Tag Archives: heat

A Heat Switch for Controlling Heat Flow Path in Electronic Systems

Schematic of the thermal switch showing the (a) ON-state with the liquid metal droplet bridging the heat source and sink and (b) OFF-state with liquid metal removed from the channel. (c) Side view image of the fabricated thermal switch device. (d) The ON and OFF thermal resistance circuits based on a 1-D heat transfer model.

A switch is a fundamental part of most electrical and mechanical devices; mechanical switches can be used to select gears in a car’s transmission or used to unlock a door; electrical switches can turn the lights in a room on and off;  semiconductor uses to route logic signals within a circuit or control bigger devices. But what about heat flows? Can we possibly control the route of heat in a device? A Thermal Switch? Well, a thermal switch is an electromechanical device which opens and closes contacts to control the flow of electrical current in response to temperature change. A Thermal switch controls the flow of current concerning the temperature change, but this doesn’t actually control the flow of heat.

Heat flow is very important to engineers, and the heat movement in a device can profoundly affect the system performance and reliability especially in an electronics system. Engineers have long desired a switch to control heat flows, but many challenges exist in the creation of such a switch. Researchers from the College of Engineering at the University of Illinois at Urbana-Champaign have developed a new technology that allows users to turn heat flows “on” or “off.” This is a great development and it’s going to impact on future electronics systems.

Heat Flow from Hot to Cool Region

“Heat flows occurs whenever you have a region on higher temperature near a region of lower temperature. In order to control the heat flow, the team engineered a specific heat flow path between the hot region and cold region and then created a way to break the heat flow path when desired” claims William King, the project co-leader and a professor at the department of mechanical science and engineering.

This technology became possible based on the principle of the “motion of a liquid metal droplet,” adds Nenad Miljkovic, assistant professor in the same department who also served as a project co-leader. “The metal droplet can be positioned to connect a heat flow path, or moved away from the heat flow path to limit the heat flow.”

The team demonstrated the technology in a system modeled after modern electronic systems, giving the potential of being deployed to our everyday devices. On one side of the switch was a heat source representing the power electronics component; on the other, liquid cooling for heat removal. When the heat switch was on, the team managed to extract heat at more than 10 W/cm2, but as soon as the heat flow was turned off, they saw a drop by nearly 100X.

According to King, the next step for the research will be to integrate the switch with power electronics on a circuit board. A working prototype will be produced later this year. The research was published in a recent edition of the journal Applied Physics Letters.

Thermal design: Get the heat out of the electronics

Häusermann has a propriety process that makes PCBs that can conduct a great amount of heat or current.

@ edn.com discuss about thermal design in electronics and how to design your board to dissipate it effectively.

If you have high-powered LEDS, or a power supply, or are trying to control larger motors, you have to get a lot of heat out of your circuit boards. The classic way to dissipate heat is to bolt your power transistor to an aluminum heat sink. That is a slow, messy, and expensive proposition, especially if you need thermal grease between the transistor and heat sink.


It’s always a good idea to make thermal management inherent in your PCB design. Experience has shown you can get about 2W of heat out of a 3×5” copper area on a conventional FR4 PCB.

Thermal design: Get the heat out of the electronics – [Link]

Lightweight Body Heat – Electricity Converter

Powering wearable technologies using thermoelectric generators (TEGs) is becoming more efficient. An undergraduate student in North Carolina University, Haywood Hunter, is producing a lightweight and an efficient wearable thermoelectric generator. It generates electricity by making use of the temperature differential between the body and the ambient air.This converter produces 20 times more electricity than other technologies (20 µwatts) and it doesn’t use any heat sink, making it lighter and much more comfortable.

Study co-lead Haywood Hunter, shows off the TEG-embedded T-shirt at work.
Study co-lead Haywood Hunter, shows off the TEG-embedded T-shirt at work.

The design begins with a layer of thermally conductive material that rests on the skin and spreads out the heat. The conductive material is topped with a polymer layer that prevents the heat from dissipating through to the outside air. This forces the body heat to pass through a centrally-located TEG that is one cm2. Heat that is not converted into electricity passes through the TEG into an outer layer of thermally conductive material, which rapidly dissipates. The entire system is only 2 millimeters, and flexible. Some limitations to size can be solved by choosing right power settings for different sizes.

Even though the wrist is the best place to use heat-electricity converters because the skin temperature is higher, the irregular contour of the wrist limits the surface area of contact between the TEG band and the skin. To solve this issue, it was recognized that the upper arm was the optimal location for heat harvesting. Meanwhile, another experiment showed that wearing the band on the chest limited air flow and heat dissipation, since the chest is normally covered by a shirt.The researchers found that the T-shirt TEGs were still capable of generating 6 µW/cm2 – or as much as 16 µW/cm2 if a person is running. It was realized then that T-shirts are just not as efficient as the upper arm bands.

TEG-embedded T-shirt (left) and TEG armband (right).
TEG-embedded T-shirt (left) and TEG armband (right).

The work was funded by National Science Foundation (NSF) and the research was done in the Nanosystems Engineering Research Center for Advanced Self-Powered Systems of Integrated Sensors and Technologies (ASSIST) at North Carolina State. This center’s mission is to create wearable, self-powered, health and environmental monitoring systems, such as devices that track heart health or monitor physical and environmental variables to predict and prevent asthma attacks.

Further details can be reached at the university website and the project’s paper.

Via: ScienceDaily