Silicon Photodiode Array Research Articles

Feline eye-inspired artificial vision for enhanced camouflage breaking under diverse light conditions.

Biologically inspired artificial vision research has led to innovative robotic vision systems with low optical aberration, wide field of view, and compact form factor. However, challenges persist in object detection and recognition against complex backgrounds and varied lighting. Inspired by the feline eye, which features a vertically elongated pupil and tapetum lucidum, this study introduces an artificial vision system designed for superior object detection and recognition in a monocular framework. Using a slit-like elliptical aperture and a patterned metal reflector beneath a hemispherical silicon photodiode array, the system reduces excessive light and enhances photosensitivity. This design achieves clear focus under bright light and enhanced sensitivity in dim conditions. Theoretical and experimental analyses demonstrate the system's ability to filter redundant information and detect camouflaged objects in diverse lighting, representing a substantial advancement in monocular camera technology and the potential of biomimicry in optical innovations.

Portable multichannel detection instrument based on time-resolved fluorescence immunochromatographic test strip for on-site detecting pesticide residues in vegetables

In this work, a portable multichannel detection instrument based on time-resolved fluorescence immunochromatographic test strip (TRFIS) was proposed for on-site detecting pesticide residues in vegetables. Its hardware consisted of a silicon photodiode and excitation light source array, a mainboard of the lower machine with STMicroelectronics 32 (STM32) and a linear stepping motor. While detecting, cardboard with 6-channel TRFIS was pulled into the cassette by the stepping motor. The peak area of the test (T) line and control (C) line of each TRFIS was sampled and calculated by software, then the concentration of the detected pesticide was obtained according to the ratio of the T to C value. This instrument could sample 6-channel TRFIS within 30 s simultaneously, and it exhibited excellent accuracy with a 2.5% average coefficient of variation for each channel (n = 12). In addition, the TRFIS was constructed by using europium oxide time-resolved fluorescent microspheres to label the monoclonal antibody against acetamiprid and form a fluorescent probe, which was fixed on the binding pad. The TRFIS was used for the detection of acetamiprid in celery cabbage, cauliflower and baby cabbage. This instrument was used to complete the qualitative and quantitative analysis of the TRFIS, so as to enhance the practical application of the detection method. This TRFIS possessed excellent linearity ranging from 0.25 mg kg−1 to 1.75 mg kg−1 for the detection of acetamiprid, and the limit of detection were 0.056–0.074 mg kg−1 in the different vegetable matrix. The platform combines the accuracy and portability of traditional test strips with the highly sensitive and efficient fluorescence intensity recognition function of detection equipment, which shows a great application prospect of multi-channel rapid detection of small molecule pollutants in the field.

Digital colorimetric sensing for real‐time gas monitoring for smart green energy system

AbstractIn this study, we demonstrate that a digital colorimetric sensor platform can transform a conventional energy system, such as gas‐insulated switchgear (GIS) into a smart green energy system. Our sensor platform consists of a colorimetric sensor film (CSF), an array of silicon photodiodes, and a low‐power‐driven fiber optical photodiode with a wireless communication protocol integrated into an information network. The photodiode measures the transmitted light of the color‐variable CSF when exposed to sulfur dioxide (SO2) gas, a decomposition by‐product of the sulfur hexafluoride (SF6) gas in GIS. We report the electrical photocurrent measurement through the CSF can measure the concentration of SO2 gas via remote and real‐time monitoring and shows a comparable behavior to UV–Vis absorption measurement. The limit of detection of the sensor, 0.78 ppm is sufficient to analyze the GIS insulation deterioration allowing green energy systems.image

Cuttlefish eye-inspired artificial vision for high-quality imaging under uneven illumination conditions.

With the rise of mobile robotics, including self-driving automobiles and drones, developing artificial vision for high-contrast and high-acuity imaging in vertically uneven illumination conditions has become an important goal. In such situations, balancing uneven illumination, improving image contrast for facile object detection, and achieving high visual acuity in the main visual fields are key requirements. Meanwhile, in nature, cuttlefish (genus Sepia) have evolved an eye optimized for vertically uneven illumination conditions, which consists of a W-shaped pupil, a single spherical lens, and a curved retina with a high-density photoreceptor arrangement and polarized light sensitivity. Here, inspired by the cuttlefish eye, we report an artificial vision system consisting of a W-shaped pupil, a single ball lens, a surface-integrated flexible polarizer, and a cylindrical silicon photodiode array with a locally densified pixel arrangement. The W-shaped pupil integrated on the ball lens balances vertically uneven illumination, and the cylindrical silicon photodiode array integrated with the flexible polarizer enables high-contrast and high-acuity imaging.

In-sensor optoelectronic computing using electrostatically doped silicon

Complementary metal–oxide–semiconductor (CMOS) image sensors allow machines to interact with the visual world. In these sensors, image capture in front-end silicon photodiode arrays is separated from back-end image processing. To reduce the energy cost associated with transferring data between the sensing and computing units, in-sensor computing approaches are being developed where images are processed within the photodiode arrays. However, such methods require electrostatically doped photodiodes where photocurrents can be electrically modulated or programmed, and this is challenging in current CMOS image sensors that use chemically doped silicon photodiodes. Here we report in-sensor computing using electrostatically doped silicon photodiodes. We fabricate thousands of dual-gate silicon p–i–n photodiodes, which can be integrated into CMOS image sensors, at the wafer scale. With a 3 × 3 network of the electrostatically doped photodiodes, we demonstrate in-sensor image processing using seven different convolutional filters electrically programmed into the photodiode network. A network of dual-gate silicon p–i–n photodiodes, which are compatible with complementary metal–oxide–semiconductor fabrication processes, can perform in-sensor image processing by being electrically programmed into convolutional filters.

A time-resolved imaging system for the diagnosis of x-ray self-emission in high energy density physics experiments.

A diagnostic capable of recording spatially and temporally resolved x-ray self-emission data was developed to characterize experiments on the MAGPIE pulsed-power generator. The diagnostic used two separate imaging systems: a pinhole imaging system with two-dimensional spatial resolution and a slit imaging system with one-dimensional spatial resolution. The two-dimensional imaging system imaged light onto the image plate. The one-dimensional imaging system imaged light onto the same piece of image plate and a linear array of silicon photodiodes. This designallowed the cross-comparison of different images, allowing a picture of the spatial and temporal distribution of x-ray self-emission to be established. The designwas tested in a series of pulsed-power-driven magnetic-reconnection experiments.

Effect of irradiation of silicon photodiode arrays for ITER radial x-ray camera investigated by measuring response and current-voltage characteristics.

The response and current-voltage (I-V) characteristics of irradiated and non-irradiated silicon photodiode arrays (SPDAs) for use in the International Thermonuclear Experimental Reactor camera are measured and compared. Irradiation experiments are carried out using a uranium-zirconium hydride pulsed reactor. The total equivalent 1MeV neutron fluence with energy above 0.01MeV is ∼9.89 × 1013ncm-2. The output signal of the irradiated SPDA (XD2) shows a nonlinear trend during the irradiation experiment. The final signal is about 5.6% of the original one in the visible light region. Tests on the Experimental Advanced Superconducting Tokamak (EAST) show that the XD2 signal is 70%-80% of that of a non-irradiated SPDA (XD3). This indicates that irradiated SPDAs can still observe plasma radiation after exposure to 9.89 × 1013ncm-2 neutron fluence. However, because the neutron fluence of external camera detectors will reach 1.4 × 1016ncm-2 in D-T phase, the SPDAs might become unusable at some point. The responsivity ratio of irradiated and non-irradiated SPDAs is about 4%-20% from 7 to 13 keV. The degradation of responsivity is related to the energy level. After irradiation, the reversed dark current rises from 0.1 to 10 nA to a level of around 1 µA. In terms of tests of XD2 on EAST, zero bias is a good working condition for irradiated SPDAs.

Vertical-junction photodiodes for smaller pixels in retinal prostheses

Objective. To restore central vision in patients with atrophic age-related macular degeneration, we replace the lost photoreceptors with photovoltaic pixels, which convert light into current and stimulate the secondary retinal neurons. Clinical trials demonstrated prosthetic acuity closely matching the sampling limit of the 100 μm pixels, and hence smaller pixels are required for improving visual acuity. However, with smaller flat bipolar pixels, the electric field penetration depth and the photodiode responsivity significantly decrease, making the device inefficient. Smaller pixels may be enabled by (a) increasing the diode responsivity using vertical p–n junctions and (b) directing the electric field in tissue vertically. Here, we demonstrate such novel photodiodes and test the retinal stimulation in a vertical electric field. Approach. Arrays of silicon photodiodes of 55, 40, 30, and 20 μm in width, with vertical p–n junctions, were fabricated. The electric field in the retina was directed vertically using a common return electrode at the edge of the device. Optical and electronic performance of the diodes was characterized in-vitro, and retinal stimulation threshold measured by recording the visually evoked potentials in rats with retinal degeneration. Main results. The photodiodes exhibited sufficiently low dark current (<10 pA) and responsivity at 880 nm wavelength as high as 0.51 A W−1, with 85% internal quantum efficiency, independent of pixel size. Field mapping in saline demonstrated uniformity of the pixel performance in the array. The full-field stimulation threshold was as low as 0.057 mW mm−2 with 10 ms pulses, independent of pixel size. Significance. Photodiodes with vertical p–n junctions demonstrated excellent charge collection efficiency independent of pixel size, down to 20 μm. Vertically oriented electric field provides a stimulation threshold that is independent of pixel size. These results are the first steps in validation of scaling down the photovoltaic pixels for subretinal stimulation.

Soft x-ray tomography measurements in the Wendelstein 7-X stellarator

The soft x-ray tomography diagnostic in the stellarator Wendelstein 7-X consists of twenty pinhole cameras, up–down symmetrically arranged in a poloidal, triangular cross-section of the plasma vessel. The x-ray emissivity is measured with 16 bit amplitude resolution at 2 MHz sampling rate along 360 lines-of-sight by silicon photodiode arrays. In the recent operation campaign data acquisition (DAQ) has been working reliable for the conducted plasma pulse lengths <1 min, however the DAQ system are ready for the foreseen 30 min plasma pulse lengths of upcoming campaigns. The bandwidth of the preamplifiers is ≈200 kHz and the sensitive energy range is approximately 1–12 keV. The measurements indicate the up–down symmetric emissivity distribution in the triangular poloidal cross-section. First tomographic reconstructions of different magnetic field configurations are consistent with the theoretically calculated flux surface topology.

Evaluating Low-Cost Optical Spectrometers for the Detection of Simulated Substandard and Falsified Medicines.

Distribution of substandard and falsified (SF) medicines is on the rise, and its impact on public health, particularly in low-resource countries, is becoming increasingly significant. Portable, nondestructive screening devices can support regulatory authorities in their defense against the spread of SF medicines. Vibrational spectroscopy is an ideal candidate due to its sampling ease and speed. In this work, five portable, among which four are considered low-cost, spectroscopic devices based on near-infrared (NIR), Raman, and mid-infrared (MIR) were evaluated to quantify active pharmaceutical ingredients (APIs) and formulation accuracy within simulated authentic, falsified, and substandard medicines. Binary sample mixtures containing a typical API in antimalarial, antiretroviral, or anti-tuberculosis medicines were assessed. In both univariate and multivariate analyses, the API quantification performance of the digital light processing (DLP) NIR spectrometer and a handheld Raman device consistently matched or exceeded that of the other NIR spectrometers and a scientific grade MIR spectrometer. In the formulation accuracy tests, data from all devices, other than the silicon photodiode array NIR spectrometer, were able to create regression models with less than 6% error. From this exploratory study, we conclude that certain portable NIR devices hold significant promise as cost-effective screening tools for falsified and potentially substandard medicines, and they warrant further investigation and development.

Neutronic analysis of ITER radial x-ray camera

The radial x-ray camera (RXC) is designed to measure the poloidal profile of plasma x-ray emission with high spatial and temporal resolution. The RXC diagnostic system consists of internal camera module and external camera module that view the core region and outer region through the vertical slots of the diagnostic first wall and diagnostics shield module of the equatorial port plug. To ensure the normal performance of the silicon photodiode array detectors of the cameras in the hard neutron irradiation environment in ITER tokamak, it is necessary to calculate neutron flux, radiation damage and the nuclear heating of the silicon photodiode array detectors and simulate the radiation maps of the range of RXC. This work estimated the nuclear environment of RXC based on Monte Carlo N-particle transport code, plasma scenarios of ITER tokamak and the RXC-integrated ITER CLITE model. The neutron flux of silicon photodiode array detectors and the lifetime of the silicon photodiode detector in the camera were calculated. The neutronic analysis results show that the shielding design has achieved the effect as expected and is able to guarantee the normal work of the detector during the ITER deuterium–deuterium phase without replacement, three detectors of the external camera can be operated during the whole deuterium–tritium phase without replacement.

PO548 A Prospective Sports Cardiology Registry of Athletes In Singapore

The Cosmic Ray Energetics and Mass (CREAM) experiment at the International Space Station (ISS) aims to elucidate the source and acceleration mechanisms of high-energy cosmic rays by measuring the energy spectra from protons to iron. The instrument is planned for launch in 2015 at the ISS, and it comprises a silicon charge detector, a carbon target, top and bottom counting detectors, a calorimeter, and a boronated scintillator detector. The top and bottom counting detectors are developed for separating the electrons from the protons, and each of them comprises a plastic scintillator and a 20×20 silicon photodiode array. Each photodiode is 2.3 cm×2.3 cm in size and exhibits good electrical characteristics. The leakage current is measured to be less than 20 nA/cm2 at an operating voltage. The signal-to-noise ratio is measured to be better than 70 using commercial electronics, and the radiation hardness is tested using a proton beam. A signal from the photodiode is amplified by VLSI (very-large-scale integration) charge amp/hold circuits, the VA-TA viking chip. Environmental tests are performed using whole assembled photodiode detectors of a flight version. Herein, we present the characteristics of the developed photodiode along with the results of the environmental tests.

Transparent Ceramic Garnet Gamma-Ray Spectrometer With Directionality

We have developed a handheld $\gamma $ -ray spectrometer based on 1024 pixels, $2.8\,\,\text {mm} \times 2.8\,\,\text {mm} \times 6$ mm in size, of gadolinium–yttrium–gallium–aluminum garnet (GYGAG) ((Gd,Y,Ce)3(Ga,Al)5O12) ceramic scintillator (total of 48-cm3 detector volume) coupled to silicon photodiode (SiPD) arrays. The SiPD arrays and readout ASIC, originally developed for medical imaging applications, have been adapted for portability in a lightweight box with heatsink and thermoelectric cooling. Custom readout firmware for $\gamma $ -ray spectroscopy has been implemented, and a system user interface was developed that runs on an Android tablet. We have optimized the processing of the GYGAG(Ce), the pixel optical coupling, and electronics readout parameters to obtain single pixel energy resolution as good as $R (662\,\,\text {keV}) = 3.1$ % full-width at half-maximum and full device resolution with singles events from all pixels summed of 4.5%. When Compton-summed events are included, full-energy peak efficiency increases by $\sim 2\times $ , and $R (662\,\,\text {keV}) = 4.7$ % is obtained for the full device. The pixelated architecture is leveraged to locate point sources of radiological materials using Compton imaging and active masking techniques. Directional detection of a 1 mCi Cs-137 source at 10 m can be made to ±10° in ~2 s.

Large-Format Geiger-Mode Avalanche Photodiode Arrays and Readout Circuits

Over the past 20 years, we have developed arrays of custom-fabricated silicon and InP Geiger-mode avalanche photodiode arrays, CMOS readout circuits to digitally count or time stamp single-photon detection events, and techniques to integrate these two components to make back-illuminated solid-state image sensors for lidar, optical communications, and passive imaging. Starting with 4 × 4 arrays, we have recently demonstrated 256 × 256 arrays, and are working to scale to megapixel-class imagers. In this paper, we review this progress and discuss key technical challenges to scaling to large format.

Optimization of soft X-ray tomography on the COMPASS tokamak

Abstract The COMPASS tokamak is equipped with the soft X-ray (SXR) diagnostic system based on silicon photodiode arrays shielded by a thin beryllium foil. The diagnostic is composed of two pinhole cameras having 35 channels each and one vertical pinhole camera with 20 channels, which was installed recently to improve tomographic inversions. Lines of sight of the SXR detectors cover almost complete poloidal cross section of the COMPASS vessel with a spatial resolution of 1-2 cm and temporal resolution of about 3 μs. Local emissivity is reconstructed via Tikhonov regularization constrained by minimum Fisher information that provides reliable and robust solution despite limited number of projections and ill-conditionality of this task. Improved border conditions and numerical differentiation matrices suppressing artifacts in reconstructed radiation were implemented in the code. Furthermore, a fast algorithm eliminating iterative processes was developed, and it is foreseen to be tested in real-time plasma control.

Quality Estimation of Agave Tequilana Leaf for Bioethanol Production

Agave tequilana is a potential biofuel crop, for which the characters of juice total soluble sugar content (TSS), dry matter content (DM), cellulose, hemicellulose and lignin content are quality criteria. Spectra of leaves were obtained using a hand-held silicon photodiode array (Si PDA)-based spectrometer with a wavelength range of 300–1100 nm and an InGaAs-based Fourier transform near infrared (FT-NIR) spectrometer with a wavelength range of 1100–2500 nm. Fresh leaves were harvested at different maturity stages, in different seasons and from two locations in Queensland during 2012–2014. Partial least square regression models were developed for DM and TSS of fresh leaf, and for cellulose, hemicellulose and lignin of dried material, with models tested on populations of independent samples collected in different years, seasons and locations. Prediction statistics for DM of fresh leaf using the Si PDA spectrometer (729–975 nm) were r2 = 0.49–0.87 and root mean square error of prediction ( RMSEP) = 2.36–1.44%, while with the use of the FT-NIR spectrometer, the prediction statistics were r2 = 0.53–0.66 and RMSEP = 2.63–2.18% (across different years, seasons and locations). Prediction statistics for TSS in fresh leaf using the Si PDA spectrometer (729–975 nm) were r2 = 0.53–0.69 and RMSEP = 1.70–1.91%, with poorer results obtained using the FT-NIR spectrometer ( r2 = 0.33–0.56; RMSEP = 1.88–2.45%). With increased sample diversity in the calibration set, NIR technology is recommended for estimation of DM and TSS in fresh Agave leaves. FT-NIR-based prediction of cellulose, hemicellulose or lignin of independent sets (of different years or cultivars) was unsatisfactory, with r2 &lt; 0.75 and bias &gt;10% of mean. These results may be improved with increased sample range, and attention to laboratory (reference method) error. However, leaf cellulose and hemicellulose content may be more easily estimated through correlation to leaf DM level ( R2 of 0.77 across all sampling events).

Compact and multi-view solid state neutral particle analyzer arrays on National Spherical Torus Experiment-Upgrade.

A compact and multi-view solid state neutral particle analyzer (SSNPA) diagnostic based on silicon photodiode arrays has been successfully tested on the National Spherical Torus Experiment-Upgrade. The SSNPA diagnostic provides spatially, temporally, and pitch-angle resolved measurements of fast-ion distribution by detecting fast neutral flux resulting from the charge exchange (CX) reactions. The system consists of three 16-channel subsystems: t-SSNPA viewing the plasma mid-radius and neutral beam (NB) line #2 tangentially, r-SSNPA viewing the plasma core and NB line #1 radially, and p-SSNPA with no intersection with any NB lines. Due to the setup geometry, the active CX signals of t-SSNPA and r-SSNPA are mainly sensitive to passing and trapped particles, respectively. In addition, both t-SSNPA and r-SSNPA utilize three vertically stacked arrays with different filter thicknesses to obtain coarse energy information. The experimental data show that all channels are operational. The signal to noise ratio is typically larger than 10, and the main noise is x-ray induced signal. The active and passive CX signals are clearly observed on t-SSNPA and r-SSNPA during NB modulation. The SSNPA data also indicate significant losses of passing particles during sawteeth, while trapped particles are weakly affected. Fluctuations up to 120 kHz have been observed on SSNPA, and they are strongly correlated with magnetohydrodynamics instabilities.

Improving Calibration Transfer between Shortwave near Infrared Silicon Photodiode Array Instruments

The use of a model developed on spectra of one (master) instrument with spectra collected using another (slave) instrument requires differences in spectra of master and slave units to be orthogonal to the calibration model. The more spectral similarity is achieved in hardware, i.e. by matching the optical characteristics of the devices, the less chemometric correction is required. The transfer of partial least squares models for total soluble solids (TSS) of intact apple fruit between instrumentation based on silicon photodiode arrays was improved by use of more accurate wavelength assignments over the wavelength range used in the model. Several transfer methodologies were trialled, including piecewise direct standardisation (PDS), transfer by orthogonal projection, model updating (MU) and difference spectrum adjustment. The difference spectrum method combined with new wavelength assignments and MU gave results comparable to the performance of the master instrument and to models directly developed on the slave instruments ( r2 = 0.95, SEP-b = 0.47 and bias = −0.03% TSS, for a population of mean = 14.45 and SD = 1.64% w/v). The use of average difference spectrum adjustment combined with MU was preferred over PDS because of ease of implementation.

Construction and testing of a Top Counting Detector and a Bottom Counting Detector for the Cosmic Ray Energetics And Mass experiment on the International Space Station

The Cosmic Ray Energetics And Mass (CREAM) mission is planned for launch in 2015 to the International Space Station (ISS) to research high-energy cosmic rays. Its aim is to understand the acceleration and propagation mechanism of high-energy cosmic rays by measuring their compositions. The Top Counting Detector and Bottom Counting Detector (T/BCD) were built to discriminate electrons from protons by using the difference in cascade shapes between electromagnetic and hadronic showers. The T/BCD provides a redundant instrument trigger in flight as well as a low-energy calibration trigger for ground testing. Each detector consists of a plastic scintillator and two-dimensional silicon photodiode array with readout electronics. The TCD is located between the carbon target and the calorimeter, and the BCD is located below the calorimeter. In this paper, we present the design, assembly, and performance of the T/BCD.

Study and simulation of the read-out electronics design for a high-resolution plastic scintillating fiber based hodoscope

This work presents the study and simulation of a high-resolution charged particle detection device for beam positioning, monitoring and calibration, together with its read-out proposal. To provide the precise positional information of the beam, the detection system has been based on Plastic Scintillating Fibers (PSF), while the read-out on a Silicon-PhotoDiode (Si-PD) array. To carry out the study, a PSF prototype with one detection plane has been experimentally tested with a β particle source. Besides, Monte Carlo simulations of the complete system have also been conducted. Both simulations and experimental tests give consistency to the results obtained. The work presented in this article show the usefulness of this proposal for high-precision charged particle positioning, achieving resolutions up to 100µm.