How To Secure Your Wi-Fi Network Against Intrusion


Insecure Wi-Fi is the easiest way for people to access your home network, leech your internet, and cause you serious headaches with more malicious behavior. Read on as we show you how to secure your home Wi-Fi network.

Why Secure Your Network?

In a perfect world you could leave your Wi-Fi networks wide open to share with any passing Wi-Fi starved travelers who desperately needed to check their email or lightly use your network. In reality leaving your Wi-Fi network open create unnecessary vulnerability wherein non-malicious users can sponge up lots of our bandwidth inadvertently and malicious users can pirate using our IP as cover, probe your network and potentially get access to your personal files, or even worse. What does even worse look like?  In the case of Matt Kostolnik it looks like a year of hell as your crazy neighbor, via your hacked Wi-Fi network, uploads child pornography in your name using your IP address and sends death threats to the Vice President of the United States. Mr. Kolstolnik was using crappy and outdated encryption with no other defensive measures in place; we can only imagine that a better understanding of Wi-Fi security and a little network monitoring would have saved him a huge headache.

Securing Your Wi-Fi Network


Securing your Wi-Fi network is a multi-step affair. You need to weigh each step and decide if the increased security is worth the sometimes increased hassle accompanying the change. To help you weigh the benefits and drawbacks of each step we’ve divided them up into relative order of importance as well as highlighted the benefits, the drawbacks, and the tools or resources you can use to stress test your own security. Don’t rely on our word that something is useful; grab the available tools and try to kick down your own virtual door.

Note: It would be impossible for us to include step-by-step instructions for every brand/model combination of routers out there. Check the brand and model number on your router and download the manual from the manufacturer’s website in order to most effectively follow our tips. If you have never accessed your router’s control panel or have forgotten how, now is the time to download the manual and give yourself a refresher.

Update Your Router and Upgrade to Third Party Firmware If Possible: At minimum you need to visit the web site for the manufacture of your router and make sure there are no updates. Router software tends to be pretty stable and releases are usually few and far between. If your manufacturer has released an update (or several) since you purchased your router it’s definitely time to upgrade.

Even better, if you’re going to go through the hassle of updating, is to update to one of the awesome third-party router firmwares out there like DD-WRT or Tomato. The third party firmwares unlock all sorts of great options including an easier and finer grain control over security features.

The hassle factor for this modification is moderate. Anytime you flash the ROM on your router you risk bricking it. The risk is really small with third-party firmware and even smaller when using official firmware from your manufacturer. Once you’ve flashed everything the hassle factor is zero and you get to enjoy a new better, faster, and more customizable router.

Change Your Router’s Password: Every router ships with a default login/password combination. The exact combination varies from model to model but it’s easy enough to look up the default that leaving it unchanged is just asking for trouble. Open Wi-Fi combined with the default password is essentially leaving your entire network wide open. You can check out default password lists here, here, and here.

The hassle factor for this modification is extremely low and it’s foolish not to do it.


Turn On and/or Upgrade Your Network Encryption: In the above example we gave, Mr. Kolstolnik had turned on the encryption for his router. He made the mistake of selecting WEP encryption, however, which is the lowest encryption on the Wi-Fi encryption totem pole. WEP is easy to crack using freely available tools such as WEPCrack and BackTrack. If you happened to read the entire article about Mr. Kolstolnik’s problems with his neighbors you’ll note that it took his neighbor two weeks, according to the authorities, to break the WEP encryption. That’s such a long span of time for such a simple task we have to assume that he also had to teach himself how to read and operate a computer too.

Wi-Fi encryption comes in several flavors for home use such as WEP, WPA, and WPA2. In addition WPA/WPA2 can be further subdivided as WPA/WPA2 with TKIP (a 128-bit key is generated per packet) and AES (a different 128-bit encryption). If possible you want to use WP2 TKIP/AES as AES is not as widely adopted as TKIP. Allowing your router to use both will enable to use the superior encryption when available.

The only situation where upgrading the encryption of your Wi-Fi network may pose a problem is with legacy devices. If you have devices manufactured before 2006 it’s possible that, without firmware upgrades or perhaps not at all, they will be unable to access any network but an open or WEP encrypted network. We’ve phased out such electronics or hooked them up to the hard LAN via Ethernet (we’re looking at you original Xbox).

The hassle factor for this modification is low and–unless you have a legacy Wi-Fi device you can’t live without–you won’t even notice the change.

Changing/Hiding Your SSID: Your router shipped with a default SSID; usually something simple like “Wireless” or the brand name like “Netgear”. There’s nothing wrong with leaving it set as the default. If you live in a densely populated area, however, it would make sense to change it to something different in order to distinguished it from the 8 “Linksys” SSIDs you see from your apartment. Don’t change it to anything that identifies you. Quite a few of our neighbors have unwisely changed their SSIDs to things like APT3A or 700ElmSt . A new SSID should make it easier for you to identify your router from the list and not easier for everyone in the neighborhood to do so.

Don’t bother hiding your SSID. Not only does it provide no boost in security but it makes your devices work harder and burn more battery life.  The short version is this: even if you “hide” your SSID it is still being broadcast and anyone using apps like inSSIDer or Kismet can see it.

The hassle factor for this modification is low. All you’ll need to do is change your SSID once (if at all) to increase recognition in a router-dense environment.


Filter Network Access by MAC Address:

Media Access Control addresses, or MAC address for short, is a unique ID assigned to every network interface you’ll encounter. Everything you can hook up to your network has one: your XBOX 360, laptop, smartphone, iPad, printers, even the Ethernet cards in your desktop computers. The MAC address for devices is printed on a label affixed to it and/or on the box and documentation that came with the device. For mobile devices you can usually find the MAC address within the menu system (on the iPad, for example, it’s under the Settings –> General –> About menu and on Android phones you’ll find it Settings –> About Phone –> Status menu).

One of the easiest ways to check the MAC addresses of your devices, besides simply reading the label on them, is to check out the MAC list on your router after you’ve upgraded your encryption and logged all your devices back in. If you’ve just changed your password you can be nearly certain the iPad you see attached to the Wi-Fi node is yours.

Once you have all the MAC addresses you can set up your router to filter based on them. Then it won’t be enough for a computer to be in range of the Wi-Fi node and have the password/break the encryption, the device intruding on the network will also need to have the MAC address of a device on your router’s whitelist.

Although MAC filtering is a solid way to increase your security it is possible for somebody to sniff your Wi-Fi traffic and then spoof the MAC address of their device to match one on your network. Using tools like Wireshark, Ettercap, and Nmap as well as the aforementioned BackTrack. Changing the MAC address on a computer is simple. In Linux it’s two commands at the command prompt, with a Mac it’s just about as easy, and under Windows you can use a simple app to swap it like Etherchange or MAC Shift.

The hassle factor for this modification is moderate-to-high. If you use the same devices on your network over and over with little change up then it’s a small hassle to set up the initial filter. If you frequently have guests coming and going that want to hop on your network it’s a hugehassle to always be logging into your router and adding their MAC addresses or temporarily turning off the MAC filtering.

One last note before we leave MAC addresses: if you’re particularly paranoid or you suspect someone is messing around with your network you can run applications like AirSnare and Kismet to set up alerts for MACs outside your white list.

Adjust the Output Power of Your Router: This trick is usually only available if you’ve upgraded the firmware to a third party version. Custom firmware allows you to dial up or down the output of your router. If you’re using your router in a one bedroom apartment you can easily dial the power way down and still get a signal everywhere in the apartment. Conversely if the nearest house is 1000 feet away, you can crank the power up to enjoy Wi-Fi out in your hammock.

The hassle factor for this modification is low; it’s a one time modification. If your router doesn’t support this kind of adjustment, don’t sweat it. Lowering the output power of your router is just a small step that makes it necessary for someone to be physically closer to your router to mess with it. With good encryption and the other tips we’ve shared, such a small tweak has a relatively small benefit.

Once you’ve upgraded your router password and upgraded your encryption (let alone done anything else on this list) you’ve done 90% more than nearly every Wi-Fi network owner out there.

Congratulations, you’ve hardened your network enough to make almost everyone else look like a better target! Have a tip, trick, or technique to share? Let’s hear about your Wi-Fi security methods in the comments.

What is a Customized SBC?

SBC – Single Board Computers

SBCs are off-the-shelf products that can be used to develop end-products or applications for a variety of industries. SBCs come along with integrated software and hardware, which includes SoC, memory, power requirements, real world multimedia and connectivity interfaces such as USB, UART, CAN, HDMI, Ethernet, SDIO, MMC, Analog Audio, display etc. The SBC approach helps system developers to focus on the application specific parts. An extensive range of SBCs based on a variety of microprocessors, memory sizes, supported interfaces and operating systems such as Windows Embedded Compact, Linux, Android etc. are available in the embedded market. This offers flexibility to the users to choose the appropriate SBC based on their cost, features and performance requirements. Low cost SBCs are widely used in academic research projects and in feature specific end-products.


However, the SBC approach suffers inherently from various drawbacks. First of all, the SBC approach leads to high switching cost to migrate to future technologies. As SBCs comes in standard sizes and real world interfaces, so it is difficult to accommodate future improvements in technology and thus the OEMs need to switch to an entirely new SBC solution. Secondly, customizing a SBC is cumbersome as the processor chipset and surrounding I/O are closely coupled due to the single-board design. Finally, space constrained applications may also struggle to use the standardized SBC available in the market.

The Computer On Module (COM) or System On Module (SOM) coupled along with a baseboard offers an equivalent solution as that of the SBCs. The COM approach separates the complex microprocessor part from the relatively simple I/O part and thus offers flexibility to customize the baseboard part based on the feature and size requirements of the end-product. Furthermore, pin-compatible modules ensure convenient and cost effective way to migrate to future technology.

A Customized SBC is an off-the-shelf embedded solution that is a combination of a COM/ SOM and a carrier board. This combination provides a desirable alternative to SBCs in developing any embedded end-products as the former offers the flexibility and scalability inherent to the COM approach and yet, is a ready-to-use complete embedded solution, one of the main benefits of the SBC approach.

Windows CE
Touch Support






Out of India: Finding the origins of horses, rhinos


An artist’s depiction of Cambaytherium thewissi. Credit: Elaine Kasmer
An artist’s depiction of Cambaytherium thewissi.
Credit: Elaine Kasmer

[dropcap]W[/dropcap]orking at the edge of a coal mine in India, a team of Johns Hopkins researchers and colleagues have filled in a major gap in science’s understanding of the evolution of a group of animals that includes horses and rhinos. That group likely originated on the subcontinent when it was still an island headed swiftly for collision with Asia, the researchers report Nov. 20 in the online journal Nature Communications.

Modern horses, rhinos and tapirs belong to a biological group, or order, called Perissodactyla. Also known as “odd-toed ungulates,” animals in the order have, as their name implies, an uneven number of toes on their hind feet and a distinctive digestive system. Though paleontologists had found remains of Perissodactyla from as far back as the beginnings of the Eocene epoch, about 56 million years ago, their earlier evolution remained a mystery, says Ken Rose, Ph.D., a professor of functional anatomy and evolution at the Johns Hopkins University School of Medicine.

Rose and his research team have for years been excavating mammal fossils in the Bighorn Basin of Wyoming, but in 2001 he and Indian colleagues began exploring Eocene sediments in Western India because it had been proposed that perissodactyls and some other mammal groups might have originated there. In an open-pit coal mine northeast of Mumbai, they uncovered a rich vein of ancient bones. Rose says he and his collaborators obtained funding from the National Geographic Society to send a research team to the mine site at Gujarat in the far Western part of India for two weeks at a time once every year or two over the last decade.

The mine yielded what Rose says was a treasure trove of teeth and bones for the researchers to comb through back in their home laboratories. Of these, more than 200 fossils turned out to belong to an animal dubbed Cambaytherium thewissi, about which little had been known. The researchers dated the fossils to about 54.5 million years old, making them slightly younger than the oldest known Perissodactyla remains, but, Rose says, it provides a window into what a common ancestor of all Perissodactyla would have looked like. “Many of Cambaytherium’s features, like the teeth, the number of sacral vertebrae, and the bones of the hands and feet, are intermediate between Perissodactyla and more primitive animals,” Rose says. “This is the closest thing we’ve found to a common ancestor of the Perissodactyla order.”

Cambaytherium and other finds from the Gujarat coal mine also provide tantalizing clues about India’s separation from Madagascar, lonely migration, and eventual collision with the continent of Asia as Earth’s plates shifted, Rose says. In 1990, two researchers, David Krause and Mary Maas of Stony Brook University, published a paper suggesting that several groups of mammals that appear at the beginning of the Eocene, including primates and odd- and even-toed ungulates, might have evolved in India while it was isolated. Cambaytherium is the first concrete evidence to support that idea, Rose says. But, he adds, “It’s not a simple story.”

“Around Cambaytherium’s time, we think India was an island, but it also had primates and a rodent similar to those living in Europe at the time,” he says. “One possible explanation is that India passed close by the Arabian Peninsula or the Horn of Africa, and there was a land bridge that allowed the animals to migrate. But Cambaytherium is unique and suggests that India was indeed isolated for a while.”

Rose said his team was “very fortunate that we discovered the site and that the mining company allowed us to work there,” although he added, “it was frustrating to knowing that countless fossils were being chewed up by heavy mining equipment.” When coal extraction was finished, the miners covered the site, he says. His team has now found other mines in the area to continue digging.

Story Source:

The above story is based on materials provided by Johns Hopkins Medicine. Note: Materials may be edited for content and length.

Journal Reference:

  1. Kenneth D. Rose, Luke T. Holbrook, Rajendra S. Rana, Kishor Kumar, Katrina E. Jones, Heather E. Ahrens, Pieter Missiaen, Ashok Sahni, Thierry Smith. Early Eocene fossils suggest that the mammalian order Perissodactyla originated in India. Nature Communications, 2014; 5: 5570 DOI: 10.1038/ncomms6570

What is a Computer-On-Module?

A Computer-On-Module (COM) / System On Module (SOM) is a highly integrated embedded computing solution that can be used to design and develop end-products for a variety of industries . The COM/SOM approach offers flexibility to system developers to focus on application development by using an off-the-shelf module that has the generic hardware and software to develop any application. This approach greatly reduces the time-to-market and development cost.

COM/SOM are generally built around microprocessors, system-on-chips, or microcontrollers. They integrate additional devices and peripherals which are needed to realise a fully functional computer, which normally includes RAM, non-volatile storage and power supplies.

They are essentially another layer of abstraction that sits above the SoC (System-on-Chip) concept, providing further integration in areas of hardware and software that are not application specific, but are application agnostic.

  • Optimized for Multicore
  • High-Speed Multimedia Interfaces (PCIe, SATA)
  • Direct Breakout™ for Easy Baseboard Routing
  • Fully Compatible Product Family
  • Small Form Factor
  • Free Support Directly from the Developers
  • 10+ Years Product Lifecycle

Carefully view the following image for the big picture 🙂

What is a Resistor?

Ads by Google Variable Resistor 5 Ohm Resistor Resistor High Voltage Resistor Component Electrical Resistor Series Resistor Resistor Values Standard Resistor Resistor Types Chip Resistors Resistor Calculator Resistor Color A resistor is an electronic component that can lower a circuit’s voltage and its flow of electrical current.
A resistor is an electronic component that can lower a circuit’s voltage and its flow of electrical current.

A resistor is a component of a circuit that resists the flow of electrical current. It has two terminals across which electricity must pass, and it is designed to drop the voltage of the current as it flows from one terminal to the other. Resistors are primarily used to create and maintain known safe currents within electrical components.

Resistance is measured in ohms, after Ohm’s law. This law states that electrical resistance is equal to the drop in voltage across the terminals of the resistor divided by the current being applied. A high ohm rating indicates a high resistance to current. This rating can be written in a number of different ways — for example, 81R represents 81 ohms, while 81K represents 81,000 ohms.

The amount of resistance offered by a resistor is determined by its physical construction. A carbon composition resistor has resistive carbon packed into a ceramic cylinder, while a carbon film resistor consists of a similar ceramic tube, but has conductive carbon film wrapped around the outside. Metal film or metal oxide resistors are made much the same way, but with metal instead of carbon. A wirewound resistor, made with metal wire wrapped around clay, plastic, orfiberglass tubing, offers resistance at higher power levels. Those used for applications that must withstand high temperatures are typically made of materials such as cermet, a ceramic-metal composite, or tantalum, a rare metal, so that they can endure the heat.

Electrical resistance was discovered by German physicist Georg Ohm in the 19th century and has since been measured in ohms
Electrical resistance was discovered by German physicist Georg Ohm in the 19th century and has since been measured in ohms


Resistors are coated with paint or enamel, or covered in molded plastic to protect them. Because they are often too small to be written on, a standardized color-coding system is used to identify them. The first three colors represent ohm value, and a fourth indicates the tolerance, or how close by percentage the resistor is to its ohm value. This is important for two reasons: the nature of its construction is imprecise, and if used above its maximum current, the value can change or the unit itself can burn up.

Every resistor falls into one of two categories: fixed or variable. A fixed resistor has a predetermined amount of resistance to current, while a variable one can be adjusted to give different levels of resistance. Variable resistors are also called potentiometers and are commonly used as volume controls on audio devices. A rheostat is a variable resistor made specifically for use with high currents. There are also metal-oxide varistors, which change their resistance in response to a rise in voltage; thermistors, which either raise or lower resistance when temperature rises or drops; and light-sensitive resistors.

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[lightbox full=”” title=”Resistors are electrical devices that manage the flow of current through a circuit.”]Resistors[/lightbox]
[lightbox full=”” title=”A variable resistor is able to manage flows of electricity at a specific level as well as below that level.”]Variable Resistor[/lightbox]
[lightbox full=”” title=”Variable resistors can be adjusted to change the level of resistance.”]Level of Resistance[/lightbox]


Source / Courtesy : WiseGeek

What Is a Capacitor?

Ben Franklin used a Leyden jar in his famous kite experiment.
Ben Franklin used a Leyden jar in his famous kite experiment.

A capacitor is a tool consisting of two conductive plates, each of which hosts an opposite charge. These plates are separated by a dielectric or other form of insulator, which helps them maintain an electric charge. There are several types of insulators used in capacitors, including ceramic, polyester, tantalum air, and polystyrene. Other common insulators include air, paper, and plastic. Each effectively prevents the plates from touching each other.

There are a number of different ways to use a capacitor, such as to store analog signals and digital data. Another type is used in the telecommunications equipment industry to adjust the frequency and tuning of telecommunications equipment. This is often referred to a variable capacitor. A capacitor is also ideal for storing electrons, but it cannot make them.


The first capacitor was the Leyden jar, invented at the Netherlands University in the 18th century. It consists of a glass jar coated with metal on the inside and outside. A rod is connected to the inner coat of metal, passed through the lid, and topped off with a metal ball. As with all capacitors, the jar contains an oppositely charged electrode and a plate that is separated by an insulator. The Leyden jar has been used to conduct experiments in electricity for hundreds of years.

A capacitor can be measured in voltage, which differs on each of the two interior plates. Both plates are charged, but the current flows in opposite directions. A capacitor contains 1.5 volts, which is the same voltage found in a common AA battery. As voltage is used, one of the two plates becomes filled with a steady flow of current. At the same time, the current flows away from the other plate.

To understand the flow of voltage in a capacitor, it is helpful to look at naturally occurring examples. Lightning, for example, works in a similar way. The cloud represents one of the plates and the ground represents the other. The lightning is the charging factor moving between the ground and the cloud.


Source / Courtesy : WiseGeek

High milk intake linked with higher fractures and mortality, research suggests

Women who drank more than three glasses of milk a day had a higher risk of death than women who drank less than one glass of milk a day. Credit: © Africa Studio / Fotolia
Women who drank more than three glasses of milk a day had a higher risk of death than women who drank less than one glass of milk a day.
Credit: © Africa Studio / Fotolia

[dropcap]A[/dropcap] high milk intake in women and men is not accompanied by a lower risk of fracture and instead may be associated with a higher rate of death, suggests observational research published in The BMJ this week.

This may be explained by the high levels of lactose and galactose (types of sugar) in milk, that have been shown to increase oxidative stress and chronic inflammation in animal studies, say the researchers.

However, they point out that their study can only show an association and cannot prove cause and effect. They say the results “should be interpreted cautiously” and further studies are needed before any firm conclusions or dietary recommendations can be made.

A diet rich in milk products is promoted to reduce the likelihood of osteoporotic fractures, but previous research looking at the importance of milk for the prevention of fractures and the influence on mortality rates show conflicting results.

So a research team in Sweden, led by Professor Karl Michaëlsson, set out to examine whether high milk intake may increase oxidative stress, which, in turn, affects the risk of mortality and fracture.

Two large groups of 61,433 women (aged 39-74 years in 1987-1990) and 45,339 men (aged 45-79 years in 1997) in Sweden completed food frequency questionnaires for 96 common foods including milk, yoghurt and cheese.

Lifestyle information, weight and height were collated and factors such as education level and marital status were also taken into account. National registers were used to track fracture and mortality rates.


Women were tracked for an average of 20 years, during which time 15,541 died and 17,252 had a fracture, of whom 4,259 had a hip fracture.

In women, no reduction in fracture risk with higher milk consumption was observed. Furthermore, women who drank more than three glasses of milk a day (average 680 ml) had a higher risk of death than women who drank less than one glass of milk a day (average 60 ml).

Men were tracked for an average of 11 years, during which time 10,112 died and 5,066 had a fracture, with 1,166 hip fracture cases. Men also had a higher risk of death with higher milk consumption, although this was less pronounced than in women.

Further analysis showed a positive association between milk intake and biomarkers of oxidative stress and inflammation.

In contrast, a high intake of fermented milk products with a low lactose content (including yoghurt and cheese) was associated with reduced rates of mortality and fracture, particularly in women.

They conclude that a higher consumption of milk in women and men is not accompanied by a lower risk of fracture and instead may be associated with a higher rate of death. Consequently, there may be a link between the lactose and galactose content of milk and risk, although causality needs be tested.

“Our results may question the validity of recommendations to consume high amounts of milk to prevent fragility fractures,” they write. “The results should, however, be interpreted cautiously given the observational design of our study. The findings merit independent replication before they can be used for dietary recommendations.”

Michaëlsson and colleagues raise a fascinating possibility about the potential harms of milk, says Professor Mary Schooling at City University of New York in an accompanying editorial. However, she stresses that diet is difficult to assess precisely and she reinforces the message that these findings should be interpreted cautiously.

“As milk consumption may rise globally with economic development and increasing consumption of animal source foods, the role of milk and mortality needs to be established definitively now,” she concludes.


Story Source:

The above story is based on materials provided by BMJ-British Medical Journal.Note: Materials may be edited for content and length.

Journal References:

  1. K. Michaelsson, A. Wolk, S. Langenskiold, S. Basu, E. Warensjo Lemming, H. Melhus, L. Byberg. Milk intake and risk of mortality and fractures in women and men: cohort studies. BMJ, 2014; 349 (oct27 1): g6015 DOI:10.1136/bmj.g6015
  2. C. M. Schooling. Milk and mortality. BMJ, 2014; 349 (oct27 1): g6205 DOI:10.1136/bmj.g6205

Magnetic mirrors enable new technologies by reflecting light in uncanny ways

Artist's impression of a comparison between a magnetic mirror with cube shaped resonators (left) and a standard metallic mirror (right). The incoming and outgoing electric field of light (shown as alternating red and white bands) illustrates that the magnetic mirror retains light's original signature while a standard metallic mirror reverses it upon reflection. Credit: S. Liu et al.
Artist’s impression of a comparison between a magnetic mirror with cube shaped resonators (left) and a standard metallic mirror (right). The incoming and outgoing electric field of light (shown as alternating red and white bands) illustrates that the magnetic mirror retains light’s original signature while a standard metallic mirror reverses it upon reflection.
Credit: S. Liu et al.

As in Alice’s journey through the looking-glass to Wonderland, mirrors in the real world can sometimes behave in surprising and unexpected ways, including a new class of mirror that works like no other.

As reported today in The Optical Society’s (OSA) new journal Optica, scientists have demonstrated, for the first time, a new type of mirror that forgoes a familiar shiny metallic surface and instead reflects infrared light by using an unusual magnetic property of a non-metallic metamaterial.

By placing nanoscale antennas at or very near the surface of these so-called “magnetic mirrors,” scientists are able to capture and harness electromagnetic radiation in ways that have tantalizing potential in new classes of chemical sensors, solar cells, lasers, and other optoelectronic devices.

“We have achieved a new milestone in magnetic mirror technology by experimentally demonstrating this remarkable behavior of light at infrared wavelengths. Our breakthrough comes from using a specially engineered, non-metallic surface studded with nanoscale resonators,” said Michael Sinclair, co-author on the Optica paper and a scientist at Sandia National Laboratories in Albuquerque, New Mexico, USA who co-led a research team with fellow author and Sandia scientist Igal Brener.

These nanoscale cube-shaped resonators, based on the element tellurium, are each considerably smaller than the width of a human hair and even tinier than the wavelengths of infrared light, which is essential to achieve magnetic-mirror behavior at these incredibly short wavelengths.

“The size and shape of the resonators are critical,” explained Sinclair “as are their magnetic and electrical properties, all of which allow them to interact uniquely with light, scattering it across a specific range of wavelengths to produce a magnetic mirror effect.”


Early Magnetic Mirror Designs

Conventional mirrors reflect light by interacting with the electrical component of electromagnetic radiation. Because of this, however, they do more than reverse the image; they also reverse light’s electrical field. Though this has no impact on the human eye, it does have major implications in physics, especially at the point of reflection where the opposite incoming and outgoing electrical fields produce a canceling effect. This temporary squelching of light’s electrical properties prevents components like nanoscale antennas and quantum dots from interacting with light at the mirror’s surface.

A magnetic mirror, in contrast, reflects light by interacting with its magnetic field, preserving its original electrical properties. “A magnetic mirror, therefore, produces a very strong electric field at the mirror surface, enabling maximum absorption of the electromagnetic wave energy and paving the way for exciting new applications,” said Brener.

Unlike silver and other metals, however, there is no natural material that reflects light magnetically. Magnetic fields can reflect and even bottle-up charged particles like electrons and protons. But photons, which have no charge, pass through freely.

“Nature simply doesn’t provide a way to magnetically reflect light,” explained Brener. Scientists, therefore, are developing metamaterials (materials not found in nature, engineered with specific properties) that are able to produce the magnetic-mirror effect.

Initially, this could only be achieved at long microwave frequencies, which would enable only a few applications, such as microwave antennas.

More recently, other researchers have achieved limited success at shorter wavelengths using “fish-scale” shaped metallic components. These designs, however, experienced considerable loss of signal, as well as an uneven response due to their particular shapes.

Mirrors Without Metals

To overcome these limitations, the team developed a specially engineered two-dimensional array of non-metallic dielectric resonators — nanoscale structures that strongly interact with the magnetic component of incoming light. These resonators have a number of important advantages over the earlier designs . First, the dielectric material they use, tellurium, has much lower signal loss than do metals, making the new design much more reflective at infrared wavelengths and creating a much stronger electrical field at the mirror’s surface. Second, the nanoscale resonators can be manufactured using standard deposition-lithography and etching processes, which are already widely used in industry.

The reflective properties of the resonators emerge because they behave, in some respects, like artificial atoms, absorbing and then reemitting photons. Atoms naturally do this by absorbing photons with their outer electrons and then reemitting the photons in random directions. This is how molecules in the atmosphere scatter specific wavelengths of light, causing the sky to appear blue during the day and red at sunrise and sunset.

The metamaterials in the resonators achieve a similar effect, but absorb and reemit photons without reversing their electric fields.


Proof of the Process

Confirming that the team’s design was actually behaving like a magnetic mirror required exquisite measurements of how the light waves overlap as they pass each other coming in and reflecting off of the mirror surface. Since normal mirrors reverse the phase of light upon reflection, evidence that the phase signature of the wave was not reversed would be the “smoking gun” that the sample was behaving as a true magnetic mirror.

To make this detection, the Sandia team used a technique called time-domain spectroscopy, which has been widely used to measure phase at longer terahertz wavelengths. According to the researchers, only a few groups in the world have demonstrated this technique at shorter wavelengths (less than 10 microns). The power of this technique is that it can map both the amplitude and phase information of light’s electric field.

“Our results clearly indicated that there was no phase reversal of the light,” remarked Sheng Liu, Sandia postdoctoral associate and lead author on the Optica paper. “This was the ultimate demonstration that this patterned surface behaves like an optical magnetic mirror.”

Next steps

Looking to the future, the researchers will investigate other materials to demonstrate magnetic mirror behavior at even shorter, optical wavelengths, where extremely broad applications can be found. “If efficient magnetic mirrors could be scaled to even shorter wavelengths, then they could enable smaller photodetectors, solar cells, and possibly lasers,” Liu concluded.

Story Source:

The above story is based on materials provided by The Optical Society. Note: Materials may be edited for content and length.

Journal Reference:

  1. Sheng Liu, Michael B. Sinclair, Thomas S. Mahony, Young Chul Jun, Salvatore Campione, James Ginn, Daniel A. Bender, Joel R. Wendt, Jon F. Ihlefeld, Paul G. Clem, Jeremy B. Wright, Igal Brener. Optical magnetic mirrors without metals.Optica, 2014; 1 (4): 250 DOI: 10.1364/OPTICA.1.000250

Ultra-fast charging batteries that can be 70% recharged in just two minutes

NTU Assoc Prof Chen holding the ultrafast rechargable batteries in his right hand, with the battery test station to his left. Credit: Image courtesy of Nanyang Technological University
NTU Assoc Prof Chen holding the ultrafast rechargable batteries in his right hand, with the battery test station to his left.
Credit: Image courtesy of Nanyang Technological University

Scientists from Nanyang Technological University (NTU Singapore) have developed a new battery that can be recharged up to 70 per cent in only 2 minutes. The battery will also have a longer lifespan of over 20 years.

Expected to be the next big thing in battery technology, this breakthrough has a wide-ranging impact on many industries, especially for electric vehicles which are currently inhibited by long recharge times of over 4 hours and the limited lifespan of batteries.

This next generation of lithium-ion batteries will enable electric vehicles to charge 20 times faster than the current technology. With it, electric vehicles will also be able to do away with frequent battery replacements. The new battery will be able to endure more than 10,000 charging cycles — 20 times more than the current 500 cycles of today’s batteries.

NTU Singapore’s scientists replaced the traditional graphite used for the anode (negative pole) in lithium-ion batteries with a new gel material made from titanium dioxide, an abundant, cheap and safe material found in soil. It is commonly used as a food additive or in sunscreen lotions to absorb harmful ultraviolet rays.

Naturally found in a spherical shape, NTU Singapore developed a simple method to turn titanium dioxide particles into tiny nanotubes that are a thousand times thinner than the diameter of a human hair.

This nanostructure is what helps to speeds up the chemical reactions taking place in the new battery, allowing for superfast charging.

Invented by Associate Professor Chen Xiaodong from the School of Materials Science and Engineering at NTU Singapore, the science behind the formation of the new titanium dioxide gel was published in the latest issue of Advanced Materials, a leading international scientific journal in materials science.

NTU professor Rachid Yazami, who was the co-inventor of the lithium-graphite anode 34 years ago that is used in most lithium-ion batteries today, said Prof Chen’s invention is the next big leap in battery technology.

“While the cost of lithium-ion batteries has been significantly reduced and its performance improved since Sony commercialised it in 1991, the market is fast expanding towards new applications in electric mobility and energy storage,” said Prof Yazami.

“There is still room for improvement and one such key area is the power density — how much power can be stored in a certain amount of space — which directly relates to the fast charge ability. Ideally, the charge time for batteries in electric vehicles should be less than 15 minutes, which Prof Chen’s nanostructured anode has proven to do.”

Prof Yazami, who is Prof Chen’s colleague at NTU Singapore, is not part of this research project and is currently developing new types of batteries for electric vehicle applications at the Energy Research Institute at NTU (ERI@N).


Commercialisation of technology

Moving forward, Prof Chen’s research team will be applying for a Proof-of-Concept grant to build a large-scale battery prototype. The patented technology has already attracted interest from the industry.

The technology is currently being licensed to a company and Prof Chen expects that the new generation of fast-charging batteries will hit the market in two years’ time. It holds a lot of potential in overcoming the longstanding power issues related to electro-mobility.

“With our nanotechnology, electric cars would be able to increase their range dramatically with just five minutes of charging, which is on par with the time needed to pump petrol for current cars,” added Prof Chen.

“Equally important, we can now drastically cut down the waste generated by disposed batteries, since our batteries last ten times longer than the current generation of lithium-ion batteries.”

The long-life of the new battery also means drivers save on the cost of a battery replacement, which could cost over USD$5,000 each.

Easy to manufacture

According to Frost & Sullivan, a leading growth-consulting firm, the global market of rechargeable lithium-ion batteries is projected to be worth US$23.4 billion in 2016.

Lithium-ion batteries usually use additives to bind the electrodes to the anode, which affects the speed in which electrons and ions can transfer in and out of the batteries.

However, Prof Chen’s new cross-linked titanium dioxide nanotube-based electrodes eliminate the need for these additives and can pack more energy into the same amount of space.

“Manufacturing this new nanotube gel is very easy,” Prof Chen added. “Titanium dioxide and sodium hydroxide are mixed together and stirred under a certain temperature. Battery manufacturers will find it easy to integrate our new gel into their current production processes.”

This battery research project took the team of four NTU Singapore scientists three years to complete and is funded by Singapore’s National Research Foundation.

Last year, Prof Yazami was awarded the Draper Prize by the National Academy of Engineering for his ground-breaking work in developing the lithium-ion battery with three other scientists.

Story Source:

The above story is based on materials provided by Nanyang Technological University. Note: Materials may be edited for content and length.

Journal Reference:

  1. Yuxin Tang, Yanyan Zhang, Jiyang Deng, Jiaqi Wei, Hong Le Tam, Bevita Kallupalathinkal Chandran, Zhili Dong, Zhong Chen, Xiaodong Chen. Nanotubes: Mechanical Force-Driven Growth of Elongated Bending TiO2-based Nanotubular Materials for Ultrafast Rechargeable Lithium Ion Batteries (Adv. Mater. 35/2014). Advanced Materials, 2014; 26 (35): 6046 DOI:10.1002/adma.201470238

Smallest Nanoantennas For High-speed Data Networks

Nano dipole antennas under the microscope: The colors reflect the different trans-mission frequencies. Credit: Photo by LTI
Nano dipole antennas under the microscope: The colors reflect the different trans-mission frequencies.
Credit: Photo by LTI

[dropcap]M[/dropcap]ore than 120 years after the discovery of the electromagnetic character of radio waves by Heinrich Hertz, wireless data transmission dominates information technology. Higher and higher radio frequencies are applied to transmit more data within shorter periods of time. Some years ago, scientists found that light waves might also be used for radio transmission. So far, however, manufacture of the small antennas has required an enormous expenditure. KIT scientists have now succeeded for the first time in specifically and reproducibly manufacturing smallest optical nanoantennas from gold.

In 1887, Heinrich Hertz discovered the electromagnetic waves at the former Technical College of Karlsruhe, the predecessor of Universität Karlsruhe (TH). Specific and directed generation of electromagnetic radiation allows for the transmission of information from a place A to a remote location B. The key component in this transmission is a dipole antenna on the transmission side and on the reception side. Today, this technology is applied in many areas of everyday life, for instance, in mobile radio communication or satellite reception of broadcasting programs. Communication between the transmitter and receiver reaches highest efficiency, if the total length of the dipole antennas corresponds to about half of the wavelength of the electromagnetic wave.

Radio transmission by high-frequency electromagnetic light waves in the frequency range of several 100,000 gigahertz (500,000 GHz correspond to yellow light of 600 nm wavelength) requires minute antennas that are not longer than half the wavelength of light, i.e. 350 nm at the maximum (1 nm = 1 millionth of a millimeter). Controlled manufacture of such optical transmission antennas on the nanoscale so far has been very challenging worldwide, because such small structures cannot be produced easily by optical exposure methods for physical reasons, i.e. due to the wave character of the light. To reach the precision required for the manufacture of gold antennas that are smaller than 100 nm, the scientists working in the “Nanoscale Science” DFG-Heisenberg Group at the KIT Light Technology Institute (LTI) used an electron beam process, the so-called electron beam lithography. The results were published recently in the journal Nanotechnology (Nanotechnology 20 (2009) 425203).

These gold antennas act physically like radio antennas. However, the latter are 10 million times as large, they have a length of about 1 m. Hence, the frequency received by nanoantennas is 1 million times higher than radio frequency, i.e. several 100,000 GHz rather than 100 MHz.

These nanoantennas shall transmit information at extremely high data rates, because the high frequency of the waves allows for an extremely rapid modulation of the signal. For the future of wireless data transmission, this means acceleration by a factor of 10,000 at reduced energy consumption. Hence, nanoantennas are considered a major basis of new optical high-speed data networks. The positive side-effect: Light in the range of 1000 to 400 nm is not hazardous for man, animals, and plants.

In the future, nanoantennas from Karlsruhe may not only be used for information transmission, but also as tools for optical microscopy: “With the help of these small nano light emitters, we can study individual biomolecules, which has not been established so far,” says Dr. Hans-Jürgen Eisler, who heads the DFG Heisenberg group at the Light Technology Institute. Moreover, the nanoantennas may serve as tools to characterize nanostructures from semiconductors, sensor structures, and integrated circuits. The reason is the efficient capture of light by nanoantennas. Thereafter, they are turned into light emitters and emit light quantums (photons).

The LTI scientists are presently also working on the specific and efficient capture of visible light by means of these antennas and on focusing this light on a few 10 nm, the objective being e.g. the optimization of photovoltaic modules.

Story Source:

The above story is based on materials provided by Helmholtz Association of German Research Centres. Note: Materials may be edited for content and length.