kHz Excitation Research Articles

Upconversion fluorescence assisted visualization of femtosecond laser filaments in Er-doped chalcohalide 65GeS2-25Ga2S3-10CsCl glass

Upconversion fluorescence of Er3+ ions (1 at. %) excited with femtosecond laser pulses of different repetition frequencies (seed laser 76 MHz, and laser amplifier 1 kHz) is studied in the Er-doped chalcohalide glass of 65GeS2-25Ga2S3-10CsCl composition. Strong weakening of fluorescence efficiency at 530 nm and 560 nm and photoinduced darkening are observed under 1 kHz excitation, which is most probably caused by free carriers generated by two-photon absorption. On the other hand, neither weakening nor photodarkening is observed under 76 MHz excitation, this being presumably due to concomitant thermal annealing. Taking an advantage of upconversion fluorescence, the femtosecond filamentation associated with positive changes in refractive index is recorded in the Er-doped 65GeS2-25Ga2S3-10CsCl glass, whereas exceeding the threshold of thermal melting is accompanied by an opposite decrease in the refractive index.

20-kW Zero-Voltage-Switching SiC-mosfet Grid Inverter With 300 kHz Switching Frequency

Although SiC- mosfet has significant advantages on switching performance over traditional Si-IGBT, the switching loss of SiC- mosfet devices at hard switching rises quickly with the increment in the switching frequency. This has narrowed down further possibilities of improving efficiency and power density of the grid inverter. Zero-voltage-switching (ZVS) space-vector-modulation (SVM) technique is introduced to further push the power density of SiC- mosfet inverter. This paper focuses on the impact of applying the ZVS-SVM to three-phase two-level SiC- mosfet inverter. With the same efficiency requirement the ZVS-SVM SiC inverter can operate at a much higher switching frequency, which gives the opportunity to further reduce the size of passive components. The loss distributions, conversion efficiencies, and volumes of passive components of both a 20-kW SiC- mosfet hard-switching inverter and a 20-kW SiC- mosfet ZVS-SVM inverter have been compared under switching-frequency range from 50 to 300 kHz. Meanwhile, a new metric called “efficiency stiffness” is proposed to compare different inverters with respect to the efficiency performance against switching-frequency characteristics. In addition, high voltage overshoot of SiC- mosfet and high thermal stress of resonant inductor are the two critical issues in the SiC- mosfet ZVS-SVM inverter with high switching frequency. A power module including seven SiC- mosfet bare dies with low stray inductance is designed for ZVS-SVM inverter instead of the existing seven discrete TO-247 package SiC- mosfet s to reduce the voltage overshoots on the switches. Besides, to reduce the power loss of the resonant inductor caused by large amplitude of current at hundreds of kHz excitation frequency, design of the inductor with distributed air gap and optimal winding thickness are studied. A 20-kW SiC- mosfet ZVS-SVM grid inverter prototype is built to verify the proposed design.

A New Venous Entry Detection Method Based on Electrical Bio-impedance Sensing.

Peripheral intravenous catheterization (PIVC) is frequently required for various medical treatments. Over 1 billion PIVC operations are performed per year in the United States alone. However, this operation is characterized by a very low success rate, especially amongst pediatric patients. Statistics show that only 53% of first PIVC attempts are successful in pediatric patients. Since their veins are small and readily rupture, multiple attempts are commonly required before successfully inserting the catheter into the vein. This article presents and evaluates a novel venous entry detection method based on measuring the electrical bio-impedance of the contacting tissue at the tip of a concentric electrode needle (CEN). This detection method is then implemented in the design of a clinical device called smart venous entry indicator (SVEI), which lights up a LED to indicate the venous entry when the measured value is within the range of blood. To verify this detection method, two experiments are conducted. In the first experiment, we measured the bio-impedance during the insertion of a CEN into a rat's tail vein with different excitation frequencies. Then three classifiers are tested to discriminate blood from surrounding tissues. The experimental results indicate that with 100 kHz excitation frequency the blood bio-impedance can be identified with accuracy nearly 100%, demonstrating the feasibility and reliability of the proposed method for venous entry detection. The second experiment aims to assess the impact of SVEI on PIVC performance. Ten naive subjects were invited to catheterize a realistic baby arm phantom. The subjects are equally divided into two groups, where one group does PIVC with SVEI and the other group uses an ordinary IV catheter. The results show that subjects using SVEI can achieve much higher success rates (86%) than those performing PIVC in a conventional way (12%). Also, all subjects assisted by SVEI succeeded in their first trials while no one succeed in their first attempt using the conventional unassisted system. These results demonstrate the proposed detection method has great potential to improve pediatric PIVC performance, especially for non-expert clinicians. This supports further investment towards clinical validation of the technology.

The dynamic excitation of a granular chain: Contact mechanics finite element analysis and experimental validation.

There is currently interest in transmitting acoustic signals along granular chains to produce waveforms of relevance to biomedical ultrasound applications. The study of such a transduction mechanism is greatly aided by the use of validated theoretical models. In view of this, a finite element analysis is presented in this paper. The dynamics of a granular chain of six, 1 mm diameter chrome steel spherical beads, was excited at one end using a sinusoidal displacement signal at 73 kHz, and terminated by a rigid support. Output from this model was compared with the solution provided by the equivalent discrete dynamics model, and good agreement obtained. An experimental configuration involving the same chain, but terminated by an annular support made of a liquid photopolymer resin was also simulated and the velocity of the last sphere obtained through simulation was compared with laser vibrometer measurement, with good agreement. This model was then extended whereby the granular chain was coupled to an acoustic medium with the properties of water, via a thin vitreous carbon cylinder. Finite element predictions of the acoustic pressure indicate that, for a 73 kHz excitation frequency, harmonic rich acoustic pulses with harmonic content close to 1 MHz are predicted.

A High-Throughput, Arbitrary-Waveform, MPI Spectrometer and Relaxometer for Comprehensive Magnetic Particle Optimization and Characterization.

Magnetic Particle Imaging (MPI) is a promising new tracer modality with zero attenuation deep in tissue, high contrast and sensitivity, and an excellent safety profile. However, the spatial resolution of MPI is limited to around 1 mm currently and urgently needs to be improved for clinical applications such as angiography and brain perfusion. Although MPI resolution is highly dependent on tracer characteristics and the drive waveforms, optimization is limited to a small subset of possible excitation strategies by current MPI hardware that only does sinusoidal drive waveforms at very few frequencies. To enable a more comprehensive and rapid optimization of drive waveforms for multiple metrics like resolution and signal strength simultaneously, we demonstrate the first untuned MPI spectrometer/relaxometer with unprecedented 400 kHz excitation bandwidth and capable of high-throughput acquisition of harmonic spectra (100 different drive-field frequencies in only 500 ms). It is also capable of arbitrary drive-field waveforms which have not been experimentally evaluated in MPI to date. Its high-throughput capability, frequency-agility and tabletop size makes this Arbitrary Waveform Relaxometer/Spectrometer (AWR) a convenient yet powerfully flexible tool for nanoparticle experts seeking to characterize magnetic particles and optimize MPI drive waveforms for in vitro biosensing and in vivo imaging with MPI.

CuBr-Ne-HBr laser with a high repetition frequency of the lasing pulses at a reduced energy deposition in the discharge

Experimental and computer studies of the CuBr laser with periodic-pulse pumping are performed with and without addition of HBr. The analysis based on the numerical simulation reveals how additions improve the lasing characteristics of this laser at both typical (10 to 20 kHz) and higher (up to 100 kHz) excitation pulse repetition frequencies during the operation with a low energy deposition in the discharge. This allows the lasing pulse repetition frequency to be increased in the experiment to 750 kHz, which does not seem to be a limit as yet.

Saturated Excitation Microscopy with Optimized Excitation Modulation

Saturated excitation (SAX) microscopy utilizes the nonlinear relation between fluorescence emission and excitation under saturated excitation to improve the spatial resolution of confocal microscopy. In this study, we theoretically and experimentally investigate the saturation of fluorescence excitation under modulated excitation to optimize the excitation conditions for SAX microscopy. Calculation of the relationships between fluorescence and excitation intensity with different modulation frequencies reveals that the lifetime of the triplet state of the fluorescent probe strongly affects the strength of the demodulated fluorescence signals. We also find that photobleaching shows little dependence on the modulation frequency. These investigations allow us to determine the optimum excitation conditions, that is, the conditions providing sufficient fluorescence saturation without strong photobleaching. For a sample stained with ATTO Rho6G phalloidin, we estimate the optimal excitation conditions, which are produced with 50 kHz excitation modulation and a 50 μsec pixel dwell time, and successfully perform three-dimensional imaging with sub-diffraction resolution.

Fourier-transformed infrared absorption spectroscopy: a tool to characterize the chemical composition of Ar–NH3–SiH4 dielectric barrier discharge

This study brings initial insight into the characterization of the gas chemical composition in a dielectric barrier discharge (DBD) by Fourier-transformed infrared absorption spectroscopy. Capitalizing on a double path of the IR beam, measurements were performed in 5 cm long, 2 mm gap plasma. As the IR beam cross-section in the plasma was 2 × 2 mm2, a translation system was used to scan the plasma along the direction of the gas flow with a 2 mm spatial resolution.In the case of Ar–SiH4(67 ppm)–NH3(133 ppm) glow-mode DBD, all IR spectra peaks from 6000 to 800 cm−1 are related to vibrations of Si–H from SiH4 and N–H from NH3. Here, the N–H vibration is observable but non-quantifiable.At 50 kHz excitation, the absolute concentration of SiH4 was measured at different positions and different power values in continuous and modulated modes. In the absence of powder formation in the plasma and for an initial density of 1.6 × 1015 cm−3, all the measurements are fitted by the same exponential decay leading to an energy of 38 eV per dissociated molecule of SiH4. The presence of powders in the plasma reduces SiH4 dissociation rate by a factor larger than 4.

TU‐E‐144‐02: Dependence of Ultrasound Echo Decorrelation On Tissue Temperature During Radiofrequency Ablation of Ex Vivo Bovine Liver

Purpose: Echo decorrelation imaging is a ultrasound imaging method that has been shown effective for mapping of thermal ablation effects on liver and tumor tissue, both ex vivo and in vivo. Quantification of tissue temperature during thermal ablation treatments would benefit treatment guidance and control. Here, the effect of tissue temperature on the mapped echo decorrelation parameter is assessed for ex vivo radiofrequency ablation (RFA). Methods: RFA treatments were performed on freshly acquired ex vivo bovine liver using a needle antenna with 500 kHz excitation for treatment voltages 30–40 V rms and durations 10–15 min. Throughout each treatment, beamformed ultrasound echo signals were recorded by a 7 MHz linear array and temperature was recorded by two thermocouples within the ultrasound image plane. Temperature maps were simulated by a finite element method, with tissue parameters determined using an unscented Kalman filter to best match measured ablation results. Echo decorrelation images were constructed from recorded echo data and correlated spatially with corresponding simulated temperature maps. Prediction of tissue temperatures over 60 °C, corresponding to local thermal ablation, was tested using receiver operating characteristic (ROC) curve analysis. Results: Strong correspondence was observed between time‐dependent echo decorrelation maps and corresponding temperature maps. Temperatures above 60 °C consistently corresponded to locally elevated echo decorrelation. Correlation coefficients between local temperature and echo decorrelation were weak but statistically significant. ROC curve analysis showed successful prediction of ablative tissue temperatures. Conclusion: Observed correspondence between local tissue temperature and echo decorrelation indicates that elevated tissue temperatures consistently cause elevated echo decorrelation. Although weak overall correlation between local echo decorrelation and tissue temperature suggests that temperature is not accurately predicted by echo decorrelation, ROC curve analysis indicates successful prediction of tissue ablation, suggesting the utility of echo decorrelation imaging as a tool for real‐time guidance and control of thermal ablation. This research was supported by NIH grants R01 CA158439 and R21 EB008483.

Radiation pressure excitation of test mass ultrasonic modes via three mode opto-acoustic interactions in a suspended Fabry–Pérot cavity

Three-mode parametric-instabilities risk stable operation of gravitational-wave detectors. Instabilities occur through time varying radiation-pressure distributions, derived from beating between two optical modes, exciting mirror acoustic modes in Fabry-Perot cavities. Here we report the first demonstration of radiation-pressure driving of ultrasonic-acoustic modes via pairs of optical modes in gravitational-wave type optical cavities. In this experiment ~0.4W of TEM01 mode and ~1kW of TEM00 mode circulated inside the cavity, an ~181.6kHz excitation was observed with amplitude ~5E-13m. The results verify the driving force term in Braginsky's parametric instability feedback model. The interaction parametric gain was (3.8+/-0.5)E-3 and mass-ratio scaled opto-acoustic overlap 2.7+/-0.4.

Transition between breakdown regimes in a temperature-dependent mixture of argon and mercury using 100 kHz excitation

The paper examines the breakdown process at 100 kHz in a changing temperature-dependent mixture of Ar and Hg and the associated transitions between breakdown regimes. Each measurement series started at 1400 K, 10 bar of Hg, and 0.05% admixture of Ar and finished by natural cooling at room temperature, 150 mbar of Ar, and 0.01% admixture of Hg. The E/N at breakdown as a function of temperature and gas composition was found to have a particular shape with a peak at 600 K, when Hg makes up for 66% of the gaseous mixture and Ar 34%. This peak was found to be an effect of the mixture itself, not the temperature effects or the possible presence of electronegative species. The analysis has shown that at this frequency both streamer and diffuse breakdown can take place, depending on the temperature and gas composition. Streamer discharges during breakdown are present at high temperatures and high Hg pressure, while at room temperature in 150 mbar of Ar the breakdown has a diffuse nature. In between those two cases, the radius of the discharges during breakdown was found to change in a monotonic manner, covering one order of magnitude from the size typical for streamer discharges to a diffuse discharge comparable to the size of the reactor.

Side-on Surface Modification of Polystyrene with an Atmospheric Pressure Microplasma Jet

An atmospheric-pressure microplasma jet operating in helium gas has been used in a side-on configuration to modify locally the surface energy of polystyrene (PS). The plasma plume and gas outflow emanating from the capillary-type discharge (8 kVp–p at 30 kHz excitation) were directed parallel to (side-on) and just above the sample surface, rather than head-on as in conventional treatment. This side-on treatment method has been shown to prevent surface damages, pitting or roughing caused by head-on treatment methods. Schlieren photography has been used to identify regions of laminar and turbulent flow in the exiting gas stream and the nature of their interaction with the substrate surface. Correlation of these observations with spatially resolved water contact angle (WCA) measurements of the treated PS, show clearly that substantial reductions in WCA (∼50–60°) occur in downstream regions where the turbulent gas mixed with air impinges the surface. In contrast, only small changes in WCA occur (∼10–20°) in regions closer to the exit orifice where the helium (He) flow is still laminar across the surface. Little or no treatment is observed for distances greater than 5 cm from the source. In addition, low levels of treatment were observed in the regions where the visible plasma glow of the jet is adjacent and parallel to the surface. The results indicate that excited air species (either mixed or entrained in the He gas flow) are the main agents causing surface covalent bond breaking leading to surface modification.

Design of Parallel Electrical Resistance Tomography System for Measuring Multiphase Flow

ERT (electrical resistance tomography) is effective method for visualization of multiphase flows, offering some advantages of rapid response and low cost, so as to explore the transient hydrodynamics. Aiming at this target, a fully programmable and reconfigurable FPGA (field programmable gate array)-based Compact PCI (peripheral component interconnect) bus linked sixteen-channel ERT system has been presented. The data acquisition system is carefully designed with function modules of signal generator module; Compact PCI transmission module and data processing module (including data sampling, filtering and demodulating). The processing module incorporates a powerful FPGA with Compact PCI bus for communication, and the measurement process management is conducted in FPGA. Image reconstruction algorithms with different speed and accuracy are also coded for this system. The system has been demonstrated in real time (1400 frames per second for 50 kHz excitation) with signal-noise-ratio above 62 dB and repeatability error below 0.7%. Static experiments have been conducted and the images manifested good resolution relative to the actual object distribution. The parallel ERT system has provided alternative experimental platform for the multiphase flow measurements by the dynamic experiments in terms of concentration and velocity.

A Linear Electrostatic Induction Motor with Coils Mounted on its Slider for Voltage Boosting

This paper introduces a linear electrostatic induction motor utilizing electrical resonance. The motor consists of two thin plastic films: the stator film and the slider film, in which fine-pitched three-phase electrodes are embedded. The motor has three coils mounted on its slider, which are connected to the slider electrodes, and driven by applying three-phase voltage to its stator electrodes. The voltages on the slider electrodes are boosted by an electrical resonance, and large thrust force is obtained. The motors capability to accelerate under load is demonstrated; it could pull up weights up to 80 g with an excitation voltage of 1 kV0-P / 12.8 kHz, which was the motors resonance frequency. The fastest motion of the slider was obtained when the excitation frequency was set slightly higher than the resonance frequency, and the motor traveled 34 mm in 0.16 seconds with 1 kV0-P / 13.1 kHz excitation, while pulling up a weight of 40 g.

Micro Fluxgate Sensor using Solenoid Coils Fabricated by MEMS Technology

In this paper, we present a micro fluxgate sensor with solenoid coils. Micro-solenoid coils were used in this fluxgate sensor as excitation and sensing elements. Two identical excitation coils in inverse series were wound around the opposite sides of the rectangular-ring-shaped magnetic core, respectively. The sensing coil was placed vertically to the excitation coils and between them. Adopting gluing and chemical wet etching, iron-based nanocrystalline alloy was used as magnetic core material. This fluxgate sensor was designed to operate based on second harmonic operation principle. 100 kHz excitation currents with different effective values were selected to characterize the fabricated fluxgate sensor. From these experiments, we obtained some results from which we found out that the greatest sensitivity of 583.1 V/T was achieved with the effective excitation current of 150 mA. In the range from -500 μT to +500 μT, the fabricated fluxgate sensor can keep a good linearity. The noise power density was 13.57 nT/Hz 0.5 at 1Hz and the noise RMS level was 23 nT in the frequency range of 10 mHz-25 Hz.

An electrostatic induction motor utilizing electrical resonance for torque enhancement

An electrostatic induction motor utilizing electrical resonance to enhance its torque is introduced in this paper. The motor has patterned electrodes embedded on both of its stator and rotor, and driven by three-phase excitation voltage applied to its stator electrodes. The rotor electrodes are connected to external inductances and resistances through slip rings. The torque of the motor is maximized at resonant condition, where the slip frequency is equal to the resonance frequency of the system. A working prototype of the motor was constructed with 18-layered film electrodes. The maximum torque of the motor was 20 mNm at 10 rpm with an excitation by three-phase voltage of 0.9 kV/8.25 kHz. The motor could start itself and rotate in balance with frictions at a speed of 75 rpm with 0.9 kV/8.35 kHz excitation.

Implementation of Time-Resolved Step-Scan Fourier Transform Infrared (FT-IR) Spectroscopy Using a kHz Repetition Rate Pump Laser

Time-resolved step-scan Fourier transform infrared (FT-IR) spectroscopy has been shown to be invaluable for studying excited-state structures and dynamics in both biological and inorganic systems. Despite the established utility of this method, technical challenges continue to limit the data quality and more wide ranging applications. A critical problem has been the low laser repetition rate and interferometer stepping rate (both are typically 10 Hz) used for data acquisition. Here we demonstrate significant improvement in the quality of time-resolved spectra through the use of a kHz repetition rate laser to achieve kHz excitation and data collection rates while stepping the spectrometer at 200 Hz. We have studied the metal-to-ligand charge transfer excited state of Ru(bipyridine)(3)Cl(2) in deuterated acetonitrile to test and optimize high repetition rate data collection. Comparison of different interferometer stepping rates reveals an optimum rate of 200 Hz due to minimization of long-term baseline drift. With the improved collection efficiency and signal-to-noise ratio, better assignments of the MLCT excited-state bands can be made. Using optimized parameters, carbonmonoxy myoglobin in deuterated buffer is also studied by observing the infrared signatures of carbon monoxide photolysis upon excitation of the heme. We conclude from these studies that a substantial increase in performance of ss-FT-IR instrumentation is achieved by coupling commercial infrared benches with kHz repetition rate lasers.

AMR gradiometer for mine detection and sensing

We used anisotropic magnetoresistors (AMR's) to build an advanced mine detector. The sensing head involves gradiometric pair of AMR sensors and a continuous-wave driven excitation coil, so the gradiometer is capable of detection ferromagnetic materials as well as diamagnetic metals. The sensors are specially arranged to suppress the large AC-excitation field, so the mine detector senses both DC and AC field gradient response of the object of interest. Being limited by the sensor noise of 214 pTrms/√Hz at 1 kHz, we were able to detect an 50x50x1.5 mm3 aluminum test object in a 20 cm-depth using a 300 μT, 1 kHz excitation field.

Effect of substrate temperature on ZnO thin film fabrication by using an atmospheric pressure cold plasma generator

AbstractUnder atmospheric pressure, homogeneous non‐equilibrium cold plasma was generated stably by high voltage pulsed power (1 kV, 20 kHz) excitation of He and O2 gases. By feeding Zn‐MOPD (C18H30O6Zn) into this plasma with He carrier gas, transparent flat ZnO films about 240 nm thick were successfully fabricated on glass substrates directly under a slit made into the cathode. Transmittance of the film is about 80% in the wavelength range from 400 to 600 nm. An XRD measurement revealed that these ZnO films had a c‐axis oriented polycrystalline structure. By increasing the substrate temperature from 250 to 400 °C, electrical resistivity of the film decreased from 0.42 Ωm to 9.4 × 10–4 Ωm. A high temperature of the substrate may change the growth pattern of ZnO film and its microstructure. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Promoting inertial cavitation by nonlinear frequency mixing in a bifrequency focused ultrasound beam

Enhancing cavitation activity with minimal acoustic intensities could be interesting in a variety of therapeutic applications where mechanical effects of cavitation are needed with minimal heating of surrounding tissues. The present work focuses on the relative efficiency of a signal combining two neighbouring frequencies and a one-frequency signal for initiating ultrasound inertial cavitation. Experiments were carried out in a water tank, using a 550 kHz piezoelectric composite spherical transducer focused on targets with 46 μm roughness. The acoustic signal scattered, either by the target or by the cavitation bubbles, is filtered using a spectral and cepstral-like method to obtain an inertial cavitation activity measurement. The ultrasound excitations consist of 1.8 ms single bursts of single frequency f 0 = 550 kHz excitation, in the monofrequency case, and of dual frequency f 1 = 535 kHz and f 2 = 565 kHz excitation, in the bifrequency case. It is shown that depending on the value of the monofrequency cavitation threshold intensity the bifrequency excitation can increase or reduce the cavitation threshold. The analysis of the thresholds indicates that the mechanisms involved are nonlinear. The progress of the cavitation activity beyond the cavitation threshold is also studied. The slope of the cavitation activity considered as a function of the acoustic intensity is always steeper in the case of the bifrequency excitation. This means that the delimitation of the region where cavitation occurs should be cleaner than with a classical monofrequency excitation.