A Vibration Energy Harvester and Power Management Solution for Battery-Free Operation of Wireless Sensor Nodes

Abstract

Electromagnetic Vibration Energy Harvesting (EM-VEH) is an attractive alternative to batteries as a power source for wireless sensor nodes that enable intelligence at the edge of the Internet of Things (IoT). Industrial environments in particular offer an abundance of available kinetic energy, in the form of machinery vibrations that can be converted into electrical power through energy harvesting techniques. These ambient vibrations are generally broadband, and multi-modal harvesting configurations can be exploited to improve the mechanical-to-electrical energy conversion. However, the additional challenge of energy conditioning (AC-to-DC conversion) to make the harvested energy useful brings into question what specific type of performance is to be expected in a real industrial application. This paper reports the operation of two practical IoT sensor nodes, continuously powered by the vibrations of a standard industrial compressor, using a multi-modal EM-VEH device, integrated with customised power management. The results show that the device and the power management circuit provide sufficient energy to receive and transmit data at intervals of less than one minute with an overall efficiency of about 30%. Descriptions of the system, test-bench, and the measured outcomes are presented.

Keywords: electromagnetic vibration-based energy harvesting; internet of things; power management; preventive maintenance.

Figure 1

The Internet of Things (IoT).

Figure 2

Stokes Power’s VEH-1: (a) illustration of the scale of the harvester with reference to a D-battery; (b) Schematic of the harvester.

Figure 3

Schematic of the experimental setup.

Figure 4

(a) RMS voltage and (b) power as function of frequency for different H values at $a_{rms}=0.4g$.

Figure 5

Vibrations measured on an industrial air compressor: (a) Time series; (b) Power spectral density.

Figure 6

Output voltage delivered by the harvester: (a) Open circuit configuration; (b) Measured across $R_L$ = 12,050 $\mathsf{\Omega }$.

Figure 7

LoRa board current consumption profile in one Rx/Tx cycle.

Figure 8

Bluetooth board current consumption profile in one Rx/Tx cycle.

Figure 9

Schematic of the power conversion and management strategy.

Figure 10

Bus voltage during cold-start.

Figure 11

Reflection of the PMIC input voltage into the harvester AC terminals: (a) Single-frequency excitation; (b) Multiple-frequency excitation.

Figure 12

Bus voltage during switching interval for different MPPT ratios.

Figure 13

Power management PCB.

Figure 14

LoRaWAN broadcasting results.

Figure 15

Broadcasting results with the CC2650 sensor node.