A Generalized Study of Coil-Core-Aspect Ratio Optimization for Noise Reduction and SNR Enhancement in Search Coil Magnetometers at Low Frequencies

Abstract

Here, a generalized induction coil sensor model (more generalized than other models) has been considered at low frequencies (within 0.1-100 Hz), and the equivalent magnetic field of the coil's thermal noise and the sensor's signal to noise ratio (SNR) were calculated theoretically based on the dimensions and geometry of the coil winding and its core. In our suggested theoretical consideration, all involved parameters were considered and optimized without any assumption and constraint, while some authors in their latest reports, have been used some assumptions and constraints in their sensor calculations (such as holding constant the sensor's volume and aspect ratio). Our calculations indicated that the equivalent magnetic field of the thermal noise can be minimized by the coil to core weight ratio. Moreover, it was found that the sensor's SNR can be maximized with only a special value of core aspect ratio (length to diameter of core ratio). The obtained theoretical results were evaluated experimentally by fabricating a search coil magnetometer model, using the optimum parameters. The resonance frequency and the parasitic capacitance of the coil were measured. Moreover, variations of the transfer function of the magnetometer, with respect to frequency, were studied. Thus, it was shown that, at low frequencies, our experimentally measured noise data exhibit better agreement with our suggested theoretical results with respect to the state of the art.

Towards ultimate low frequency air-core magnetometer sensitivity

“…Various analytical solutions have been proposed to optimise the design of air-core magnetometers 6 and closely related ferromagnetic-core induction magnetometers 7 , 8 . Analytical solutions can offer a direct understanding of how different variables affect the theoretical sensitivity of magnetometers.…”

“…In what follows, numerical models for two popular pre-amplification modes are first presented, followed by an outline of non-tuned current-to-voltage and tuned voltage-to-voltage designs. The non-tuned current-to-voltage design, commonly known as the trans-impedance amplifier, is desirable in many applications due to the linear frequency gain response and excellent sensitivity at very low frequencies 5 – 8 , 10 , 12 , 14 . The tuned voltage-to-voltage design has the potential to provide additional sensitivity with narrower bandwidths, most often used in high frequency applications.…”

A Deep Learning-Based Electromagnetic Signal for Earthquake Magnitude Prediction

“…Compared with other research methods such as geology, geophysics, and geochemistry, there is a fast response in electromagnetic detection technology which can respond to crustal movement several days, or even hours, before [ 22 , 23 , 24 ]. In fact, the measurement depth of the electromagnetic sensor is directly related to its frequency band range, and the sensitivity of the sensor is also inseparable from the measurable range of seismic magnitude [ 25 , 26 , 27 , 28 ]. Therefore, it is important to design an electromagnetic sensor with broadband, high sensitivity, and low noise for earthquake monitoring.…”

Experimental Assessment of a Magnetic Induction-Based Receiver for Magnetic Communication

“…These magnetic sensors are known to have high sensitivity characteristics [8]. Specifically, the MI sensor based on a ferromagnetic core [18]- [20] has a sensitivity within tens of pT/√Hz, which is superior to the above-mentioned sensitivity of magnetic sensors. This MI sensor also has the advantages of small size, low cost, and easy implementation, so it could be a viable alternative for use as a receiving element in magnetic communication.…”

“…Accordingly, it can increase the range of communication. In this paper, a differential MI sensor [33], [34] with two ferromagnetic cores is proposed as a receiving element instead of a conventional MI sensor based on a ferromagnetic core [18]- [20]. Generally, the differential MI sensor reduces common mode noise, and the output voltage of the sensor shows increased characteristics compared with the conventional MI sensor.…”