# Isotropic IoT-Based Magnetic Flux Density Meter Implementation for ELF Field Measurements +
## 8 Conclusions and Future Aspects  
This study presents the implementation of an isotropic Extremely Low Frequency (ELF) IoT-based meter, as enhanced in our previous work [30]. The prototype circuit can measure the magnetic flux density from 100 nT up to 10 \(\upmu\)T with 3 square identical sensor probes in vertical alignment, providing isotropic field measurements in the X, Y, and Z planes. The meter has a flat response across the operating frequency range from 40 Hz to 10 kHz. The proposed low-cost device can measure all magnetic fields from sources such as transformers, electric motors, heaters, hair dryers, and power supply network and their harmonic frequencies. An Arduino UNO Wi-Fi Rev.2 board with the integrated WiFiNINA module is responsible for data transferring from the sensor to the cloud, as a complete IoT solution. The measured field can be displayed on any mobile device with Wi-Fi connectivity, supported by the Blynk application via Android and iOS operating systems or web interface. As a future aspect, an improved version of the proposed isotropic meter could be used to implement a distributed EMF IoT sensors network to remotely monitor ELF magnetic field exposure in an interestingly high-risk area. Furthermore, the Arduino FFT feature could also depict the measured magnetic field strength within its harmonic frequencies in future improved implementation. The presence of magnetic fields in urban and semi-urban areas may be exploited as an emergency backup energy source to power low-consumption electronic devices, like Internet of Things (IoT) sensors. In our study, an ELF energy harvesting (EH) circuit implementation was also presented for the utilization of the alternating magnetic field (50 Hz) derived from the operation of transformers, power supplies, and other consumer devices both at the laboratory and at near-distance of medium voltage substations of the electrical public distribution network. Experimental measurements showed that the (DC) harvesting voltage can reach up to 4.2 volts with a magnetic field of 33 \(\upmu\)T, which is caused by the operation of an electric hair dryer, and can fully charge the 100 \(\upmu\)F storage capacitor (\(C_{s}\)) of the proposed EH system in about 3 min. The usage of a higher value of coil inductance (with a simultaneous change in the capacitance of the capacitor) causes a more sensitive circuit for efficient energy harvested from the magnetic fields of the devices, operating in power frequency (50 Hz). Figure 13: (**a**) The harvesting voltage is up to 8 Volt near the metal cabin in a medium voltage substation of the public electricity distribution network using the proposed MF-EH. (**b**) The average value of the magnetic flux density is about 34 \(\upmu\)T, as shown from experimental measurements in a metal cabin of a medium voltage substation within an urban fabric during peak hours. **Author Contributions:** Conceptualization, M.G.T. ; methodology, M.G.T. and G.A.A. ; software M.G.T. ; validation, M.G.T. ; formal analysis, M.G.T., G.A.A., D.V., T.Y. and D.S. ; investigation, M.G.T., G.A.A., D.V., T.Y. and D.S. ; resources, M.G.T., G.A.A., D.V., T.Y. and D.S. ; data curation, M.G.T. ; writing--original draft preparation, M.G.T. ; writing--review and editing, M.G.T., D.V., T.Y. and D.S. ; visualization, M.G.T. ; supervision, D.V., T.Y. and D.S. ; project administration, D.V. ; funding acquisition, D.V. All authors have read and agreed to the published version of the manuscript. The present article is part of the PhD thesis of [PERSON]. The implementation of the doctoral thesis was co-financed by Greece and the European Union (European Social Fund-ESF) through the Operational Programme \"Human Resources Development, Education and Lifelong Learning\" in the context of the Act \"Enhancing Human Resources Research Potential by undertaking a Doctoral Research\" Sub-action 2: IKY Scholarship Programme for PhD candidates in the Greek Universities (MIS-5113934). **Institutional Review Board Statement:** Not applicable.