The researchers showed the devices kept working despite intense ionizing radiation and heat by dipping them for two hours into the core of the University of Utah’s research reactor. They also built simple circuits with the devices.
Ionizing radiation can quickly fry electronic circuits, so heavy shielding must be used on robots such as those sent to help contain the meltdowns at the Fukushima Daiichi nuclear power plant after Japan’s catastrophic 2011 earthquake and tsunami.
“Robots were sent to control the troubled reactors, and they ceased to operate after a few hours because their electronics failed,” says Massood Tabib-Azar, a professor of electrical and computer engineering at the University of Utah and the Utah Science Technology and Research initiative.
“We have developed a unique technology that keeps on working in the presence of ionizing radiation to provide computation power for critical defense infrastructures,” he says. “Our devices also can be used in deep space applications in the presence of cosmic ionizing radiation, and can help robotics to control troubled nuclear reactors without degradation.”
The new devices are “logic gates” that perform logical operations such as “and” or “not” and are a type of device known as MEMS or micro-electro-mechanical systems. Each gate takes the place of six to 14 switches made of conventional silicon electronics.Development of the new logic gates and their use to build circuits such as adders and multiplexers is reported in a study set for online publication this month in the journal Sensors and Actuators. The research was conducted by Tabib-Azar, University of Utah electrical engineering doctoral student Faisal Chowdhury and computer engineer Daniel Saab at Case Western Reserve University in Cleveland.
The study was funded by the Defense Advanced Research Projects Agency.
“Its premier goal is to keep us ready,” says Tabib-Azar. “If there is a nuclear event, we need to be able to have control systems, say for radars, to be working to protect the nation. There are lots of defense applications both in peacetime and wartime that require computers that can operate in the presence of ionizing radiation.”In April, the Defense Advanced Research Projects Agency issued a call for the development of robots to deal with stricken nuclear reactors to reduce human exposure to deadly radiation. In May, NASA said it was seeking proposals for new shields or materials able to resist radiation in space. Circuits built with the new devices also could resist intense heat in engines to monitor performance, Tabib-Azar says.
MEMS: Ability to Withstand Radiation Overcomes Drawbacks
Current radiation-resistant technologies fall into two categories: conventional complementary silicon-oxide semiconductor electronics shielded with lead or other metals, and the use of different materials that inherently resist radiation.“Electronic materials and devices by their nature require a semiconducting channel to carry current, and the channel is controlled by charges,” Tabib-Azar says. Radiation creates current inside the semiconductor channel, and “that disrupts the ability of the normal circuitry to control the current, so the signal gets lost.”
Two Kinds of Logic Gates
For the study, Tabib-Azar and colleagues built two kinds of logic gate, each with two inputs (0 or 1) and thus four possible combinations of inputs (0-0, 0-1, 1-0, 1-1). The input and output are electrical voltages:
-- An AND gate, which means “and.” If both inputs – A and B – are true (or worth 1 each), then the output is true (or equal to 1). If input A or B or both are false (worth 0), then the output is false (or equal to 0).
-- An XOR gate, which means “exclusive or.” If input A doesn’t equal B (so A is 0 and B is 1 or A is 1 and B is 0), the output is true (equal 1). If both A and B are either true (1) or false (0), the output is false (0).
“In a sense, you can say these are switches with multiple outcomes,” rather than just off-on (0-1), says Tabib-Azar. “But instead of using six [silicon] switches separately, you have one structure that gives you the same logic functionality.”
“Let’s say you want to decide whether to go to dinner tonight, and that depends on if the weather is nice, if you feel like it,” he says. “In order to make that decision, you have a bunch of ‘or’ statements and a bunch of ‘and’ statements: ‘I’ll go to dinner if the weather is nice and I feel like it.’ ‘I like to eat Italian or French.’ You put these statements together and then you can make a decision.”“To analyze this using silicon computers,” Tabib-Azar says, “you need a bunch of on-off switches that have to turn on or off in a particular sequence to give you the output, whether you go to dinner or not. But just a single one of these [MEMS logic gate] devices
can be designed to perform this computation for you.”Contacts:
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