Multiple Photodiodes Research Articles

Indoor Positioning for Multiphotodiode Device Using Visible-Light Communications

With the widespread use of light-emitting diodes (LEDs) for lighting, their ability to support communications through visible light has become promising for various wireless applications. In particular, visible-light communication (VLC) assisted indoor positioning enjoys its unique advantage of electromagnetic interference immunity and high accuracy. Instead of directly extending conventional wireless positioning using radio-frequency equipment, we consider the indoor positioning specified for a popular VLC scenario where the target device has multiple photodiodes (PDs) while having no help from other fixed receiving nodes with known coordinates. A general framework is presented for multi-PD device positioning by exploiting relative positions, as well as the received signal strength indications, of the multiple PDs. Moreover, the feasible condition for realizing effective positioning is also presented. Finally, we validate the accuracy of the proposed method via numerical tests.

Experimental Demonstration of VLC-Based Vehicle-to-Vehicle Communications Under Fog Conditions

Vehicle-to-vehicle (V2V) communication using visible light communication (VLC) technology under fog conditions is presented. Fog is known as one of the most detrimental atmospheric conditions that causes outdoor optical wireless communications to be unreliable. The effect of the fog conditions is experimentally analyzed in the VLC-based V2V system. Recognizing the least attenuation coefficient and a taillight color of a vehicle, a red light-emitting diode (LED) was employed in the experiment. In addition, a Fresnel lens and multiple photodiodes are utilized to efficiently counteract the impairment caused by fog. The experimental results demonstrate that the proposed VLC-based V2V system offers a reliable V2V data transmission over the fog-impaired optical channel with a relatively high signal-to-noise ratio (SNR), even under a heavy-fog condition.

Reconstruction of Axisymmetric Temperature and Gas Concentration Distributions by Combining Fan-Beam TDLAS With Onion-Peeling Deconvolution

Fan-beam tunable diode laser absorption spectroscopy (TDLAS) system was combined with onion-peeling deconvolution to reconstruct axisymmetric temperature and gas concentration distributions. The fan-beam TDLAS system consists of two tunable distributed feedback diode lasers at 7185.597 and 7444.36 cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> , a cylindrical lens and multiple photodiode detectors in a linear detector array. When a well-collimated laser beam penetrates through a cylindrical lens, a fan-beam laser was formed. Then, the fan-beam laser penetrates through the target region and is detected by the photodiode detectors in the detector array. After transforming the fan-beam geometry to equivalent parallel-beam geometry, axisymmetric temperature and gas concentration distributions can be reconstructed using the onion-peeling deconvolution. To obtain the reconstruction results with higher accuracy, a revised Tikhonov regularization method was adopted in the onion-peeling deconvolution. In this paper, numerical simulation and experimental verification were carried out to validate the feasibility of the proposed methods. The results show that the proposed methods can be used to on-line monitor the axisymmetric temperature and gas concentration distributions with higher accuracy and robustness in combustion diagnosis.

High Power Photodiodes for Microwave Applications

High Power Photodiodes for Microwave Applications

InSb Mid-Infrared Photon Detector for Room-Temperature Operation

We developed a small InSb mid-infrared (2–7 µm wavelength range) photon detector that operates at room temperature. The photodiode was made from (hetero epitaxial) InSb layers that were grown on a semi-insulating GaAs substrate by molecular beam epitaxy. To suppress the effects of the diffusion current of the p–i–n photodiode, we used an AlInSb barrier layer that raises the resistance of the photodiode. We also optimized the device's doping concentration and the infrared incidence window structure. These optimization steps realized high photoelectric current output in a room-temperature environment. We also increased the signal-to-noise ratio of the detector by connecting multiple photodiodes in series. The size of this detector is 1.9×2.7×0.4 mm3 and the detectivity is 2.8×108 cm Hz1/2/W at 300 K. This is a practical IR detector that can be used in general signal amplification ICs.

Wearable PPG Sensor Matrix for Cardiovascular Assessment

Wearable biomonitoring systems and smart textiles for healthcare are gaining more importance and significance in the R&amp;D sphere due to their potentials in healthcare and sports. Such biomonitoring systems offer a number of advantages in comparison to the conventional equipment proving mobility of the wearer during a long-term monitoring of vital parameters. There are different options to set up the physiological monitoring using wireless and wearable technologies. One of the scenarios is addressing textiles as a carrier of electronics. Moreover, those differ by their functional applications, registered physiological parameters and technology solutions. Still, the most demanded biomonitoring smart systems focus on the examination of cardiovascular conditions due to the urgency of the problem in the public health. Furthermore, cardiovascular and haemodynamic parameters are initial physiologic criteria in sports physiology and in individual training. The common method for cardiovascular assessment is registration of heart electric potentials. Nevertheless, this research addresses photoplethmography (PPG) as an optional approach to acquire the information on cardiovascular and hemodynamic activity. The aim of the study is to develop a textile integrated optical sensor matrix for telemetric cardiovascular assessment. Two reflectance sensors with single and multiple photodiodes (PDs) based on a novel signal conversion were designed and adopted to textiles. Designed prototypes were evaluated for their technical parameters and biomonitoring performance in rest conditions. The acquired physiological data was analyzed by the custom developed software and compared to the reference data obtained by the medical ECG monitor. Overall, the textile adopted wearable systems with both types of PPG sensors have demonstrated high signal accuracy and potentials for wearable applications.

Feasibility study of a current mode gamma radiation dosimeter based on a commercial pin photodiode and a custom made auto-ranging electrometer

An experimental study has been conducted to evaluate the feasibility of a current mode gamma radiation dosimeter, consisting of a commercial PIN photodiode as a radiation sensor, and a custom made auto-ranging electrometer for real-time measurement of the PIN photodiode?s response under radiation exposure. The radiation induced direct current response for single PIN photodiodes with different active areas, as well as for multiple PIN photodiodes connected in parallel, has been investigated. Three types of commercial silicon PIN photodiodes have been chosen for evaluation - S1223, BPW34, and PS100-6-CER2 PIN. During the experiment, five samples have been tested - three samples made of single PIN photodiodes (one sample of each photodiode type) and two samples formed by connecting multiple photodiodes in parallel (two BPW34 photodiodes in parallel and four BPW34 photodiodes in parallel). The samples have been irradiated with a 60Co gamma ray source and the relations between the induced photocurrent and the dose rate, and between the accumulated charge and the absorbed dose, have been determined. For measuring the photodiodes response, a custom made auto-ranging electrometer controlled by a personal computer, and capable of measuring direct currents from 50 pA to 10 mA with relative error less than 2.5%, has been used. Obtained results have shown very good linearity between the dose rate and the induced photocurrent for dose rates ranging from 0.93 Gy/h to 67 Gy/h. Also, very good linearity has been observed between the accumulated charge and the absorbed dose for all tested samples, within the investigated range of absorbed doses from 472 mGy to 3.3 Gy. On the basis of the obtained results, a simple model has been derived, enabling the estimation of the photodiode?s current response as a function of the dose rate and the photodiode?s geometry (active area and depletion layer width).

Intelligent sun-tracking system based on multiple photodiode sensors for maximisation of photovoltaic energy production

To maximise the energy collected by a given photovoltaic system (PVS), it is important to track the position of the sun so that the PV panels are exposed to the maximum global radiation at any given time. Thus, it is useful to determine the direction of the maximum global radiation, which does not correspond with the condition of orthogonality between the plane of the array and the beam component of the solar radiation. Thus, it is worthwhile to investigate a low-cost solar radiation sensing system that can determine this direction. The proposed system consists of a structure of nine photodiodes (FDs); a suitable analysis of the output signals calculates the azimuth and solar height angles, which are related to the direction of maximum solar irradiance. This paper reports the development of hardware (HW) and software (SW) for a prototype system, which is called SoliSector. Outdoor experimental results regarding testing and calibration of the proposed system are also reported.

Watching single lipids move

Multiple photodiode detectors are used to track the transit of dye-labeled single lipids through an excitation spot at high resolution.

Photo-battery fabricated in silicon on sapphire CMOS

A report is presented on the design and characterisation of an energy harvesting circuit fabricated in silicon on sapphire CMOS technology. The insulating sapphire substrate permits the connection of multiple photodiodes in series to obtain a higher output voltage, and its optical transparency allows for backside illumination. The conversion efficiency of the photo-battery is measured at greater than 1% for wavelengths ranging from infrared to ultraviolet. An active silicon area of 1 cm 2 at 50001x ambient illumination yields approximately 60 muW of power.

Comparisons Of Single And Multi-probe Near Infrared Spectroscopy Signals During Progressive Treadmill Exercise

Over the past few years, near infrared spectroscopy (NIRS) has become a popular technique for the non-invasive determination of local oxygen saturation and blood flow in human skeletal muscle. PURPOSE The purpose of this study was to determine if any differences exist between two NIRS systems using different methods of signal sampling during progressive treadmill exercise. The Inspectra model 325 tissue spectrometer (Hutchinson Technology Inc.) measures a scaled single depth second derivative optical attenuation value which is empirically calibrated to percent hemoglobin oxygen saturation, thereby estimating percent tissue oxygen saturation (%StO2). The NIRO-300 oxygenation monitor (Hamamatsu) spatially resolves light attenuation at multiple photodiode segments (multiple send to receiver distances) to monitor the attenuation slope and thus determine a tissue oxygen index (TOI) from a light transport theoretical equation. METHODS 10 healthy subjects (age=24±1 yrs) exercised on treadmill to voluntary fatigue. Resting data were recorded for 3 min supine and 3 min sitting prior to exercise. At the completion of exercise 5 min recovery data were also recorded. %StO2 and TOI were measured continuously. Arterial saturation (%SpO2 from the finger), along with HR and RPE was also measured at the end of each stage. RESULTS As expected, HR and RPE increased with progressive stages of exercise, while measures of %SpO2 did not change throughout the test. Reviewing only a few seconds of data from each system, we saw greater fluctuation in TOI (+5%), perhaps reflecting subtle variations in muscle blood flow, where StO2 values were more stable (+1%), perhaps due to conditioning of the signal. When reviewing changes throughout an entire graded TM test, TOI had a small range from rest to maximal exercise (∼20%). StO2 values were more robust (∼60%) perhaps reflecting more accurate changes in oxygen saturation in working muscle. Both %StO2 and TOI had a significant relationship with HR, RPE and estimated oxygen consumption (rs>0.8). CONCLUSION The NIRO-300 (TOI) may provide subtle changes in tissue oxygen saturation, but the Inspectra (%StO2) may be more sensitive to overall changes in oxygen saturation than the NIRO-300. In either case, there is a strong relationship in metabolic parameters and NIRS data from both systems.

Car window antitrapping optical fiber system based on a fiber speckle pattern

A car window antitrapping optical fiber system based on a speckle pattern from a multimode fiber installed in the window frame is proposed and demonstrated. The speckle pattern change is measured by an array of photodiodes whose output signal data are processed by computer through an analog-to-digital (A/D) converter to control the window motor. Experimental results show that the proposed system with multiple photodiodes, along with an appropriate processing algorithm, runs well. The processing algorithm is also presented.

Force spectroscopy with a large dynamic range using small cantilevers and an array detector

The important characteristics of a detector for force spectroscopy measurements are sensitivity, linearity and dynamic range. The commonly used two-segment detector that measures the position of a light beam reflected from the force-sensing cantilever in an atomic force microscope becomes nonlinear when the beam shifts significantly onto one of the segments. For a detection setup optimized for high sensitivity, such as needed for the use with small cantilevers, it is shown both experimentally and theoretically that the dynamic range extends to an upper detection limit of only about 115 nm in cantilever deflection if &amp;lt;10% nonlinearity is required. A detector is presented that circumvents that limitation. This detector is based on a linear arrangement of multiple photodiode segments that are read out individually. With such an array detector, the irradiance distribution of the reflected beam is measured. The reflected beam not only shifts in position but also deforms when the cantilever deflects because the bent cantilever acts as a curved mirror. The mean of the distribution, however, is a linear function of cantilever deflection in both theory and experiment. An array detector is consequently well suited for force measurements for which both high sensitivity and a large dynamic range are required.

Design of an Inertial Fusion Energy Target Tracking and Position Prediction System

Driver beams must hit targets accurately in an inertial fusion energy power plant. Current requirements are less than ±200 μm for indirect drive targets and ±20 μm for direct drive targets. A recent target tracking and position prediction experiment was carried out using indirect drive target sized projectiles.1 The results of that scaled experiment extrapolate to a standard deviation of 220 μm error in position prediction at power plant size. Greater accuracy will be required, especially for direct drive targets. Greater standoff between the detectors and the targets (previously about 3 cm) will also be required to allow for detector shielding. Diffraction effects are expected to be more important with greater standoff and accuracy requirements.An improved optical target tracking and position prediction system is being designed, as part of the Target Injection and Tracking Experiment at General Atomics, to achieve the above requirements. Concepts for improving accuracy include the use of multiple photodiode arrays, a temperature controlled environment, vibration-limiting detector mounts, additional detector stations, improved electronic noise suppression, and constant-brightness laser light sources. The current status of this design work is presented.

Silicon photodiode for optical channel waveguides

An etched mesa silicon photodiode suitable for detecting light propagating in optical channel waveguides has been fabricated. The diode width of 7 μm was slightly less than that of the channel waveguide, thus minimizing junction capacitance and the effect of detection noise caused by unguided substrate light. The fabrication technique can be applied to produce on a single Si wafer multiple photodiodes electrically isolated from each other. Optical energy was coupled from (out-diffused)LiNbO3 channel waveguides into the photodiodes by means of evanescent field coupling.