Laser Doppler Sensor

Laser Doppler anemometry Laser Doppler sensor... 

An attractive feature of fiber sensors is the possibility of performing in vivo tests and monitoring. Numerous fiber-optic sensors have already been described that measure physical parameters of the human body [41]. Pressure, temperature, physiological flow, strain, motion, displacement, or flow velocity can be monitored by optical methods such as variable reflection, laser Doppler velocimetry, optical holography, or diffraction. In this section the application of optosensing methods to the determination of molecular species encountered in clinical and biomedical analysis is described. 

Known measuring techniques comprise local physical methods (hydrophones, thermoacoustic sensors, aluminum foil erosion, optical sound pressure and velocity sensors, radiation pressure scale, laser-Doppler anemometry), local chemical methods (Weissler reaction, chemiluminescence, electrochemical sensors), global chemical methods (model reactions), and sonoluminiscence (single-bubble sonoluminescence SBSL, multibubble sonoluminescence MBSL). 

Real-time wall shear stress is difficult to monitor precisely because it varies in space and time. MEMS sensors provide high spatial resolution to resolve variations in shear stress in a 3D bifurcation model for small-scale hemodynamics. The application of MEMS sensors with backside wire bonding G ig. fib) captured the spatial variations in shear stress in a 3D bifurcation model (Fig. 8). The measured skin friction coefficients at various positions correlated well with values derived from the exact Navier-Stokes solution of the flow within the bifurcation [13]. Therefore, the development of MEMS sensors has enabled the precise measurements of spatial variations in shear stress for small-scale hemodynamics otherwise difficult with conventional technologies such as computed tomography (CT scan), magnetic resonance imaging (MRI), ultrasound, and laser Doppler velocimetry. 

Laser Doppler velocimetry (LDV) Laser Doppler velocity profile sensor Micro laser Doppler velocimetry (p-LDV)... 

Mkro Laser Doppler Velocimetry (p-LDV), Fig. 2 Applicatirai of a profile sensor (one concept of mido-LDV) velocity profile measuiement in... 

In summary, the crmcept of the profile sensor results in three major advantages compared to conventional laser Doppler velocimetry ... 

Czarske J, Biittner L, Razik T, Muller H (2002) Boundary layer velocity measurements by a laser Doppler profile sensor with micrometre spatial resolution. Meas Sci Technol 13(12) 1979-1989... 

Konig J, Voigt A, Biittner L, Czarske J (2010) Precise micro flow rate measurements by a laser Doppler velocity profile sensor with time division multiplexing. Meas Sci Technol 21, 074005 (9 pp)... 

Konig J, Miihlenhoff S, Eckert K, Biittner L, Odenbach S, Czarske J (2011) Velocity measurements inside the concentration boundary layer during copper-magneto-electrolysis using a novel laser Doppler profile sensor. Electrochim Acta 56 6150-6156... 

Voigt A, Bayer C, Shirai K, Biittner L, Czarske J (2008) Laser Doppler field sensor for high resolution flow velocity imaging without camera. Appl Opt 47(27) 5028-5040... 

Skin blood flow (SBF) was measured using a laser Doppler blood perfusion monitor (Vasamedics Laserflo Blood Perfusion Monitor BPM ). The monitor was cormected to the computer via the computer s USB port The sensor used to monitor the superficial skin blood flow fed data into the monitor, and this data was collated by a voltage data logger this was then offloaded to the computer s OTLM programme. OTLM recorded the electrical signal produced by the flow of blood in the superficial vessels in the skin, and thus, as for humidity, the units of the raw data were millivolts (mV). 

Micro Laser Doppler Velodmetiy ( r-LDV), Figure 1 Application of a profile sensor(one concepf of micro-LDV) velocity profile measurement In a microchannel... 

Micro Laser Doppler Velocimetiy (iji-LDV), Hgure 2 Fringe systems of the laser Doppler velocity profile sensor... 

Nassif H, Gindy M, Davis J (2005) Comparison of laser Doppler vibrometer with contact sensors for monitoring bridge deflection and vibration. NDT Int 38(3) 213-218... 

The temperature distribution in the loop is measured with chromel-alumel thermocouples and two Pt-100 temperature sensors for reference measurements. Absolute pressure is measured at the top of the riser and at the inlet of the core. The liquid level in the steam dome is measured with a differential pressure sensor. The differential pressure over the friction settings of the individual channels is a measure for the flow distribution over the coolant channels and bypass channels. The total flow in the loop is measured at 2 different positions with electromagnetic flow meters. The void fraction at a given height can be measured with gamma transmission techniques. At a fixed height at the top of the riser the radial void distribution is measured with a wire-mesh sensor, which measures the conduction of the two-phase mixture on a two-dimensional grid. Furthermore, laser doppler anemometry is used to study the local liquid velocity in the core or in the riser. 

TOPFLOW will be equipped with advanced two-phase instrumentation mainly and adapted and developed in Rossendorf, such as wire-mesh sensors, needle-shaped conductivity probes with integrated thermocouple, gamma and X-ray tomography and passive ultrasonic droplet probes. Additionally, laser-doppler anemometry and a phase-doppler particle analyser are available. Two of these devices, the needle-shaped conductivity probes with integrated thermocouple and the wire-mesh sensors will be described in detail. 

An application for multiplexed diode-laser sensors with a potentially large impact is for measurements of important parameters at several locations in a gas turbine combustion system. In this example, illustrated schematically in Fig. 24.1, the multiplexed diode lasers are applied for simultaneous absorption measurements in the inlet, combustion, afterburner, and exhaust regions. For example, measurements of O2 mass flux at the inlet may be determined at the inlet from Doppler-shifted O2 absorption lineshapes near 760 nm. Measurements of gas temperature and H2O concentrations in the combustion and afterburner regions may be determined from H2O lineshape measurements near 1.4 pm. Finally, measurements of velocity, temperature, and species concentrations (e.g., CO, CO2, unburned hydrocarbons) may be recorded in the exhaust for the determination of momentum flux (component of thrust) and combustor emissions. 

As shown in Fig. 12 fluid flow can be determined by measuring the doppler shift in laser radiation scattered from particles in the moving fluid stream. No sensor is required in the moving stream. The laser radiation focal point can be moved across the flow tube to measure velocity profiles. Fluid linear flows from 0.01 to 5000 inches (0.03 centimeter to 127 mctersi per second hate been measured. Contaminants, such as smoke, may have to be added to gases to provide scattering centers for the laser beam. 

Rathbone et al. (1989) used a similar probe to determine particle velocity parallel to the surface. The difference is that the central fiber is the sensor of the Fiber Optic Doppler Anemometry (FODA), and it transmits light from a 5 mW He-Ne laser. Particles illuminated by the central fiber scatter light to the surrounding fibers as they passed the probe. When the particles passed over two fibers in succession, the transit time at cross correlation maximum can be obtained. In principle, by correlating the strongest signals from the fibers, it should be possible to determine the direction or different components of particle velocity. However, the measurement was carried out in a two-dimensional fluidized bed, and relatively few data were obtained. 

It is the only moving deflection measuring device that uses Doppler laser sensors to measure deflection. In fact, the main difference of the TSD from all other deflectometers is that it measures the velocity of deflection rather than displacement. 

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