Printing Sensors And Food
3D printing technology could be the next big thing. Using 3D printers, solid objects can be produced directly from a computer-aided digital design.

The technology is based on an additive process. Objects are created by laying down successive layers of material processes. One effort, the RepRap project, is an initiative to develop a low-cost, 3D printer that can print most of its own components.

Another effort, Fab@Home, is an open-source, personal fabrication technology. “The RepRap is oriented toward self-replication, making its own parts, while Fab@Home is aiming toward printing static and dynamic objects,” according to the Fab@Home Web site.

Personal fabricators consist of chassis, tool heads and electronics. The Fab@Home system is said to produce any static or dynamic object out of materials that can be deposited through a syringe, such as miniature models, custom food products and electrical parts. Fab@Home systems can make products using household silicone rubber caulk, epoxy, cheese, chocolate, cake frosting, ceramic clay, PlayDoh and gypsum plaster.

In a new R&D effort, the University of Warwick has devised a simple, conductive thermoplastic composite for 3D printing. The material, dubbed carbomorph, can be used in a low-cost 3D printer to print electronic sensors that can sense mechanical flexing and capacitance changes.

Researchers have printed objects with embedded flex sensors. They have also printed touch-sensitive buttons like a computer game controller. And they even printed a mug, which can tell how full it is.

The next step is to print the wires and cables in computers. This advance in low-cost 3D printing could offer a new paradigm in the field. Fabricators could print sensors and electronics without requiring complex or expensive materials incorporating additives such as carbon nanotubes.

On its Web site, Simon Leigh, who is associated with the School of Engineering at the University of Warwick, said: “We set about trying to find a way in which we could actually print out a functioning electronic device from a 3D printer. In the long term, this technology could revolutionize the way we produce the world around us, making products such as personal electronics a lot more individualized and unique and in the process reducing electronic waste.”

Dog Sniffing Chips
The University of California at Santa Barbara (UCSB) has designed a sensor that mimics the biological mechanism of canine scent receptors. Using microfluidic technology, the device is sensitive to trace amounts of certain vapor molecules, and able to tell a specific substance apart from similar molecules. The device could one day detect explosives, narcotics and even diseases.

The detector is based on a free-surface microfluidic and surface-enhanced Raman spectroscopy (SERS) chemical detection system. The detector is designed to operate on principles inspired by canine olfaction.

The unit consists of a large free-surface-to-volume ratio microfluidic channel. It allows for polar or hydrophilic airborne analytes to be partitioned from the surrounding gas phase into the aqueous phase for detection, according to UCSB.

Concept illustration of the microscale free-surface microfluidic channel as it concentrates vapor molecules that bind to nanoparticles inside a chamber. A laser beam detects the nanoparticles, which amplify a spectral signature of the detected molecules. Source: UCSB

The microfluidic stream can concentrate certain molecules by up to 6 orders of magnitude. The SERS can enhance the Raman signal by 9–10 orders of magnitude for the molecules residing in the “hot spots,” according to researchers.

It provides continuous, real-time monitoring of a particular vapor-phase analytes at concentrations of 1 ppb, according to researchers. Detection performance was demonstrated using a nominal 1 ppb, 2,4-dinitrotoluene (2,4-DNT) vapor stream entrained within N2 gas.

On its Web site, Carl Meinhart, professor of mechanical engineering at UCSB, said: “Dogs are still the gold standard for scent detection of explosives. But like a person, a dog can have a good day or a bad day, get tired or distracted. We have developed a device with the same or better sensitivity as a dog’s nose that feeds into a computer to report exactly what kind of molecule it’s detecting.”

Roman DSA
The University of Illinois and Northwestern University have devised spheres that synchronize their movements as they self-assemble into a spinning microtube.

The researchers use tiny particles called Janus spheres, named after the Roman god. Janus is usually a two-faced god because he looks to the future and the past.

One half of each sphere is coated with a magnetic metal. When put into a rotating magnetic field, each sphere spins in a gyroscopic motion. The spheres spin at the same frequency. They also face a different direction. As the two particles approach one another, they synchronize their motions and begin spinning around a shared center.

The spheres assemble themselves into a microtube, and the entire tube spins. Applications for the technology include medicine, chemistry and engineering. One potential application of a self-assembled microtube is to transport and release cargo.

“Traditionally in self-assembly, you make a specific building block that will organize into a specific structure,” said Erik Luijten, a professor of materials science and engineering and of applied mathematics at Northwestern, on the university’s Web site. “If you want a different structure you have to make a different building block. Here now, with one building block, we can control the structure by exploiting the synchronization effect.”

—Mark LaPedus

Research firm devises phase-change transistor
Japan’s Riken Advanced Science Institute has created a new phase-change transistor type using vanadium dioxide materials. Demonstrated at about 1 volt in room temperature, the technology could provide a building block for low power devices, non-volatile memory and optical switches, according to Riken. The mission of Riken is to conduct comprehensive research in science and technology.

Riken has devised what it calls a metal–insulator–semiconductor field-effect transistor. The device uses the electrostatic accumulation of electrical charge on the surface of a strongly-correlated material. Riken made use of a fast phase-change material called vanadium dioxide. Vanadium dioxide transforms the material from a metal to an insulator. The phase change takes place at about 68 degrees Celsius.

Vanadium-dioxide double-layer transistor in off and on states. Source: Riken.

Riken discovered that electrostatic charging at a surface drives all the previously localized charge carriers in the bulk material into motion. This leads to the emergence of a three-dimensional metallic ground state, according to researchers.

This non-local switching of the electronic state is achieved by applying a voltage of only about 1 Volt. The results were reported in Nature.

Panasonic devises artificial photosynthesis system
Japan’s Panasonic has developed an artificial photosynthesis system that converts carbon dioxide to organic materials by illuminating it with sunlight at an efficiency of 0.2%.

The key enabler to this system is a nitride semiconductor technology. The development could be a foundation for a system capturing and converting wasted carbon dioxide from incinerators, power plants and industrial activities.

Carbon dioxide is one of the substances responsible for the greenhouse effect. Current artificial photosynthesis systems use structures such as organic complexes or plural photo-electrodes.

Panasonic’s artificial photosynthesis system has a simple structure. The company discovered that nitride semiconductor has the capability to excite the electrons with enough high energy for the carbon dioxide reduction reaction. In this case, nitride semiconductors can be used as a photo-electrode for carbon dioxide reduction.

The reduction process itself takes place on a metal catalyst at the opposite side of a nitride semiconductor photo-electrode. The metal catalyst plays a role in selecting and accelerating the reaction. The system with a nitride semiconductor and a metal catalyst generates mainly formic acid from carbon dioxide and water with light at a world’s top efficiency of 0.2%.

This development was presented at the 19th International Conference on the Conversion and Storage of Solar Energy held in Pasadena, California on July 30, 2012.

—Mark LaPedus