# Isotropic IoT-Based Magnetic Flux Density Meter Implementation for ELF Field Measurements +
## 1 Introduction

Table 1: The Electric and Magnetic field reference levels in the European Union for general public exposure focused on Extreme Low Frequencies (ELF) [1,4]. and public places is presented. The Narda EFA-300 provides field analysis using an FFT computation in combination with built-in, isotropic, magnetic field probes, as shown in Figure 2. The measurement process is intended to be substantially simplified by this new generation of equipment. The Narda EFA-300 incorporates the novel STD (Shaped Time Domain) mode in addition to detecting the RMS and peak values using the conventional filter technique, providing simple but reliable measurement even in complex environments. Regarding the magnetic field measurements, the Narda EFA-300 analyzer can detect fields from 1 nT to 31.6 mT over the operating frequency range of 5 Hz to 32 kHz. The authors in [15] introduced a broadband monitoring system for electromagnetic radiation exposure assessment, focused on RF frequencies (from radio and TV broadcastings, mobile telephony systems, Wi-Fi, and TETRA communications) in 2006. The proposed system called \"SMS-K\", has been implemented for recording the \(E\)-field on a 24 h basis and sending the data to a central database via a GSM connection, as an early-stage EMF IoT platform. The real-time measurements are available via a web interface for citizens' information within the framework of the \"FASMA\" project [16], supported by Wind Hellas Telecommunications SA. Thereinafter, other EMF monitoring projects called \"HERMES\" (2002) [17], \"Pedion 24\" (2006) [18], and \"National Observatory of Electromagnetic Fields\" (2015) [19] were developed for the continuous remote monitoring of electromagnetic radiation via a distributed network of fixed meters in Greece. In these projects, the Narda area monitors AMS-8061/G [20], AMB-8059 [21], and AMB-8057-03/G [22] were used only for \(E\)-field measurements at a wide operating frequency band (100 kHz-7 GHz). The measurement data from each stand-alone station are sent to the central database via the 3G/GPRS network for citizens' information through the web portal of the project. Undeniably, the existence of magnetic fields in urban and semi-urban environments could be used as another emergency energy source (under certain conditions) to power low-consumption devices, such as IoT sensors. Numerous locations could be beneficial for sensors where the magnetic flux density may be high enough to power a low-consumption WSN's node, such as in high voltage substations, near railways, etc. Several published studies have covered the research on the magnetic flux density levels (\(B\)) under overhead power lines [23]. Researchers have verified that the flux density close to the ground is within legal limits. It stands to reason that different types of pylons will have varying overhead power line physical structures and typical line currents, leading to variable magnetic flux densities. The authors in [24] propose a novel and efficient harvesting bow-tie coil to scavenge the magnetic field energy under overhead power lines, enabling the self-powering of a large number of sensors. In contrast to the typical way of placing the energy harvester on the power lines, the proposed coil does not need to be fastened to the line and may be put just above the ground, allowing for the powering of sensors with a larger volume. Figure 2: The internal structure of Narda PMM EHP-50C probe-analyzer for measurements of magnetic and electric fields over the frequency range 5 Hz to 100 kHz. The identical circular sensor probes are devoted to isotropic field measurements in the X, Y, and Z planes [13; 14]. The work in [25] presents a study of a generator that can continually charge batteries for pulsed communications, using the magnetic field created by high-voltage DC lines. In its implementation, no expensive magnetic material is required; however, several insulating issues, including the Corona phenomenon in transmission lines, should be taken into account for the proposed mounted harvester to be used in practice.