Paper-based wireless sensor detects explosive devices
using inkjet-printed devices.”
Tentzeris explained that the key to printing components, circuits and antennas lies in novel “inks” that contain silver nanoparticles in an emulsion that can be deposited by the printer at low temperatures — around 100 degrees Celsius. A process called sonication helps to achieve optimal ink viscosity and homogeneity, enabling uniform material deposition and permitting maximum operating effectiveness for paper-based components.
“Ink-jet printing is low-cost and convenient compared to other technologies such as wet etching,” Tentzeris said. “Using the proper inks, a printer can be used almost anywhere to produce custom circuits and components, replacing traditional clean-room approaches.”
Low-cost materials — such as heavy photographic paper or plastics like polyethylene terephthalate — can be made water resistant to ensure greater reliability, he added. Inkjet component printing can also use flexible organic materials, such as liquid crystal polymer (LCP), which are known for their robustness and weather resistance. The resulting components are similar in size to conventional components but can conform and adhere to almost any surface.
Naishadham explained that the same inkjet techniques used to produce RF components, circuits and antennas can also be used to deposit the functionalized carbon nanotubes used for sensing. These nanoscale cylindrical structures — about one-billionth of a meter in diameter, or 1/50,000th the width of a human hair — are functionalized by coating them with a conductive polymer that attracts ammonia, a major ingredient found in many IEDs.
Sonication of the functionalized carbon nanotubes produces a uniform water-based ink that can be printed side-by-side with RF components and antennas to produce a compact wireless sensor node.
“The optimized carbon nanotubes are applied as a sensing film, with specific functionalization designed for a particular gas or analyte,” Song said. “The GTRI sensor detects trace amounts of ammonia usually found near explosive devices, and it can also be designed to detect similar gases in household, healthcare and industrial environments at very low concentration levels.”
The sensor has been designed to detect ammonia in trace amounts — as low as five parts per million, Naishadham said.
The resulting integrated sensing package can potentially detect the presence of trace explosive materials at a distance, without endangering human lives. This approach, called standoff detection, involves the use of RF technology to identify explosive materials at a relatively safe distance. The GTRI team has designed the device to send an alert to nearby personnel when it detects ammonia.
The wireless sensor nodes require relatively low power, which could come from a number of technologies including thin-film batteries, solar cells or power-scavenging and energy-harvesting techniques. In collaboration with Tentzeris’s and Wong’s groups, GTRI is investigating ways to make the sensor operate passively, without any power consumption.
“We are focusing on providing standoff detection for those engaged in military or humanitarian missions and other hazardous situations,” Naishadham said. “We believe that it will be possible, and cost-effective, to deploy large numbers of these detectors on vehicles or robots throughout a military engagement zone.”
