# Radio-frequency energy harvesting for communicating materials: Application to the construction industry

Michaël David, William Derigent, Gaël Loubet, Alexandru Takacs, Daniela Dragomirescu

## ► To cite this version:

Michaël David, William Derigent, Gaël Loubet, Alexandru Takacs, Daniela Dragomirescu. Radio-frequency energy harvesting for communicating materials: Application to the construction industry. 31st IEEE International Conference on Electronics Circuits and Systems, ICECS 2024, Nov 2024, Nancy, France. 10.1109/ICECS61496.2024.10848725. [hal-04831840](https://HAL Id: hal-04831840)

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# Radio-Frequency Energy Harvesting for Communicating Materials: Application to the Construction Industry

Michaël David

CRAN Laboratory, CNRS UMR 7039,
Université de Lorraine.
Vandoeuvre-lès-Nancy, FRANCE.
michael.david@univ-lorraine.fr
0000-0003-2071-5751

William Derigent

CRAN Laboratory, CNRS UMR 7039,
Université de Lorraine.
Vandoeuvre-lès-Nancy, FRANCE.
william.derigent@univ-lorraine.fr
0000-0002-6542-5515

Gaël Loubet

LAAS-CNRS, CNRS, INSA, Université de
Toulouse.
Toulouse, FRANCE.
gael.loubet@laas.fr
0000-0003-3347-0036

Alexandru Takacs

LAAS-CNRS, CNRS, UPS, Université de Toulouse.
Toulouse, FRANCE.
alexandru.takacs@laas.fr
0000-0001-5485-7817

Daniela Dragomirescu

LAAS-CNRS, CNRS, INSA, Université de Toulouse.
Toulouse, FRANCE
daniela.dragomirescu@laas.fr
0000-0001-8589-6093

***Abstract***— This paper deals with the design of a communicating material dedicated to the Structural Health Monitoring of concrete structures for more than thirty years. To reach this longevity, a two-level Wireless Sensor Network made of Sensing Nodes and Communicating Nodes is proposed. To enhance the lifespan of the "communicating concrete", a key innovation addressing the energy related challenge is presented: an original radiative electromagnetic (or RF) Wireless Power Transfer system for powering the buried Sensing Nodes; aiming to ensure the efficient and sustainable operation of the "communicating concrete" over an extended period.

***Keywords***— Communicating concrete, Simultaneous Wireless Information and Power Transfer (SWIPT), RF Wireless Power Transfer (WPT), Wireless Sensor Networks (WSN), Battery-Free Wireless Sensors, Cyber-Physical System (CPS), Energy efficiency.

## I. INTRODUCTION

The idea of "communicating materials", introduced by [1], envisions materials capable of interacting with their environment, sensing, processing, storing and sharing data. These materials can retain these properties even after undergoing transformations such as drilling, milling, cutting, or assembly. This concept has found applications in various industries (e.g., textile, wood, etc.) but although promising, it poses a significant longevity challenge, especially in construction [2].

Sustainability of the system is essential for the adoption in the construction industry ecosystem. Ensuring consistent energy consumption and reliable communications between nodes is vital for maintaining system stability. Any imbalance can result in inefficiencies and potential network failures. The challenges associated with "communicating materials" span multiple domains, including materials science, cybersecurity, energy efficiency, and sustainability. Meeting these challenges is crucial to unlocking the full potential of this concept

The Cyber-Physical System (CPS) architecture proposed to realize a "communicating concrete" is presented in Section II.

The Radio Frequency Wireless Power Transfer (WPT) system proposal and experiments are exposed in Section III. Section IV is then dedicated to some conclusions and perspectives.

## II. DESIGN OF A CYBER-PHYSICAL SYSTEM FOR "COMMUNICATING CONCRETE"

Fig. 1 illustrates the framework of a "communicating concrete" which is a Cyber-Physical System. The physical world is composed of concrete components which embed devices organized in a Wireless Sensor Network (WSN). The digital world serves as an information system containing the physical data of concrete elements. This information can then be utilized by other systems, such as Building Information Modelling (BIM) platforms, or Digital Twins.

The Wireless Sensor Network is composed of two types of nodes: the Sensing Nodes (SN) and the Communicating Nodes (CN). The SN measure parameters (e.g., temperature, relative humidity, mechanical deformation, and/or dielectric resistivity (to estimate the corrosion rate)) and transmit wirelessly the measured data to CN. The mesh network of CN then processes, exchanges and transfers the data to the different information systems. To wrap the whole concrete lifecycle, an energy-efficient network is required. As a result, SN are battery-free low-power wireless nodes, wirelessly powered by radiative electromagnetic (or RF) Wireless Power Transfer, controlled by the CN. These latter components constitute the internal network of a "communicating concrete" system.

Communicating Nodes are armed with two radio communication interfaces: (1) a near-range interface used for inter-CN communications; and (2) a long-range interface used to send data to information systems via the Internet. The proposed system enables the continuous monitoring of product-related information required all along the concrete lifecycle (e.g., temperature, moisture, mechanical constraints, estimation of the corrosion rate, etc.).
<figure><img src="image_2.png" /><figcaption>Fig. 1. Physical and digital architectures of a "communicating concrete".</figcaption></figure>

### III. IMPLEMENTATION OF BATTERY-FREE WIRELESS SENSING NODES POWERED BY RF WIRELESS POWER TRANSFER

To implement a "communicating concrete", low-power battery-free wireless Sensing Nodes were developed. Section A highlights their generic design and Section B their characterisation, especially in real use-cases.

#### A. *Design of the Sensing Nodes*

The Sensing Nodes are imagined to be completely incorporated into the core of reinforced concrete from the manufacturing stage of a reinforced concrete element, and thus, become physically unreachable for the rest of their life. During their lifespan (expected to last at least thirty years), they must:
- measure data on the state of health of the reinforced concrete;
- transmit wirelessly the collected data, from and through this reinforced concrete, which is a highly inhomogeneous material for which there are no simple model, and which is also, a harsh environment for the propagation of electromagnetic waves [3];
- be energy autonomous.

Fig. 2 shows the generic architecture of the Sensing Nodes.

Different types of sensors were implemented, in order to measure: (i) temperature and relative humidity; (ii) an estimation of the mechanical deformation using a strain gauge; and (iii) dielectric resistivity using a Wenner probe, and whose evolution over time enables the corrosion rate to be estimated. These parameters are among the most relevant for the Structural Health Monitoring (SHM) of reinforced concrete [4].

<figure><img src="image_3.png" /><figcaption>Fig. 2. Block diagram of the architecture of the Sensing Node.</figcaption></figure>

Two wireless communication technologies were tested: (i) LoRaWAN (cf. Fig. 3(a)), that achieves lossless communication ranges expressed in hectometres even in indoors configurations (i.e., reinforced concrete walls and floors have a little impact), at the cost of a medium (or even high) power consumption compared with other wireless communication technologies dedicated to IoT (Internet of Things); and (ii) Bluetooth Low Energy (BLE) (cf. Fig. 3(b)), that achieves loss less communication ranges limited to nearly a couple of tens of metres in indoors configurations (i.e., reinforced concrete walls and floors have a significant impact), at the advantage of a low power consumption compared with LoRaWAN.

In the two cases, in order to reduce the power consumption of the Sensing Nodes by removing listening periods, unacknowledged directional unpaired communications are employed from the Sensing Nodes to the Communicating Nodes. In this way, the Sensing Nodes cannot be reached by wireless communications (and therefore cannot be updated or corrected over-the-air in case of evolutions or errors), increasing also their security by removing a potential attack channel.

The energy autonomy of the Sensing Nodes was considered with regards to the energy required for a full process, i.e., (i) measurement, (ii) processing/formatting, and (iii) wireless transmission of data. Because batteries cannot meet the lifespan requirements, ambient energy harvesting and WPT techniques were explored [5]. Ambient energy harvesting solutions are based on the scavenging of residual energy available in the environment. On the contrary, WPT employs dedicated and controllable power sources to be less dependent of the deployment environment. Electromagnetic WPT solutions can be divided into two categories: near-field and far field. The former is based on (resonant or non-resonant) inductive and/or capacitive effects, while the latter on radiations. This last, using electromagnetic waves, is privileged to reach range of use over ten meters while complying with the local regulations, including the maximum Equivalent Isotropic Radiated Power (EIRP),
which depend in particular on the frequency [6]. As described in [7], the ISM 868 MHz frequency band seems to provide a good trade-off between the size of the antenna (and therefore of the SN) and the range of use, thanks to a maximum EIRP of 2 Watts.

To store locally and efficiently the little amount of energy required for a full process without using a battery, a local energy buffer (i.e., a (super)capacitor) is employed conjointly with a Power Management Unit (PMU) whose role is to manage the power harvested by the rectenna (i.e., an antenna and a rectifier). This PMU must be capable of cold-starting and must operate with the lowest possible input powers. Here, this is followed by a dc-to-dc converter to provide the active components of the Sensing Node with a regulated supply voltage.

The Simultaneous Wireless Information and Power Transfer (SWIPT) paradigm concerns the simultaneous use of a propagation medium (here, electromagnetic waves) for wireless communication and WPT, as in the presented WSN [8]. In the proposed implementation using LoRaWAN, a single antenna and a RF circulator are used to answer this paradigm.

## B. Experimental Characterisation and Results

The implemented prototypes of the Sensing Nodes are illustrated in Fig. 3 and are described in depth in [7] and [9], respectively for LoRaWAN and BLE technologies.

The presented battery-free wireless Sensing Nodes are wirelessly powered by RF WPT and require a minimum power of -17 dBm at the input of the rectifier, even for a cold-start procedure. As the instantaneous dc power required by the Sensing Node to perform a full process is always higher than the available input RF power, a "store then use" strategy is implemented to power the Sensing Node. In the target application, this is not a problem as the monitored parameters change very slowly (a few measurements a day can be more than enough) and the density of Sensing Nodes limits the impact of a long periodicity specific to each of them.

In the case of the LoRaWAN implementation, a 2.2 mF supercapacitor is used to store 21 mJ, as 16.5 mJ are required to run a full process, i.e., temperature and relative humidity and/or mechanical deformation and/or dielectric resistivity measurement, data formatting to provide a payload of 4 bytes, and wireless transmission of a 17-bytes frame with an output power of +4 dBm and a data rate of 5470 bps, for the shortest possible transmission time. In the case of BLE implementation, a 220 µF supercapacitor is used to store 2.0 mJ, as 1.2 mJ are required to run a full process, i.e., temperature and relative humidity and/or dielectric resistivity measurement, data formatting to provide a payload of 3 bytes, and wireless transmission of three advertising 19-bytes frames on three different advertising channels, with an output power of +0 dBm and a data rate of 1 Mbps. The redundancy is applied here to ensure lossless communications. These quantities of stored energy are overestimated by around 20% compared with the requirements measured for a full process, in order to compensate for the variability and ageing of components.

The periodicity of functioning and the energy efficiency, both a function of the available RF input power, are relevant figures of merit, presented in [7] and [9], respectively for LoRaWAN and BLE. For instance, and for the LoRaWAN

<figure><img src="image_4.png" /><figcaption>Fig. 3. Photographs of the implemented prototype of the Sensing Node employing (a) LoRaWAN and (b) Bluetooth Low Energy.</figcaption></figure>

implementation, a first charge for performing a full process (from an empty supercapacitor) lasts between about 17 hours 21 minutes for the lowest possible input power (-17 dBm), and about 30 seconds for an input power of +15 dBm. A recharge between two consecutive full process lasts about between 7 hours and 59 minutes at for the lowest possible input power and 6 seconds at +15 dBm. In terms of energy efficiency at the SN level (i.e., the ratio of the output dc energy required for a complete process to the energy available at the input of the Sensing Node (i.e., the RF power at the input of the rectenna integrated over a period of interest)), this is 2.16% and 11.54% for a first charge and between 3.68% and 36.71% for recharges, according to [7]. For the BLE implementation, the (re)charging times are shorter. For instance, for an input power about -11.33 dBm, a first charge last 17 minutes and 53 seconds and a recharge 8 minutes and 21 seconds, and for about -3.33 dBm, a first charge last 54 seconds and a recharge 27 seconds.

An initial estimate of the maximum range of use can be calculated in an ideal theoretical case (i.e., without multipath, etc.) using the Friis transmission formula. This computation is a function of the frequency, the gain of the antenna used in the harvester, the radiated RF power generated by the power source, and the power targeted at the input of rectifier used in the harvester. For instance, -17 dBm of RF power can be harvested at the output port of the RF receiving antenna (gain: +5.0 dBi) at 13.78 metres far away from the RF power source with an EIRP of +33 dBm (or 2 W) at 868 MHz. Also, at 5 metres, -7.2 dBm could be harvested, that says a first charge of about 20 minutes and 50 seconds, and recharges of about 6 minutes and 9 seconds. Today, the deployment area for WSN using battery-free and wirelessly powered Sensing Nodes is mainly constrained by WPT (and more specifically the regional regulations for wireless communications, which are considered as the legal framework), and also not by the wireless communications, even in the case of harsh propagation environment, such as reinforced concretes [6].

There are several advantages to reducing as much as possible the RF power needed at the input of the Sensing Node to operate: (i) the operating distances can be maximised for the same frequency, receiving antenna gain, and radiated RF power; and (ii) the (re)charging times can be minimized, for the same operating distance, frequency, receiving antenna gain, and radiated RF power. The (re)charging times are highly dependent of the quantity of energy that must be stored by the Sensing Node, and also, can be shortened by limiting this last, that says by constraining the energy required for a full process.
To validate the correct functioning of the Cyber-Physical System, several qualitative tests were performed in realistic configurations, as illustrated in Fig. 4.

From the setup pictured in Fig. 4(a), an indoor distance of 11 metres between the RF power source of the Communicating Node and a single Sensing Node was tested in a complex environment. In this configuration, the longest distance tested for WPT in low-power IoT applications and in compliance with regional wireless communication regulations was recorded. As explained above, greater distances could be reached, as a RF power of -17 dBm could be available at the output port of the current SN receiving antenna at a distance of nearly 14 metres.

In the setup depicted in Fig. 4(b), a meshed network of 2 Communicating Nodes (one connected to the Internet) and 4 Sensing Nodes (3 located in air cavities in a reinforced concrete beam) was deployed. WPT was performed over several meters, part of which was in reinforced concrete (at least 15 centimetres with metal reinforcing bars). Temperature, relative humidity and dielectric resistivity were monitored during days. In this configuration, the main Communicating Node can wirelessly power and control all the Sensing Nodes located within an omnidirectional volume of several metres. In addition, all measured data transmitted via LoRaWAN frames is correctly retrieved, but also processed, stored and shared with the second Communicating Node and remote servers via the Internet.

Finally, although the Sensing Nodes are inaccessible both physically and through wireless data communications, they operating periodicity can be reconfigured dynamically, wirelessly and remotely though to the WPT downlink and the amount of power made available to them. This reconfiguration can be performed by the Communicating Nodes by tuning the waveform, output power or duty cycle of the RF power source.

## IV. CONCLUSION

This paper outlines the key scientific and technological advancements in applying the "Communicating Materials" idea to the construction industry, focusing on the preliminary design.

<figure><img src="image_5.png" /><figcaption>Fig. 4. Photographs of experimental set-ups implementing the proposed Cyber-Physical System in real use-cases: (a) in a basement with lot of metallic elements (especially, in walls and floors) and (b) in a reinforced concrete beam.</figcaption></figure>

The study particularly addresses and improves the energy sustainability of the physical component. A communicating architecture featuring a two-level Wireless Sensor Network was proposed, including Sensing Nodes harvesting RF energy radiated from Communicating Nodes.

This work introduces battery-free and energy-autonomous wireless Sensing Nodes that are wirelessly powered and controlled by radiative electromagnetic Wireless Power Transfer system, setting a new standard for embedded sensors in materials. These Sensing Nodes also meet the requirement of the Simultaneous Wireless Information and Power Transfer paradigm over the same ISM 868 MHz frequency band and by using a single antenna when using LoRaWAN.

Future efforts will aim to optimize the overall efficiency of the Wireless Power Transfer system by using beam focusing techniques to concentrate the generated power. Additional research will include developing fully integrated prototypes, integrating these sensors on flexible substrates, and creating packaging that can be entirely embedded in wet concrete.

## ACKNOWLEDGMENT

This work was supported in part by the French National Research Agency (ANR) under the McBIM Project (Communicating Material at the Disposal of the Building Information Modelling) under Grant ANR-17-CE10-0014, and in part by the Région Occitanie under the OPTENLOC Project.

## REFERENCES

[1] S. Kubler, W. Derigent, A. Thomas, and E. Rondeau, "Problem definition methodology for the "Communicating Material" paradigm," *IFAC Proceedings Volumes*, vol. 43, no. 4, pp. 198-203, 2010, doi: 10.3182/20100701-2-PT-4011.00035.

[2] M. David, W. Derigent, G. Loubet, A. Takacs, and D. Dragomirescu, "Communicating Materials: Communicating Concrete Development for Construction Industry," *IEEE Transactions on Industrial Informatics*, 2024, doi: 10.1109/TII.2024.3352261.

[3] S. Stefanov, G. Frølund, S. S. Zhekov, O. Franek, and G. F. Pedersen, "Dielectric properties of common building materials for UWB propagation studies," *IEEE Antennas and Propagation Magazine*, vol. 62, no. 1, pp. 72-8, 2020, doi: 10.1109/MAP.2019.2955680.

[4] S. Taheri, "A review on five key sensors for monitoring of concrete structures," *Construction and Building Materials*, vol. 204, pp. 492-509, 2019, doi: 10.1016/j.conbuildmat.2019.01.172.

[5] G. Peruzzi, and A. Pozzebon, "A review of energy harvesting techniques for Low Power Wide Area Networks (LPWANs)," *Energies*, vol. 13, no. 13, p. 3433, 2020, doi: 10.3390/en13133433.

[6] European Union, COMMISSION IMPLEMENTING DECISION (EU) 2017/1483 of 8 August 2017 amending Decision 2006/771/EC on harmonisation of the radio spectrum for use by short-range devices and repealing Decision 2006/804/EC, Official Journal of the European Union, Decision C(2017) 5464, 2017.

[7] G. Loubet, A. Sidibe, P. Herail, A. Takacs, and D. Dragomirescu, "Autonomous Industrial IoT for Civil Engineering Structural Health Monitoring," *IEEE Internet of Things Journal*, vol. 11, no. 5, pp. 8921-8944, 2024, doi: 10.1109/JIOT.2023.3321958.

[8] T. D. P. Perera, D. N. K. Jayakody, S. K. Sharma, S. Chatzinotas, and J. Li, "Simultaneous wireless information and power transfer (SWIPT): Recent advances and future challenges," *IEEE Communication Surveys Tutorials*, vol. 20, no. 1, pp. 264-302, 2018, doi: 10.1109/COMST.2017.2783901.

[9] A. Sidibe, G. Loubet, A. Takacs, L. Sanogo, and D. Dragomirescu, "Battery-free Bluetooth Low Energy Wireless Sensor Powered by Radiative Wireless Power Transfer," in *2023 21st IEEE Interregional NEWCAS Conference (NEWCAS)*, Edinburgh, Scotland, IEEE, pp. 1-4, 2023, doi: 10.1109/NEWCAS57931.2023.10198088.