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Researchers Developed Hybrid 3D Printing Method To Make Flexible Wearable Devices

Wearable electronic devices that intend to track and measure the body’s movements must be soft enough to flex and stretch to accommodate every body-movement. But, integrating rigid electronics on skin-like flexible materials has proven to be challenging. Clearly, Such components cannot stretch like soft materials can, and this mismatch frequently causes wearable devices to fail. Recently scientists solved this problem by developing a new method called hybrid 3D printing.

Making wearble devices using Hybrid 3D Printing method
Making wearable devices using Hybrid 3D Printing method

A collaboration between the Wyss Institute, Harvard’s John A. Paulson School of Engineering and Applied Sciences, and the Air Force Research Laboratory, has resulted in developing hybrid 3D printing method. It combines soft, electrically conductive inks, and matrix materials with rigid electronics into a uniformly stretchable device. Alex Valentine, a Staff Engineer at the Wyss Institute says,

With this technique, we can print the electronic sensor directly onto the material, digitally pick-and-place electronic components, and print the conductive interconnects that complete the electronic circuitry required to ‘read’ the sensor’s data signal in one fell swoop.

To make the circuits and the flexible layers, the researchers use thermoplastic polyurethane (TPU), both pure and with silver flakes. The method is quite easy to understand. As both the substrate and the electrodes contain TPU, they firmly adhere to one another while they are co-printed layer-by-layer. After the solvent evaporates completely, both of the inks harden, forming an integrated system that is both flexible and stretchable.

As the ink and substrate are 3D-printed, the scientists have complete control over where and how the conductive features are patterned. Thus they can design circuits to create soft electronic devices of nearly every size and shape. The hybrid 3D printing method enables development of flexible, durable wearable devices that move with the body.

A ring that is made using flexible conductingmaterial
A ring that is made using flexible conducting materials

Conductive materials exhibit changes in their electrical conductivity when stretched. Soft sensors, that detect movements, are made of those materials and are coupled with a programmable microcontroller to process those data. The microcontroller also transmits the data to communicate in a human-understandable way. As a proof-of-concept, the team created two devices – a wearable device that indicates how much the wearer’s arm is bending and a pressure sensor in the shape of a person’s left foot.

Watch the video to know about them,

Researchers Innovated Highly Effective Silicon Microchannel Thermal coolers For Processors

One of the limiting factors for the computing power of processors is the operating temperature. A research team led by Dr. Wolfram Steller, Dr. Hermann Oppermann, and Dr. Jessika Kleff from the Fraunhofer Institute for Reliability and Microintegration IZM, has developed a new as well as an efficient cooling method by integrating microchannels into the silicon interposer. For the first time, it is possible to cool down high-performance processors from the bottom as well.

The integration of microchannels into the silicon interposer
The integration of microchannels into the silicon interposer boosts cooling and processor performance

When processors get too hot to work properly, they reduce their clock speed and operating voltage. In order to protect the CPU and motherboard from getting fried, the processors either reduce their computing speed or even shut off completely. Until now, cooling elements and fans are used to avoid overheating the heat-sensitive components. The researchers found a way to cool processors from the top as well as from below using a liquid-based cooling system.

The research team reports that the innovation can achieve a significant increase in performance. The scientists have also integrated passive elements for voltage regulators, photonic ICs, and optical waveguides into the interposer. This enables highly effective cooling and therefore higher performance. For this purpose, microchannel structures with tightly sealed vias are installed in the silicon interposer, which is located between the processor and the printed circuit board.

Interposers are responsible for the electrical supply and cooling of the processor. Every 200 micrometers, interposers are equipped with electrical connections to ensure the processor’s power supply and data transmission. In order to be able to absorb heat and channel it away from the processor, the researchers at Fraunhofer IZM created microfluid channels that allow coolant to be circulated through vias.

The main challenge to the researchers was to integrate the small channels into the interposer and seal them very tightly in order to separate them from the electrical paths. The solution they came up with is interesting – the interposer is made of two silicon plates – horizontally extending cooling channels and vertically extending channels. They are combined in a complementary manner.

Dr. Hermann Oppermann, the group leader at Fraunhofer IZM, said,

Up to now, the cooling structures are not very close to the computer core itself, which means the coolers are mostly applied from above. The closer you get to the heat source, the better the temperature can be limited or the output increased. In high-performance computing, in particular, the data rates are continuously increasing. Therefore, it is important to have an effective cooling to ensure a higher clock rate.

Researchers Developed Highly Durable Washable And Stretchable Solar Cells

Scientists of Japanese research institute RIKEN and the University of Tokyo have successfully developed a product that allows solar cells to continue to provide solar power after being washed, stretched and compressed. Takao Someya of Riken Center for Emergent Matter Science, a designated national R&D Institute in Japan, led the research team.

Washable and stretchable solar cell
Washable and stretchable solar cell

The research results were published in the journal Nature Energy and illustrated a photovoltaic material that could be used to make washable outer garments and wearable devices. The researchers say that the innovated solar cells will be a power source to low-power devices and can also be worn concurrently. This innovation might solve one of the biggest challenges of the Internet of Things (IoT), the requirement of a reliable power source to keep all devices connected.

The newly invented solar cells could power wearable devices that include health monitors and sensors for analyzing the heartbeat and body temperature. This could make prevention and early detection of potential medical problems possible. Though the concept of wearable solar cells is not unique, the previous wearable solar cell solutions suffered from the lack of one vital property i.e. long-term stability in air and water, including resistance to deformation.

The recent stretchable solar cell innovation has successfully achieved all of the most important features and is creating the way for the top-notch quality of modern wearable technology. The material on which their new device is based on is called PNTZ4T – a highly efficient polymer solar cell capable of small photon energy loss. The scientists deposited the device onto a parylene film which was then placed onto an acrylic-based elastomer. The construction method has proved to be particularly very durable.

The device produced 7.86 milliwatts per square meter based on a sunlight simulation of 100 milliwatts per square meter before considering resistance and durability. It showed the least decrease in efficiency when soaked in the water and when stretched. The efficiency decreased by only 5.4 percent and 20 percent respectively. Kenjiro Fukuda of RIKEN Center for Emergent Matter Science said,

We were very gratified to find that our device has great environmental stability while simultaneously having a good efficiency and mechanical robustness. We very much hope that these washable, lightweight and stretchable organic photovoltaic will open a new avenue for use as a long-term power source system for wearable sensors and other devices.

Researchers Develop Long Range Backscatter Sensors That Consume Almost No Power

Researchers at the University of Washington developed a new backscatter sensors that can operate over long ranges with very little power. The researchers demonstrated for the first time that the device runs on almost zero power and can transmit data across distances of up to 2.8 kilometers.

The long-range backscatter system developed by UW researchers
The long-range backscatter system developed by UW researchers

Backscatter communication works by emitting a radio signal and then monitoring the reflections of that signal from sensors. As the transmitter generates the signal, the sensors themselves require very little power. But this kind of system badly suffers from noise. Noise can be added anywhere – on the transmitter side, on the channel or on the sensor array. The key to solving this problem is a new type of signal modulation called chirp spread spectrum.

By using the chirp spread spectrum modulation technique, the team was able to transmit data up to 2.8 kilometers while the sensors themselves consumed only a few microwatts of power. Such extremely low power consumption lets them run by harvested ambient energy and very small printed batteries. The cost is surprisingly cheap too. The sensors would cost just 10 to 20 cents per unit if bulk purchased.

Today’s flexible electronics and other sensors need to operate with very low power typically can’t communicate with other devices more than a few feet or meters away. By contrast, the University of Washinton’s long-range backscatter system achieved pretty strong coverage throughout a 4800-square-foot house, an office area including 41 rooms, and a one-acre vegetable farm at extremely low power and low cost.

Shyam Gollakota, the lead faculty and associate professor in the Paul G. Allen School of Computer Science & Engineering, said,

Until now, devices that can communicate over long distances have consumed a lot of power. The tradeoff in a low-power device that consumes microwatts of power is that its communication range is short. Now we’ve shown that we can offer both, which will be pretty game-changing for a lot of different industries and applications.

These low-power sensors have endless potential applications. They can be used for everything from wearable health monitors to scientific data collection devices. Though there are no confirmed products yet, the team has created few prototypes in the form of flexible sensors worn on the skin, smart contact lenses, and more.

New Ultrathin Semiconductors Can Make More Efficient and Ten Times Smaller Transistors Than Silicon

The researchers at Stanford University have discovered two ultrathin semiconductors – hafnium diselenide and zirconium diselenide. They share or even exceed some of the very important characteristics of silicon. Silicon has a great property of forming “rust” or silicon dioxide (SiO2) by reacting with oxygen. As the SiO2 acts as an insulator, chip manufacturers implement this property to isolate their circuits on a die. The most interesting fact about these newly discovered semiconductors is, they also form “rust” just like silicon.

enlarged cross-section of an experimental chip made of ultrathin semiconductors
An enlarged cross-section of an experimental chip made of ultrathin semiconductors

The new materials can also be contracted to functional circuits just three atoms thick and they require much less energy than silicon circuits. Hafnium diselenide and zirconium diselenide “rust” even better than silicon and form so-called high-K insulator. The researchers hope to use these materials to design thinner and more energy-efficient chips for satisfying the needs of future devices.

Apart from having the ability to “rust”, the newly discovered ultrathin semiconductors also have the perfect range of energy band gap – a secret feature of silicon. The band gap is the energy needed to switch transistors on and it is a critical factor in computing. Too low band gap causes the circuits to leak and make unreliable. Too high and the chip takes excessive energy to operate and becomes inefficient. Surprisingly, Hafnium diselenide and zirconium diselenide are in the same optimal range of band gap as silicon.

All this and the diselenides can also be used to make circuits which are just three atoms thick, or about two-thirds of a nanometer, something silicon can never do. Eric Pop, an associate professor of electrical engineering, who co-authored with post-doctoral scholar Michal Mleczko in a study paper, said,

Engineers have been unable to make silicon transistors thinner than about five nanometers, before the material properties begin to change in undesirable ways.

If these semiconductors can be integrated with silicon, much longer battery life and much more complex functionality can be achieved in consumer electronics. The combination of thinner circuits and desirable high-K insulation means that these ultrathin semiconductors could be made into transistors 10 times tinier than anything possible with silicon today. As Eric Pop said,

There’s more research to do, but a new path to thinner, smaller circuits – and more energy-efficient electronics – is within reach.

Researchers Developed VO2 Based MEMS Mirror Actuator That Requires Very Low Power

A joint research by the US Air Force Research Laboratory Sensors Directorate and Michigan State University have developed micro-electromechanical systems (MEMS) actuator based on smart materials, specifically vanadium dioxide (VO2). In the room temperature, Vanadium dioxide exhibits the Mott transition. It is a not-well-understood phenomenon known to occur in transition metal chalcogenides and transition metal oxides.

VO2 Based Mott - MEMS Mirror Actuator
VO2 Based Mott – MEMS Mirror Actuator

The research team was able to use VO2 thin films for making complex mirror support structures to create a programmable tilting mirror. Transition-metal oxides like VO2 require little energy to drive the transition and less than more conventional actuation technologies. This enables implementation of transition-metal oxide based MEMS in battery powered and mobile devices.

When an input voltage of 1.1V is applied, the mirror platform achieves the maximum vertical displacement of 75 microns. The average power consumption per mirror actuator is 6.5mW and the total power consumption is 26.1mW for the entire device. The Mott-MEMS actuator mirror showed vertical movements and tilt angles of 75 micrometers and 5.5 degrees, respectively.

While testing, vanadium dioxide (VO2) displayed hysteric behavior or memory effect. That means the current response to externally applied electrical force is dependent on the previous response. Such behavior will let the researchers predict its response nature for certain electrical signals and they can program the actuators to generate different types of responses.

Nelson Sepulveda, a professor of electrical and computer engineering at Michigan State University, said in a statement issued by Wright-Patterson Air Force Base,

The actuation of such devices using smart phase-change materials represents a new operating principle that enables their programming and reduces power consumption.

The study opened a new door in the development of MEMS mirror actuation technology, which could incorporate the use of the hysteresis of smart materials like VO2 for programming tilt angles and vertical displacements in MEMS mirrors. The researchers are focusing on developing programmable MEMs mirrors and improving the design to achieve more precise control and larger movements.

Rechargeable Magnesium Batteries – Safer And Cheaper Than Li-ion Batteries

Researchers at the University of Houston reported in the journal Nature Communications the discovery of a new design that significantly improves the development of a battery based on magnesium. Magnesium batteries are considered as safe resources of power supply – unlike traditional lithium-ion batteries. They are not flammable or subject to exploding – but their ability to store energy is very limited. But the latest discovery of the new design for the battery cathode drastically increases the storage capacity.

Energy diagrams for the intercalation and diffusion of Mg2+ and MgCl+
Energy diagrams for the intercalation and diffusion of Mg2+ and MgCl+ in magnesium batteries

In order to make magnesium batteries, the magnesium-chloride bond must be broken before inserting magnesium into the host, and this is very hard to do. Hyun Deog Yoo, the first author of the paper, said,

First of all, it is very difficult to break magnesium-chloride bonds. More than that, magnesium ions produced in that way move extremely slowly in the host. That altogether lowers the battery’s efficiency.

The new battery technology stores energy by inserting magnesium monochloride into titanium disulfide, which acts as a host. By keeping the magnesium-chloride bond intact, the cathode showed much faster diffusion than traditional magnesium batteries.

The researchers managed to achieve a storage capacity density of 400 mAh/g – a quadruple increase compared with 100 mAh/g for earlier magnesium batteries. This achievement even overpowered the 200 mAh/g cathode capacity of commercially available lithium-ion batteries. Yoo, who is also the head investigator with the Texas Center for Superconductivity at UH, confirmed this fact.

The cell voltage of a magnesium cell is only 1V which is significantly less than a lithium-ion battery which has 3.7V cell voltage. Higher cell voltage and high cathode capacity made Li-ion batteries the standard. Li-ion batteries suffer from an internal structural breach, known as dendrite growth what makes them catch fire. Being an earth-abundant material, magnesium is less expensive than lithium and is not prone to dendrite growth.

The magnesium monochloride molecules are too large to be inserted into the titanium disulfide using conventional methods. The trick they developed is to expand the titanium disulfide to allow magnesium chloride to be inserted rather than breaking the magnesium-chloride bonds and inserting the magnesium alone. Retaining the magnesium-chloride bond doubled the charge the cathode could store. Yoo said,

We hope this is a general strategy. Inserting various polyatomic ions in higher voltage hosts, we eventually aim to create higher-energy batteries at a lower price, especially for electric vehicles.

Next Generation Solar Cell That Can Capture Nearly All Energy of Solar Spectrum

Researchers developed a multijunction solar cell on a GaSb substrate that can efficiently convert the long-wavelength photons typically lost in a multijunction solar cell into electricity. This prototype cell has an efficiency of 44.5% which is higher than conventional solar cells.

Next Generation Solar Cell To Absorb Nearly All Solar Spectrum
Next Generation Solar Cell To Absorb Nearly All Solar Spectrum

A GaAs-based cell is stacked mechanically with the GaSb-based materials to create a four-terminal, five junction cell with a spectral response range covering the region containing greater than 99% of the available direct-beam power from the Sun reaching the surface of the Earth. By comparison, the most typical solar cell can convert only one fourth of the available energy into electricity.

The working principle of this new solar cell is slightly different than the commonly available one. The cell is assembled in a mini-module that has a lens with a geometric concentration ratio of 744 suns. The lenses to concentrate sunlight onto tiny, microscale solar cells. As the solar cells have a very tiny form factor of  1 mm², solar cells using more complicated materials can be developed cost effectively.

The stacked cell acts like a filter with a particular material in each layer to absorb a specific range of wavelength of sunlight. The stacking procedure uses the transfer-printing technique which enables three dimensional modeling of these super-tiny devices with a high degree of precision.

Around 99 percent of the power contained in direct sunlight reaching the surface of Earth falls between wavelengths of 250 nm and 2500 nm. The entire range is not accessible by conventional solar panels as they are made from abundant, cheaper materials, such as silicon. Matthew Lumb, the lead author of the study and a research scientist at the GW School of Engineering and Applied Science, said,

Our new device is able to unlock the energy stored in the long-wavelength photons, which are lost in conventional solar cells, and therefore provides a pathway to realizing the ultimate multi-junction solar cell.

The cost of this specific solar cell is pretty high due to the high-end materials used and complex technologies implemented. However, the researchers achieved the upper limit of possibility in terms of efficiency. The new solar cell shows much promise in spite of being highly expensive. perhaps in future, the production cost can be reduced and the similar solar cell will be available commercially in the market.

Carrageenan, a seaweed derivative, can stabilize lithium-sulfur batteries surprisingly

Lithium-sulfur batteries are suitable for both vehicle and grid applications as they are ultra-cheap, high-energy devices. Sulfur is a very low-cost material and the energy capacity is much higher than that of lithium-ion. So, lithium-sulfur is one chemistry that can possibly meet the demand for energy storage at a cheap price. However, the serious problem is, lithium-sulfur batteries suffer from significant capacity fading that makes them almost practically unusable. But, Lawrence Berkeley National Laboratory researchers’ recent surprising discovery could fix this problem.

Carrageenan is extracted from this red seaweeds
Carrageenan is extracted from this red seaweeds

The research team at Berkley Laboratory surprisingly found that carrageenan, a substance extracted from red seaweeds, acts as a good stabilizer in lithium-sulfur batteries. Better stability in a battery means more charge-discharge cycle and an extended lifetime. Gao Liu, the leader of the research team, said,

It (Carrageenan) actually worked just as well as the synthetic polymer—it worked as a glue and it immobilized the polysulfide, making a really stable electrode.

Lithium-sulfur batteries are already been used commercially in limited applications but the “critical killer” in the chemistry is that the sulfur starts to dissolve and creates polysulfide shuttling effect. Polysulfide shuttling is the primary cause of failure in lithium-sulfur (Li-S) battery cycling. To solve the problem, the research team was experimenting with a synthetic binder that holds all the active materials in a battery cell together.

A binder is like a glue and battery makers want this glue to be inert. The synthetic polymer Liu experimented with, worked remarkably well. The reason is, by chemically reacting with the sulfur, the binder formed a covalent bonding structure and was able to stop it from dissolving. This finding motivated the researchers to find a natural material that would do the same thing. Finally, they discovered that carrageenan has similar chemical properties as the synthetic polymer they used in their initial experiments.

Bekley Lab's researcher is working with advanced light source
Berkley Lab’s researcher is working with advanced light source

With this discovery to stabilize lithium-sulfur batteries­ Liu now wants to improve the lifetime of lithium-sulfur batteries even further. The target of the researchers is to get thousands of cycles from lithium-sulfur chemistry. They are striving to find answers to questions like after this polymer binds with sulfur, what happens next? How does it react with sulfur, and is it reversible? Liu said,

Understanding that will allow us to be able to develop better ways to further improve the life of lithium-sulfur batteries.

As lithium-sulfur batteries are much more lightweight, cheaper, and have higher energy density compared to lithium-ion batteries, they are ideal for airplanes and drones. Hence, Berkeley Lab researchers’ surprising discovery may be a game changer in the world of batteries.

SYNTHETIC SENSORS, All-In-One Smart Home Sensor

In the era of Internet of Things, we wanted most of our home appliances to become smart. But currently, smart devices may cost much more than their offline counterparts and they often do not communicate with each other. Trying to overcome these limitations, A Ph.D student invented a way to turn entire rooms into smart with a single low-cost device called “Synthetic Sensors“.

Gierad Laput, is a Ph.D. student of computer-human interaction at Carnegie Mellon University. His research program explores novel sensing technologies for mobile and wearable computing, smart environments, and the Internet of Things.

Synthetic Sensor is a general purpose sensor that is powered directly from a wall socket and tracks ambient environmental data to monitor an entire room. It removes the need to attach additional hardware to each of home appliances.

We explore the notion of general-purpose sensing, wherein a single, highly capable sensor can indirectly monitor a large context, without direct instrumentation of objects. Further, through what we call Synthetic Sensors, we can virtualize raw sensor data into actionable feeds, whilst simultaneously mitigating immediate privacy issues. We use a series of structured, formative studies to inform the development of new sensor hardware and accompanying information architecture. We deployed our system across many months and environments, the results of which show the versatility, accuracy and potential of this approach.

The device uses machine learning to recognize the events that happen in the room, like recognizing a particular sound pattern as taking a paper towel, but it cannot monitor when the roll may need to be changed. However, by using a “second order” sensors, the devices can capture counts and send notifications of the need to replenish. This capability can be scaled to an unlimited degree giving consumers highly specific and applicable feedback.

Developers can use the recognized events as triggers for other IoT applications. For example, one could use “left faucet on” to activate a room’s left paper towel dispenser and automatically schedule a restock when its supply runs low.

The Synthetic Sensor is still in prototyping phase, you can learn more about it by visiting its website and read the research paper. Watch this video to see Synthetic Sensors in action: