Researchers from The University of Tokyo recently developed an innovative thermal sensor with a thin plastic base that is rolled.
As the devices shrink and power up, increasing heat, it is now an issue in areas that weren’t something to consider not too long ago. More than just cutting some vent holes in the case or putting in the addition of a fan is required as a cooling technique. These easy fixes might have worked in the past, but nowadays, designing the thermal properties of a product is just as crucial to the EMI and the integrity of the signal.
A heat map of enclosures. Image (modified) made available by the MentorMAD/Wikimedia Commons (CC BY-SA 4.0)
Designers have to now be able to measure and monitor temperature in a manner that can be able to fit into the design, fit within the budget and represent the operational environment. Researchers from University of Tokyo (UT) University of Tokyo (UT) could provide an answer that is compatible with all these criteria.
Common Practices for Thermal Characterization
Some of the most costly chips in the market today come with thermal sensors to guard against overheating and thermal runaway. PC boards that are essential to the mission may incorporate these sensors in crucial areas. However, space and cost restrictions often prevent monitoring more than a handful of critical areas. Instead, engineers should try to resolve issues with temperature before the production process begins.
In the course of development, designers worried about temperature typically attach sensors to the areas that might be problematic for the prototype to determine the thermal properties of the shakedown. The software for thermal simulation can also assist in determining the characteristics of the final product.
Limitations of Thermal Monitoring–And a Solution
While these approaches are reasonable and mostly effective, they run into limits with compact equipment or equipment operating in difficult-to-simulate settings. Thermal sensors, which are made of wires and tiny semiconductor components, aren’t compact enough to fit into the present range of ultra-miniaturized semiconductors or small designs. They may provide an image of the thermal properties of isolated points rather than the whole system operating.
To solve this problem, a group at UT has created a flexible thermal sensor that could help designers precisely monitor and characterize circuit components with a lower price and with less impact on the physical design of the items. The sensors were developed by sputtering the material deposition onto the PET material and then etching the sensor.
Researchers at the University of Tokyo used a technique of etching and sputtering to create a flexible thermal sensor. Image as a courtesy from The University of Tokyo
The thin film can be used in places that other sensors can’t. Furthermore, it can be used in manufacturing to monitor the product for a lifetime without having a major effect on the mechanical arrangement of the device.
How the Thermal Sensor Works
The majority of thermal sensors are based heavily on the thermoelectric Seebeck effect (SE), which is the process of heating two different substances (usually semiconductors or metals) that results in the flow of electricity. Alessandro Volta himself discovered the origins of the phenomenon of thermoelectricity all time back in 1794. The phenomenon was named after Thomas Seebeck, who independently discovered it in 1821.
If heat is applied on the joint end of two different materials, the difference in temperature between the hot joined and non-joined parts of the circuit triggers electrons that cause them to shift across the material from another via the joint. The electron flow is proportional to the differential and is easily measured.
The thermocouple is a typical. The difference in temperature between the T sensing and ref excites electrons for them to travel through the connection between the wires. Image as a courtesy of Wikimedia Commons (CC0 1.0)
The new sensors from UT use a less commonly known but related thermoelectric/thermomagnetic effect called the anomalous Nernst effect (ANE). Like the Seebeck effects, ANE converts heat into electricity. It is, however, ANE relies on magnetic materials and operates in a plane parallel to heat. This, when combined with UT’s method to deposit magnetic materials that are based on gallium and iron film, results in a flat sensor.
The circuit etched uses an alternate arrangement to cancel off the Seebeck effect and provide an accurate reading of the Nernst effect. Image by permission from the University of Tokyo
One of the challenges in using ANE one of the issues is that SE, which is thermoelectric, is stronger and blocks the ANE reading of the area. It is because the UT method neutralizes SE through alternating patterns. This lets the etched circuit give a more accurate thermal image of the region.
Potential Applications of the New Thermal Sensor
Prior to this research, thermoelectric sensors were bulky in size, a bit awkwardly sized, fragile, and difficult to integrate into applications other than point-source. This research suggests the possibility of form-fitting, flexible thermoelectric sensors that could be used in almost any type of application.