This is Science: Putting triboelectricity at the service of humanity

Apparently, it is precisely this principle that the group of Professor Wang ( Wang ), who successfully combines work at the Beijing Institute of Nanoenergy and Nanosystems and the University of Technology of Georgia, has chosen its maxim. Over the past six months, a total of 7 papers were published only in the journal of the American Chemical Society ACSNano (impact factor 12.062), and we'll talk about them today. Moreover, these systems have real chances to become the main powering of wearable sensors and smart clothes.

Instead of the preface

At the beginning of this year, the work was published and its brief retelling at Habré on the production of electricity through triboelectricity. It looked then like some kind of exotic, perhaps not having normal use in the national economy, although the authors of the article indicated that an autonomous weather station could be created on the basis of the development. Imagine my surprise when, as from a horn of plenty, articles in a high-rating magazine began to crumble in which a lot of methods of using static electricity were proposed.

But let's start with the main thing - with a small excursion into physics and repetition of the material of the previous article. So, many of us have encountered in everyday life such a phenomenon as triboelectricity , that is, electricity (or more precisely, charge separation) that occurs when two materials or substances rub off (for example, with different densities). In this case, such a separation of charges can be described by two main characteristics: the actual value of the charge (or current) and the potential difference. Of course, these characteristics depend on many parameters: humidity, temperature, the nature of the materials used, and so on.

If you, dear Habr's Fan, have a synthetic blanket at home, then in the dark, turning over this blanket, you can see sparks slipping between the body or certain parts of it, and also smell the “thunderstorm” (ozone) and nitrogen oxides. Similar examples are the experiences from the Bredun channel “Simple Science”:

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Or another:


Usually, in physics lessons at school this effect is presented as something useless or even harmful (for example, for computer equipment, in aviation), however, this is not quite so - let's turn to examples.

Hört ihr mich?

“Can you hear me?” - as was sung in one song of the German group Rammstein. Yes, the authors of the work said with confidence, who suggested using a tribogenerator for a self-powered microphone, acoustic body positioning, and more for acoustic weights.

The scheme of the developed device is presented below. It is worth noting that it is not much different from all the usual microphone , with the only difference that instead of electromagnetic effects, such as a change in induction or capacitor capacitance, the measured characteristic is, as is the case with the tribogenerator , current.


Diagram of a self-powered microphone and an acoustic wave detector ( PET - polyethylene terephthalate, PTFE - teflon)

Of course, acoustic characteristics were also determined. Naturally, the higher the volume (the closer the sound source is to the microphone itself), the better such a microphone works, but you should not forget that the device does not require an external power source, the signal can potentially be amplified by the receiver.


Electrical and acoustic characteristics of the device received: (a) open circuit voltage, (b) short circuit current, (c) the dependence of these characteristics on the distance to the active element and (d) the directivity pattern of the microphone

Since the microphone has such a directivity pattern, then it’s a sin not to create a position detector of the sound source, and a self-powered one. Actually, this was done on the basis of signal correlations between several sources:


An example of using a device for detecting a sound source

And that's not all, also this kind of membrane can be used to weigh objects through sound, as demonstrated in this video . Scientists managed to achieve a sensitivity of 270 mV / mg, weighing masses from 40 mg to 400 mg. In principle, such scales can find their application in the jewelry industry due to the extremely low price and high sensitivity.

A video on the operation of the microphone and sound position detector can be viewed on the official website or Yandex-Disk .

The original article is in ACSNano (DOI: 10.1021 / nn4063616).

Here and there, back to you and me - electricity.

(a, b) Triboelectric generator circuit. (c-e) Polymer film ( Kapton ) with copper contacts assembled and disassembled

This device looks slightly khm-khm ... erotic, but what to do, science requires sacrifice. If in the first article a polymer plate with a small copper area oscillated between two electrodes, now the electric charge accumulates when two polymer films are moved relative to each other, as shown in the figure:


The principle of operation of the triboelectric generator (a), as well as simulation data for this system (bf).

The authors also published a couple of videos (you can see it from the official website of the publisher or from Yandex-Disk ), how you can activate this tribogenerator from the movement of waves or humans.

And although the maximum output power is only 10-12 mW (1.36 W / m ² ) at a current of about 300 μA and at a speed of 1 m / s for the device shown, it can potentially be used for navigation beacons, and also, what the hell is not jokes, in wearable "smart" clothes to feed the built-in cardiometer or tracker, for example. We'll talk more about this at the very end of the article.

The original article is in ACSNano (DOI: 10.1021 / nn500694y).

The logical continuation of this work was the development of two models of an electric power generator using waves and raindrops.

In the first case, the roll-in wave brings with it some charge, which is “absorbed” by the fluorinated polyethylene propylene ( FEP ) polymer film, as shown in the figure:


Scheme of operation of triboelectric generator based on tidal waves

The power of such a generator is at the level of units W / m ² , but given the fact that such a facility can be placed along an unused coast, the prospects are, in principle, encouraging and tempting. In addition, rain or flowing water can also be used to generate electricity - video (the official website of the publisher or Yandex-Disk ).

The original article is in ACSNano (DOI: 10.1021 / nn5012732).

In the second case, a more complex dual-circuit system was used, which allows converting not only electrostatic electric energy from rolling drops, but also receiving energy from the shock interaction of the drops with the surface.


The general scheme of a double-circuit triboelectric generator: the first circuit - titanium dioxide nanoparticles, ensuring non-wettability of the surface and the rolling of raindrops; the second circuit - silicon dioxide nanoparticles in contact with the teflon film upon impact of a falling drop

A drop, falling on the inclined surface of such a generator, carries with it a certain charge (suppose a positive one), and in the process of digging over the surface electrifies the polymer film (negatively, respectively), and the copper electrode only “collects” this excess negative charge. The second circuit works on the principle described several times above: silicon dioxide nanoparticles in contact with a teflon film upon impact, creating a potential difference and electrifying. The details of the work of the two circuits separately in a schematic view are presented below:



Ultimately, the first contour gives a power of about 1.3 W / m ² , while a contour that utilizes the mechanical energy of the droplets to fall allows an additional 0.3-0.4 W / m ² to be obtained. In addition, on the basis of such systems, self-powered sensors of various molecules can be created. In particular, the article presents an example with an ethanol sensor, which allows determining the fractions of a percent of a given compound. And in the conditions of large megacities, it can be sensors of various gases to determine the ecological state of air.

Video showing the operation of the device can be viewed on the official website of the publisher or c Yandex-Disk .

The original article is in ACSNano (DOI: 10.1021 / nn501983s).

Towards wearable charging systems

And the last couple of articles to date, which I would like to talk about, is actually devoted to the charging prototype, which in a couple of years can be embedded in our casual clothing for elements of smart clothing.


Scheme of the concept for the generation of triboelectricity due to compression and tension

The essence of this development lies in the fact that when compressed or stretched again, static or triboelectricity arises, which can be stored when walking or running and directed, for example, to charging your smartphone in your pocket. In principle, such systems can also be used to generate electricity from falling drops or tidal waves, as demonstrated above. And although the power generated is not so high (~ 0.4 W / m ² ), it was quite enough to power the LED array in the experiments performed (see video ).

Also, the authors published several videos demonstrating the operation of the device, which can be viewed on the official website of the publisher or with Yandex-Disk .

The original article is in ACSNano (DOI: 10.1021 / nn502618f).

However, the maximum power of the platform for generating triboelectricity described above is achieved at a frequency of contractions of more than 100 Hz, which, you see, is more interesting for athletes, but in the second paper, scientists created a fabric based on ordinary cotton threads, which allows electricity to be generated by muscle contractions when walking, for example, or a simple pat.


New fabric that allows you to generate electricity: special fibers are woven into the usual cotton

In this case, cotton fibers are first covered with carbon nanotubes, and then some of them are additionally Teflon. Further, pairs of such fibers are woven into ordinary fabric and can work as a triboelectricity generator due to the displacement and friction of the fibers against each other.


Electric principle of operation of two fibers for obtaining triboelectricity

Again, it should be noted that the power density of such devices is not as great as we would like, as well as the accumulated charge - just a few nCl for half a minute, however, this is enough to revive the monochrome display with a simple movement of your finger (see video ).

Or, such a small amount of electricity may well be enough for some sensor embedded in clothes, for example, a thermometer, for activation of which it is enough just to pat at the location of the tribogenerator.


Wearable self-powered thermometer - one more step towards wearable electronics

Video demonstrations can be viewed on the official website of the publisher or on Yandex-Disk .

Original article in ACSNano (DOI: 10.1021 / nn501732z)

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Full list of published articles This is Science on GeekTimes:
This is Science: Simple and Cheap Solar Energy
This is Science: Is graphene life or death?
This is Science: Blow and Get Electricity
This is Science: Silicon Electronics: Bend Me Completely!
This is Science: Resilient quantum dot display
This is Science: Putting triboelectricity at the service of humanity
This is Science: 3D optical printing moves to the micro level
This is Science: What's inside a neuromorph chip?
This is Science: News from graphene fields
This is Science: 3D lithography to masses
This is Science: The discharge of alkaline batteries or why the battery jumps
This is Science: microcannons and nano-core
This is Science: wearable electronics and triboelectricity. Part 1
This is Science: wearable electronics and triboelectricity. Part 2

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