23 Jan 2021, "A New Portable ELF Schumann Resonance Receiver." Part 5; Measurements and conclusions.
24( PART 5 -- Measurements On The Field-Results )
In order to confirm and improve the system’s operation, we made short-term measurements (few hours) mainly in “almost” white zones in the region of Epirus (NW Greece). Those spots as well as geographical coordinates and distance from the EM pollution are shown on Table 6. Except the last spot (chapel at Doliana), all the other places are in the countryside not suitable for long-term housing of our SR detection and monitoring system. Finally, the measurement equipment have been installed at the fifth spot, a chapel located at a small gorge, 570 m above the sea level and around 1 km away from man-made electromagnetic pollution (Fig. 10). The SR system starts measuring on 19 January 2016 with concurrent recordings, with few time gaps due to electronic equipment maintenance and local interference. Since June 2016, ETA Lab’s SR measurement station has been added to the list of worldwide Schumann resonance stations [30].
[ TABLE 6 -- Short and Long-Term Measurements ]
[ FIGURE 10 -- Long-Term Measurement Spot ]
To verify that the primary aim of this work was achieved, which was to design and implement a standalone, portable, and low-cost system able to measure as much SR harmonics as possible, we present power spectrums with 60 cm back-to-back magnetic antenna and N-S orientation with 10-min acquisition time (Fig. 11). Each figure additionally contains noise and fitting curves based on nonlinear least square regression, using Lorentzian-like function as described at [29]. For the first six modes, resonant frequencies, Q factors, and peak powers are summarized in Table 7. Although detailed analysis and validation of the record data is beyond the scope of this work, additional results are presented to document the system’s operability. Specifically, frequency mean value and standard deviation for the first six modes and for May 2017 are shown on Table 8. Frequency variation versus time, for the first week of May 2017, for mode 1 is shown in Fig. 12. Daily frequency variation, with maximum values around (8.00 ± 0.05) Hz for the first 4 days and (7.90 ± 0.05) Hz for the last 3 days, is noticed. Respectively, minimum frequency values lie around (7.75 ± 0.05) Hz and (7.55 ± 0.05) Hz. For all 7 days, maximum frequency values occur between 2:00 am and 6:00 am while minimum frequency values occur between 11:00 am and 3:00 pm, which yields similar frequency patterns for mode 1. These day-to-night and day-to-day variations are interpreted mainly by the inhomogeneities and the anisotropy in the Earth-ionosphere waveguide.
[FIGURE 11 -- Power Spectrum Of Recorded Signal ]
[ TABLE 7 -- SR Data ]
[ TABLE 8 -- SR Mean Values and Standard Deviations ]
[ FIGURE 12 -- Freq. Variation Over A Week, Mode 1 ]
Conclusions
A new portable ELF receiver for Schumann resonance detection and monitoring is presented in detail in this paper. The system is comprised of a self-designed induction coil sensor and six filtering and amplification stages. In the presented system, two magnetic field antennas, with a weight of 2.2 kg and size of 300 × 25 mm each were developed. The main self-resonance frequency of the single induction coil is 480 Hz. The low-noise implemented signal conditioning stages have an equivalent input noise as low as 2.88 nV/√Hz and a total passband gain from 86 to 112 dB at 10 Hz. The experimental results have also demonstrated the system’s feasibility in measuring clearly up to the sixth SR harmonic. Since January 2016, the measurement system has been installed near North-West borders of Greece measuring and storing SR initially with one magnetic coil and since June 2016 with two magnetic coils back to back. The system’s remote monitoring, validation of 18 months of data, and installation of E-W magnetic coil antenna are included in a short-term future work.
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Cite this article:
Votis, C.I., Tatsis, G., Christofilakis, V. et al. A new portable ELF Schumann resonance receiver: design and detailed analysis of the antenna and the analog front-end. J Wireless Com Network 2018, 155 (2018). https://doi.org/10.1186/s13638-018-1157-7