In a new study, researchers at the Indian Institute of Science (IISc) show how a brain-inspired image sensor can go beyond the diffraction limit of light to detect miniscule objects such as cellular components or nanoparticles invisible to current microscopes. Their novel technique, which combines optical microscopy with a neuromorphic camera and machine learning algorithms, presents a major step forward in pinpointing objects smaller than 50 nanometers in size. The results are published in Nature Nanotechnology.

Since the invention of optical microscopes, scientists have strived to surpass a barrier called the diffraction limit, which means that the microscope cannot distinguish between two objects if they are smaller than a certain size (typically 200-300 nanometers). Their efforts have largely focused on either modifying the molecules being imaged, or developing better illumination strategies – some of which led to the 2014 Nobel Prize in Chemistry. “But very few have actually tried to use the detector itself to try and surpass this detection limit,” says Deepak Nair, Associate Professor at the Centre for Neuroscience (CNS), IISc, and corresponding author of the study.

Transformation of cumulative probability density of ON and OFF processes allows localisation below the limit of classical single particle detection (Credit: Mangalwedhekar et al, 2023)

Measuring roughly 40 mm (height) by 60 mm (width) by 25 mm (diameter), and weighing about 100 grams, the neuromorphic camera used in the study mimics the way the human retina converts light into electrical impulses, and has several advantages over conventional cameras. In a typical camera, each pixel captures the intensity of light falling on it for the entire exposure time that the camera focuses on the object, and all these pixels are pooled together to reconstruct an image of the object. In neuromorphic cameras, each pixel operates independently and asynchronously, generating events or spikes only when there is a change in the intensity of light falling on that pixel. This generates sparse and lower amount of data compared to traditional cameras, which capture every pixel value at a fixed rate, regardless of whether there is any change in the scene. This functioning of a neuromorphic camera is similar to how the human retina works, and allows the camera to “sample” the environment with much higher temporal resolution – because it is not limited by a frame rate like normal cameras – and also perform background suppression.

“Such neuromorphic cameras have a very high dynamic range (>120 dB), which means that you can go from a very low-light environment to very high-light conditions. The combination of the asynchronous nature, high dynamic range, sparse data, and high temporal resolution of neuromorphic cameras make them well-suited for use in neuromorphic microscopy,” explains Chetan Singh Thakur, Assistant Professor at the Department of Electronic Systems Engineering (DESE), IISc, and co-author.

View of the microscopy setup (Credit: Rohit Mangalwedhekar)

In the current study, the group used their neuromorphic camera to pinpoint individual fluorescent beads smaller than the limit of diffraction, by shining laser pulses at both high and low intensities, and measuring the variation in the fluorescence levels. As the intensity increases, the camera captures the signal as an “ON” event, while an “OFF” event is reported when the light intensity decreases. The data from these events were pooled together to reconstruct frames.

To accurately locate the fluorescent particles within the frames, the team used two methods. The first was a deep learning algorithm, trained on about one and a half million image simulations that closely represented the experimental data, to predict where the centroid of the object could be, explains Rohit Mangalwedhekar, former research intern at CNS and first author of the study. A wavelet segmentation algorithm was also used to determine the centroids of the particles separately for the ON and the OFF events. Combining the predictions from both allowed the team to zero in on the object’s precise location with greater accuracy than existing techniques.

“In biological processes like self-organisation, you have molecules that are alternating between random or directed movement, or that are immobilised,” explains Nair. “Therefore, you need to have the ability to locate the centre of this molecule with the highest precision possible so that we can understand the thumb rules that allow the self-organisation.” The team was able to closely track the movement of a fluorescent bead moving freely in an aqueous solution using this technique. This approach can, therefore, have widespread applications in precisely tracking and understanding stochastic processes in biology, chemistry and physics.

REFERENCE:

Mangalwedhekar R, Singh N, Thakur CS, Seelamantula CS, Jose M, Nair D, Achieving nanoscale precision using neuromorphic localization microscopy, Nature Nanotechnology (2023).

https://www.nature.com/articles/s41565-022-01291-1

CONTACT:

Deepak Nair
Associate Professor
Centre for Neuroscience (CNS)
Indian Institute of Science (IISc)
Email: deepak@iisc.ac.in
Phone: 080-22933535
Website: https://cns.iisc.ac.in/deepak/index.html

Chetan Singh Thakur
Assistant Professor
Department of Electronic Systems Engineering (DESE)
Indian Institute of Science (IISc)
Email: csthakur@iisc.ac.in
Phone: 080-22933608
Website: https://labs.dese.iisc.ac.in/neuronics/

IMAGE CAPTIONS AND CREDITS:

Image 1: Transformation of cumulative probability density of ON and OFF processes allows localisation below the limit of classical single particle detection (Credit: Mangalwedhekar et al, 2023)

Image 2: View of the microscopy setup (Credit: Rohit Mangalwedhekar)

NOTE TO JOURNALISTS:

a) If any of the text in this release is reproduced verbatim, please credit the IISc press release.
b) For any queries about IISc press releases, please write to news@iisc.ac.in or pro@iisc.ac.in.

23 February 2023

– Kaustubh Roy

Lightning strikes can be dangerous for aircraft. But studying this phenomenon in the field is quite difficult. Researchers at the Indian Institute of Science (IISc) have developed a unique computational model to simulate how lightning can strike an aircraft. The insights they have gleaned from this model can help design better lightning protective measures for aircraft.

Lightning strikes can damage the aircraft surface, lead to temporary disruptions in electrical and electronic systems or even cause permanent damage, and in extreme cases, cause ignition of the fuel-air mixture around the engine, leading to an explosion. “Usually, an aircraft gets struck by lightning once every 1,000 hours,” says Udaya Kumar, Professor at the Department of Electrical Engineering, IISc, whose lab has been investigating this phenomenon in recent years. “There have been a lot of incidents in the last century where things have been very catastrophic.”

The first step in protecting aircraft from lightning is identifying the most common regions on the aircraft where lightning can attach or hit. Kumar and his team realised that current approaches to this identification were grossly oversimplified, and set out to develop a more comprehensive computational model. The model and the data obtained from it have been published in Atmosphere.

Kumar’s lab has been studying lightning protection for the past few years. In previous studies, his team has analysed the effectiveness of lightning rods in safeguarding tall buildings in a thunderstorm. They have developed unique models that have addressed several long-standing issues of lightning current evolution. In the past, he was also involved in the design of a lightning protective system for Indian satellite launch pads and has conducted research on different protective schemes.  In the current study as well as in ongoing work, they have focused on modelling how lightning impacts aircraft, in order to develop suitable protective measures.

In the usual downward cloud-to-ground lightning, leaders – precursors to lightning arcs – are initiated at the cloud, which propagate towards the ground. However, field data, as well as the model developed, clearly show that in more than 90% of the cases, the leader discharges are initiated at the aircraft. The model developed by the IISc team is applied to two different aircraft geometries: a DC10 passenger aircraft and the SDM fighter aircraft model. It involves extensive computation of the electric field around the aircraft and suitable modelling of the electrical discharges.

With the model, the scientists were able to obtain estimates of the minimum ambient electric field required for initiation of lightning leader discharges from the aircraft. These values, the researchers say, are in good agreement with measured data from instrumented aircraft flown through thunderstorms, such as NASA’s Storm Hazard Program. Moreover, the aircraft is not perfectly parallel to the ground during take-off and landing, and the model is able to simulate how these changes in orientation can affect the electric field. The role of atmospheric conditions such as humidity and air pressure are also taken into account in the model. It also showed that aircraft at higher altitudes had a greater affinity for lightning strikes.

In ongoing studies, the team is planning to investigate several related issues. Firstly, what could be the peak value of the lightning stroke current for aircraft-initiated lightning? Secondly, what could be the local changes around the aircraft during the lightning strike evolution? In addition, they are investigating disruptions to the internal electrical equipment when struck by lightning. Kumar’s lab has also carried out a first-of-its-kind experiment on a small military aircraft by injecting it with enormous amounts of current – intended to emulate lightning discharge – and by collecting electric field data from inside the craft.

Kumar and his team suggest that such studies can aid in reliable quantification of the lightning threat, and enable optimised design of lightning protective measures.

REFERENCES: 

Das S, Kumar U, Modeling of Bi-Polar Leader Inception and Propagation from Flying Aircraft Prior to a Lightning Strike, Atmosphere (2022) 

https://doi.org/10.3390/atmos13060943 

Das S, Kumar U, Comparative analysis for inception of positive connecting leader from a cruising and grounded aircraft, 2022 36th International Conference on Lightning Protection (ICLP)  

https://ieeexplore.ieee.org/document/9942520 

Das S, Kumar U, Quantitative study on efficacy of lightning rod on building, 2022 IEEE International Conference on High Voltage Engineering and Applications (ICHVE) 

https://ieeexplore.ieee.org/document/9961455/ 

CONTACT: 
Udaya Kumar
Professor and Chair, Department of Electrical Engineering
Indian Institute of Science (IISc)
udayk@iisc.ac.in
Phone: +91 80 2293 3177
Website:  https://ee.iisc.ac.in/~uday/  
IMAGE CAPTION AND CREDIT:   
Tejas under lightning current injection experiment (Image courtesy: Udaya Kumar)

NOTE TO JOURNALISTS: 

a) If any of the text in this release is reproduced verbatim, please credit the IISc press release.
b) For any queries about IISc press releases, please write to news@iisc.ac.in or pro@iisc.ac.in.