Photodiode Signal Research Articles

Optical Wireless N-CSK with Modified Pseudo Orthogonal M-Sequence Sets

In this paper, N-CSK (N parallel Codes Shift Keying) using modified pseudo orthogonal M-sequence sets (MPOMSs) to realize the parallel combinatory spread spectrum (PC/SS) communication system for the optical communications is proposed. Moreover, the upper bound of data transmission rate and the bit error rate (BER) performance of this N-CSK system using the chip-level detection are evaluated through theoretical analysis by taking into account the scintillation, background-noise, avalanche photo-diode (APD) noise, thermal noise, and signal dependence noise. It is shown that the upper bound of data transmission rate of the proposed system is better than those of OOK/CDM and SIK/CDM. Moreover, the upper bound of data transmission rate of the proposed system can achieve about 1.5[bit/chip] when the code length of MPOMS is 64[chip].

Lab-on-a-Chip Ochratoxin A Detection Using Competitive ELISA in Microfluidics with Integrated Photodiode Signal Acquisition

Ochratoxin A (OTA), a mycotoxin which occurs naturally in a variety of crops (e.g. cereals, grapes), can contaminate feedstock and beverages derived from these crops (e.g. wine and beer) [1]. OTA detection is critical for food safety since exposure through consumption is related to potential health risks, namely cancer [2]. Food and beverages commercialized in Europe must follow the European Commission regulations for the amount of OTA allowed.In this work, OTA detection was developed and performed based on indirect competitive enzyme linked immunosorbent assays (icELISA) perfomed inside polydimethylsiloxane microchannels. The microfluidic icELISA is integrated with hydrogenated amorphous silicon photodiodes microfabricated on a glass substrate for a fast, reliable, and portable OTA detection and quantification system.

Experimental investigation on the self-ignition of pressurized hydrogen released by the failure of a rupture disk through tubes

Hydrogen is expected to be used as a clean energy carrier. However, when high-pressure hydrogen is suddenly released into the air through tubes, self-ignition can occur by a diffusion ignition mechanism. In this paper, the phenomena of self-ignition and flame propagation during the sudden release of high-pressure hydrogen were investigated experimentally. Experimental results show that self-ignition can occur when bursting pressure is sufficiently high in spite of the shortness of the tube. For example, self-ignition was observed at a bursting pressure as high as 23.5 MPa with 50 mm long tube. When self-ignition successfully occurs, a hydrogen jet flame is produced by the ignition. The flame is then stabilized at the tube outlet. From photodiode signals and flame images, the propagation of a flame inside the tube is confirmed and the flame is detected near the rupture disk as the bursting pressure increases. When the tube length is not long enough to produce self-ignition, a hydrogen flame is observed in the only boundary layer at the end of tube and it quenches after the flame exits the tube. Consequently, the formation of a complete flame across the tube is important to initiate self-ignition, which sustains a diffusion flame after jetting out of the tube into the air. Also, in order to establish a complete flame across the tube, it is necessary to have sufficient length such that the mixing region is generated by multi-dimensional shock–shock interactions.

SU‐GG‐T‐354: Development and Evaluation of a Low Cost, EBT2 Film‐Based Real‐Time Dosimeter

Purpose: To develop and evaluate a low‐cost GafChromic film‐based real‐time dosimeter for practical radiation dosimetry. Method: The dosimeter employs EBT2 film chips, LEDs at 680 nm and 618 nm, a photodiode, and plastic optical fibers. Red light from the LED, modulated by sinusoidal signal, is guided with a φ=1 mm fiber toward a film chip as small as 2×2 mm2. Transmitted light is carried by another φ=0.5 or 1 mm fiber toward the photodiode. A Java program generates the sinusoidal signal, samples the photodiode signal and computes its amplitude in real time via FFT. Dose response to 6MV photon beams was characterized with a Siemens Primus linac and a Varian Novalis radiosurgery linac. Scp of the Novalis linac was measured down to 0.6×0.6 cm2 using multiple film chips. Results: The dosimeter has 16‐bit resolution with a SNR of ∼80 dB. At 680 nm, optical density responded to dose linearly at ∼10−4/cGy up to 75 Gy. At 618 nm, response was approximately 30 times greater. Response was non‐linear but easily approximated with a cubic polynomial. The accuracy of the dosimeter was estimated to be better than 2% if the film is allowed to settle for one day. The accuracy of the real‐time dosimetry is affected by the settling time the optical density takes to reach asymptotic value. The Scp, measured by the dosimeter was comparable to ion chamber and diode detectors down to sizes of 4.2×4.2 cm2, but was reduced as field size decreased, e.g. by ∼4% at 1.2×1.2 cm2. Conclusions: A real‐time, low‐cost dosimeter was developed based on radiochromic‐film at 618 nm. It can be easily implemented and conveniently used for in‐vivo dosimetry given its demonstrated accuracy. Research is supported by Department of Radiation Oncology, University of Nebraska Medical Center. GafChromic film is provided by the International Specialty Products.

Magnetohydrodynamics control of capillary Z-pinch discharge by using a triangular current pulse for lasing a H-like N recombination soft x-ray laser

In expansion cooling phase of pinched nitrogen plasma generated by fast capillary discharge, it might be possible to realize lasing a Blamer α recombination SXRL, which requires a rapid cooling of nonequilibrium plasma. It is effective to decrease the discharge current rapidly in reducing the additional heating caused by the joule heating and the magnetic compression of plasma as quickly as possible. The shaping of discharge current waveform was demonstrated with a transmission line and its effect on expanding plasma dynamics were investigated through magnetohydrodynamics (MHD) calculation, and validity of the MHD calculation in the expansion phase was shown using the discharge photographs taken by using a high speed camera. As a result, strong radiation from the H-like N ion at the maximum pinch, which is in the current decay phase of the triangular current with peak amplitude of over 70 kA and pulse width of 60 ns, has been confirmed in x-ray photodiode signals at wavelength of less than 2.5 nm, to clarify the existence of the Lyman series and continuum of the H-like N ion. Without additional heating by the discharge current after the generation of the fully stripped nitrogen ions, it might be possible to generate the population inversion between the principal quantum number n=2 and 3.

Video-speed detection of the absolute position of a light point on a large-area photodetector based on luminescent waveguides

A large-area photosensor is presented that uses the coupling of light into the planar waveguide mode of a polycarbonate foil by luminescent dyes to extend the active area of silicon photodiodes attached to the surface of the foil in a regular pattern. The photodiode signal is directly related to the distance between the point where light is coupled into the foil and the photodiode, thus enabling a precise recovery of the position of a localized light signal hitting the foil. We present a large-area device that can trace the movement of a light point generated by a laser pointer hitting its surface.

Analysis of single photon detector based on the reflection of coaxial cables

In this paper are analyzed the characteristics of the single photon detector (SPD) with using coaxial cables as reflection lines to cancel transient spikes noises, particularly,the characteristics of variations in bias voltage of the avalanche photodiode (APD) and output signal. Based on the theoretical analyses,the principle of the timing relation between single photon pulses and the two gate pluses is discussed. Also, the condition and the effect of transient spikes cancellation are achieved. And the minimal detecting period is obtained. Finally,we conduct some experiments to verify our theory. In our experiment,the noise rejection ratio is 25.1dB. The results accord with our theory satisfactorily. Our results will be helpful in designing and optimizing single photon detectors.

Fully integrated blue/UV SOI CMOS photosensor for biomedical and environmental applications

In this paper, we present a microsystem for measuring optical power in blue/UV wavelengths (from ? = 200 nm to ? = 450 nm) which includes a photodiode and the analog processing circuit of the photodiode signal, fully integrated in 2 μm SOI CMOS technology. The photodiode has a maximum responsivity for ? = 400 nm. Th photosensor functions as a current to frequency converter. Measurements of the microsystem illuminated by blue and UV LEDs demonstrate the good linear behavior, sensitivity and efficiency of the system.

Three-Dimensional Magnetic Field Measurements in a Single SERF Atomic-Magnetometer Cell

We show that a single-cell spin-exchange relaxation-free (SERF) atomic magnetometer can be used for 3-D field measurements. The 3-D operation is achieved by optically pumping the magnetometer cell in successive layers perpendicular to the laser probe beam and by collecting the signals with a photodiode array. The vapor cell is thus divided into voxels acting as local atomic magnetometers. Each voxel's contribution to the probe linear polarization rotation is proportional to the convolution of the local polarization and the magnetic field. The layers are pumped in sequence without waiting for the atomic polarization in the previously pumped layer to relax to zero, consequently, reducing the total measurement time. The photodiode signals are the sum of accumulated linear polarization rotation caused by all the layers. These signals are processed by a deconvolution algorithm that extracts the information originating from each individual voxel. Our theoretical analysis and experimental results show that the time of a single-layer pumping can be reduced below the atomic-cell relaxation time constant, with almost no loss of precision.

Real-time data processing and magnetic field pitch angle estimation of the JET motional Stark effect diagnostic based on Kalman filtering

A novel technique for the real-time measurement of the magnetic field pitch angle in JET discharges using the motional Stark effect diagnostic is presented. Kalman filtering techniques are adopted to estimate the amplitude of the avalanche photodiode signals' harmonics that are relevant for the pitch angle calculation. The proposed technique {for extended technical details of the generic algorithm see [R. Coelho and D. Alves, IEEE Trans. Plasma Sci. 37, 164 (2009)]} is shown to be much more robust and provides less noisy estimates than an equivalent lock-in amplifier scheme, in particular when dealing with edge localized modes.

Fabrication and performance characteristics of a CsI(Tl)/PIN diode radiation sensor for industrial applications

CsI(Tl)/PIN diode radiation sensors were fabricated for application in various fields such as an NDT and an environmental radiation monitoring system. CsI(Tl) crystals of 11×11×21 mm 3 were processed as optical grade from a CsI(Tl) ingot and matched with PIN diodes in consideration of the light loss and the external impact. The photodiode signal is amplified by a low-noise preamplifier and a pulse shape amplifier. At room temperature, the fabricated CsI(Tl)/PIN diode radiation sensors demonstrate an energy resolution of 7.9% for 660 keV gamma rays and 4.9% for 1330 keV. The fluctuation of the directional dependency was below 14% from 0 to 90 degree for the incident 660 keV gamma rays. The compactness, the low-voltage power supply and the physical hardness are very useful features for industrial applications of the fabricated CsI(Tl)/PIN diode sensor.

넓은 동적 범위를 가지는 CMOS Image Sensors OFD(Over Flow Drain) 픽셀 설계

We propose a new image pixel architecture which has OFD(Over Flow Device) node by improving conventional 3TR pixel structure. Newly designed pixel consists of photo diode which is verified with HSPICE simulation, PMOS reset transistor, several NMOS and several PMOS transistors. Photodiode signals from each PMOS and NMOS are detected by Reset PMOS. These output signals give enough chances to detect wide operation coverage because OFD node has overflow photocurrent. According to various light intensity, we analyzed characteristic of the output voltage with a SPICE tool. Proposed pixel output has specific value which can detect possible from <TEX>$0.1{\mu}W/cm^2$</TEX> to <TEX>$10W/cm^2$</TEX> light intensity. It has wide-dynamic range of 160 dB.

System modelling of a lateral force microscope

To quantitatively analyse lateral force microscope measurements one needs to develop amodel able to relate the photodiode signal to the force acting on the tip apex. In this paperwe focus on the modelling of the interaction between the cantilever and the optical chain.The laser beam is discretized by a set of rays which propagates in the system. Theanalytical equation of a single ray’s position on the optical sensor is presented as afunction of the reflection’s state on top of the cantilever. We use a finite elementanalysis on the cantilever to connect the optical model with the force acting on thetip apex. A first-order approximation of the constitutive equations are derivedalong with a definition of the system’s crosstalk. Finally, the model is used toanalytically simulate the ‘wedge method’ in the presence of crosstalk in 2D. Theanalysis shows how the torsion loop and torsion offset signals are affected by thecrosstalk.

Plasma jet acceleration of dust particles to hypervelocities

A convenient method to accelerate simultaneously hundreds of micron-size dust particles to a few km/s over a distance of about 1m is based on plasma drag. Plasma jets which can deliver sufficient momentum to the dust particles need to have speeds of at least several tens of km/s, densities of the order of 1022m−3 or higher, and low temperature ∼1eV, in order to prevent dust destruction. An experimental demonstration of dust particles acceleration to hypervelocities by plasma produced in a coaxial gun is presented here. The plasma flow speed is deduced from photodiode signals while the plasma density is measured by streaked spectroscopy. As a result of the interaction with the plasma jet, the dust grains are also heated to high temperatures and emit visible light. A hypervelocity dust shower is imaged in situ with a high speed video camera at some distance from the coaxial gun, where light emission from the plasma flow is less intense. The bright traces of the flying microparticles are used to infer their speed and acceleration by employing the time-of-flight technique. A simple model for plasma drag which accounts for ion collection on the grain surface gives predictions for dust accelerations which are in good agreement with the experimental observations.

Signal and noise performance of large-area PIN photodiodes and charge-sensitive preamplifiers for gamma radiography

Using 5 cm long CsI (Tl) crystal scintillators, large-area PIN-type photodiodes of 1 cm×1 cm, and a low-noise charge-sensitive preamplifier, two gamma-ray detectors were manufactured. One detector used PIN-type photodiodes fabricated in the process of Electronics and Telecommunications Research Institute (ETRI) and the other one was based on Hamamatsu PIN-type photodiodes of S-3590-01. Gamma spectroscopies were performed and analyzed for both Co-60 and Cs-137 gamma sources. The first detector showed energy resolutions (FWHM) of 6.4% and 5.5% for 1.17 and 1.33 MeV, which were similar to energy resolutions of the second detector for Co-60, but the second detector showed 6.6% better resolution than the first detector's 11.8% for Cs-137. For 10 h exposure of Co-60 (14.5 μCi), noise equivalent quanta (NEQ) and spectroscopy for both detectors have been investigated in detail. The NEQ of 25% increased after the exposure and degradations of the FWHMs of 26% and 11% have been found for 1.17 and 1.33 MeV, respectively.

Calibration of lateral force measurements in atomic force microscopy with a piezoresistive force sensor

We present here a method to calibrate the lateral force in the atomic force microscope. This method makes use of an accurately calibrated force sensor composed of a tipless piezoresistive cantilever and corresponding signal amplifying and processing electronics. Two ways of force loading with different loading points were compared by scanning the top and side edges of the piezoresistive cantilever. Conversion factors between the lateral force and photodiode signal using three types of atomic force microscope cantilevers with rectangular geometries (normal spring constants from 0.092 to 1.24 N/m and lateral stiffness from 10.34 to 101.06 N/m) were measured in experiments using the proposed method. When used properly, this method calibrates the conversion factors that are accurate to +/-12.4% or better. This standard has less error than the commonly used method based on the cantilever's beam mechanics. Methods such of this allow accurate and direct conversion between lateral forces and photodiode signals without any knowledge of the cantilevers and the laser measuring system.

Acoustic and Optical Monitoring of High-Power CO&lt;sub&gt;2 &lt;/sub&gt; Laser Cutting

In this paper, the development of a monitoring system for high-power CO2 laser cutting of thick steel plates (&gt;15 mm) is reported. The aim of this system is to increase the robustness and autonomy of the laser cutting process of thick plates, which is still characterized by more narrow process windows compared to cutting of thin sheets. The applicability for monitoring purposes of two types of sensors is investigated: the acoustic microphone and the photodiode. For both types, correlation between the sensor output and the cut quality is investigated. Both contour cutting and piercing are covered in the study. The full penetration of the piercing can be monitored by both sensors. Furthermore quantitative relations between cut quality parameters and photodiode signal parameters could be determined: the mean level of the photodiode signal correlates well with the drag of the striations and dross formation, whereas the standard deviation proves to correlate well with the occurrence of burning defects and the cut edge roughness.

Easy and direct method for calibrating atomic force microscopy lateral force measurements.

We have designed and tested a new, inexpensive, easy-to-make and easy-to-use calibration standard for atomic force microscopy (AFM) lateral force measurements. This new standard simply consists of a small glass fiber of known dimensions and Young's modulus, which is fixed at one end to a substrate and which can be bent laterally with the AFM tip at the other end. This standard has equal or less error than the commonly used method of using beam mechanics to determine a cantilever's lateral force constant. It is transferable, thus providing a universal tool for comparing the calibrations of different instruments. It does not require knowledge of the cantilever dimensions and composition or its tip height. This standard also allows direct conversion of the photodiode signal to force and, thus, circumvents the requirement for a sensor response (sensitivity) measurement.

Fluorometric Measurements of Intermolecular Distances between the α- and β-Subunits of the Na+/K+-ATPase

The Na+/K+-ATPase maintains the physiological Na+ and K+ gradients across the plasma membrane in most animal cells. The functional unit of the ion pump is comprised of two mandatory subunits including the alpha-subunit, which mediates ATP hydrolysis and ion translocation, as well as the beta-subunit, which acts as a chaperone to promote proper membrane insertion and trafficking in the plasma membrane. To examine the conformational dynamics between the alpha- and beta-subunits of the Na+/K+-ATPase during ion transport, we have used fluorescence resonance energy transfer, under voltage clamp conditions on Xenopus laevis oocytes, to differentiate between two models that have been proposed for the relative orientation of the alpha- and beta-subunits. These experiments were performed by measuring the time constant of irreversible donor fluorophore destruction with fluorescein-5-maleimide as the donor fluorophore and in the presence or absence of tetramethylrhodamine-6-maleimide as the acceptor fluorophore following labeling on the M3-M4 or M5-M6 loop of the alpha-subunit and the beta-subunit. We have also used fluorescence resonance energy transfer to investigate the relative movement between the two subunits as the ion pump shuttles between the two main conformational states (E1 and E2) as described by the Albers-Post scheme. The results from this study have identified a model for the orientation of the beta-subunit in relation to the alpha-subunit and suggest that the alpha- and beta-subunits move toward each other during the E2 to E1 conformational transition.

New technique for studying nanoscale friction at sliding velocities up to 200mm∕s using atomic force microscope

Micro-/nanoelectromechanical devices and components operate at high sliding velocities. Studies of tribological properties of materials by atomic force microscope (AFM) are limited to low velocity regime (&amp;lt;100–250μm∕s) due to inherent instrument limitation of AFM. To overcome the limitation of AFM working velocity, a custom-calibrated ultrahigh velocity stage has been incorporated for tribological investigation up to 200mm∕s. The stage is driven by a piezoactuator which is controlled using proportional-integral-derivative algorithm. Friction data are obtained by processing the AFM laser photodiode signals using a high sampling rate data acquisition system. The friction data obtained from the modified setup at high sliding velocities are compared with the results from conventional AFM friction measurement. The effects of scan size, rest time, and velocity on the friction force and adhesive force for single crystal silicon (100) with native oxide have been studied.