A new type of material generates electrical current very efficiently from temperature differences

Prof. Ernst Bauer in the lab
Credit TU Wein

A new type of material generates electrical current very efficiently from temperature differences. This allows sensors and small processors to supply themselves with energy wirelessly.

Thermoelectric materials can convert heat into electrical energy. This is due to the so-called Seebeck effect: If there is a temperature difference between the two ends of such a material, electrical voltage can be generated and current can start to flow. The amount of electrical energy that can be generated at a given temperature difference is measured by the so-called ZT value: The higher the ZT value of a material, the better its thermoelectric properties.

The best thermoelectrics to date were measured at ZT values of around 2.5 to 2.8. Scientists at TU Wien (Vienna) have now succeeded in developing a completely new material with a ZT value of 5 to 6. It is a thin layer of iron, vanadium, tungsten and aluminium applied to a silicon crystal.

The new material is so effective that it could be used to provide energy for sensors or even small computer processors. Instead of connecting small electrical devices to cables, they could generate their own electricity from temperature differences. The new material has now been presented in the journal “Nature”.

Electricity and Temperature

“A good thermoelectric material must show a strong Seebeck effect, and it has to meet two important requirements that are difficult to reconcile,” says Prof. Ernst Bauer from the Institute of Solid State Physics at TU Wien. “On the one hand, it should conduct electricity as well as possible; on the other hand, it should transport heat as poorly as possible. This is a challenge because electrical conductivity and thermal conductivity are usually closely related.”

At the Christian Doppler Laboratory for Thermoelectricity, which Ernst Bauer established at TU Wien in 2013, different thermoelectric materials for different applications have been studied over the last few years. This research has now led to the discovery of a particularly remarkable material – a combination of iron, vanadium, tungsten and aluminium.

“The atoms in this material are usually arranged in a strictly regular pattern in a so-called face-centered cubic lattice,” says Ernst Bauer. “The distance between two iron atoms is always the same, and the same is true for the other types of atoms. The whole crystal is therefore completely regular”.

However, when a thin layer of the material is applied to silicon, something amazing happens: the structure changes radically. Although the atoms still form a cubic pattern, they are now arranged in a space-centered structure, and the distribution of the different types of atoms becomes completely random. “Two iron atoms may sit next to each other, the places next to them may be occupied by vanadium or aluminum, and there is no longer any rule that dictates where the next iron atom is to be found in the crystal,” explains Bauer.

This mixture of regularity and irregularity of the atomic arrangement also changes the electronic structure, which determines how electrons move in the solid. “The electrical charge moves through the material in a special way, so that it is protected from scattering processes. The portions of charge travelling through the material are referred to as Weyl Fermions,” says Ernst Bauer. In this way, a very low electrical resistance is achieved.

Lattice vibrations, on the other hand, which transport heat from places of high temperature to places of low temperature, are inhibited by the irregularities in the crystal structure. Therefore, thermal conductivity decreases. This is important if electrical energy is to be generated permanently from a temperature difference – because if temperature differences could equilibrate very quickly and the entire material would soon have the same temperature everywhere, the thermoelectric effect would come to a standstill.

Electricity for the Internet of Things

“Of course, such a thin layer cannot generate a particularly large amount of energy, but it has the advantage of being extremely compact and adaptable,” says Ernst Bauer. “We want to use it to provide energy for sensors and small electronic applications.” The demand for such small-scale generators is growing quickly: In the “Internet of Things”, more and more devices are linked together online so that they automatically coordinate their behavior with each other. This is particularly promising for future production plants, where one machine has to react dynamically to another.

“If you need a large number of sensors in a factory, you can’t wire all of them together. It’s much smarter for the sensors to be able to generate their own power using a small thermoelectric device,” says Bauer.

Learn more: New Material Breaks World Record Turning Heat into Electricity

 

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Significantly extending Wi-Fi range without needing new hardware

BYU assistant professor of computer engineering Phil Lundrigan. Photo by BYU Photo

Protocol doesn’t require new hardware; works with existing devices

A group of researchers led by a BYU computer engineering professor has created a protocol that significantly extends the distance a Wi-Fi-enabled device can send and receive signals.

The engineering innovation requires no new hardware to enhance the signal range for “internet of things” devices, like a door sensor or motion detector, but can extend the distance these devices can be installed from a Wi-Fi access point by more than 60 meters, according to test results.

“That’s the really cool thing about this technology: it’s all done in software,” said Phil Lundrigan, assistant professor of computer engineering at BYU. “In theory, we could install this on almost any Wi-Fi enabled device with a simple software update.”

The new protocol is called On-Off Noise Power Communication and is programmed right on top of the existing Wi-Fi protocol using the same hardware. While Wi-Fi requires speeds of at least one megabit per second (1 Mbps) to maintain a signal, the “ONPC” protocol Lundrigan and his co-authors created can maintain a signal on as low as 1 bit per second — one millionth of the data speed required by Wi-Fi.

BEYOND WIFI; GOING FOR NOISE

To do so, Lundrigan, Neal Patwari of Washington University (in St. Louis) and Sneha Kasera of the University of Utah adjusted the transmitter in a Wi-Fi-enabled device to send wireless noise in addition to data. They programmed into the Wi-Fi sensor a series of 1s and 0s, essentially turning the signal on and off in a specific pattern. The Wi-Fi router was able to distinguish this pattern from the surrounding wireless noise (from computers, televisions and cell phones) and therefore know that the sensor was still transmitting something, even if the data wasn’t being received.

“If the access point (router) hears this code, it says, ‘OK, I know the sensor is still alive and trying to reach me, it’s just out of range,’” Patwari said. “It’s basically sending 1 bit of information that says it’s alive.”

But according to Lundrigan, 1 bit of information is sufficient for many Wi-Fi enabled devices that simply need an on/off message, such as a garage door sensor, an air quality monitor or even a sprinkler system. During their research, the authors successfully implemented their ONPC protocol, along with a cleverly named application to manage the protocol (“Stayin’ Alive”), ultimately extending the range of an off-the-shelf device 67 meters beyond the range of standard Wi-Fi.

The researchers made clear to point out that their ONPC protocol is not meant to replace Wi-Fi or even long-range wireless protocols like LoRa, but is meant to supplement Wi-Fi. Specifically, only when Stayin’ Alive detects that the Wi-Fi device has lost its connection, it starts transmitting data using ONPC.

That being said, authors believe the innovation could make LoRa even longer range or be used on top of other wireless technologies. “We can send and receive data regardless of what Wi-Fi is doing; all we need is the ability to transmit energy and then receive noise measurements,” Lundrigan said. “We could apply this to cellular or Bluetooth as well.”

The research was presented on October 22 at the International Conference on Mobile Computing and Networking in Los Cabos, Mexico. MobiCom is one of the premier computer engineering conferences, with an acceptance rate for papers usually under 20 percent, and closer to 15 percent this year.

Lundrigan runs the Network Enhanced Technologies Lab (NET) at BYU. NET is focused on building real systems that enhance and extend wireless networks, Internet of Things, security, privacy and reliability. Take a look at what they’re up to right now: https://netlab.byu.edu/projects/

Learn more: Researchers create way to significantly extend Wi-Fi range for smart-home devices

 

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Indoor solar cells to power the internet of things

Credit: Thor Balkhed

Swedish and Chinese scientists have developed organic solar cells optimised to convert ambient indoor light to electricity. The power they produce is low, but is probably enough to feed the millions of products that the internet of things will bring online.

As the internet of things expands, it is expected that we will need to have millions of products online, both in public spaces and in homes. Many of these will be the multitude of sensors to detect and measure moisture, particle concentrations, temperature and other parameters. For this reason, the demand for small and cheap sources of renewable energy is increasing rapidly, in order to reduce the need for frequent and expensive battery replacements.

This is where organic solar cells come in. Not only are they flexible, cheap to manufacture and suitable for manufacture as large surfaces in a printing press, they have one further advantage: the light-absorbing layer consists of a mixture of donor and acceptor materials, which gives considerable flexibility in tuning the solar cells such that they are optimised for different spectra – for light of different wavelengths.

New combination of materials

Researchers in Beijing, China, led by Jianhui Hou, and Linköping, Sweden, led by Feng Gao, have now together developed a new combination of donor and acceptor materials, with a carefully determined composition, to be used as the active layer in an organic solar cell. The combination absorbs exactly the wavelengths of light that surround us in our living rooms, at the library and in the supermarket.

The researchers describe two variants of an organic solar cell in an article in Nature Energy, where one variant has an area of 1 cm2 and the other 4 cm2. The smaller solar cell was exposed to ambient light at an intensity of 1000 lux, and the researchers observed that as much as 26.1% of the energy of the light was converted to electricity. The organic solar cell delivered a high voltage of above 1 V for more than 1000 hours in ambient light that varied between 200 and 1000 lux. The larger solar cell still maintained an energy efficiency of 23%.

“This work indicates great promise for organic solar cells to be widely used in our daily life for powering the internet of things”, says Feng Gao, senior lecturer in the Division of Biomolecular and Organic Electronics at Linköping University.

Design rules

”We are confident that the efficiency of organic solar cells will be further improved for ambient light applications in coming years, because there is still a large room for optimization of the materials used in this work”, Jianhui Hou, professor at the Institute of Chemistry, Chinese Academy of Sciences, underlines.

The result is a further advance in research within the field of organic solar cells. In the summer of 2018, for example, the scientists, together with colleagues from a number of other universities, published rules for the construction of efficient organic solar cells (see the link given below). The article collected 25 researchers from seven universities, and was published in Nature Materials. The research was led by Feng Gao. These rules have proven to be useful along the complete pathway to efficient solar cell for indoor use.

Spin off company

The Biomolecular and Organic Electronics research group at Linköping University, under the leadership of Olle Inganäs (now professor emeritus), has been for many years a world-leader in the field of organic solar cells. A few years ago, Olle Inganäs and his colleague Jonas Bergqvist, who is co-author of the articles in Nature Materials and Nature Energy, founded, and are now co-owners of a company, which focusses on commercialising solar cells for indoor use.

Learn more: Welcome indoors, solar cells

 

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mmX is a low-power, low-cost network for 5G connectivity: A true enabler for the Internet of Things

mmX device via University of Waterloo

Researchers at the University of Waterloo have developed a cheaper and more efficient method for Internet-of-Things devices to receive high-speed wireless connectivity.

With 75 billion Internet of Things (IoT) devices expected to be in place by 2025, a growing strain will be placed on requirements of wireless networks. Contemporary WiFi and cellular networks won’t be enough to support the influx of IoT devices, the researchers highlighted in their new study.

Millimeter wave (mmWave), a network that offers multi-gigahertz of unlicensed bandwidth — more than 200 times that allocated to today’s WiFi and cellular networks, can be used to address the looming issue. In fact, 5G networks are going to be powered by mmWave technology. However, the hardware required to use mmWave is expensive and power-hungry, which are significant deterrents to it being deployed in many IoT applications.

“To address the existing challenges in exploiting mmWave for IoT applications we created a novel mmWave network called mmX,” said Omid Abari, an assistant professor in Waterloo’s David R. Cheriton School of Computer Science. “mmX significantly reduces cost and power consumption of a mmWave network enabling its use in all IoT applications.”

In comparison to WiFi and Bluetooth, which are slow for many IoT applications, mmX provides much higher bitrate.

“mmX will not only improve our WiFi and wireless experience, as we will receive much faster internet connectivity for all IoT devices, but it can also be used in applications, such as, virtual reality, autonomous cars, data centers and wireless cellular networks,” said Ali Abedi, a postdoctoral fellow at the Cheriton School of Computer Science. “Any sensor you have in your home, which traditionally used WiFi and lower frequency can now communicate using high-speed millimeter wave networks.

“Autonomous cars are also going to use a huge number of sensors in them which will be connected through wire; now you can make all of them wireless and more reliable.”

Learn more: Researchers develop low-power, low-cost network for 5G connectivity

 

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Could copper nanoparticles replace expensive gold and silver in next generation electronic devices?

Same Properties, Lower Cost

Japanese scientists have developed a technique to transform a copper-based substance into a material that mimics properties of precious and pricey metals, such as gold and silver.

The new medium, made of copper nanoparticles (very small copper-based structures) has promising applications in the production of electronic devices that would otherwise depend on expensive gold and silver counterparts. It is also suitable in the fabrication of electronic components using printing technologies that are recognized as environmentally friendly production methods.

The study was published on January 29 in Scientific Reports, an online open access journal managed by Nature.

The development of the Internet of Things (IoT) has quickly increased the demand for thin and wearable electronic devices. For example, IoT depends on communication between devices, which requires antennas that have so far required expensive gold and silver-based metal composites.

To date, existing techniques for the preparation of copper nanoparticles have not been ideal as they resulted in impurities attaching to the material. Since these impurities could only be removed via extremely high temperatures, copper nanoparticles that were created at room temperature were impure and thus could not solidify into usable parts. Until now, this has been one of the hurdles to creating a more cost-effective alternative to gold and silver parts in electronic devices.

The joint study between researchers at Tohoku University and Mitsui Mining & Smelting Co., Ltd in Tokyo reports the successful synthesis of copper nanoparticles with the ability of solidifying at much lower temperatures while remaining pure. The team has altered the structure of the copper nanoparticles and rendered them more stable so that they do not degrade at low temperatures.

Copper nanopastes with low-temperature sintering property for printed electronics and die attachment.
Credit: Kiyoshi Kanie

“Copper has been an attractive alternative material in the preparation of electric circuits. The most important part of using copper is altering it so that it solidifies at low temperatures. So far, that has been difficult because copper readily interacts with the moisture in the air and degrades, which turns into unstable nanoparticles. With the methods used in this study that alter the structure of the carbon and thereby making it more stable, we have successfully overcome this instability issue,” adds Kiyoshi Kanie, Ph.D., associate professor at the Institute of Multidisciplinary Research for Advanced Materials of Tohoku University.

The researchers hope to expand the application of their copper-based nanoparticles beyond just electronics. They believe that this material will be useful in other sectors as well. “Our method effectively created copper nanoparticle-based materials that can be utilized in various types of on-demand flexible and wearable devices that can be fabricated easily via printing processes at a very low cost,” Kanie adds.

Learn more: Copper-Based Alternative for Next-Generation Electronics

 

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