Valery Sheverev

Micro-optical force sensor concept based on whispering gallery mode resonators

A micro-optical force sensor concept based on the morphology-dependent shifts of optical modes of dielectric microspheres is investigated. The optical resonances, commonly referred to as the whispering gallery modes (WGM), were excited by evanescently coupling light from a tunable diode laser using a tapered single-mode fiber. A compressive force applied to the sphere induces a change in both the shape and the index of refraction of the sphere leading to a shift in WGM. By tracking the shifts, the force magnitude is determined using solid silica as well as solid and hollow Polymethyl-methacrylate (PMMA) microsphere resonators. A measurement sensitivity as high as dlambda/dF=7.664 nm/N was demonstrated with a 960 mum hollow PMMA sphere.

Acoustic dispersion in glow discharge plasma: A phenomenological analysis

A phenomenological analysis is carried out to investigate the propagation of sound wave in the positive column of a glow discharge plasma. Specifically, the effect of local energy transfer from the discharge into the gas is studied. The analysis shows that the density fluctuations cause variations in the energy transfer rate. This effect is found to be a function of the plasma parameters and acoustic wave frequency thus leading to acoustic dispersion. The conclusion confirms earlier mathematical treatment of the problem [Kolosov et al., AIAA Paper No. 99-4882, 1999] and provides a physical explanation of the phenomenon.

Chemi-ionization in neon plasma

The density of electrons formed in binary collisions of 2p53s neon atoms was measured in the afterglow of a low pressure glow discharge by observing the high energy tail of the electron energy distribution function (EEDF) using a Langmuir probe. In the afterglow, the bulk plasma electrons thermalize but the density of 2p53s neon atoms remains significant. In an ionizing collision, a pair of these atoms releases high energy (∼11.6 eV) electrons which form a characteristic peak in the EEDF. Simultaneously with the chemi-ionization electrons, the densities of 1s2, 1s3, 1s4, and 1s5 neon atoms were independently measured using diode laser absorption spectroscopy. It was found that the data obtained are described well by a single chemi-ionization reaction when the 2p53s configuration is considered a single state. The corresponding rate coefficient, found to be (3.2±0.4)×10−10 cm3 s−1 at a temperature of 310 K, is recommended for use in discharge modeling.

A Micro-Optical Wall Shear Stress Sensor Concept Based on Whispering Gallery Mode Resonators

In this paper we discuss a novel micro optical wall shear stress sensor concept based on whispering gallery mode (WGM) shifts of dielectric resonators. The optical resonator, which is a sphere with a diameter of several hundred microns, serves as the sensing element. The wall shear force acting on a moveable plate is transmitted mechanically to the microsphere. As a result of the applied force, the morphology (both shape and refractive index) of the resonator is perturbed leading to a shift of the optical resonance (WGM). By monitoring the shifts to WGMs, measurement of the wall shear stress is accomplished. Shape perturbations of the order of a nanometer can be detected with this optical method. Therefore, the whole sensor system is essentially rigid. Preliminary experiments using a prototype sensor design show promise.

Real-Time Assessment of Granule Densification in High Shear Wet Granulation and Application to Scale-up of a Placebo and a Brivanib Alaninate Formulation

Real-time monitoring and control of high shear wet granulation (HSWG) using process analytical technologies is crucial to process design, scale-up, and reproducible manufacture. Although significant progress has been made in real-time measurement of granule size distribution using focused beam reflectance measurement (FBRM), real-time in-line assessment of granule densification remains challenging. In this study, a drag force flow (DFF) sensor was developed and used to probe wet mass consistency in real-time. In addition, responses from FBRM and DFF sensors were compared to assess complementarity of information on granulation progress from the two probes. A placebo and a brivanib alaninate formulation were granulated with different concentrations of binder or water, respectively, while measuring granule size growth, densification, and DFF sensor response. The DFF sensor was able to quantitatively characterize with high resolution a response of wet mass consistency distinct from granule size distribution. The wet mass consistency parameter correlated well with granule densification, which was shown as a critical material attribute that correlated with tablet dissolution. In addition, application of DFF sensor to scale-up of granulation was demonstrated. These results showed the value of wet mass consistency measurement using DFF for WG monitoring and control.

Propagation of sound in glow discharge plasma

Propagation of sound in a medium where the rate of local heat addition is a function of gas density is analysed theoretically and the results are applied for modelling the experimentally observed effect of amplification of acoustic waves by an extended glow discharge in air. The model adequately describes the experimental dependences of the gain on the wave frequency and discharge power density and predicts that the amplification of sound by an unconfined glow discharge in air increases with discharge current density but does not change noticeably with gas pressure when the current density is kept constant. Quantitative estimates indicate that a gain of as high as 1 m−1 (or 9 dB for a 60 dB wave passing through 1 m of plasma) could be realized using a discharge in air with a current density of 100 mA cm−2.

Measurement of gas temperature and convection velocity profiles in a dc atmospheric glow discharge

Gas temperature and convective velocity distributions are presented for an unconfined glow discharge in air at atmospheric pressure, with electric currents ranging between 30 and 92 mA. The vertically oriented discharge was formed between a pin anode (top) and an extended cathode. The temperature and velocity profiles were measured using laser-induced Rayleigh scattering and laser Doppler anemometry techniques, respectively. The temperature field exhibited a conical shape with the radius of hot temperature zone increasing toward the anode. A maximum temperature of 2470 K was observed on the discharge axis with the discharge current of 92 mA. Air velocity measurements around the discharge demonstrated that the shape and magnitude of the temperature field are strongly affected by natural convection. Estimates indicate that convective losses may account for more than 50% of the power input into the positive column of the discharge. The measured temperature fields and convective velocity profiles provide a se...

Distribution of gas temperature in an unconfined glow discharge plasma

An analysis is carried out to determine radial temperature distributions in the cylindrical positive column of a glow discharge formed in air in free space without confining walls. The analysis considers discharge with current densities lower than 100 mA/cm2 and at gas pressures of several tens of Torr. The plasma is represented by a set of hydrodynamic equations that include the balances for electron number density, translational energy, and the vibrational energy. The equations are solved using an iterative method to obtain gas temperatures for a range of plasma conditions. The results show that increasing discharge current densities lead to higher gas temperatures on plasma axis, however, unlike in the case with glow discharge restricted by dielectric walls, increased current densities also lead to wider radial profiles of temperature. Increased gas pressure, while leading to higher on-axis gas temperatures, results in narrower temperature profiles, mainly due to the reduced diffusion rates and vibrati...

Performance of a Whispering Gallery Mode Resonator - Based Micro -Optical Force Sensor

In this paper, we investigate the performance of a prototype micro -optical force sensor and discuss issues related to its sensitivity and calibration. The measurement concept is based on the shifts in the optical resonances of small dielectric spheres. The optical resonances, commonly referred to as t he whispering gallery modes (WGM), are excited by evanescently coupling light from a tunable diode laser using a tapered single mode fiber. The spheres are of the order of several hundred microns in diameter. The WGMs of the spheres are observed as sharp d ips in the transmission spectrum through the fiber. A compressive force applied to the sphere induces a change in both the shape and the index of refraction of the sphere. These changes, in turn, lead to a shift in the optical resonance (WGM). We built and analyzed the performance of micro -sensor prototypes using silica and polymer (Polymethyl Methacrylate or PMMA) dielectric spheres. In the case of PMMA, we used both solid and hollow spheres as sensor. The solid silica and hollow PMMA sensors offer the low est and highest measurements sensitivity, respectively. The silica sensors have the largest force range. As expected, smaller sensor sizes lead to increased sensitivity.

Evolution of a vortex in glow discharge plasma

The evolution of a vortex in glow discharge plasma is studied analytically. Specifically, the mechanism of local energy deposition into the flow by the plasma is considered and its effect on the structure of an inviscid vortex is analyzed. The vortex is modeled by a set of Euler’s equations while the energy transferred by the plasma into the gas is represented by Rayleigh mechanism. In this mechanism, the amount of heat addition is a function of local gas density. The analysis indicates that the plasma can have a considerable effect on the structure of a vortex. The inviscid calculations show that in a uniform discharge, a 1 cm vortex dies out in a fraction of a second.