LED Array Research Articles

Experimental demonstration of blue light transmitter with 30 Mbps modulated rate and 1.69 W optical power for underwater wireless optical communication based on chip-on-board light-emitting diode array

Recently, a light-emitting diode (LED) was used as an optical source in the transmitter for underwater wireless optical communication (UWOC) because it has a large divergence angle that makes establishing the communication link easier. In practice, there are several discrete LEDs in the transmitter to enlarge its output power. However, with the increase in the number of LEDs, the parasitic resistance and inductance in the light source is larger too, which affects the quality of the modulated signal. Also, using more discrete LEDs enlarges the luminous surface, which is disadvantageous to improving the tolerance to water pressure for UWOC equipment. To reduce such influences, a transmitter is proposed with a chip-on-board LED array because it has a smaller luminous surface, parasitic resistance, and inductance. Using such a transmitter, a UWOC system is established and tested in a large experimental tank. The results show that it could realize a 19 m communication distance with a 30 Mbps rate in water with an attenuation coefficient that is about 0.26 m − 1. The output power is 1.69 W, and the radiation intensity is approximately a Lambert distribution with a 120 deg divergence angle. Further analysis shows that the communication distance could increase to 90.5 m in clear water with a 0.02 m − 1 attenuation coefficient, and the emission light could cover 86.5% of the solid angle of the hemisphere space. The speed is higher than the same class light source in the previous sea trails, and the combination performance of angle coverage area, distance, and speed is suitable for ocean engineering. The proposed method is useful, simple, low-cost, and pragmatic, which makes it easy to popularize and apply.

Adjustable lighting system based on circadian rhythm for human comfort

The artificial lighting condition in which humans are exposed have been proven as a harmful factor on their well-being, which is regulated mainly by circadian rhythm. Especially since the COVID-19 pandemic, where external factors forced the society to adapt into new standards when it comes to their jobs and regular activities, lockdowns and work-from-home made most people start spending a portion of their life exposed to artificial sources of light. Technological advances have made lights more efficient and improved their intensity. Light-emitting diodes (LEDs), for example, generally produce high-intensity bluish tone light, which may affect the circadian rhythm. However, it is possible to create lighting systems able to vary the intensity and correlated color temperature (CCT) of the lighting. This work proposes a lighting system that allows adjusting the intensity and CCT of light via remote control on a smartphone application synchronized with time, following a pattern that aims avoid the undesirable artificial lighting effects on circadian rhythm. Using two LED arrays containing 10 LEDs each, suitable results were reached, presenting maximum difference of 3.35 % for CCT and 5.57 % for luminous flux in comparison with reference values.

Viability Improvement of Three-Dimensional Human Skin Substitutes by Photobiomodulation during Cultivation.

Three-dimensional (3D) cultured skin containing vascular networks is a useful skin substitute that enables rapid reperfusion after transplantation. During its cultivation, however, insufficient nutrient delivery to the thick cultured tissue from the surrounding culture medium decreases the tissue viability. To solve this problem, in this study, we applied photobiomodulation (PBM), which can optically activate the electron transport chain of mitochondria, to human 3D skin cultures constructed using the layer-by-layer cell coating technique. PBM was applied once 5 days after the start of epidermal differentiation using a light-emitting diode array with a center wavelength of 440, 523, 658 or 823 nm at a constant light intensity of 15 mW cm-2 for 50 or 600 s. Two days after PBM, we assessed the viability of the tissues by a water-soluble tetrazolium-8 assay, adenosine triphosphate measurements and live/dead cell imaging, and the results showed that the PBM at 823 nm for 50 s (0.75 J cm-2 ) significantly improved the viability of the 3D-cultured skin.

Outlier Elimination in Rough Surface Profilometry with Focus Variation Microscopy

Rough surfaces such as metal additive manufactured surfaces are quite challenging for measurement. Artifacts caused by irregular and difficult-to-measure geometries are inevitable. Removing all the artifacts would cause a portion of surface information to be missing. Different from previous works, the postprocessing in this paper includes an additional step to eliminate artifacts based on autocorrelation functions of particular subimages instead of simply removing them. This increases the accuracy with respect to surface roughness and provides a more comprehensive view on the topography. In addition, a dome shape LED array ring light is proposed to provide all-round lighting due to the high degree of irregularity of workpiece surfaces. The experimental results obtained from FVM are validated and compared with the given roughness values of a Rubert Microsurf 329 comparator test panel as well as measurement results of a metal additive workpiece by a confocal microscope.

Comparison of OOK-RZ and 4-PPM performances in Li-Fi systems using LED arrays

Light Fidelity (Li-Fi) is an advanced visible light communication (VLC) technic in which light emitting diodes (LEDs) are used for data transfer. In this article, a Li-Fi system using LED arrays is examined for indoor visible light communication. Lighting and data transmission simulations are made for return to zero on off keying (OOK-RZ) and 4-ary pulse position modulation (4-PPM) techniques with taking into account the optical path differences. Signal to noise ratios (SNRs) for both modulation techniques are calculated and used for comparison. Results of the simulations showed that data transmission rate up to 500 Mbps at FOV angle of 60° can be achieved for both modulation techniques.

Introduction to Fourier Ptychography: Part I

Abstract:Fourier ptychography is an emerging computational microscopy technique that can generate gigapixel-scale images of biological samples. With only the addition of a low-cost LED array to a standard digital microscope and a reconstruction algorithm, Fourier ptychography overcomes the fundamental trade-off between a microscope's resolution and field-of-view without any moving parts. This article is the first in a three-part series that aims to introduce the fundamentals of the technology to the broader microscopy community and beyond, using intuitive explanations.

Intense Study on Measuring Blood Glucose Level of Humans using Non-Invasive Method v.0

Abstract: Diabetes mellitus, additionally referred to as Hyperglycemia, is one of the most common disorders in the world. It happens because of the excess amount of glucose present in the blood. It impacts about 422 million humans worldwide, with the bulk residing in low- and middle-profits countries, and diabetes is at once accountable for 1.5 million deaths every year. Regular tracking of glucose is important for the management of diabetes. The current proposal involves an aggregated method of using an array of Near-infrared LEDs to non-invasively measure the concentration of glucose in the body. An array of NIR led & Laser is fitted into a wearable device, manufactured from thermoplastic polyurethane (TPU) and the light of appropriate wavelength could be absorbed with the help of glucose found in blood and the attenuated light could be sensed with the aid of using the photodiode that's used to transform the light energy into a voltage signal. This signal could then be amplified and fed as an input to the microcontroller in which the glucose level is calculated using regression analysis. The calculated value of glucose could be displayed on the output display unit and the data is transferred through Bluetooth to an android application for storage and display in application. They do not produce any medical waste, limit the danger of infection, and enhance pain management.

Beam controlled lighting design: An approach towards optimization of road lighting design

LED based street lighting has been introduced everywhere for energy saving aspect. The Optical Control of LED is very much possible with change of beam angles. This beam-angle based switching of LED based street lighting installations is a new area to be explored. Global research says LED is an energy saving light source. But during low or off traffic hours, portion of LED arrays of a luminaires may be switched on/off on the basis of beam-angle. The light level is reduced. The ‘beam-angle switching’definitely ensures energy saving, but the investigation of the human performance under this condition is also necessary. There is no such evidence available in favour of the effectiveness of ‘beam-angle switching’ on human performance. In this paper an experimentation based studies have been conducted to identify the driver’s response during the object detection under different lighting conditions as PRO, COUNTER and FULL GLOW of a LED luminaire. The visibility study has been carried out in a simulated road to prove the effectiveness of this beam-angle based switching from the human performance as well as energy saving point of view.

Combinatorial wound healing therapy using adhesive nanofibrous membrane equipped with wearable LED patches for photobiomodulation.

Wound healing is the dynamic tissue regeneration process replacing devitalized and missing tissue layers. With the development of photomedicine techniques in wound healing, safe and noninvasive photobiomodulation therapy is receiving attention. Effective wound management in photobiomodulation is challenged, however, by limited control of the geometrical mismatches on the injured skin surface. Here, adhesive hyaluronic acid–based gelatin nanofibrous membranes integrated with multiple light-emitting diode (LED) arrays are developed as a skin-attachable patch. The nanofibrous wound dressing is expected to mimic the three-dimensional structure of the extracellular matrix, and its adhesiveness allows tight coupling between the wound sites and the flexible LED patch. Experimental results demonstrate that our medical device accelerates the initial wound healing process by the synergetic effects of the wound dressing and LED irradiation. Our proposed technology promises progress for wound healing management and other biomedical applications.

3D time-lapse imaging of a mouse embryo using intensity diffraction tomography embedded inside a deep learning framework.

We present a compact 3D diffractive microscope that can be inserted directly in a cell incubator for long-term observation of developing organisms. Our setup is particularly simple and robust, since it does not include any moving parts and is compatible with commercial cell culture containers. It has been designed to image large specimens (>100×100×100µm3) with subcellular resolution. The sample's optical properties [refractive index (RI) and absorption] are reconstructed in 3D from intensity-only images recorded with different illumination angles produced by an LED array. The reconstruction is performed using the beam propagation method embedded inside a deep-learning network where the layers encode the optical properties of the object. This deep neural network is trained for a given multiangle intensity acquisition. After training, the weights of the neural network deliver the 3D distribution of the optical properties of the sample. The effect of spherical aberrations due to the sample holder/air interfaces are taken into account in the forward model. Using this approach, we performed time-lapse 3D imaging of preimplantation mouse embryos over six days. Images of embryos from a single cell (low-scattering regime) to the blastocyst stage (highly scattering regime) were successfully reconstructed. Due to its subcellular resolution, our system can provide quantitative information on the embryos' development and viability. Hence, this technology opens what we believe to be novel opportunities for 3D label-free live-cell imaging of whole embryos or organoids over long observation times.

Fourier ptychography multi-parameunter neural network with composite physical priori optimization.

Fourier ptychography microscopy(FPM) is a recently developed computational imaging approach for microscopic super-resolution imaging. By turning on each light-emitting-diode (LED) located on different position on the LED array sequentially and acquiring the corresponding images that contain different spatial frequency components, high spatial resolution and quantitative phase imaging can be achieved in the case of large field-of-view. Nevertheless, FPM has high requirements for the system construction and data acquisition processes, such as precise LEDs position, accurate focusing and appropriate exposure time, which brings many limitations to its practical applications. In this paper, inspired by artificial neural network, we propose a Fourier ptychography multi-parameter neural network (FPMN) with composite physical prior optimization. A hybrid parameter determination strategy combining physical imaging model and data-driven network training is proposed to recover the multi layers of the network corresponding to different physical parameters, including sample complex function, system pupil function, defocus distance, LED array position deviation and illumination intensity fluctuation, etc. Among these parameters, LED array position deviation is recovered based on the features of brightfield to darkfield transition low-resolution images while the others are recovered in the process of training of the neural network. The feasibility and effectiveness of FPMN are verified through simulations and actual experiments. Therefore FPMN can evidently reduce the requirement for practical applications of FPM.

Quantum dot-integrated GaN light-emitting diodes with resolution beyond the retinal limit

Near-eye display technology is a rapidly growing field owing to the recent emergence of augmented and mixed reality. Ultrafast response time, high resolution, high luminance, and a dynamic range for outdoor use are all important for non-pixelated, pupil-forming optics. The current mainstream technologies using liquid crystals and organic materials cannot satisfy all these conditions. Thus, finely patterned light-emissive solid-state devices with integrated circuits are often proposed to meet these requirements. In this study, we integrated several advanced technologies to design a prototype microscale light-emitting diode (LED) arrays using quantum dot (QD)-based color conversion. Wafer-scale epilayer transfer and the bond-before-pattern technique were used to directly integrate 5-µm-scale GaN LED arrays on a foreign silicon substrate. Notably, the lithography-level alignment with the bottom wafer opens up the possibility for ultrafast operation with circuit integration. Spectrally pure color conversion and solvent-free QD patterning were also achieved using an elastomeric topographical mask. Self-assembled monolayers were applied to selectively alter the surface wettability for a completely dry process. The final emissive-type LED array integrating QD, GaN, and silicon technology resulted in a 1270 PPI resolution that is far beyond the retinal limit.

Rectangular module for large scale solar simulator based on high-powered LEDs array

The article describes a large scale of rectangular light source design comprised of six different types of high-power light emitting diodes (LEDs). The new modular based on the LED solar simulator with the greatest size using the symmetrical LED positioning method. The experiment provided the irradiation of the solar simulator in the class AAA over 416 cm 2 . The rectangular LED module illustrated the uniform distribution of the irradiance across the sample plane area. It reached the class A of air mass 1.5 for global spectrum (AM1.5G) (1000 W/m 2 ) covering the 400 nm to 1100 nm wavelength range. The proposed system offered a spectral match of 100%, the temporal instability equivalent to 0.611%, and a non-uniformity of irradiance less than 2%. When the proposed solar simulator was tested in solar cell characteristics under standard test conditions, it was found that the short circuit current error between the sample solar cell under our solar simulator and the standard solar simulator was less than 0.538%. This proposed design is, therefore, an interesting design that can be applied easily and economically further for large scale solar simulators with its modular system.

Vision-Based High-Resolution Tactile Sensor By Using Visual Light Ring

In this letter, a vision-based high-resolution pressure array sensor with sensitivity enhanced by using visual light ring was proposed. The sensor consists of a transparent flexible layer integrating micropillar array and an image sensor with circular array light emitting diodes (LEDs). When pressure is applied to the micropillar, the surface of the substrate around the micropillar produces a concave, and the edges of the concave reflect the light of the LED array to form visual light ring in the image sensor. A relationship between the pressure and the size of the visual light ring was established. The sensitivity using the light ring was increased by three times compared with using deformation of the micropillar. The sensor achieves a high resolution of 625 sensing points per cm², which was higher than that on the finger of a human. Thus, the sensor will be a competitive solution to artificial tactile system which is of great importance for intelligent robots.

Robust multi-angle structured illumination lensless microscopy via illumination angle calibration.

Multi-angle structured illumination lensless (MASIL) microscopy enables high-resolution image recovery over a large field of view. Successful image recovery of MASIL microscopy, however, relies on an accurate knowledge of the multi-angle illumination. System misalignments and slight deviations from the true illumination angle may result in image artifacts in reconstruction. Here we report a MASIL microscopy system that is robust against illumination misalignment. To calibrate the illumination angles, we design and use a double-sided mask, which is a glass wafer fabricated with a ring-array pattern on the upper surface and a disk-array pattern on the lower surface. As such, the illumination angles can be decoded from the captured images by estimating the relative displacement of the two patterns. We experimentally demonstrate that this system can achieve successful image recovery without any prior knowledge of the illumination angles. The reported approach provides a simple yet robust resolution for wide-field lensless microscopy. It can solve the LED array misalignment problem and calibrate angle-varied illumination for a variety of applications.

Development of a UVC-based disinfection robot

PurposeThe disinfection robot developed by the authors and team focuses on achieving fast and precise disinfection under a given or specific disinfection zone. This looks to solve problems with traditional robots that pay less attention to the level, efficiency and zones of disinfection. To effectively support and guarantee normal running for the whole system, a digital twin system is applied to the disinfection robot. This study aims to achieve fast, precise and thorough disinfection via the developed mobile robot.Design/methodology/approachThe designed robot is composed primarily of the following three parts: a mobile platform, a six-axis robotic arm and a ultraviolet-C (UVC) LED array. The UVC LED array is installed on the end-effector to achieve large-scale, precise manipulation. The adoption of all types of advanced sensors and the development of an intuitive and user-friendly client interface are helpful in achieving remote control, path planning, data monitoring and custom disinfection functions.FindingsDisinfection of three different locations in the laboratory was performed; the dosage distribution of the surface as radiated by the UVC robot was detected; and feasibility of development was validated.Originality/valueThe developed disinfection robot achieved fast, precise and thorough disinfection for a given or specific disinfection zone.

Space-based correction method for LED array misalignment in Fourier ptychographic microscopy

Fourier ptychographic microscopy is a super-resolution technique, which could break through the Space-Band-Product (SBP) limit of the system by employing varied-illumination and phase retrieval algorithm. A LED array is used to provide angularly varying illuminations, which is portable and cheap. However, the installation accuracy of the LED array is not sufficient, resulting in position misalignment errors. The misalignment errors not only cause the calculation error of the sub-apertures in the frequency domain, but also the artifacts in reconstruction images. Although some correction methods have been proposed, the correction ability of these methods cannot deal with the misalignment errors well. In this paper, we proposed a misalignment errors correction method. This method uses the Particle swarm optimization (PSO) algorithm to search the four misalignment parameters (Δx, Δy, θ, Δh) in space domain. It is termed as Space based correction (SBC) method. Compared with the state-of-art methods, the SBC method is more stable and accuracy.

Morphology analysis of unlabeled red blood cells based on quantitative differential phase contrast microscopy.

The current classical blood smear technique to observe the morphology of single red blood cells (RBCs) for classification is a laborious and error-prone process. To objectively evaluate the morphology of blood cells, we established a method of computational imaging based on a programmable light emitting diode array. By using quantitative differential phase contrast (qDPC), we characterized the morphology of unlabeled RBCs as well as blood smears. By focusing on comparing the difference of imaging between unlabeled RBCs and stained RBCs under multimode microscopic imaging technology, we demonstrated that qDPC could clearly differentiate discocytes and spherocytes in both unlabeled RBCs and blood smears. The phase map provided by quantitative phase imaging further enhanced the classification accuracy. According to statistical analysis from morphological indexes, the qDPC imaging has a significantly improvement in non-circularity, texture inhomogeneity and equivalent diameters of cells. Thus, this method has a significant superiority in the capability to analyze the morphology of RBCs and could be applied to clinical assays for determining morphological, functional, and structural deterioration of RBCs.

Towards real-time self-powered sensing with ample redundant charges by a piezostack-based frequency-converted generator from human motions

This paper presents a piezostack-based frequency up-converting generator for scavenging ultra-low frequency (lower than 5 Hz) vibration energy associated with human motion. The generator, consisting of a force amplifier, a piezoelectric stack, a spring-mass system, and a spring limiter, realizes ultra-low frequency conversion mainly through the impact-induced frequency conversion effect. To estimate the output voltage of the generator numerically, we built a two-degree-of-freedom (2DOF) equivalent model based on the mechanical structure of the harvester. Moreover, we conducted five series of experiments to investigate the output performance of a fabricated prototype. The prototype generates an instantaneous peak-peak output power of 5.56 W (averaged power of 0.93 mW) excited by human running motions. A 'SHU' LED array was lighted up in real-time successfully. We then tested the performance of the prototype in a real-time self-powered system. The generator is able to power a watch and a thermometer in real-time. More importantly, when the excitation stops, they are powered by redundant charges for approximately 50 minutes and 1 minute, respectively. This research can make an essential contribution to ultra-low frequency vibration energy harvesting and the realization of real-time self-powered wearable devices.

LED-based Hyperspectral Endoscopic Imaging.

Hyperspectral endoscopy can offer multiple advantages as compared to conventional endoscopy. Our goal is to design and develop a real-time hyperspectral endoscopic imaging system for the diagnosis of gastrointestinal (GI) tract cancers using a micro-LED array as an in-situ illumination source. The wavelengths of the system range from ultraviolet to visible and near infrared. To evaluate the use of the LED array for hyperspectral imaging, we designed a prototype system and conducted ex vivo experiments using normal and cancerous tissues of mice, chicken, and sheep. We compared the results of our LED-based approach with our reference hyperspectral camera system. The results confirm the similarity between the LED-based hyperspectral imaging system and the reference HSI camera. Our LED-based hyperspectral imaging system can be used not only as an endoscope but also as a laparoscopic or handheld devices for cancer detection and surgery.