{'fraction_non_alphanumeric': 0.01977186311787072, 'fraction_numerical': 0.0007604562737642585, 'mean_word_length': 4.848888888888889, 'pattern_counts': {'":': 0, '<': 0, '<?xml version=': 0, '>': 0, 'https://': 0, 'lorem ipsum': 0, 'www.': 0, 'xml': 0}, 'pii_count': 0, 'substrings_counts': 0, 'word_list_counts': {'cursed_substrings.json': 0, 'profanity_word_list.json': 0, 'sexual_word_list.json': 0, 'zh_pornsignals.json': 0}}
Imaging of Magnetic Nanoparticles Using a Second Harmonic of Magnetization With DC Bias Field

We have developed a method to improve the detection sensitivity for the magnetization M of magnetic nanoparticles (MNPs) using a high Tc superconducting quantum interference device magnetometer. The M response of MNP to an applied magnetic field H(M-H characteristics) can be divided into a linear region and a saturation region, which are separated at a transition point Hk. When applying an excitation ac magnetic field (Hac) and an additional dc bias field Hdc = Hk, the second harmonic of M reaches a maximum due to the nonlinearity of its M-H characteristics. This harmonic is stronger than any other harmonics, including a third harmonic. The advantage of using the second harmonic response is that the response can be measured even in a small field Hac. The M response of MNP was systematically analyzed and experimentally demonstrated. For conventional detection using a third harmonic, the amplitude of the Hac must be larger than the threshold level, which is almost the same as Hk. Detection methods using a second harmonic can be applied to magnetic particle imaging. We finally demonstrate the construction of a 1-D image of two separated bottle-shaped MNP samples using the method with a lock-in amplifier.