2024
9.
Yip Fun Yeung; Fangzhou Xia*; Mikio Furokawa; Takayuki Hirano; Kamal Youcef-Toumi
SymPO:One-Pass Fault Prediction For Non-Stationary Dynamics Journal Article Forthcoming
In: IEEE Transactions on Neural Network and Learning Systems (under review), Forthcoming.
BibTeX | Tags: Automation, Intelligence, Mechatronics, Method, Modeling & Simulation, Signal Processing, Theory
@article{2024IEEETNNLS,
title = {SymPO:One-Pass Fault Prediction For Non-Stationary Dynamics},
author = {Yip Fun Yeung and Fangzhou Xia* and Mikio Furokawa and Takayuki Hirano and Kamal Youcef-Toumi},
year = {2024},
date = {2024-01-01},
urldate = {2024-01-01},
journal = {IEEE Transactions on Neural Network and Learning Systems (under review)},
keywords = {Automation, Intelligence, Mechatronics, Method, Modeling & Simulation, Signal Processing, Theory},
pubstate = {forthcoming},
tppubtype = {article}
}
8.
Abhishek Patkar; Qinghui Meng*; Hanrui Wang; Fangzhou Xia*; Kamal Youcef-Toumi
Time Delay based Neural Network Control of Permanent Magnet Synchronous Motors Journal Article Forthcoming
In: IEEE Transactions on Power Electronics (under review), Forthcoming.
BibTeX | Tags: Automation, Design, Experimentation, Instrumentation, Intelligence, Mechatronics, Modeling & Simulation, Motion Control, Theory
@article{2024IEEETPEL,
title = {Time Delay based Neural Network Control of Permanent Magnet Synchronous Motors},
author = {Abhishek Patkar and Qinghui Meng* and Hanrui Wang and Fangzhou Xia* and Kamal Youcef-Toumi},
year = {2024},
date = {2024-01-01},
urldate = {2024-01-01},
journal = {IEEE Transactions on Power Electronics (under review)},
keywords = {Automation, Design, Experimentation, Instrumentation, Intelligence, Mechatronics, Modeling & Simulation, Motion Control, Theory},
pubstate = {forthcoming},
tppubtype = {article}
}
7.
Jiajie Qiu^; Hongjin Kim^; Fangzhou Xia*; Kamal Youcef-Toumi
Flexure-based Multi-actauted Vibration Suppression System for OHT Wafer Transfer Vehicles Journal Article Forthcoming
In: IEEE/ASME Transactions on Mechatronics (in preparation), Forthcoming.
BibTeX | Tags: Automation, Experimentation, Instrumentation, Mechatronics, Modeling & Simulation, Motion Control
@article{2024TMech,
title = {Flexure-based Multi-actauted Vibration Suppression System for OHT Wafer Transfer Vehicles},
author = {Jiajie Qiu^ and Hongjin Kim^ and Fangzhou Xia* and Kamal Youcef-Toumi},
year = {2024},
date = {2024-01-01},
urldate = {2024-01-01},
journal = {IEEE/ASME Transactions on Mechatronics (in preparation)},
publisher = {IEEE},
keywords = {Automation, Experimentation, Instrumentation, Mechatronics, Modeling & Simulation, Motion Control},
pubstate = {forthcoming},
tppubtype = {article}
}
2023
6.
Lois Wampler^; Fangzhou Xia^*; Yip Fun Yeung; Takayuki Hirano; Ali Alshehri; Mikio Furokawa; Kamal Youcef-Toumi
A Doppler Radar with a Sweeping Lock-in Demodulator for Machine Vibration Sensing Journal Article
In: IEEE Sensors Journal, 2023.
Abstract | Links | BibTeX | Tags: Automation, Experimentation, Instrumentation, Mechatronics, Modeling & Simulation, Sensor, Signal Processing, Theory
@article{2023IEEESensors,
title = {A Doppler Radar with a Sweeping Lock-in Demodulator for Machine Vibration Sensing},
author = {Lois Wampler^ and Fangzhou Xia^* and Yip Fun Yeung and Takayuki Hirano and Ali Alshehri and Mikio Furokawa and Kamal Youcef-Toumi},
doi = {10.1109/JSEN.2023.3325820},
year = {2023},
date = {2023-10-31},
urldate = {2023-10-31},
journal = {IEEE Sensors Journal},
abstract = {Data-driven predictive maintenance of modern machinery has the potential to increase equipment lifespan and decrease manufacturing costs. Vibration analysis can effectively diagnose potential problems in machines. A Doppler radar can be used as a sensor that provides non-contact, inexpensive real-time machine vibration data collection without necessitating line-down time. Implementation with Software Defined Radio (SDR) allow easy adjustment of excitation signals based on application needs. Conventional Fast Fourier Transformation based vibration analysis requires large amounts of data to achieve high spectral resolution needed for fault detection, which can be inefficient and computationally too expensive. In this work, we propose to use a sweeping lock-in amplifier to achieve high frequency resolution with small amounts of data by processing windowed sections of Doppler-shifted radio signals. This algorithm can reliably measure the Doppler shift frequency corresponding to the travelling speed of a moving object and identify the frequency of oscillating target with small amplitude, with the latter widely present in machine vibration. The distinguishing condition of the two cases is mathematically derived. The proposed algorithm is studied in simulation with triangular displacement waveform for simplicity of analysis and sinusoidal waveform for generic applications. For experimental verification, speaker vibration at a known frequency is analyzed to achieve an accuracy of 0.025 Hz within the known vibration frequency. This method is robust to the presence of noise frequencies and capable of detecting multiple frequencies.},
keywords = {Automation, Experimentation, Instrumentation, Mechatronics, Modeling & Simulation, Sensor, Signal Processing, Theory},
pubstate = {published},
tppubtype = {article}
}
Data-driven predictive maintenance of modern machinery has the potential to increase equipment lifespan and decrease manufacturing costs. Vibration analysis can effectively diagnose potential problems in machines. A Doppler radar can be used as a sensor that provides non-contact, inexpensive real-time machine vibration data collection without necessitating line-down time. Implementation with Software Defined Radio (SDR) allow easy adjustment of excitation signals based on application needs. Conventional Fast Fourier Transformation based vibration analysis requires large amounts of data to achieve high spectral resolution needed for fault detection, which can be inefficient and computationally too expensive. In this work, we propose to use a sweeping lock-in amplifier to achieve high frequency resolution with small amounts of data by processing windowed sections of Doppler-shifted radio signals. This algorithm can reliably measure the Doppler shift frequency corresponding to the travelling speed of a moving object and identify the frequency of oscillating target with small amplitude, with the latter widely present in machine vibration. The distinguishing condition of the two cases is mathematically derived. The proposed algorithm is studied in simulation with triangular displacement waveform for simplicity of analysis and sinusoidal waveform for generic applications. For experimental verification, speaker vibration at a known frequency is analyzed to achieve an accuracy of 0.025 Hz within the known vibration frequency. This method is robust to the presence of noise frequencies and capable of detecting multiple frequencies.
5.
Jiajie Qiu^; Hongjin Kim^; Fangzhou Xia*; Kamal Youcef-Toumi
Multi-axis Active Vibration Suppression for Wafer Transfer Systems Best Paper Proceedings Article
In: IEEE/ASME Advanced Intelligent Mechatronics, 2023.
Abstract | Links | BibTeX | Tags: Actuator, Automation, Design, Experimentation, Instrumentation, Mechatronics, Modeling & Simulation, Motion Control, Theory
@inproceedings{2023AIM,
title = {Multi-axis Active Vibration Suppression for Wafer Transfer Systems},
author = {Jiajie Qiu^ and Hongjin Kim^ and Fangzhou Xia* and Kamal Youcef-Toumi},
url = {https://ieeexplore.ieee.org/document/10196218},
year = {2023},
date = {2023-06-27},
urldate = {2023-06-27},
booktitle = {IEEE/ASME Advanced Intelligent Mechatronics},
abstract = {Vibration suppression is critical in precision mechatronic systems for nanofabrication. For automated wafer handling in semiconductor plants, Overhead Hoist Transport (OHT) vehicles transport wafers carried in Front Opening Unified Pods (FOUPs); while the wafers are transported in a FOUP, semiconductor chips are at risk of damage by excited small particles due to mechanical vibration. Active suppression of the FOUP vibrations has been proposed to improve the production yield. However, there are two main challenges that make it a non-trivial problem. First, moving FOUPs carried by the OHT vehicles have no external anchoring point as a momentum source for control efforts. Second, no sensor attachment is permitted on mass-production FOUPs, which makes feedback control more challenging without measurement. Since the goal is to suppress the large FOUP acceleration peaks instead of eliminating all vibration, an inertia-based counterbalancing system is designed to address these challenges. To validate this idea, a custom testbed is designed for multi-axis vibration generation and suppression. A Disturbance Observer-Based Controller (DOBC) is developed and implemented on the hardware. During the experiment, 38 percent of the OHT hand unit vibration (and 42 percent of FOUP vibration) suppression is achieved in the OHT travel direction. Moreover, multi-axis FOUP-level acceleration-peak reduction is achieved to verify the effectiveness of the proposed method. },
keywords = {Actuator, Automation, Design, Experimentation, Instrumentation, Mechatronics, Modeling & Simulation, Motion Control, Theory},
pubstate = {published},
tppubtype = {inproceedings}
}
Vibration suppression is critical in precision mechatronic systems for nanofabrication. For automated wafer handling in semiconductor plants, Overhead Hoist Transport (OHT) vehicles transport wafers carried in Front Opening Unified Pods (FOUPs); while the wafers are transported in a FOUP, semiconductor chips are at risk of damage by excited small particles due to mechanical vibration. Active suppression of the FOUP vibrations has been proposed to improve the production yield. However, there are two main challenges that make it a non-trivial problem. First, moving FOUPs carried by the OHT vehicles have no external anchoring point as a momentum source for control efforts. Second, no sensor attachment is permitted on mass-production FOUPs, which makes feedback control more challenging without measurement. Since the goal is to suppress the large FOUP acceleration peaks instead of eliminating all vibration, an inertia-based counterbalancing system is designed to address these challenges. To validate this idea, a custom testbed is designed for multi-axis vibration generation and suppression. A Disturbance Observer-Based Controller (DOBC) is developed and implemented on the hardware. During the experiment, 38 percent of the OHT hand unit vibration (and 42 percent of FOUP vibration) suppression is achieved in the OHT travel direction. Moreover, multi-axis FOUP-level acceleration-peak reduction is achieved to verify the effectiveness of the proposed method.
4.
Fangzhou Xia*; Kamal Youcef-Toumi; Thomas Sattel; Eberhard Manske; Ivo W. Rangelow
Active Probe Atomic Force Microscopy with Quattro-Parallel Cantilever Arrays for High-Throughput Large-Scale Sample Inspection Journal Article
In: Journal of Visualized Experiments, pp. e65210, 2023, ISSN: 1940-087X.
Abstract | Links | BibTeX | Tags: Atomic Force Microscopy, Automation, Experimentation, Instrumentation, Material Science, Mechatronics, MEMS, Method, Sensor
@article{2023JoVE,
title = {Active Probe Atomic Force Microscopy with Quattro-Parallel Cantilever Arrays for High-Throughput Large-Scale Sample Inspection},
author = {Fangzhou Xia* and Kamal Youcef-Toumi and Thomas Sattel and Eberhard Manske and Ivo W. Rangelow},
url = {https://www.jove.com/t/65210},
doi = {10.3791/65210},
issn = {1940-087X},
year = {2023},
date = {2023-06-16},
urldate = {2023-06-16},
journal = {Journal of Visualized Experiments},
pages = {e65210},
abstract = {An Atomic Force Microscope (AFM) is a powerful and versatile tool for nanoscale surface studies to capture 3D topography images of samples. However, due to their limited imaging throughput, AFMs have not been widely adopted for large-scale inspection purposes. Researchers have developed high-speed AFM systems to record dynamic process videos in chemical and biological reactions at tens of frames per second, at the cost of a small imaging area of up to several square micrometers. In contrast, inspecting large-scale nanofabricated structures, such as semiconductor wafers, requires nanoscale spatial resolution imaging of a static sample over hundreds of square centimeters with high productivity. Conventional AFMs use a single passive cantilever probe with an optical beam deflection system, which can only collect one pixel at a time during AFM imaging, resulting in low imaging throughput. This work utilizes an array of active cantilevers with embedded piezoresistive sensors and thermomechanical actuators, which allows simultaneous multi-cantilever operation in parallel operation for increased imaging throughput. When combined with large-range nano-positioners and proper control algorithms, each cantilever can be individually controlled to capture multiple AFM images. With data-driven post-processing algorithms, the images can be stitched together, and defect detection can be performed by comparing them to the desired geometry. This paper introduces principles of the custom AFM using the active cantilever arrays, followed by a discussion on practical experiment considerations for inspection applications. Selected example images of silicon calibration grating, highly-oriented pyrolytic graphite, and extreme ultraviolet lithography masks are captured using an array of four active cantilevers ("Quattro") with a 125 {textmu}m tip separation distance. With more engineering integration, this high-throughput, large-scale imaging tool can provide 3D metrological data for extreme ultraviolet (EUV) masks, chemical mechanical planarization (CMP) inspection, failure analysis, displays, thin-film step measurements, roughness measurement dies, and laser-engraved dry gas seal grooves.},
keywords = {Atomic Force Microscopy, Automation, Experimentation, Instrumentation, Material Science, Mechatronics, MEMS, Method, Sensor},
pubstate = {published},
tppubtype = {article}
}
An Atomic Force Microscope (AFM) is a powerful and versatile tool for nanoscale surface studies to capture 3D topography images of samples. However, due to their limited imaging throughput, AFMs have not been widely adopted for large-scale inspection purposes. Researchers have developed high-speed AFM systems to record dynamic process videos in chemical and biological reactions at tens of frames per second, at the cost of a small imaging area of up to several square micrometers. In contrast, inspecting large-scale nanofabricated structures, such as semiconductor wafers, requires nanoscale spatial resolution imaging of a static sample over hundreds of square centimeters with high productivity. Conventional AFMs use a single passive cantilever probe with an optical beam deflection system, which can only collect one pixel at a time during AFM imaging, resulting in low imaging throughput. This work utilizes an array of active cantilevers with embedded piezoresistive sensors and thermomechanical actuators, which allows simultaneous multi-cantilever operation in parallel operation for increased imaging throughput. When combined with large-range nano-positioners and proper control algorithms, each cantilever can be individually controlled to capture multiple AFM images. With data-driven post-processing algorithms, the images can be stitched together, and defect detection can be performed by comparing them to the desired geometry. This paper introduces principles of the custom AFM using the active cantilever arrays, followed by a discussion on practical experiment considerations for inspection applications. Selected example images of silicon calibration grating, highly-oriented pyrolytic graphite, and extreme ultraviolet lithography masks are captured using an array of four active cantilevers ("Quattro") with a 125 {textmu}m tip separation distance. With more engineering integration, this high-throughput, large-scale imaging tool can provide 3D metrological data for extreme ultraviolet (EUV) masks, chemical mechanical planarization (CMP) inspection, failure analysis, displays, thin-film step measurements, roughness measurement dies, and laser-engraved dry gas seal grooves.
3.
Yip Fun Yeung*; Fangzhou Xia; Juliana Covarrubias; Mikio Furokawa; Takayuki Hirano; Kamal Youcef-Toumi
Robotic Method and Instrument to Efficiently Synthesize Faulty Conditions and Mass-Produce Faulty-Conditioned Data for Rotary Machines Proceedings Article
In: IEEE International Conference on Robotics and Automation (ICRA), 2023.
Abstract | Links | BibTeX | Tags: Actuator, Automation, Design, Experimentation, Instrumentation, Intelligence, Mechatronics, Motion Control, Theory
@inproceedings{2023ICRA,
title = {Robotic Method and Instrument to Efficiently Synthesize Faulty Conditions and Mass-Produce Faulty-Conditioned Data for Rotary Machines},
author = {Yip Fun Yeung* and Fangzhou Xia and Juliana Covarrubias and Mikio Furokawa and Takayuki Hirano and Kamal Youcef-Toumi},
url = {https://ieeexplore.ieee.org/document/10161055},
year = {2023},
date = {2023-05-29},
urldate = {2023-05-29},
booktitle = {IEEE International Conference on Robotics and Automation (ICRA)},
abstract = {Condition synthesis is vital for generating data for fault detection and diagnosis studies. Traditional methods rely heavily on human labor. This study proposes a robotic method and its instrument to efficiently synthesize faulty conditions and mass-produce data to develop fault detection and diagnosis algorithms. The first contribution is the formalization of a new approach called Robotic Condition Synthesis, which shifts the traditionally labor-intensive task of condition synthesis to a robot-based force control task. The second contribution is developing a new robotic manipulator, which is more effective than current lab-grade robots for the tasks involved in the Robotic Condition Synthesis. The third contribution is empirical evidence of the superiority of this new robot in performing the Robotic Condition Synthesis tasks. This study also explores the potential of the new robot by conducting a three-dimensional system identification of a rotordynamic plant, which lays the foundation for more advanced Robotic Condition Synthesis policies in the future.},
keywords = {Actuator, Automation, Design, Experimentation, Instrumentation, Intelligence, Mechatronics, Motion Control, Theory},
pubstate = {published},
tppubtype = {inproceedings}
}
Condition synthesis is vital for generating data for fault detection and diagnosis studies. Traditional methods rely heavily on human labor. This study proposes a robotic method and its instrument to efficiently synthesize faulty conditions and mass-produce data to develop fault detection and diagnosis algorithms. The first contribution is the formalization of a new approach called Robotic Condition Synthesis, which shifts the traditionally labor-intensive task of condition synthesis to a robot-based force control task. The second contribution is developing a new robotic manipulator, which is more effective than current lab-grade robots for the tasks involved in the Robotic Condition Synthesis. The third contribution is empirical evidence of the superiority of this new robot in performing the Robotic Condition Synthesis tasks. This study also explores the potential of the new robot by conducting a three-dimensional system identification of a rotordynamic plant, which lays the foundation for more advanced Robotic Condition Synthesis policies in the future.
2.
Jiajie Qiu^; Hongjin Kim^; Fangzhou Xia*; Kamal Youcef-Toumi
Disturbance Rejection Control for Active Vibration Suppression of OHT Wafer Transfer Vehicles Journal Article
In: Machines, vol. 11, no. 2, pp. 125, 2023.
Abstract | Links | BibTeX | Tags: Actuator, Automation, Design, Experimentation, Instrumentation, Mechatronics, Modeling & Simulation, Motion Control, Theory
@article{2023Machines,
title = {Disturbance Rejection Control for Active Vibration Suppression of OHT Wafer Transfer Vehicles},
author = {Jiajie Qiu^ and Hongjin Kim^ and Fangzhou Xia* and Kamal Youcef-Toumi},
url = {https://www.mdpi.com/2075-1702/11/2/125},
doi = {10.3390/machines11020125},
year = {2023},
date = {2023-01-01},
urldate = {2023-01-01},
journal = {Machines},
volume = {11},
number = {2},
pages = {125},
abstract = {In modern semiconductor fabrication plants, automated Overhead Hoist Transport (OHT) vehicles transport wafers in Front Opening Unified Pods (FOUPs). Even in a cleanroom environment, small particles excited by the mechanical vibration of the FOUP can still damage the chips if such particles land on the critical area of the wafers. To minimize the vibration excitation force transferred to the FOUP, this research focuses on controlling the vibration displacement level of an OHT Hand Unit—interface between the OHT vehicle and the FOUP. However, since the OHT vehicle and the FOUP keep traveling, the target system is floating and there exists no external anchoring point for a controlling force source. In addition, no sensor attachments are permitted on mass-production FOUPs, which makes this vibration level suppression problem more challenging. In this research, a custom testbed is designed to replicate the acceleration profile of the OHT vehicle under its travel motion. Then, system modeling and identification is conducted using simulation and experiment to verify the fabricated testbed design. Finally, a Disturbance Observer-Based Controller (DOBC) is developed and implemented on a custom active vibration suppression actuator with inertia force-based counterbalancing to reduce peak vibration amplitude from 870 µm to 230 µm.},
keywords = {Actuator, Automation, Design, Experimentation, Instrumentation, Mechatronics, Modeling & Simulation, Motion Control, Theory},
pubstate = {published},
tppubtype = {article}
}
In modern semiconductor fabrication plants, automated Overhead Hoist Transport (OHT) vehicles transport wafers in Front Opening Unified Pods (FOUPs). Even in a cleanroom environment, small particles excited by the mechanical vibration of the FOUP can still damage the chips if such particles land on the critical area of the wafers. To minimize the vibration excitation force transferred to the FOUP, this research focuses on controlling the vibration displacement level of an OHT Hand Unit—interface between the OHT vehicle and the FOUP. However, since the OHT vehicle and the FOUP keep traveling, the target system is floating and there exists no external anchoring point for a controlling force source. In addition, no sensor attachments are permitted on mass-production FOUPs, which makes this vibration level suppression problem more challenging. In this research, a custom testbed is designed to replicate the acceleration profile of the OHT vehicle under its travel motion. Then, system modeling and identification is conducted using simulation and experiment to verify the fabricated testbed design. Finally, a Disturbance Observer-Based Controller (DOBC) is developed and implemented on a custom active vibration suppression actuator with inertia force-based counterbalancing to reduce peak vibration amplitude from 870 µm to 230 µm.
2020
1.
Fangzhou Xia*; Chen Yang; Yi Wang; Kamal Youcef-Toumi
Model and Controller Design for High-speed Atomic Force Microscope Imaging and Autotuning Proceedings Article
In: ASPE Spring Topical Meeting on Design and Control of Precision Mechatronic Systems, American Society for Precision Engineering 2020.
Abstract | Links | BibTeX | Tags: Atomic Force Microscopy, Automation, Instrumentation, Mechatronics, Modeling & Simulation, Motion Control, Theory
@inproceedings{2020ASPE,
title = {Model and Controller Design for High-speed Atomic Force Microscope Imaging and Autotuning},
author = {Fangzhou Xia* and Chen Yang and Yi Wang and Kamal Youcef-Toumi},
url = {https://zenodo.org/record/5048303#.Y5icmnbMJD8},
year = {2020},
date = {2020-01-01},
urldate = {2020-01-01},
booktitle = {ASPE Spring Topical Meeting on Design and Control of Precision Mechatronic Systems},
organization = {American Society for Precision Engineering},
abstract = {Atomic Force Microscope (AFM) is a powerful nano-scale surface measurement instrument. However, significant operator experience is needed for successful imaging under various conditions. Parameters of the PID controller for probe deflection or oscillation regulation are tuned by the operator based on visual inspection of the trace and retrace tracking performance. With the development of high-speed AFM and for the purpose of operation overhead reduction, automated parameter tuning of the controller is needed. In this work, we propose a series of control and image improvement methods starting first with an automated PID controller tuning and adjustment method. The imaging speed can also be adjusted based on an error metric. Second, three methods including location-based scanning, line-based feedforward and error-corrected line scan, are proposed for image-level performance improvement. Third, in cases where topography variation and material properties are non-uniform across the sample surface, the controller needs to adapt to such changes on the fly to maintain stability and good tracking performance. Considering the complexity in contact mechanics and the requirement of high-bandwidth real-time operation, a single neuron PID is designed for model-free adaptive tracking. With a lumped parameter AFM model created in Matlab Simulink, the proposed algorithms are evaluated in simulation to demonstrate their effectiveness. With the proposed architecture, the methods can be used individually or together based on application to improve imaging performance.},
keywords = {Atomic Force Microscopy, Automation, Instrumentation, Mechatronics, Modeling & Simulation, Motion Control, Theory},
pubstate = {published},
tppubtype = {inproceedings}
}
Atomic Force Microscope (AFM) is a powerful nano-scale surface measurement instrument. However, significant operator experience is needed for successful imaging under various conditions. Parameters of the PID controller for probe deflection or oscillation regulation are tuned by the operator based on visual inspection of the trace and retrace tracking performance. With the development of high-speed AFM and for the purpose of operation overhead reduction, automated parameter tuning of the controller is needed. In this work, we propose a series of control and image improvement methods starting first with an automated PID controller tuning and adjustment method. The imaging speed can also be adjusted based on an error metric. Second, three methods including location-based scanning, line-based feedforward and error-corrected line scan, are proposed for image-level performance improvement. Third, in cases where topography variation and material properties are non-uniform across the sample surface, the controller needs to adapt to such changes on the fly to maintain stability and good tracking performance. Considering the complexity in contact mechanics and the requirement of high-bandwidth real-time operation, a single neuron PID is designed for model-free adaptive tracking. With a lumped parameter AFM model created in Matlab Simulink, the proposed algorithms are evaluated in simulation to demonstrate their effectiveness. With the proposed architecture, the methods can be used individually or together based on application to improve imaging performance.
Dr. Fangzhou Xia
Research Scientist
Mechanical Engineering Department
Physics Department
Massachusetts Institute of Technology