energy harvesting, sensors, sensing devices, hydraulics

Self-sustaining low-power wireless sensors

Powering sensors in remote areas has posed a challenge ever since sensing devices allowed us to collect data. Some areas are difficult or time-consuming to reach. Perhaps it’s a hazardous area, where we don’t want to send workers for routine data collection.

Power over Ethernet (PoE), the ability to provide power and data connectivity over the same cabling, has been an allowable windfall for hardwired devices. But sensors in those remote areas tend to be wireless these days, so PoE is of little benefit, save for the ability to power wireless access points.

This often requires other solutions to keep those devices supplied with enough power to collect and transmit data. Sometimes that means sending personnel out to hazardous areas to change batteries. However these sensing devices often require very little energy and just as often can find a source for that energy readily available.

“We estimate 67 µW are required for a low-data-rate wireless sensor,” said Ken Cunefare, Ph.D, who spoke at the Fluid Power Systems Conference in Rosemont, Illinois, this past November. Cunefare is a professor at Georgia Institute of Technology (www.gatech.edu), in charge of the Integrated Acoustics Laboratory at the George W. Woodruff School of Mechanical Engineering.

He spoke about his team’s research into energy harvesting from hydraulic systems and using hydraulic pressure ripple, what we call “noise,” as power source. Cunefare and his group are looking at this energy harvesting as enabling technology for remote wireless sensing.

“We could use pressure ripple,” he explained. “We can utilize a piezoelectric stack coupled to the pressure ripple to produce electric power from the hydraulic system. We've gone through seven generations of devices.”

The pressure ripple can be 5% or more of the load pressure. “That can be kW level noise,” said Cunefare. “There's an awful lot of energy in fluid-borne noise. We're not talking about getting kW of power. We're talking about microWatt (µW) or milliWatt (mW) energy. There's enough power available in that pressure ripple for a low-data-rate wireless sensor. The active component is piezoelectric material or element.”

For testing the hydraulic pressure energy harvesting (HPEH), a mounting block is placed in-line with fluid flow. “Pressure ripple and voltage output are coupled,” explained Cunefare. “We're not losing any energy there in how we interface to the fluid. From our Gen 1 device, we've gotten up to 2,187 µW. To demonstrate this will work, there's a wireless sensing node called a Cymbet board. Plug in an energy harvester.”

Prototypes demonstrate proof of concept, claimed Cunefare. “It's an enabling technology,” he said. “We're looking to transfer this technology to others who have this interest. We're now up to 3,300 µW from various prototypes and ripple. Now we're up to Gen 5, 6, and 7 going into test. It enables wireless remote sensing. And, on mobile equipment, there's actually enough energy in the track motor.”

To see Cunefare’s entire presentation, visit http://www.nfpa.com/events/pdf/2013-fpsc/025-advanceshydraulicnoiseenergyharvesting.pdf.