Noise reduction process with generalized harmonics analysis for high-temperature superconducting quantum interference device magnetocardiography

Generalized harmonic analysis was applied to a high-temperature superconducting quantum interference device (SQUID) magnetocardiograph signal processing system. The noise frequencies in the signal waveform were calculated by the generalized harmonic analysis (GHA) and the noise components with these frequencies were subtracted from the acquired signal data. Two types of the subtraction procedure were demonstrated: one using the adaptive filtering algorithm and the other a simple subtraction. In both case,,,, the noise components were reduced. The former system performed rapid calculations but generated an artificial noise in the high-frequency region. because of rough GHA estimation, while in the latter case, the calculation was time-consuming but the noise estimation was carried out accurately, because of the precision of GHA procedure. In the present study, a distinctive noise component at 16 Hz was completely Suppressed by the GHA prediction noise reduction process, The proposed systems were well suited for application to an unshielded high-temperature SQUID system.