Measurements, characteristics, and origin of new electromagnetic interference on magnetocardiographic measurements

Abstract

In order to eliminate the influence of the large-amplitude magnetic field noise that has complicated magnetocardiographic studies since October 2009, we have performed high-accuracy measurement of the environmental magnetic field noise in the vicinity of Beijing Subway Line 4 using a three-component height Tc radio frequency (rf) superconducting quantum interference device (SQUID). By analysing the spatial form and other characteristics of the time and the frequency domains and by calculating the circumferential magnetic field distribution based on a duel-end feeding system model, we reach the following conclusions: (i) the main source of magnetic field noise is the magnetic field generated by the subway trains, and (ii) the magnetic field interference results mainly from the imbalance between traction current and return rail current that is caused by the leakage current.

Analysis of influence of RF power and buffer gas pressure on sensitivity of optically pumped cesium magnetometer

“…In recent years, studies on ultrahigh sensitivity magnetometers, like alkali-metal magnetometer based on pumped atoms operating in a spin-exchange relaxation free regime [2] and diamond-based magnetometer using dense nitrogen-vacancy centers as magnetic sensors [3] have made much progress. On the other hand, high sensitivity magnetic sensors, like superconducting quantum interface device (SQUID) have many meaningful applications, like the measurement of electromagnetic interference on magnetocardiographic measurement [4] and the detection of brain auditory evoked magnetic field. [5] However, the optically pumped cesium magnetometer (CsOPM) is still one kind of commercial quantum magnetometer and, until recently, there have been still many research groups interested in this kind of magnetometer.…”

Development of an HTS-SQUID-Based Receiver for Long-Range Magnetic Induction Communication in Extreme Environments

“…In the frequency range from about 100 to 1600 Hz, there were many spikes in the spectrum at frequencies of higher-order harmonics of 50 Hz. We suspect these characteristic peaks originated from the large electromagnetic disturbances caused by nearby instruments or facilities powered with the 50 Hz power line, although the specific origin was difficult to identify because, as aforementioned, the measurements were taken at daytime in a physics building with lots of equipment running simultaneously and with a subway station right next to it [34]. It was also observed in the measurement that sometimes the environmental disturbances can become so large that the unshielded SQUID will become temporally inoperable.…”

“…We believe this should be attributed to the presence of excess noise in the measurement arising from the environmental electromagnetic interferences that are not included in the calculation. As mentioned above, the strong environmental interferences could be coupled with the SQUID via the pick-up coil, and such excess noise often features broadband behavior at low frequencies [34].…”

High contrast atomic magnetometer based on coherent population trapping

“…Highly sensitive magnetometers capable of measuring magnetic fields below 1 pT are important for many applications such as geophysical surveying, space science, nuclear magnetic resonance, non-destructive testing, medical diagnoses, gravitational wave detection, etc. [1][2][3][4][5][6][7][8][9][10] We use a technique called coherent population trapping, which was discovered more than thirty years ago by Alzetta et al [11] and is usually observed with a bichromatic field consisting of two resonant laser fields with the frequency difference varying in the vicinity of ground-state hyperfine splitting. At exact twophoton resonance, atoms are optically pumped into a coherent superposition of atomic ground states, which is called the dark state.…”