Source: Original article appears in the October 2018 issue of the Wire Journal International.
Free subscription is required to read the digital version of the article. The feature on DexMat is on pages 52-53.
Source: Original article appears in the October 2018 issue of the Wire Journal International.
Free subscription is required to read the digital version of the article. The feature on DexMat is on pages 52-53.
Now researchers at Ulsan National Institute of Science and Technology (UNIST) in South Korea have made a nanomembrane out of silver nanowires to serve as flexible loudspeakers or microphones. The researchers even went so far as to demonstrate their nanomembrane by making it into a loudspeaker that could be attached to skin and used it to play the final movement of a violin concerto—namely, La Campanella by Niccolo Paganini.
In research described in the journal Science Advances, the Korean researchers embedded a silver nanowire network within a polymer-based nanomembrane. The decision to use silver nanowires rather than the other types of nanomaterials that have been used in the past was based on the comparative ease of hybridizing the nanowires into the polymer.
In addition, the researchers opted for nanowires because the other materials like graphene and carbon nanotubes are not as mechanically strong at nanometer-scale thickness when in freestanding form, according to Hyunhyub Ko, an associate professor at UNIST and coauthor of the research. It is this thickness that is the critical element of the material.
“The biggest breakthrough of our research is the development of ultrathin, transparent, and conductive hybrid nanomembranes with nanoscale thickness, less than 100 nanometers,” said Ko. “These outstanding optical, electrical, and mechanical properties of nanomembranes enable the demonstration of skin-attachable and imperceptible loudspeaker and microphone.”
The nanomembrane loudspeaker operates by emitting thermoacoustic sound through the oscillation of the surrounding air brought on by temperature differences. The periodic Joule heating that occurs when an electric current passes through a conductor and produces heat leads to these temperature oscillations.
For the operation of the microphone, the hybrid nanomembrane is sandwiched between elastic films with tiny patterns. In this way, the nanomembrane can precisely detect the sound and the vibration of the vocal cords based on a triboelectric voltage that results from the contact with the elastic films. In these loudspeakers and microphones, the silver nanowires enable both the electrical conductivity and give the nanomembranes their freestanding strength.
While the researchers demonstrated the technology by applying a thin film of the nanomembrane on skin, this may not turn out to be a practical application of the technology, according to the researchers. This is because the performance of the thermoacoustic loudspeaker is proportional to the speaker size and temperature change of the speaker.
If it were directly attached to the skin, the input power level per unit area would increase too much for the generation of a large sound.
Ko added: “For the commercial applications, the mechanical durability of nanomebranes and the performance of loudspeaker and microphone should be improved further.”
Researchers at Tokyo Institute of Technology have developed flexible terahertz imagers based on chemically “tunable” carbon nanotube materials. The findings expand the scope of terahertz applications to include wrap-around, wearable technologies as well as large-area photonic devices.
Carbon nanotubes (CNTs) are beginning to take the electronics world by storm, and now their use in terahertz (THz) technologies has taken a big step forward.
Due to their excellent conductivity and unique physical properties, CNTs are an attractive option for next-generation electronic devices. One of the most promising developments is their application in THz devices. Increasingly, THz imagers are emerging as a safe and viable alternative to conventional imaging systems across a wide range of applications, from airport security, food inspection and art authentication to medical and environmental sensing technologies.
The demand for THz detectors that can deliver real-time imaging for a broad range of industrial applications has spurred research into low-cost, flexible THz imaging systems. Yukio Kawano is of the Laboratory for Future Interdisciplinary Research of Science and Technology, Tokyo Institute of Technology (Tokyo Tech). In 2016 he announced the development of wearable terahertz technologies based on multiarrayed carbon nanotubes.
Kawano and his team have since been investigating THz detection performance for various types of CNT materials, in recognition of the fact that there is plenty of room for improvement to meet the needs of industrial-scale applications.
Now, they report the development of flexible THz imagers for CNT films that can be fine-tuned to maximize THz detector performance.
Publishing their findings in ACS Applied Nano Materials, the new THz imagers are based on chemically adjustable semiconducting CNT films.
By making use of a technology known as ionic liquid gating, the researchers demonstrated that they could obtain a high degree of control over key factors related to THz detector performance for a CNT film with a thickness of 30 micrometers. This level of thickness was important to ensure that the imagers would maintain their free-standing shape and flexibility.
“Additionally,” the team says, “we developed gate-free Fermi-level tuning based on variable-concentration dopant solutions and fabricated a Fermi-level-tuned p?n junction CNT THz imager.” In experiments using this new type of imager, the researchers achieved successful visualization of a metal paper clip inside a standard envelope.
The bendability of the new THz imager and the possibility of even further fine-tuning will expand the range of CNT-based devices that could be developed in the near future.
Moreover, low-cost fabrication methods such as inkjet coating could make large-area THz imaging devices more readily available.
 Ionic liquid gating: A technique used to modulate a material’s charge carrier properties.
 Fermi level: A measure of the electrochemical potential for electrons, which is important for determining the electrical and thermal properties of solids. The term is named after the Italian-American physicist Enrico Fermi.
 p-n junction: Refers to the interface between positive (p-type) and negative (n-type) semiconducting materials. These junctions form the basis of semiconductor electronic devices.
Tokyo Institute of Technology. “Scientists fine-tune carbon nanotubes for flexible, fingertip-wearable terahertz imagers.” ScienceDaily. ScienceDaily, 28 June 2018. <www.sciencedaily.com/releases/2018/06/180628105041.htm>
A team from the University of Cincinnati—in a partnership with the Wright-Patterson Air force base—are working to take advantage of the properties of carbon nanotubes in developing new applications for soldiers in the field.
“The major challenge is translating these beautiful properties to take advantage of their strength, conductivity and heat resistance,” UC professor Vesselin Shanov, who co-directs UC’s Nanoworld Laboratories, said in a statement.
Graduate student Mark Haase has worked with Air Force researchers over the past year to find applications for carbon nanotubes using X-ray computer tomography to analyze samples.
“This pushes us to work in groups and to specialize,” Haase said in a statement. “These are the same dynamics we see in corporate research and industry. Engineering is a group activity these days so we can take advantage of that.”
The researchers used chemical vapor deposition to grow the carbon nanotubes on silicon wafers the size of a quarter under heat in a vacuum chamber.
“Each particle has a nucleation point,” Haase said. “Colloquially, we can call it a seed. Our carbon-containing gas is introduced into the reactor. When the carbon gas interacts with our ‘seed,’ it breaks down and re-forms on the surface. We let it grow until it reaches the size we want.”
UC’s Nanoworld Lab set a world record in 2007 by growing a nanotube that stretched nearly two centimeters, the longest carbon nanotube array produced in a lab at the time. The lab can currently create nanotubes that are substantially longer.
They were able to stretch the little fibrous square over an industrial spool in the lab to convert the sheet of carbon to a spun thread that can be woven into textiles.
“It’s exactly like a textile,” Shanov said. “We can assemble them like a machine thread and use them in applications ranging from sensors to track heavy metals in water or energy storage devices, including super capacitors and batteries.”
This ultimately could lead to a much lighter load for soldiers in battle.
“As much as one-third of the weight they carry is just batteries to power all of their equipment,” Haase said. “So even if we can shave a little off that, it’s a big advantage for them in the field.”
The study was published in Materials Research Express.
Full article by Kenny Walter – Digital Reporter @RandMagazine here.
Today’s aerospace and aircraft industries focus on size, weight, power, and cost (SWaP-C), and cost is now often figured for program or operational life, which may total thousands of dollars per pound. This gives tremendous impetus and justification to accept high-cost new technology to obtain weight savings.
Satellites have always paid extra to reduce weight since each payload pound may cost more than $5,000 to launch. Studies by the Center for Strategic and Budgetary Assessments (CSBA) show that the new F-35 has a $4,500 cost per pound over the aircraft’s operational program life
until 2070. (For comparison, the cost per pound for the F-22 is estimated at $3,500.) The F-35 has projected production of2,557 aircraft for the U.S. and nine for export customers scheduled through 2037. Therefore, a weight reduction of just 20lbs per plane could result in savings of $230,000,000! Even if this is off by 50%, the expected benefits already are driving new industry developments.
In addition to fighter aircraft, each ounce is also critical in future soldier wearables, UAVs, portable radars, vehicle communications, and other equipment to increase survivability, mission endurance, and success.
Interconnect weight savings are being obtained by incorporating higher contact density, composite materials, combinational multi-port connectors, and other approaches. However, a new technology involving carbon nanotubes (CNTs) is emerging and offers a lightweight alternative to copper wire and other conductive shielding materials. A carbon nanotube is produced as a layer of carbon atoms in a tubular configuration, in single- or multiple-walled versions.
CNTs are being mixed with polymers to create high-strength, lightweight composite materials. CNT fibers can be made into conductive sheets and tapes, which offer a myriad of potentials. Optimal performance may result from spinning CNT fibers into conductive threads (referred to as yarn) to potentially replace copper wires in harnesses, motor windings, and shields.
Another important gain is reliability. CNT fibers and yarn can withstand millions of bending cycles, while standard fiber/wire would have yielded many times. The minimum bending radius requirements of today’s cable is not applicable for CNT fibers and cables.
Market potentials for CNT technology are bringing new companies into the forefront. Nanocomp Technologies offers commercial CNT fibers created using a carbon vapor deposition (CVD) reactor and then formed into sheets or fibers that can be twisted into shields or primary conductors. Another supplier is Syscom Advanced Materials Inc., which provides a variety of metal-clad fibers.
DexMat Inc. in Houston produces CNT fiber using a wet acid process that draws multiple fibers that can be shaped into a shield or primary conductor, and future developments for include flat tape. The company boasts a strong Ph.D. cadre from nearby Rice University where they have successfully fabricated coaxial cable inner and outer conductors by coating a solution of CNTs in chlorosulfonic acid to achieve a two-times better conductivity than seen previously. This may prove an attractive alternative to commercial coax cable using tin-coated-copper with comparable attenuation and greater mechanical durability with 97% reduced mass, according to the company.
Usually, the outer conductor is the heaviest portion of today’s cables. In coax, the outer conductor provides both signal transmission and electromagnetic shielding. While shielding does not require high conductivity in the outer conductor, signal loss (i.e., signal attenuation) through the transmission line is significantly affected by the conductivity and architecture of the outer conductor. The new solution-coated CNT outer conductors offer near-term application potentials. Several connector companies are reportedly studying termination techniques.
TE Connectivity has been working to use CNT materials for shielding and data transmission cables. In a paper presented at the 2012 IWCS Conference, Dr. Stefanie Harvey, senior manager for corporate strategy, reported that they had achieved greater than 50dB shielding effectiveness in the GHz range, and their “data transmission cables using a yarn format perform comparably to MIL-STD-1553.” In the January 5, 2016 issue of ASSEMBLY, Dr. Harvey reviewed how replacing the braid in RG-58 cable would reduce weight from 38.8 grams per meter (g/m) to 11.5g/m, while replacing the center conductor with CNT yarn would further reduce weight to 7.3g/m for a combined weight reduction of 80%.
Composites are used to replace heavy copper wire with metal plated aramid fibers for use in wire and cable EMI shielding. EMI shielding made with plated aramid fibers can reduce weight by as much as 80%, leading to major weight reduction depending on the size of the aircraft or satellite. Aramid fibers are a class of strong, heat-resistant synthetic fibers, the best known of which is DuPont™ Kevlar®, used in ballistic-rated body armor.
Carlisle Interconnect Technologies (formerly Micro-Coax Inc.) provides a unique weight-reducing EMI/RFI shielding solution using their proprietary high-strength ARACON® brand metal clad fibers. Ron Souders, technical director, Carlisle Interconnect Technologies, advises that, for typical applications, switching to ARACON allows a weight savings of 80% when compared to traditional metal braided or woven EMI shielding products. This offers the conductivity of an outer metal coating with the strength, light weight, and flexibility of aramid fiber.
*Note: DexMat also provides products for shielding applications not mentioned in this article.
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Ron Souders further explained that the specific gravity of aramid fiber is only 1.44g/cc, compared to copper at 8.9g/cc, and that, even with the addition of metal coatings, the specific gravity of ARACON fibers ranges from 3 – 5g/cc. The tensile strength (measured in kilopounds per square inch, or Ksi) of the aramid core (350Ksi) is from three to 10 times higher than that of traditional or high-strength copper cores, which typically span 35 to 95Ksi. Since ARACON fibers behave like a textile, they are far more flexible and compliant than metal.
The benefits offered by CNT fiber, whether as EMI/RFI shielding, signal or coaxial cable, or other new components, have prompted the Naval Air Systems Command (NAVAIR) in Patuxent River, Maryland, to sponsor the establishment of suitable “Military Specification for Conductive Carbon Conductors used in Aircraft Wiring,” eventually with QPL sources. The proposed formal qualification program should stabilize components and materials for future use.
CNT technology also was included in a recent multiple-day RF coordination meeting held in February by the Defense Logistics Agency (DLA) at the Defense Supply Center Columbus (DSCC). Suppliers of basic CNT materials, wire, cables, cable assembles, and signal and RF/microwave connectors are now working on both application-specific and generalized products to achieve the weight reduction and reliability benefits offered by CNT and other metallized fibers.
Original story by David Shaff – April 28, 2017
Abstract: The effects of electromagnetic interactions in electrical systems are of growing concern due to the increasing susceptibility of system components to electromagnetic interference (EMI), use of automated electronic systems, and pollution of the electromagnetic environment with electromagnetic emissions. The effects of EMI can be detrimental to electronic systems utilized in space missions; even small EMI issues can lead to total mission failure, resulting in significant mission delays and economic loss. Additionally, NASA is challenged to find ways of effectively shielding sensitive electronic equipment from EMI without adding significant weight to space flight vehicles and satellites in order to manage fuel costs. The solution for both issues resides in the use of carbon nanotubes (CNTs), which offer the most promising solution for reducing spacecraft wire weight. CNTs are an alluring alternative to conventional conductors used in coaxial data cables because they combine mechanical strength, electrical conductivity, and low density. DexMat has developed a novel CNT deposition process for directly applying CNTs onto dielectric materials to produce an electrically conductive EMI shield. By placing a premium on the quality of raw CNTs, DexMat has created a product with increased potential to reduce cable weight while minimizing insertion losses when incorporated into wire. In the proposed research, DexMat seeks to develop a small-scale CNT Tape production process and continue the development of the CNT separation processes. The need for CNT Tape was discovered while obtaining feedback from potential customers that noted the desire for a product format that allows for quick and easy integration into existing manufacturing processes without the need for outsourcing processes.
Project Details: https://www.sbir.gov/sbirsearch/detail/1426213
Abstract: This SBIR Phase I project strives to reduce aircraft wire weight in order to improve aircraft range and reduce operating costs. Commercial and military aerospace companies are heavily concerned with fuel costs associated with aircraft operation, as this expense contributes significantly to the total costs of the company. Substantial reductions in aircraft weight could save millions of dollars per plane over its operating lifetime. For example, eliminating a single pound from a military fighter aircraft can save up to $3,000 over its lifetime, as well as increase its operating range, capacity to carry a larger payload and extend its time-on-station capabilities. These cost savings will benefit commercial aviation companies from decreased expense, resulting in a higher net income. Enhanced financial performance promotes company growth and the creation of more jobs throughout all levels of the organization. Increased income and job growth in this sector with stimulate continued national economic growth, providing benefit to the government via tax collections and increased commercial sector performance. National defense and aerospace sectors would also benefit from fuel cost reductions reducing costs and greenhouse gas emissions. This project directly aligns with the NSF mission to progress science, advance national prosperity and secure the national defense. This project provides innovative contribution to wire development and manufacturing through the use of a carbon nanotube deposition process in order to produce shielding for wires. This process is versatile and can be used to produce cables with a commercial metal inner conductor or a carbon nanotube fiber bundle as inner conductor and a specific conductivity similar to tin. It combines high strength, electrical conductivity and thermal conductivity with low density, which makes them ideal for applications where weight reduction is a priority, specifically in aerospace applications. Until now, only minor reductions in wire weight have been achieved, through advances in composite connectors, thermoplastic cable clamps, downsizing connectors and using thinner wall insulation. The use of carbon nanotubes would remove the need for component removal due to decreased weight. The goal of this project is to prove out a continuous roll-to-roll wire coating process to produce carbon nanotube electromagnetic interference shields suitable for a large volume manufacturing operation. This will be accomplished through the use of foundationary methods of carbon nanotube deposition developed prior to this Phase I project. This project will produce the methods required for developing roll-to-roll continuous carbon nanotube wire coating.
Project Details: https://www.sbir.gov/sbirsearch/detail/1191963
Abstract: In an era of reduced Defense budgets and increasing threats, military planners are seeking new technologies to reduce operating costs and increase operation capabilities for space and aviation platforms, and weight reduction is an attractive target. For example, transportation costs to geosynchronous orbits using a NASA reusable launch vehicle are close to $10,000 per pound of payload. Copper wiring, which makes up as much as one-third of the weight of a 15-ton satellite and 20 miles of an F-22 aircraft, is a clear target for weight reduction. Half of this wire weight is typically in the EMI shielding. Developing new lightweight, conductive materials that replace copper in the shielding and core conductor could serve as a lead candidate for radically reducing this weight. Carbon nanotubes (CNTs) combine high strength, electrical and thermal conductivity with low density, which makes them ideal for applications where weight reduction is a priority. DexMat is commercializing CNT technology that has shown the highest published values for conductivity and mechanical strength of CNT materials. This Phase II Proposal will continue developing CNT-based cables with solution-processing technology capable of producing high performance CNT fibers and coatings, without the use of binders and wetting agents.
Project Details: https://www.sbir.gov/sbirsearch/detail/1412727
This paper aims to explore the shielding potential of light-weight carbon nanotube (CNT) film materials against gamma-ray generated from americium-241 (241Am) and caesium-137 (137Cs). The influence factors of gamma mass attenuation coefficient of CNT film laminates were investigated to reveal structure-property relationship. The results showed that CNT film materials had bigger mass attenuation coefficients than carbon fiber reinforced composites, suggesting stronger radiation interaction induced by CNT’s cylindrical nanostructure. CNT alignment was proved to be conducive to the improvement of mass attenuation coefficient and gamma attenuation ratio. Aligned CNT film laminate with the thickness of 10 mm had a mass attenuation coefficient of 0.086 cm2 /g and attenuation ratio of 4.9% against gamma-ray exposed to 137Cs, which were higher than those of aluminum, iron or copper sheets. CNT film material demonstrated its potential for the application of light-weight gamma-ray safety equipment and devices.
Download full paper at: https://houstontx.library.ingentaconnect.com/content/asp/me/2016/00000006/00000005/art00010