Superparamagnetic nanoparticle detection using second harmonic of magnetization response

We introduce a method to improve the detection sensitivity for the magnetization M of superparamagnetic nanoparticles (MNP). The M response of MNP to an applied magnetic field H (M–H characteristics) could be divided into a linear region and a saturation region, which are separated at a transition point H k. When applying an excitation magnetic field (H ac ) with a frequency ω0 and an additional dc bias field H dc = H k, the second harmonic of M reaches the maximum due to the nonlinearity of the M–H characteristics. It is stronger than any other harmonics and responsible for small H ac without a threshold. The second harmonic selected as the readout criterion for M response of MNP is systematically analyzed and experimentally proven

Improved Characteristics of Integrated HTS rf SQUID on Bicrystal SrTiO3 Substrate Resonator Covered with HTS Thin Films in Flip-Chip Geometry

AbstractIntegrated high-temperature superconductor (HTS) radio-frequency (rf) superconducting quantum interference devices (SQUIDs) based on a bicrystal SrTiO3 substrate was investigated for application to magnetic contaminant detection. By covering a wide superconducting weak link and/or a slit of the YBa2Cu3O7-x SQUID with HTS thin films in flip-chip geometry, characteristics such as effective area and 1/f noise profile of the SQUID were successfully improved. By installing the covered SQUID in a magnetic contaminant detection system, it was demonstrated that the system can detect a tungsten ball of 15μm in diameter with a signal to noise ratio of about 2

Measurement of metallic contaminants in food with a high-Tc SQUID

We have proposed and demonstrated a high-Tc SQUID system for detecting metallic contaminants in foodstuffs. There is a demand for the development of systems for detecting not only magnetic materials but also non-magnetic materials such as Cu and aluminium in foodstuffs to ensure food safety. The system consists of a SQUID magnetometer, an excitation coil and a permanent magnet. For a non-magnetic sample, an AC magnetic field is applied during detection to induce an eddy current in the sample. For a magnetizable sample, a strong magnetic field is applied to the sample prior to the detection attempt. We were able to detect a stainless steel ball with a diameter of 0.1 mm and a Cu ball less than 1 mm in diameter, for example