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. 2022 May 27;22(11):4054.
doi: 10.3390/s22114054.

A Multifunctional Battery-Free Bluetooth Low Energy Wireless Sensor Node Remotely Powered by Electromagnetic Wireless Power Transfer in Far-Field

Affiliations

A Multifunctional Battery-Free Bluetooth Low Energy Wireless Sensor Node Remotely Powered by Electromagnetic Wireless Power Transfer in Far-Field

Alassane Sidibe et al. Sensors (Basel). .

Abstract

This paper presents a multifunctional battery-free wireless sensing node (SN) designed to monitor physical parameters (e.g., temperature, humidity and resistivity) of reinforced concrete. The SN, which is intended to be embedded into a concrete cavity, is autonomous and can be wirelessly powered thanks to the wireless power transmission technique. Once enough energy is stored in a capacitor, the active components (sensor and transceiver) are supplied with the harvested power. The data from the sensor are then wirelessly transmitted via the Bluetooth Low Energy (BLE) technology in broadcasting mode to a device configured as an observer. The feature of energy harvesting (EH) is achieved thanks to an RF-to-DC converter (a rectifier) optimized for a low power input level. It is based on a voltage doubler topology with SMS7630-005LF Schottky diode optimized at -15 dBm input power and a load of 10 kΩ. The harvested DC power is then managed and boosted by a power management unit (PMU). The proposed system has the advantage of presenting two different power management units (PMUs) and two rectifiers working in different European Industrial, Scientific and Medical (ISM) frequency bands (868 MHz and 2.45 GHz) depending on the available power density. The PMU interfaces a storage capacitor to store the harvested power and then power the active components of the sensing node. The low power digital sensor HD2080 is selected to provide accurate humidity and temperature measurements. Resistivity measurement (not reported in this paper) can also be achieved through a current injection on the concrete probes. For wireless communications, the QN9080 system-on-chip (SoC) was chosen as a BLE transceiver thanks to its attractive features: a small package size and extremely low power consumption. For low power consumption, the SN is configured in broadcasting mode. The measured power consumption of the SN in a deep-sleep mode is 946 µJ for four advertising events (spaced at 250 ms maximum) after the functioning of sensors. It also includes voltage offset cancelling functionality for resistivity measurement. Far-field measurement operated in an anechoic chamber with the most efficient PMU (AEM30940) gives a first charging time of 48 s (with an empty capacitor) and recharge duration of 27 s for a complete measurement and data transmission cycle.

Keywords: Bluetooth low energy (BLE); Internet of Things (IoT); power management unit (PMU); structural health monitoring (SHM); wireless communications; wireless power transmission (WPT); wireless sensor node.

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Conflict of interest statement

The authors declare no conflict of interest. The funders had no role in the design of the study; in the collection, analyses or interpretation of data; in the writing of the manuscript; or in the decision to publish the results.

Figures

Figure 1
Figure 1
Legacy advertising.
Figure 2
Figure 2
Block diagram of the architecture of the implemented sensing node.
Figure 3
Figure 3
Schematic of the implemented rectifier.
Figure 4
Figure 4
Flowchart of the functioning of the BLE SN in broadcasting mode.
Figure 5
Figure 5
The current consumption profile of the BLE SN during broadcasting, obtained with the power measurement tool of MCUXpresso IDE software. The different states are identified: (1) SN is power off; (2) Indicates the start-up, initialisation and calibration after power supplying the SN; (3) is the 4 advertisements made by the SN with data; (4) is the sleep mode between adv. event for low power consumption; (5) is the consumption needed to stop broadcasting and cancel the voltage offset for resistivity measurement.
Figure 6
Figure 6
Current consumption profile of the BLE SN during advertising event.
Figure 7
Figure 7
Load time of the storage capacitor (cold start, first recharge and then a recharge) with the BQ25570 for an RF power of −6 dBm (868 MHz) at the input of the rectifier.
Figure 8
Figure 8
Load time across the storage capacitor (cold start, first recharge and then a recharge) with the AEM30940 for an RF power of −6 dBm (868 MHz) at the input of the rectifier.
Figure 9
Figure 9
Photo of the fabricated sensing node with the nomenclature of each part.
Figure 10
Figure 10
Experimental setup of measuring the charging evolution of the storage capacitor.
Figure 11
Figure 11
Voltage evolution in time from an empty storage capacitor of the configuration with PMU BQ25570 (top) and AEM30940 (bottom).
Figure 12
Figure 12
Charge duration of the SN with an 868 MHz rectifier for different selected PMUs.
Figure 13
Figure 13
Sensing node connected to an optimized antenna.
Figure 14
Figure 14
Measurement setup of the charge duration of the SN connected to an antenna in an anechoic chamber.
Figure 15
Figure 15
Measured charge duration of the SN with a connected antenna in an anechoic chamber with different EIRP power levels.

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