tool in bioscience, it is difficult to offer simultaneous high resolution, fast speed, large volume, and good biocompatibility in a single imaging technique. Thus, when determining the image data required to quantitatively test a complex biological hypothesis, it often becomes evident that multiple imaging techniques are necessary. Recent years have seen an explosion in development of novel fluorescence microscopy techniques, each of which features a unique suite of capabilities. In this Technical Perspective, we highlight recent studies to illustrate the benefits, and often the necessity, of combining multiple fluorescence microscopy modalities. We provide guidance in choosing optimal technique combinations to effectively address a biological question. Ultimately, we aim to promote a more well-rounded approach in designing fluorescence microscopy experiments, leading to more robust quantitative insight.

Heat transfer to bouncing droplets on superhydrophobic surfaces

This study experimentally and theoretically investigates the dynamics and heat transfer to impinging water droplets on superhydrophobic surfaces heated below the boiling temperature. Different from impingement on hydrophilic substrates, the droplets rebound from the surface after the spreading and retraction stages. Experiments are performed using simultaneous high speed video and infrared (IR) imaging to capture droplet dynamics and temperature variation during the transient event. Thermal images allow estimation of bulk droplet temperature change during contact such that the cooling effectiveness for an individual droplet can be estimated. A similarity solution is utilized to yield a model for the transient heat flux at the droplet-wall interface, where convection inside the droplet is accounted for. The experimental and theoretical results for the cooling effectiveness show good agreement. It is revealed that the cooling effectiveness increases with Weber number but decreases with droplet diameter and surface cavity fraction (the ratio of cavity area to total surface area).

Decoupling of biomechanics of hyoid movement and bolus flow in preterm infants

Determining the timing of bolus passage over the airway, and into the esophagus, is critical for biomechanical studies of swallowing. Videofluroscopy is the gold standard for determining fluid movement, but is not always possible. Hylolaryngeal movement, measured from light film or standard videography, is a reliable marker for adult human swallowing, but its validity for the biomechanics of swallowing in immature infants is unknown. We tested the relationship between hyolaryngeal movement from light camera data compared to bolus movement from video fluoroscopy in pre‐term and term infant pigs.Three term and four pre‐term pigs were fed from a bottle containing barium and a milk solution. At seven days after birth pigs were recorded feeding from the bottle using simultaneous high speed (100 fps) x‐ray and light video cameras. In the light video, the frame of most rapid elevation of the hyoid was scored as the swallow. In the x‐ray, the swallows were scored as the beginning of posterior bolus movement. The number of frames separating x‐ray and light camera swallow identifications was calculated for each swallow.Hyoid movement was found to be closely correlated to bolus movement in term pigs, but no correlation existed in pre‐term pigs. The mean frame offsets for term and pre‐term pigs were different (Wilcox test, p<0.001). The variance for the pre‐term pigs was significantly larger (Levene's test p<0.001).The light videos were found to be a good measure of swallows in term pigs, but were not a good measure of swallows in pre‐term pigs. The biomechanics of bolus movement are altered in the neurologically poorly coordinated pre‐term pigs. Specifically, hyolaryngeal elevation and bolus movement are decoupled in pre‐terms whereas they are tightly coordinated in term pigs. Prematurity leads to altered form function relationships through immature development.Support or Funding InformationNICHD grant 088561This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Experimental investigation of entropy waves generated from acoustically excited premixed swirling flame

Entropy waves play an important role in the production of indirect combustion noise and thermoacoustic instability. The characteristics of entropy waves from swirling flames have not been systematically investigated. Here, a premixed methane/air swirl burner was built with upstream acoustic excitation from a loudspeaker. A joint infrared imaging and tunable diode laser absorption spectroscopy (TDLAS) thermometry measurement was carried out to investigate the entropy waves generated in this burner. The infrared imaging technique provides qualitative images of the distribution, propagation and dissipation of entropy waves while the TDLAS technique provides quantitative measurement of temperature fluctuation. Time resolved measurements of the swirling flame bulk velocity, CH* chemiluminescence, gas temperature and infrared images were simultaneously obtained, demonstrating that entropy waves were generated from the premixed swirling flame under external acoustic excitation. Entropy waves were shown to be greatly influenced by the amplitude and frequency of acoustic waves. They also showed dissipation as the entropy waves propagate downstream according to the attenuated temperature fluctuation and infrared radiation intensities. Simultaneous high speed infrared imaging and particle image velocimetry measurements showed that the temperature non-uniformities arise from engulfment and mixing through periodic vortex roll-up.

Investigation of lubricant induced pre-ignition and knocking combustion in an optical spark ignition engine

An experimental study was performed to investigate lubricant oil induced pre-ignition and knocking combustion process in a single cylinder spark ignition (SI) engine with full bore overhead optical access. Lubricant oil was deliberately injected to the exhaust area through a specially modified direct injector to trigger the stochastic pre-ignition in a premixed air and fuel mixture. Simultaneous heat release analysis and high speed combustion imaging were used to study the pre-ignition and combustion processes. Outlier detection based on robust statistical methods was validated as an effective and efficient approach to identify sporadic pre-ignition. When pre-ignition occurred, the pre-ignited flame-front exhibited much faster propagating speed than that of the normal spark-ignited flame-front in the first stage of flame development. In several cycles, pre-ignition was followed by the pre-ignited propagating flame-front and then a separate spark-ignited flame-front before they subsequently merged together. In a few other cycles, pre-ignition led to heavy knocking combustion caused either by the auto-ignition close to the flame-front or near the cylinder wall, or both. The ultimate knock intensity of such cycles was determined by the timing, size, and location of end-gas auto-ignition of the unburned gas. Furthermore, optical detection of the oil droplet entrained combustion in the cycle subsequent to the knocking combustion cycle implied that high frequency oscillation pressure waves ejected lubricant from the piston-ring crevice.

Maturational Change in Quiet Respiration Versus Respiration While Feeding In Infant Mammals

Respiratory rhythm and rate differ in quiet respiration as compared to respiration when infants are suckling and swallowing. How this difference changes in neonates up through the time of weaning is unknown. We tested the hypotheses that (1) rhythm and rate change with age as a function of increasing size but that (2) significant changes in the coordination of respiration with swallowing reflect an increased ability to protect the airway in advance of weaning. We obtained a sample of 9 infant pigs from two unrelated litters and measured quiet respiration, either while sleeping or anesthetized, from 3 to 24 days of age. In the same animals, we measured respiration while feeding from 7 to 24 days of age. Quiet respiration was recorded with a plesthymograph, either while animals were sleeping or lightly anesthetized. Respiration and feeding was recorded using simultaneous high speed videoflurography (XROMM) and plesthysmography. We found minor changes with age in quiet respiration. The within‐session, usually about 1 minute, variation in respiratory rate, decreased significantly with age. Variation in respiration during feeding did not change with age. However, the timing of the coordination between swallowing and respiration changed significantly as animals approached weaning age. The maturational differences in the two types of breathing may reflect different aspects of development. The reduction in variation in quiet respiration may be due to a maturing nervous system, whereas the changes in timing and coordination between swallowing and breathing may be necessary for airway protection as young mammals move to eating solid food.Support or Funding InformationThis work is supported by NIH HD088561 to RZG.This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Two-dimensional heat transfer coefficients with simultaneous flow visualisations during two-phase flow boiling in a PDMS microchannel

Infrared (IR) thermography was combined with simultaneous high speed flow visualisation and pressure measurements from integrated pressure sensors inside the microchannel, in order to produce two-dimensional (2D) high spatial and temporal resolution two-phase heat transfer coefficient (HTC) maps across the full domain of a polydimethylsiloxane (PDMS) high aspect ratio (a = 22) microchannel (Dh = 192 μm). High spatial and temporal resolution two-dimensional wall temperature measurements and pressure data were obtained for a range of mass fluxes (G = 7.37–298 kg m−2 s−1) and heat fluxes (q = 13.64–179.2 kW m−2) using FC-72 as the working liquid. The 3D plots of HTC provided fine details of local variations during bubble nucleation, confinement, elongated bubble, slug flow and annular flow regime. The optical images from the channel top revealed the local flow regimes and were correlated with simultaneous thermal images obtained from the channel base. The 3D plots of the 2D two-phase heat transfer coefficient with time across the microchannel domain were correlated with vapour-liquid dynamics and liquid film thinning (from the contrast of the optical images) which caused suspected dryout. The correlation between the synchronised at the same frame rate high-resolution thermal and optical images will assist in a better understanding of the heat transfer mechanisms during two-phase flow boiling in microchannels. This work intends to give a better insight into heat transfer coefficient spatial variation during flow instabilities with two-dimensional heat transfer coefficient plots as a function of time during a cycle of liquid–vapour alternations.

Stick and slip mechanisms in the acoustic emissions of ice fracture

Arctic ice noise has been qualitatively described in terms of crashing and cracking noises. Ships navigating through icy waters and colliding with icebergs have reported distinctive cracking sounds characteristic to the specific environmental conditions and the location. Many previous field studies of ice acoustics have been done with measurements from isolated, single hydrophones. These have provided useful physical insights into the ambient noise characteristics of ice, but the underlying mechanisms of the sounds are still not well understood. The mechanical properties of ice have been extensively studied in laboratory settings, but few studies have examined the acoustics emissions during fracture with respect these properties. The salinity content of sea ice can significantly influence fracture. The acoustics of ice fracture in water and air is investigated in laboratory using simultaneous acoustic and high speed optical measurements. Also, the mechanical properties of ice samples as a function of salinity were studied with three point bending. A stick and slip mechanism found in fracture of low salinity ice is supported by an Empirical Mode Decomposition of the acoustic signals.

Effects of thermodynamic conditions on the end gas combustion mode associated with engine knock

Super-knock is the main obstacle to improve power density and engine efficiency of modern gasoline engines. To understand the mechanism of super-knock, this study presents an investigation on the end gas combustion process of stoichiometric isooctane/oxygen/nitrogen mixture using a rapid compression machine (RCM), under the thermodynamic conditions close to those of production engines. The combustion process was captured by simultaneous high speed direct photography and pressure acquisition in the RCM. Three end gas combustion modes: no-auto-ignition, sequential auto-ignition, and detonation under different initial conditions were identified and characterized. The super-knock in engine was confirmed to be the result of detonation by comparing the pressure oscillation, thermodynamic state, and pressure rise relative to isochoric combustion with those of detonation observed in the RCM. The experimental results also indicate that the possibility of detonation occurrence increases with increasing initial pressure under the same compression ratio. However, comparing to the pressure, temperature has less effect on detonation formation. It was found that the end gas combustion mode is closely related to the mixture energy density. Generally, as the mixture energy density increases, the end gas combustion mode gradually transits from no-auto-ignition to sequential auto-ignition, and then to detonation. The first auto-ignition spots commonly appear in the mixture near the cylinder wall. The detonation was initiated by near-wall auto-ignition.

Interaction of Flame Flashback Mechanisms in Premixed Hydrogen–Air Swirl Flames

An experimental study is presented on the interaction of flashback originating from flame propagation in the boundary layer (1), from combustion driven vortex breakdown (2) and from low bulk flow velocity (3). In the investigations, an aerodynamically stabilized swirl burner operated with hydrogen–air mixtures at ambient pressure and with air preheat was employed, which previously had been optimized regarding its aerodynamics and its flashback limit. The focus of the present paper is the detailed characterization of the observed flashback phenomena with simultaneous high speed (HS) particle image velocimetry (PIV)/Mie imaging, delivering the velocity field and the propagation of the flame front in the mid plane, in combination with line-of-sight integrated OH*-chemiluminescence detection revealing the flame envelope and with ionization probes which provide quantitative information on the flame motion near the mixing tube wall during flashback. The results are used to improve the operational safety of the system beyond the previously reached limits. This is achieved by tailoring the radial velocity and fuel profiles near the burner exit. With these measures, the resistance against flashback in the center as well as in the near wall region is becoming high enough to make turbulent flame propagation the prevailing flashback mechanism. Even at stoichiometric and preheated conditions this allows safe operation of the burner down to very low velocities of approximately 1/3 of the typical flow velocities in gas turbine burners. In that range, the high turbulent burning velocity of hydrogen approaches the low bulk flow speed and, finally, the flame begins to propagate upstream once turbulent flame propagation becomes faster than the annular core flow. This leads to the conclusions that finally the ultimate limit for the flashback safety was reached with a configuration, which has a swirl number of approximately 0.45 and delivers NOx emissions near the theoretical limit for infinite mixing quality, and that high fuel reactivity does not necessarily rule out large burners with aerodynamic flame stabilization by swirling flows.

The effect of ethanol blending on mixture formation, combustion and soot emission studied in an optical DISI engine

Abstract In various research studies, ethanol blended fuels have shown reduced particulate matter (PM) emissions in comparison to gasoline and its surrogate fuels in direct-injection spark-ignition (DISI) engines. However, there are also studies reporting increased particulate concentration for fuels with low ethanol content. In this work the mixture formation and sooting combustion behavior of isooctane and the mixture E20 (20 vol% of ethanol in isooctane) is analyzed for catalyst heating operation. These operating conditions are critical as they strongly contribute to overall soot emissions in driving cycles. Simultaneous high speed imaging of OH ∗ –chemiluminescence and natural soot luminosity measurements are performed in combination with primary particle concentration measurements using a laser induced incandescence (LII) sensor in the engine exhaust duct. At these operating conditions E20 exhibits a higher sooting tendency as compared to isooctane. In order to identify the reason for increased soot formation, the mixture formation process is analyzed by planar laser induced fluorescence (LIF) measurements. The results show that soot was formed in fuel rich regions with incomplete evaporated fuel droplets remaining from the injection event. A different evaporation process of E20 fuel spray and mixing behavior is indicated showing a more compact rich mixture cloud with surrounding lean areas near the spark plug region. This mixture stratification is characterized by higher cyclic variations and constitutes a significant source of soot formation.

An experimental investigation of super knock combustion mode using a one-dimensional constant volume bomb

Super knock induced by pre-ignition in highly boosted spark ignition engines can cause very high peak pressure, which may lead to severe engine damage. Although it is difficult to investigate the mechanism of super-knock due to its inherent randomness, the very high peak pressure implies that super knock may relate to detonation. In this study, a tube-like one-dimensional constant volume bomb, which simplifies the geometry of a real engine's combustion chamber near top dead center, was used to better understand the fundamental phenomenon underlying super knock. H2/O2 mixture was used to maintain reaction intensity even at lower pressure than that in real highly boosted engines. Simultaneous high speed shadowgraphy and pressure measurement were conducted to study the effects of initial pressure and temperature on combustion mode and flame propagation. By comparing the frequencies of super knock pressure oscillation in the boosted engine and after-detonation pressure wave in the constant volume bomb, a relation can be found between the super knock and detonation. The experimental results also show that the detonation tendency of H2/O2 mixture in the constant volume bomb increases with increasing initial pressure but decreases with increasing initial temperature, indicating that the mixture density i.e. energy density plays an important role in detonation onset.

Simultaneous High Speed Schlieren and Direct Imaging of Ignition Process with Digitally Enhanced Visualisation

Abstract In this paper, a combined method of schlieren and digital colour image processing is developed to study the effect of ignition location on the propagation of propane diffusion flames. The early weak blue flame is visualised through selective digital imaging enhancement techniques, which have revealed that a typical orange diffusion flame is often formed inside a blue flame pocket at the beginning of the ignition when ignited at the centreline of the fuel jet. When the ignition location towards the out edge of the fuel/air mixing boundary, the orange flame shifted and gradually broke the blue flame pocket. In the meantime, the flame was observed to propagate faster. The ratio of orange flame areas rose and the blue flame area fell accordingly.

Phase Resolved Analysis of Flame Structure in Lean Premixed Swirl Flames of a Fuel Staged Gas Turbine Model Combustor

A scaled model of a gas turbine (GT) burner with coaxially mounted swirlers has been used to study the effects of fuel staging on the behavior of lean premixed methane air flames. Lean flames are known to be susceptible to instabilities that can lead to unsteady operation, flame extinction, and thermo-acoustic oscillations. High speed (10 kHz) laser and optical diagnostic techniques have been used to investigate the fuel staging effect on the mechanisms involved in such instabilities. Methane air flames at atmospheric pressure have been investigated at a constant thermal power of 58 kW. The global equivalence ratio was kept constant, while the fuel staging was varied. The bulk flow velocity at the exit plane was kept constant at 20 m/s. Simultaneous high speed OH PLIF, OH* CL, and acoustic measurements were performed at kHz repetition rate to characterize the flames and determine the operability limits of the combustor. The characterization measurements reveal significant changes in flame shape for various staging ratios as well as onset of self-excited thermo-acoustics in flames with more than 55% fuel injection in the outer swirler. The phase resolved analysis of the OH* CL revealed pulsation in the heat release due to acoustics in flames with higher percentage of fuel in the outer swirler. Comparison of the pressure oscillation in the combustion chamber with the heat release yielded a clear picture regarding the feedback mechanism that sustains the self-excited thermo-acoustic pulsations. The variation of local equivalence ratio of the mixture seems to be the driving force that initiates the onset of acoustics pulsations.

Dimming-discrete-multi-tone (DMT) for simultaneous color control and high speed visible light communication

Visible light communication (VLC) using LEDs has attracted significant attention recently for the future secure, license-free and electromagnetic-interference (EMI)-free optical wireless communication. Dimming technique in LED lamp is advantageous for energy efficiency. Color control can be performed in the red-green-blue (RGB) LEDs by using dimming technique. It is highly desirable to employ dimming technique to provide simultaneous color and dimming control and high speed VLC. Here, we proposed and demonstrated a LED dimming control using dimming-discrete-multi-tone (DMT) modulation. High speed DMT-based VLC with simultaneous color and dimming control is demonstrated for the first time to the best of our knowledge. Demonstration and analyses for several modulation conditions and transmission distances are performed, for instance, demonstrating the data rate of 103.5 Mb/s (using RGB LED) with fast Fourier transform (FFT) size of 512.