Thursday, January 16, 2025
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A group of researchers from the Institute of Micro and Nanotechnology have been working for two years on a device that can recharge itself using the heat and movement from the human body, thanks to a new thermoelectric material.
By Sandra Carbajo
When we talk about projects to improve energy efficiency, we usually think of large infrastructure. However, there are small innovations that can be very useful in our everyday lives, especially with those devices that we always have with us. We are talking about cellphones, smart watches, wireless headphones, and so forth. All those small tech items called wearables that are already an extension of ourselves and that must be charged regularly when used.
Can you imagine doing away with external chargers and having them recharge with energy from your own body? This idea, which seems like science fiction, was the spark that led a group of ten researchers from the Institute of Micro and Nanotechnology (IMN), part of CSIC, to start working on self-rechargeable devices that use the energy we produce as humans. The first question that comes to mind, naturally, is obvious: how.
"There are two types of energy that we can use from the human body: heat and movement," explains Marisol Martín González, head of the project at Planet Energy. "When we see ourselves with an infrared camera, we can see that the human body is emitting more heat than the surroundings. What we have done, in this case, is use that heat difference to generate a small amount of electricity that we can build up and is enough to power those small devices that we have with us 24 hours a day."
Regarding movement, Marisol points out that when walking, kinetic energy is produced, and it can be converted into electricity if it comes into contact with other materials. In fact, they started working only with body heat and now they have also added movement.
A multifaceted project
Two years ago, the group led by Marisol Martín began to bring about this pioneering idea. Calling them pioneering is far from meaningless, as they are part of the 8 to 10% of lucky few who were given access to the prestigious Advanced Grants (AdG) program of the European Research Council, which is focused on disruptive and high-risk projects and funded with 2.5 million euros.
"We had been working with thermoelectric materials for some time. We had used them to generate heat from a car's exhaust pipe, converting it into electricity to recharge the battery," the researcher recalled. But the human body has other special characteristics And the temperature difference between our body and the environment is only a few degrees, so it is not easy to leverage the difference to generate enough electricity.
Faced with this dilemma, Marisol and her team had to solve a number of issues vital to the viability of this self-charging device. The first of these was the material. A flexible surface is needed to absorb body heat, such as a headband or watch band. “The problem is that most of the existing materials are polymer-based (plastics) and these have very low conductivity, which means that the heat is lost,” the lead researcher explained. “Then I thought of a way to make those plastics into highly thermally conductive materials without losing that flexibility.” By changing the molecular structure, Marisol created a highly thermally conductive, fully electrically insulating polymer that is also flexible.
Once this issue was overcome, the next stumbling block was how heat is dissipated from our body. It does so perpendicularly, i.e. it dissipates it outwards. “The devices that had been generated until then used very thick layers in order to take advantage of that heat so that the device would not become thermalized, not losing that thermoelectric feature,” she explains.
Thus, to harness the heat to convert it into electricity, Marisol found a way to replicate the operation of an electrical circuit, with a small difference: it would be a thermal circuit that would absorb the heat that would be transformed into energy.
In this multifaceted project, there was still one more difficulty. This time electronic: “There are no DC-DC converters (type of power converter that transforms direct current from one voltage level to another) that allow you to work at the low voltages we need to harness electricity from our devices.”
The million dollar question: is it viable?
Step by step, Marisol Martín proudly confesses that they already have all the systems set up and are conducting concept tests. In fact, when conducting this interview, the researcher acknowledged that in the last few weeks they had managed to gather enough energy to turn on a sensor and send a signal via Bluetooth. This is a massive step considering they are in the initial phase and still have three years ahead of them.
This project opens the door not only to the aforementioned wearables, but also to other medical devices such as insulin pumps, which must be in operation 24/7 for the lives of people with diabetes. "If we can provide energy to those sensors using our own heat and movement, we save ourselves from having to take it off to charge it, which in turn avoids greater evils."
Facing the question of whether we will soon see this invention on the streets, Marisol is cautious but does admit that "in three more years we will have a very interesting result."
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