About

Jon Longtin is a Professor and Interim Chair in the Department of Mechanical Engineering at Stony Brook University. His research focuses on short-pulse laser-material interactions, precision laser measurement techniques, and microscale heat transfer. His work involves exploring the interactions between laser systems and materials at small scales, developing advanced measurement methods, and understanding heat transfer phenomena at microscale levels. As a faculty member, he contributes to the advancement of laser-based technologies and their applications in engineering, emphasizing precision and microscale processes.

Research topics

• Engineering
• Nuclear engineering
• Chemistry
• Computer Science
• Materials science
• Environmental science
• Electrical engineering
• Mathematics
• Electronic engineering
• Thermodynamics
• Mathematical optimization
• Mechanics
• Waste management
• Physics
• Mechanical engineering
• Automotive engineering

Selected publications

• Multi-Material Topology and Magnetization Co-Optimization of Circular Halbach Arrays Via a Cardinal Basis Function-Based Level Set Method

  Journal of Mechanical Design · 2026-02-06

  article

  Abstract A Halbach array is a specialized arrangement of permanent magnets that generates a strong, uniform magnetic field in a designated region and suppresses it elsewhere. This configuration has been widely applied in magnetic levitation systems, electric motors, particle accelerators, and magnetic resonance imaging devices due to its high efficiency, reduced weight, and precise directional control. Linear Halbach arrays concentrate the field on one side, making them suitable for applications such as maglev trains and conveyor systems. Cylindrical Halbach arrays, with magnets arranged in a circular configuration, produce a uniform internal field while minimizing the external field, which is advantageous in brushless motors and imaging systems. The traditional design of Halbach arrays has relied heavily on engineering intuition because of the complexity of magnet placement and orientation. With advances in numerical methods, topology optimization now provides a systematic approach to determining both material distribution and magnetization directions to maximize magnetic flux in the target region. In this article, we propose a cardinal basis function (CBF)-based level set method for the design of circular Halbach arrays capable of generating an area-averaged magnetic field. The finite difference method is employed to optimize magnetization directions simultaneously with geometry, providing additional design flexibility. The CBF-based level set method reduces computational cost and accelerates convergence, improving the overall efficiency of the optimization. Furthermore, multi-material topology optimization is incorporated, enabling the addition of permanent magnets with distinct magnetization directions to achieve greater control over magnetic flux distribution.

  PublisherDOI

• Shape and Topology Optimization of Circular Halbach Array Using a Cardinal Basis Function (CBF) Based Parametric Level Set Method

  2025-08-17 · 1 citations

  article

  Abstract A Halbach array is a specialized arrangement of permanent magnets designed to generate a strong, uniform magnetic field in the designated region. This unique configuration has been widely utilized in various applications, including magnetic levitation (maglev) systems, electric motors, particle accelerators, and magnetic seals. The advantages of Halbach arrays include high efficiency, reduced weight, and precise directional control of the magnetic field. Halbach arrays are commonly categorized into two configurations: linear and cylindrical. A linear Halbach array produces a concentrated magnetic field on one face and is frequently employed in maglev trains and conveyor systems to ensure stable and efficient operation. In contrast, a cylindrical Halbach array consists of magnets arranged in a ring, generating a uniform magnetic field within the cylinder while suppressing the external field. This configuration is particularly advantageous in applications such as brushless electric motors and magnetic resonance imaging (MRI) systems. Traditionally, the design of electromagnetic systems incorporating Halbach arrays relied on engineers’ expertise and intuition due to the complexity of the permanent magnet configuration. However, advancements in numerical methods, particularly topology optimization, have introduced a systematic approach to optimizing the shape and distribution of permanent magnets within a given design domain. In the context of Halbach array design, topology optimization aims to maximize the total magnetic flux within a designated region while simultaneously determining the optimal material distribution to achieve a specified design objective. This approach enhances the performance and efficiency of Halbach arrays, providing a more precise and automated framework for their development. In this paper, we propose a Cardinal Basis Function (CBF)-based level-set method for designing a circular Halbach array capable of generating a uniform magnetic field within a designated region. The CBF-based level-set method offers significant computational advantages by reducing the computational cost and accelerating the convergence process. This approach enhances the efficiency of the optimization process, making it a promising technique for the systematic design of Halbach arrays.

  PublisherDOI

• IN MEMORIAM: PROFESSOR DARRELL W. PEPPER â A TRIBUTE TO AN EXCEPTIONAL ENGINEERING EDUCATOR AND RESEARCHER

  Computational Thermal Sciences An International Journal · 2024-01-01

  articleOpen access

  This is an in-memoriam honoring Professor Darrell W. Pepper as an exceptional researcher, educator, and engineer.

  PublisherOA PDFDOI

• Cocurrent loop thermosyphon heat transfer system for sub-ambient evaporative cooling and cool storage

  OSTI OAI (U.S. Department of Energy Office of Scientific and Technical Information) · 2023-01-23

  articleOpen access1st authorCorresponding

  Provided is a cocurrent loop thermosyphon system and method for operation thereof. The system includes a first rising tube having first and second ends; a condenser having first and second ends, with the first end connected to the second end of the first rising tube; a return tube having a first end connected to the second end of the condenser; a second rising tube having a first end connected to a second end of the return tube; a pump that pumps liquid within the second rising tube; and an evaporator having a first end connected to the second end of the second rising tube. The second end of the evaporator outputs vapor created by a change in state of the liquid to the first end of the first rising tube.

  PublisherOA PDF

• Robust Topology Optimization of Synchronous Reluctance Motors Using Cardinal Basis Function Based Level Set Method

  2023-08-20 · 1 citations

  article

  Abstract Synchronous reluctance motors (SynRMs) have gained considerable attention in the field of electric vehicles as they reduce the need for permanent magnets in the rotor, resulting in less material and manufacturing costs. However, their lower average torque and torque ripple vibrations have been identified as key issues that require resolution. In this study, we present a SynRM design framework employing the cardinal basis functions (CBF)-based parametric level set method. The SynRms design problem is recast as a variational problem constrained by Maxwell’s equations which describe the behavior of electric and magnetic fields in the SynRM. A continuum shape sensitivity analysis is carried out using the material derivative and adjoint method. A distance regularization energy function is employed to maintain the level set function as a signed distance function during the optimization. The parametric topology optimization problem is computationally solved using the Method of Moving Asymptotes (MMA). To demonstrate the effectiveness of our approach, we present a numerical example that compares the torque characteristics of the optimal design with those of a reference design. Preliminary results show that the optimized SynRM has a 30.30% increase in average torque, along with a slight increase in torque ripple, compared to the reference model.

  PublisherDOI

• AUTOMATED, INTELLIGENTLY MODULATING STOVES (AIMS) TO REDUCE RESIDENTIAL SPACE HEATING EMISSIONS

  2023-01-01

  articleOpen access
  PublisherOA PDFDOI

• Enabling residential heating decarbonization through hydronic low-temperature thermal distribution using forced-air assistive devices

  Applied Energy · 2023-10-20 · 4 citations

  articleOpen access

  Space heating represents approximately one-tenth of the United States’ energy use and has a breadth of potential for emission reduction. An element of space heating, hydronic heat distribution methods, use water supply temperatures up to 82.2 °C (180 °F). However, this operating temperature can be incompatible with high-efficiency heat generation systems, which typically provide heating temperatures of up to 60 °C (140 °F). In this work, a low-cost retrofit solution is developed using experimentally validated computational tools by incorporating an airflow distributor that preferentially directs the airflow from a fan to enhance heat transfer over the finned-tube heat exchanger found in conventional baseboards. The same heat output of traditional baseboard heat distribution systems operating at higher water supply temperatures (71.1 – 82.2 °C) can also be achieved at lower temperatures (≤ 60 °C). Specifically, results indicate that the technology can produce more than a 46.7% improvement in the heat transfer output at temperatures as low as 60 °C (140 °F), effectively matching the same output range achieved by 71.1 – 82.2 °C (160–180 °F) water supply temperatures. An important benefit of this solution is that it utilizes the existing infrastructure as opposed to requiring the replacement of the entire distribution system. Additionally, this technology enables existing building infrastructure to be coupled with newer, high-efficiency heating systems such as condensing boilers, solar-thermal systems, and geothermal/air-to-water heat pumps that may produce lower water supply temperatures (60 °C). A geospatially resolved techno-economic and environmental analysis is completed and presented to further understand the equivalent carbon footprint of enabling higher efficiency heat generation systems with the improved efficiency heat distribution system disclosed. Using 2021 grid-average emission factors, an emission reduction of up to a 67.5% decrease (2658 kgCO2/yr) for a single-family home, depending on state and climate region, could be realized by replacing a traditional natural gas-fired boiler with an air-to-water heat pump coupled to the same high-temperature heat distribution system along with the low-cost retrofit solution. A complete CO2 emission reduction of 6688 kgCO2/yr, depending on state and climate region, could be realized if all electricity is further renewably sourced. Thus, this study provides a possible pathway towards enabling the reduction of operational emissions in space heating.

  PublisherDOI

• Cyclops

  2022-08-11 · 7 citations

  articleOpen access

  The ultimate goal of virtual reality (VR) is to create an experience indistinguishable from actual reality. To provide such a "life-like" experience, (i) the VR headset (VRH) should be wireless so that the user can move around freely, and (ii) the wireless link, connecting the VRH to a high-performance renderer, should support high data rates (tens to hundreds of Gbps). Industry is already pushing towards such wireless VRHs; however, these wireless links can only support a few Gbps rates. In general, current radio-frequency (RF) links (including mmWave) are not able to provide desired data rates. In this paper, we build a system, we call Cyclops, which uses free-space optical (FSO) technology to create a high-bandwidth VR wireless link. FSO links are capable of very high data rates (up to Tbps) due to the high frequencies of light waves and narrow beams. The main challenges in developing an effective FSO link are: (i) designing a link with sufficient movement tolerance, and (ii) developing a viable tracking and pointing (TP) mechanism which maintains the link while the VRH moves. As traditional TP approaches seem infeasible in our context, we develop a novel TP approach based on learning techniques, leveraging the VRH's inbuilt tracking system. We build robust 10 Gbps and 25Gbps link prototypes from commodity components, demonstrate their viability for expected movement speeds of a VRH, and show that, with certain custom-built components, we can support much higher movement speeds and bandwidths.

  PublisherOA PDFDOI

• Topology Optimization of Permanent Magnets for Generators Using Level Set Methods

  2022 · 3 citations

  • Computer Science
  • Computer Science
  • Mathematical optimization

  Abstract Generators are considered as the core application of electromagnetic machines, which require high-cost rare-earth-based permanent magnets. The development of generators is moving toward high efficiency and increased environmental friendliness. Minimizing the use of rare earth materials such as magnetic materials under the premise of machine performance emerges as a challenging task. Topology optimization has been promisingly applied to many application areas as a powerful generative design tool. It can identify the optimal distribution of magnetic material in the defined design space. This paper employs the level-set-based topology optimization method to design the permanent magnet for generators. The machine under study is a simplified 2D outer rotor direct-drive wind power generator. The dynamic and static models of this generator are studied, and the magnetostatic system is adopted to conduct the topology optimization. The optimization goals in this study mainly focused on two aspects, namely the maximization of the system magnetic energy and the generation of a target magnetic field in the region of the air gap. The continuum shape sensitivity analysis is derived by using the material time derivative, the Lagrange multiplier method, and the adjoint variable method. Two numerical examples are investigated, and the effectiveness of the proposed design framework is validated by comparing the performance of the original design against the optimized design.

  PublisherDOI

• The Corevent 2020: An Open-Source, Rapid Design-Buildtest Emergency Ventilator Developed for Covid-19

  Technology & Innovation · 2022-03-01

  article1st authorCorresponding

  In the first quarter of 2020, SARs-CoV-2 (COVID-19) infections began to grow at an alarming rate despite drastic measures to reduce infection rates. Severe COVID-19 cases required mechanical ventilation, resulting in ventilator shortages worldwide. To address the ventilator shortages, the authors developed the CoreVent 2020, an emergency-use ventilator for adult patients that was designed, built, and tested in ten days. The CoreVent 2020 is a pressure-cycled, time-limited ventilator with a breath-assist mode that operates on standard pressurized oxygen and medical air. It provides adjustable peak inspiratory pressure (PIP) and positive end-expiratory pressure (PEEP). A medical-grade commercially available breathing circuit is used to minimize non-medical component requirements. The CoreVent 2020 was fabricated in-house at Stony Brook University Hospital and tested on three mechanical lung simulators in which the operating modes and alarm features were demonstrated. Animal studies were also performed in both normal breathing mode and breath-assisted modes. Arterial blood gas measurements confirmed that the ventilator provided satisfactory ventilation for the test subjects. The COVID-19 pandemic presented unique constraints on the design and innovation process not normally encountered in typical practice. Design decisions such as component choice, delivery time, and ease of high-volume, rapid manufacturing influenced all aspects of the design process. This aspect of the design/innovation process is also discussed, as well as an introductory discussion on how training and simulations can be developed so that innovation can occur efficiently in future crises situations.

  PublisherDOI

Recent grants

• SST: Enabling Concepts in Embedded Sensors, Sensor Manufacturing and Integration

  NSF · $747k · 2004–2009

Frequent coauthors

• Sanjay Sampath

  Stony Brook University

  75 shared

• Ju Sun

  Deakin University

  37 shared

• Chunzhen Fan

  Zhengzhou University

  34 shared

• S. Tankiewicz

  Senseonics (United States)

  26 shared

• Gaosheng Fu

  25 shared

• Lei Zuo

  University of Michigan–Ann Arbor

  23 shared

• R. J. Gambino

  23 shared

• Jinggao Li

  Lanzhou University of Technology

  21 shared

Education

• Ph.D., Mechanical Engineering

  Stony Brook University

  2000

• M.S., Mechanical Engineering

  Stony Brook University

  1996

• B.S., Mechanical Engineering

  University of New Hampshire

  1994

Awards & honors

• 1996 JSPS Postdoctoral Fellowship
• 1997 NSF CAREER and PECASE awards
• 1998 Excellence in Teaching Award