Tag Archives: Bahman Tavassoli

Liquid Crystal Thermography Provides Precise Heat Maps

It is critical for the engineers to accurately determine temperature of a design, whether it is at the chip, component, board, or system level, to ensure that the design will function properly and maintain its optimal performance over its expected lifetime and meet its specified mean time between failures (MTBF). Thermal management of electronics is unarguably a critical component of the design phase.

To optimize thermal management, it is also critical to get an accurate picture of the heat distribution across a device or a board. One of the most precise methods for mapping temperature is liquid crystal thermography (LCT). LCT uses thermochromic liquid crystals (TLC) to give engineers a visual representation of the heat distribution based on the changing colors of the TLC when heated.

Liquid Crystal Thermogrpahy

Liquid crystal thermography systems give a visual representation of the heat on a device, board, or system using thermochromic liquid crystals, high-resolution cameras, and an LED light source. (Advanced Thermal Solutions, Inc.)

LCT technology has been around since the 1950s and has been used in the electronics industry since the 1980s. In 1975, researchers published a review of LCT and it applications in the study of convective heat transfer that determined the method provided “both qualitative and quantitative heat transfer and fluid flow information to be obtained on heated objects placed in forced convection environments.” [1]

The authors added, “In addition to yielding precise quantitative heat transfer information, the liquid crystal thermographic technique afforded the opportunity to visually observe the effects of flow separation, the separation bubble region, the turbulent boundary layer, and the turbulent wake on the surface temperature of the heated cylinder.”

What are Thermochromic Liquid Crystals?

Thermochromic liquid crystals are the key to the LCT process. Rather than changing from a solid to a liquid when heated, TLC have an intermediate liquid-crystal phase and the temperature in which this phase-change takes place is precisely defined depending on the composition of the crystals. The phase-change causes the TLC, which starts as transparent, to reflect different wavelengths of light, represented visually as different colors.

Liquid Crystal Thermography

TLC readings using thermVIEW Lite software from ATS. The TLC shows up as different colors depending on the heat applied, while the software is calibrated to give precise temperature readings. (Advanced Thermal Solutions, Inc.)

As explained by Dr. Bahman Tavassoli in an article for Laser Focus World, “Normally clear or slightly milky in appearance, liquid crystals change in appearance over a narrow range of temperature, called the color-play interval. This is the interval between the first (red) and last (blue) reflection. The displayed color is red at the low-temperature margin of the color-play interval and blue at the high end. Within the color-play interval, the colors change smoothly from red to blue as a function of rising temperature, with blue light corresponding to the clearing-point temperature.” [2]

To visualize the temperature response of the TLC, a bright and stable white light is required to remove the infrared and ultraviolet radiation from the output spectrum. Tavassoli explained, “Any IR energy present in the incident light spectrum will cause unwanted radiant heating of the test surface. Exposure to UV radiation can cause rapid deterioration of the TLC surface, which will result in unreliable color-temperature responses.”

Temperature ranges for the TLC material are established by the manufacturers. Narrow-band TLC have bandwidths below 1-2°C, while wide-band TLC range between 5-20°C. TLC are typically designated by a two-color/temperature system. For instance, R35C5W would indicate that the TLC would show up as red starting at 35°C and that the blue start temperature would be 5°C above the red, allowing engineers to see the estimated bandwith of the TLC.

TLC are inherently oily, and their thermal performance degrades from exposure to chemicals and UV radiation, so manufacturers have developed microencapsulation or polymer dispersion methods to make the materials easier to use in laboratory settings. Microencapsulation provides high resistance to contamination, but the polymer dispersion method provides a more brilliant color response. [3]

How do you use Liquid Crystal Thermography systems?

To obtain the most accurate results from LCT, a smooth and contamination-free surface is important. Test surfaces and calibration tools should be cleaned with alcohol, if possible, and dried before the process begins. A thin and uniform coating of black paint is applied to the test surface and dried using a hot air gun at low temperature. Once the surface is dry, the TLC materials can be applied to the test surface. [4]

A bright, stable, white light source is required to obtain an accurate reflected light intensity from the TLC-coated surface. As explained by Dr. Kaveh Azar in an introduction to LCT techniques, “Consistent light source settings and lighting-viewing arrangements between calibration and actual testing are essential to minimize color-temperature interpretation errors.”

Calibration is the key to using LCT. According to Dr. Tavossoli, the system for calibrating TLC is similar to calibrating the voltage-temperature response of a thermocouple. TLC is subjected to known temperature levels and the response is recorded with a color-sensitive camera. The response is recorded at different temperature levels on a test surface and the system develops calibration files that can later be used to interpret the response of TLC on the device being studied.

The following graph shows the relationship between temperature and color of a range of TLC:

Liquid Crystal Thermography

While TLC response is visible to the naked eye, the LTC system uses a high-resolution, solid-state color camera and calibrated software to more precisely determine the temperature.

Advanced Thermal Solutions, Inc. (ATS) has recently added to its line of LCT systems to provide a cost-effective tool for temperature mapping studies. tvLYT™ is accurate, easy to assemble, and easy to use. It comes in a portable case containing the arm, high-resolution macroscopic optic camera, LED light source, black paint, and TLC material for the required temperature range. tvLYT™ can be quickly connected to a computer through a USB and uses thermVIEW™ Lite software (downloadable on the ATS website) to calibrate the readings and provide precise results.

Liquid Crystal Thermography

The tvLYT™ liquid crystal thermography system from ATS provides highly accurate temperature mapping capability using TLC. (Advanced Thermal Solutions, Inc.)

For more information about tvLYT™, visit https://www.qats.com/Products/Instruments/Surface-Thermography/tvLYT.

What are the benefits of LCT?

There are several techniques for measuring temperature across a system, including the use of thermocouples and resistance thermometers. These are common techniques used in labs across the world, but there are challenges and limitations to that method.

As one report noted, “Traditional techniques employing sensors such as thermocouples and resistance thermometers can measure temperature at individual locations. Hence, a large number of sensors are required for complete mapping of the surface. Since physical sensors occupy space, the measurements are to be interpreted as spatial averages. This route may prove to be disadvantageous in regions of localized peaks and valleys of heat transfer. Liquid crystal thermography proves to be useful under these circumstances.” [5]

The tools for thermal imaging, which visualize IR emissions to show heat patterns, continue to improve, seemingly by the day, and several companies have released cameras that can be attached to a mobile phone to improve the mobility and accessibility of thermal imaging. [6] IR cameras can give a quick visualization of the heat emitted from a device and are excellent tools for finding hot spots at the system level, but they lack the precise temperature readings that LCT captures and accuracy counts in thermal management.

Comparison of LCT and IR systems. [4]

LCT gives engineers flexibility. It can be used in to measure temperature across micron-level electronic circuits or large-scale gas turbines. LCT is used in a wide range of applications from detecting lamination in composite polymer materials [7] to studying turbulent boundary layers in a water tunnel [8] to biomedical studies [9] such as testing for skin cancer, breast cancer, blood circulation, and more.

Because precision is the most important benefit to using LCT for temperature mapping studies, ATS has offered four free calibrations during the first year after purchasing tvLYT™ and also lifetime technical support.

For more information about ATS liquid crystal thermography systems, or thermochromic liquid crystal materials, visit https://www.qats.com/Products/Instruments/Surface-Thermography.

If you have questions about any ATS product or its consulting and design surfaces, contact ATS at ats-hq@qats.com.

1. http://heattransfer.asmedigitalcollection.asme.org/article.aspx?articleid=1436225
2. https://www.laserfocusworld.com/articles/print/volume-41/issue-12/features/thermal-imaging-liquid-crystal-thermography-characterizes-heat-issues.html
3. https://www.electronics-cooling.com/1995/10/making-surface-temperature-measurements-using-liquid-crystal-thermography/#
4. https://www.ewh.ieee.org/soc/cpmt/presentations/cpmt0201b.pdf
5. http://www.nptel.ac.in/courses/112104039/pdf_version/lecture35.pdf
6. https://www.thermal.com/compact-series.html
7. https://onlinelibrary.wiley.com/doi/pdf/10.1002/pc.20453
8. https://www.sciencedirect.com/science/article/pii/S0924424715300224
9. http://zm8pc.ippt.gov.pl/papers/JCPT_2014012610120554.pdf

Q&A: ATS Thermal Engineer Sridevi Iyengar

Sridevi Iyengar

ATS thermal and field application engineer Sridevi Iyengar does CFD modeling (like the one shown above) and on-site consulting for ATS from her location near Bangalore, India. (Advanced Thermal Solutions, Inc.)

Advanced Thermal Solutions, Inc. field application and thermal engineer Sridevi Iyengar recently spoke with Marketing Communications Specialist Josh Perry about her career in engineering and the work that she does for ATS. Iyengar works near her home in Bangalore, India and provides ATS with CFD simulations and on-site support for customers in the region.

In this Q&A, Iyengar speaks about why she became an engineer in the first place, how she came to work at ATS, the type of projects that she works on, the challenges that she faces as a woman in a male-dominated industry, and what it is like working halfway around the world from the engineers at ATS’ Norwood, Mass. campus.

JP: How did you get interested in engineering? How did it all start for you?
SI: I was a good student in high school and in college and my father is a metallurgical engineer. He was a professor in one of the premier institutes in India, the Indian Institute of Science. When we were at the crossroad, during 12th grade, honestly the bright students either went into medicine or engineering and since my math skills were pretty good and I’d been to the Indian Institute of Science a couple of times I had written the entrance examinations for both streams. For engineering, I got into a very good school.

Although I didn’t know about the different disciplines of engineering, I happened to go into chemical engineering because that’s what my rank got me into. I liked it because chemical is kind of a fusion between math and physical phenomena and so that’s where my engineering journey started.

After my Bachelor’s, I wanted to do higher studies. I got married and came to the United States and I wanted to continue in my field of study. I didn’t want to move into software like pretty much everybody else from India when they move to the U.S. I wanted to keep myself different and I had a lot of support for that from my family. The first place I set up home is Norwood, Mass. (in 1993). I was preparing for my GRE and contemplating whether I should take my AGRE but I got positive responses from a couple of schools that I was also keen on getting into. I had options. One was the University of Massachusetts – Lowell, one was Rutgers University and the University of California – San Diego. I chose San Diego.

I was actually accepted into the doctoral program, however at UC-San Diego I liked the fluid mechanics and heat transfer program but then I didn’t want to jump into a Ph. D. without really having real world experience. I wanted to finish my Master’s, work for a few years and then maybe come back if I was interested. Much to my disappointment of my dad, I dropped out of the doctorate program with my Master’s and entered the job scene.

My entry into thermal engineering was kind of by chance. My first job was with Structural Dynamics Research Corporation (SDRC) in San Diego. It was the advanced test and analysis group. I had a background in heat transfer and fluid mechanics and therefore I joined as an intern and they made me do a little bit of this and that. The software associated with the IDEAS master series for electronics cooling was MAYA-ESC electro-systems cooling and TMG (thermal model generator) and we did a project for Cisco Systems in the Bay Area. I worked for about a year and half at ATA-SDRC. SDRC was doing a lot of projects for defense and their core area was becoming more and more defense and I was not a U.S. citizen so it was very difficult for them to assign me to projects because I didn’t have security clearance. At that time I jumped ship and I joined Cisco Systems as a mechanical engineer.

JP: How did you hear about Advanced Thermal Solutions, Inc.? How did you end up working here?
SI: ATS, the company, I knew even when I was at Cisco back in 1999. I was with Cisco until 2005 and at that time I knew about Advanced Thermal Solutions because as a mechanical engineer my job was also to source heat sinks. Also, that it was based in Norwood kind of struck a chord and it remained in my mind. I had known a lot about [ATS CEO, President and founder] Dr. Kaveh Azar because a close colleague of mine had worked closely with Kaveh. And of course Qpedia Thermal eMagazine was/is a very useful online journal.

How I joined ATS was a very, very chance meeting. We moved back to India in 2009 and I was working for an aluminum extrusion company in their thermal management division. It’s a Swedish company called Sapa. Sapa opened an office in India and it was just the sales manager and myself in the Indian team when I started. I worked with Sapa for three years and I was working for their global application team, half working for Sweden and half trying to set up the market in India. At Sapa I did a little bit more than thermal management. Sapa acquired an extrusion facility and also had a machining/anodizing unit. I was exposed to various aspects of manufacturing with regards to aluminium extrusions, fabrication etc., and worked on several other projects, which needed someone who could work with the customers and the manufacturing team at Sapa – sort of like a liaison and the engineering hand of the sales person.

When I quit Sapa, I thought I would go freelance doing electronics cooling consulting and I met one of the sales channel partners for ATS and with him I went and met Dr. Kaveh and Shashwat Shashwat (ATS Product Realization Manager), who were visiting India. This was in May of 2014 and initially it was just supposed to be a ‘hello, how are you’ meeting, but then we started talking and having common professional contacts and interests made it a very interesting interaction. We had lunch and when I came back home that evening Shashwat called me and asked if I was interested in working for ATS. I had no doubts whether I would take this opportunity; I took it with both hands. It’s worked out very well for me so far.

JP: What kinds of projects are you working on for ATS?
SI: There were two things for me, the mandate. One was that we wanted to beef up our presence in India. We already had a sales presence and we were selling heat sinks through Digi-Key and if the engineers know what they want then it’s not a big deal, but it helps them so much to know that there is technical staff from ATS present in India and in Bangalore in the southern region. They call and they say, ‘We’re looking at this heat sink, do you think it’s okay?’ Otherwise they send an email and then they wait for Norwood to reply. So, my role was to support the local sales partners that we have. They do the initial sales call and everything, but then if there’s anything technical they can say, ‘You know, ATS has a presence here? We have this engineer who is in electronic cooling and she has experience.’ I’ve gone to several meetings with them.

Secondly, for the U.S. customers, when it comes to CFD simulations like FloTherm then I work very closely with Norwood. In fact, I’ve done quite a few projects with [ATS field application engineers] Greg Wong or Peter [Konstalilakis], Vineet [Barot] too. A lot of times there are CFD simulations, they face the customers, they get the answers and I run the simulation and build the models here, do the analysis, we discuss the results and they send it to the customer.

JP: Is there a lot of collaboration between yourself and the engineers here in Norwood?
SI: Almost daily. I am online pretty much every day from 6 and on Wednesdays and Fridays we have the team meeting. On other days, I usually chat up with my counterpart on the project and, if it’s a major project, then the discussion is fairly involved. A lot of times, I’ll have a lot of questions so I’ll contact my teammates during my evening and he’ll take it up with the customer, get all the questions answered and by the time morning rolls around everything is sent to me by email and I get through my day. There is a lot of collaboration.

JP: Looking at thermal engineering as a whole, where do you see the industry going?
SI: People realize the importance of up-front thermal design and these folks who are dealing with high-powered components are aware of the importance of up-front thermal design. However there are still a lot of projects in which the hardware engineers are still not zoned into thinking of up-front thermal management, it’s coming in as kind of a ‘Oh it’s too hot, let’s do something about it’ approach. However, I think that mindset is changing a lot and I think the next-gen heat sinks like vapor chambers, heat pipes, and nano-materials will really start making their appearance more and more in thermal solutions because we’re getting to a point where the run of the mill is not cutting it.

JP: Do you see that change coming fairly quickly? In this industry, it seems like things change every day.
SI: The mindset should change because there’s always an aversion towards liquid and PCB. The more we educate people and the fact that we see everything in liquid cooling systems working…It takes some time for them to know that, okay it is a fairly fail-safe method. It will take at least a year or two and it should be running at that time and then people will catch on. It’s not something that can be easily brought on, I think, because generally we know that liquids and electronic components don’t mix. To assure them that it will not mix and there’s no chance of it coming into contact, I think that’s the stumbling block.

It’s market education and also having systems out there functioning, so that we can show them it’s not just theoretical. You have systems in practice and I think that makes a difference. If we can show it in theory, it doesn’t help as much because in theory everything looks wonderful, so we need to show them in practice and all the possible problems that can come up have been addressed and it is working in the field not just in the test lab.

JP: As a woman in a predominantly male-dominated industry, has it been difficult at all?
SI: In India, even back in 1993, we had a lot of engineers who were graduating but a lot of them didn’t stay back in what I call hardcore engineering. People used to go into information technology because they thought somehow it was more suitable for the women in the workforce situation. But I personally, I’ve had a fulfilling time and it is good to distinguish yourself and be different. The work that we do at ATS is hardcore engineering and we have engineers to lead us. We have Dr. Kaveh Azar and Dr. Bahman Tavassoli who have years of engineering experience and yeah sometimes they come down hard on us but that’s because they know what they’re doing. They’ve been there, done that, and they want to extract the best out of you and they want you to think like an engineer always. That’s what is unique of working at ATS.

JP: Do you hope to inspire other women to not only join the field, but stick with the ‘hardcore’ engineering?
SI: Yeah, absolutely. There have been young women who have reached out to me, young engineers who graduated in India, and I tell them have patience and learn the skills needed to get a job. It’s very easy to learn a few programming languages and jump into IT, especially in India right now, but you’re going to be just like anybody else. If your heart really lies in engineering, you should stick on, network, upgrade your skills and you’ll definitely find a job. The first job is everything you need and after that, if you do well there, then the path is smooth.

JP: How has it been for you as a ‘distant worker’ in terms of not being located here in Norwood? We have a lot of great technology like Skype and GoToMeeting, how have you found it being a ‘distant worker’?
SI: Since I interact with the engineers on an almost daily basis it is not that different. ATS engineers and the customers are very understanding of the time difference and accommodate the meetings, if any, so that it is not totally at unearthly hours for me. I also have the freedom to have my own schedule and that is very helpful since I am a working mother. I’ve been to ATS once and so I have met most of the team there.

The only thing is that I don’t have that touch and feel. Sometimes the ATS engineers have the heat sinks/components on their desk and they’re looking at it. A lot of times they will look at it, turn it around and these are things that I will have to accomplish through video call on Skype or the engineers take pictures and send them to me. But it’s not the same. That’s the only drawback. And of course when you folks have your team lunches/picnics … I feel left out.

JP: From our conversation, it sounds like you really like challenging projects?
SI: I think we all like to be challenged once in a while. With involved models, one of the challenges was I’d have to remotely log in and run the model in the 12-core PC and ensure nobody is logged in and I used to run it through the night and post-process it via remote connection. I’d transfer the results over and make the PowerPoint. However I was given a super fast simulation computer locally so all I need is a VPN connection. Even if the VPN connection goes down, FloTherm will not cut off the simulation and it runs through the solve.

Every now and then I support local customers with their heat sink selection requests. Some local customers have asked for training sessions as well, which is something I would like to start fairly soon.

To learn more about Advanced Thermal Solutions, Inc., visit www.qats.com or contact ATS at 781.769.2800 or ats-hq@qats.com.

ATS welcomes engineering students from Tufts

Tufts University

Dr. Bahman Tavassoli of Advanced Thermal Solutions, Inc. gives a demonstration of a wind tunnel to Dr. Marc Hodes (left) and a group of students from Tufts University. (Advanced Thermal Solutions, Inc.)

On Friday, Oct. 14, Advanced Thermal Solutions, Inc. (ATS) welcomed Dr. Marc Hodes and a group of six mechanical engineering students from Tufts University to its Norwood, Mass. campus. The students learned about the company, its products, and took a tour of two of ATS’ four laboratories to see some of the testing equipment utilized by ATS engineers.

After a welcome from ATS founder, President and CEO Dr. Kaveh Azar, the students enjoyed a brief introduction from Marketing Director John O’Day about the company, its products, and the importance of thermal management in the design of today’s high-powered electronics.

The lab tours were led by Dr. Bahman Tavassoli, ATS Chief Technologist. First, he took the students into the Characterization Lab to demonstrate the BWT-104 open-loop wind tunnel and the CLWT-067 closed-loop wind tunnel. The students learned how ATS engineers use Candlestick sensors, thermocouples and the iQ-200 to measure air velocity, temperature, and pressure across a PCB using one system. There was also a thermVIEW Liquid Crystal Thermography unit set up, in which ATS engineers use infrared (IR) cameras to examine hot spots on a cold plate.

Tufts University

Students take a closer look at ATS testing equipment. (Advanced Thermal Solutions, Inc.)

Dr. Bahman Tavassoli

Dr. Tavassoli answers questions from Tufts University students. (Advanced Thermal Solutions, Inc.)

The Tufts students learned more than simply how the testing processes worked. They also learned why thermal management is an important consideration in the early stages of a design. Dr. Tavassoli and Dr. Hodes spoke of their professional experiences in the field of thermal engineering and where projects had gone wrong when thermal issues were not considered in the planning stages.

Dr. Azar also joined the students in the lab to show them the wicking material being used by ATS engineers in state-of-the-art vapor chamber designs.

Tufts University

ATS CEO, President and founder Dr. Kaveh Azar speaks with the student from Tufts in the Characterization Lab. (Advanced Thermal Solutions, Inc.)

After the Characterization Lab, the students were taken into the Electronics Lab and were given a demonstration of the Water Flow Visualization equipment. ATS engineers use the equipment to test how air will flow through a system.

The students asked numerous questions of Dr. Tavassoli to get a better idea of the important concepts of thermal engineering that were presented in the 90-minute visit to ATS. Now, the students will have the real-world applications that they saw at ATS in mind when learning the concepts of thermodynamics, thermal fluids, and more in their Tufts courses.

To learn more about Advanced Thermal Solutions, Inc., visit www.qats.com or contact ATS at 781.769.2800 or ats-hq@qats.com.

New Hardcover Collection of Qpedia Electronics Thermal Management Articles Now Available from ATS