Department of Defense planners want to know when enemy troops are on the move, when vehicles are approaching or when other potentially hostile activity is unfolding. Existing sensors can regularly detect those movements, but those sensors often have limited battery life, constraining their usefulness and sometimes need to be changed as often as every three days.

Researchers at the Defense Advanced Research Projects Agency (DARPA) say they are making headway on the problem.

Launched in 2015, the project aims to develop sensors that can function in standby mode, lying almost dormant and switching on only when a signal is captured. Such devices could go for 10 years on a single charge.

The research agency named the project the Near Zero Power RF and Sensor Operations, or N-ZERO.

DARPA-funded work at the University of California – San Diego last year showed the project’s potential. Researchers were able to run a sensor that consumed just 4.5 nanowatts of energy, generated no false alarms, and detected 100 percent of trial events. Phase two, now underway, seeks to achieve far greater levels of sensitivity.

“We are ahead of where we wanted to be, but will still have a ways to go,” said Troy Olsson, DARPA’s Microsystems Technology Office (MTO) Program Manager.

The program got a boost in September when a DARPA-backed research team at Northeastern University published its findings in the journal Nature Nanotechnology. Their work on a “plasmonically-enhanced micromechanical photoswitch” moved the N-ZERO concept a step forward, adding to the growing body of fundamental science supporting the emerging capability.

Far from being a theoretical exercise, DARPA officials say N-ZERO could have profound battlefield implications. The ability to sense subtle environmental changes — consistently, without having to worry about the sensor’s power drain — can make a material difference to soldiers in the field.

“We are looking at sensing acoustic, vibrational, infrared and chemical signatures, all of which are associated with specific events that are very infrequent, but that are also time-sensitive and cannot be missed,” Olsson said.

The net effect would be a persistent early warning system that warfighters could rely on.

“We want to alert people so they have time to put on their personal protective gear, so our soldiers are safe from those kinds of attacks,” Olsson said.

That’s a tall order. Experts in the realm of connected devices, or the Internet of Things (IoT), say the military faces a significant hurdle as it looks to extend the longevity and the sensitivity of its sensor apparatus.

Unlike industrial uses, military planners don’t have the luxury of switching on sensors periodically for spot-checks. Rather, “military-grade sensors must be constantly receiving input, yet retain the capacity to enter dormant mode to conserve power,” wrote researcher Yitaek Hwang in the industry blog IoT for All.

The military has set a high bar for itself, Hwang said. The Defense Department hopes to shrink its sensors’ power consumption with a 1,000-times improvement over the current technology.

Today’s sensor solutions present what Olsson describes as a series of shortfalls, with power supply as a critical factor. In some situations, sensors can be hard-wired into local power, but that approach is expensive and often not portable.

“In other cases, they change the batteries every three days, for example in certain chemical sensors that surround our facilities,” he said.

That’s tedious, and not 100 percent reliable.

The proposed solution, a “wake-up” sensor that watches and waits, consuming only a tiny amount of power, brings with it certain technological challenges. A typical sensor will use amplifiers to heighten its signal, in order to enhance detection. But amplification requires energy. “There is no technology that can amplify signal in that way, at these very low power levels,” Olsson said. “We have come up with a way to apply voltage gain while consuming zero standby power.”

Looking ahead, DARPA will likely seek out expertise from industry, where the rapid rise of IoT has drawn attention to issues around power and persistence.

“I want to get a sense from the commercial side about what they are doing in that space. We have seen a number of applications in the commercial sector that do relate to N-ZERO technology,” he said. “They may be able to take us to applications that DoD could not achieve on its own because of the expense, and possibly drive down the cost.”