1. Processing and analyzing MRI Quantitative susceptibility mapping (QSM) data for studying Alzheimer's disease (AD) related neurodegeneration
2. Data acquisition and signal processing from sensors of medical interest
3. Design and fabrication of optoelectronics sensors for clinical applications
In this project, we analyze quantitative susceptibility mapping (QSM) data from numerous patients and healthy controls to study Alzheimer's disease (AD) related neurodegenerative changes in human brain. Raw phase image is collected in MRI scanner. Then the data goes through a pipeline to unwrap phase, remove background phase, and generate susceptibility map using STAR-QSM technique in the STI Suite toolbox. Later using QSM and compartmentalized susceptibility generated using DECOMPOSE-QSM data from multiple patients is analyzed using standard statistical analysis and different machine learning algorithms.
In this past project, we acquired the signal from two different channel and based on two different algorithms selected the more accurate channel or combined the signals to get a good estimate of heart rate and PPG pulse. The algorithms are based on template matching and variance of heart rate.
In this past project, I made photodiodes based on printing techniques namely blade coating, inkjet printing, screen printing and so on. The organic photodiodes we developed in Arias Research Group has shown good performance in acquiring a better signal (higher SNR) in PPG (Photoplethysmography). Also, the organic phototransistor had shown sublinear response and good framerate as an image sensor. I also worked on making the circuits for signal acquisition from these devices and sensors.
The design of InGaAs/GaAsSb type-II photodetector is challenging as a transition occurs from a valance band state in GaAsSb to a conduction band state in InGaAs. The valance and conduction band structures of the superlattice need to be solved using a rigorous technique such as 8 band k.p method. Although k.p method is quite popular in determining the characteristics of quantum heterostructures, the development of a robust and compact k.p simulator for type I, type II, strained, unstrained, single and multiquantum well structures is challenging. In the present work, we have developed an extensive 8 band k.p simulator that can be used to compute the band structure and dispersion relation of a wide range of materials. As our simulator is temperature and strain inclusive, it shows better accuracy and robustness in the computation of device bandstructure. The wavefunction and energy dispersion relation derived from the simulator has been later utilized to compute the absorption coefficient of our chosen InGaAs/GaAsSb material system. The absorption coefficient of InGaAs/GaAsSb/InP type II quantum well system is not extensively studied in the available literature. Present work contributes in this area to reduce the gap between available experimental and simulation work. Finally, we have designed structure that produces 1.3 times stronger absorption and 1.7 times weaker dark current than the lattice-matched structure. We have also operated a device at a higher wavelength (3.7 µm) at room temperature.
Design of Quantum Cascade Structure for Thermo-Photovoltaic energy conversion
Analysis of Quantum Cascade Structure for Thermo-Photovoltaic energy conversion
In this research I have designed efficient quantum cascade structures which are capable to convert thermo-photovoltaic energy to electrical energy. In conventional solar cells the temperature of the source is around 5000K. But in our case the source was thermal and hence the temperature was around 1200K. The spectra and a sample structure to absorb energy from that structure are shown in the following figures.
Maruf Ahmed, Jingjia Chen, Arvin Arani, Matthew L Senjem, Petrice M Cogswell, Clifford R Jack Jr, Chunlei Liu, "The diamagnetic component map from quantitative susceptibility mapping (QSM) source separation reveals pathological alteration in Alzheimer's disease-driven neurodegeneration," NeuroImage, September 2023. doi: 10.1016/j.neuroimage.2023.120357
Xiaodong Wu, Maruf Ahmed, Yasser Khan, Margaret E Payne, Juan Zhu, Canhui Lu, James W Evans, Ana C Arias, "A potentiometric mechanotransduction mechanism for novel electronic skins," Science advances, Vol 6, July 2020. doi: 10.1126/sciadv.aba1062
Yasser Khan, Donggeon Han, Jonathan Ting, Maruf Ahmed, Ramune Nagisetty, Ana C Arias, "Organic multi-channel optoelectronic sensors for wearable health monitoring," IEEE access, Vol 7, September 2019. doi: 10.1109/ACCESS.2019.2939798
Maruf Ahmed, Jingjia Chen, Yann Cobigo, Suzanne Baker, and Chunlei Liu, "DECOMPOSE-QSM improves the tracking of iron-related neurodegenerative pathology," 2023 ISMRM & ISMRT Annual Meeting & Exhibition, June 2023.
Maruf Ahmed and Muhammad Anisuzzaman Talukder, "Intersubband transition based efficient photovoltaic energy conversion," 7th International Conference on Electrical & Computer Engineering (ICECE), 2012, pp. 331-334, Dec. 2012. doi: 10.1109/ICECE.2012.6471554 URL: http://ieeexplore.ieee.org/xpl/login.jsp?tp=&arnumber=6471554
M. Ahmed, A.K.M.D. Hossain, and M.A. Talukder, "Quantum cascade structures for efficient thermo-photovoltaic energy conversion," Photonics Global Conference (PGC), Dec. 2012. doi: 10.1109/PGC.2012.6458003 URL: Quantum+cascade+structures+for+efficient+thermo-photovoltaic+energy+conversion