Tong Qing Yang

High T/sub c/ SQUID system and magnetic marker for biological immunoassays

High T/sub c/ SQUID system is developed for the detection of the biological binding-reaction between antigen and its antibody. In this measurement, the antibody is labeled with magnetic nanoparticles, and the magnetic signal from the nanoparticles is measured. The excitation field of a few mT is applied in parallel to the SQUID in order to magnetize the nanoparticles. Due to mechanical misalignment, however, the vertical component of the excitation field couples to the SQUID, and degrades the system performance. In order to solve this problem, we develop two methods. One is the use of a compensation field in the case of the flux dam, and the other is the use of a switch instead of the flux dam. We also develop a magnetic marker utilizing Fe/sub 3/O/sub 4/ nanoparticle with diameter of d=25 nm. The nanoparticle is embedded in the polymer with typical diameter of 80 nm, and COOH is attached around the surface of the polymer. The properties of the marker are discussed.

Biological immunoassay utilizing magnetic marker and high Tc superconducting quantum interference device magnetometer

Detection of the biological binding-reaction between an antigen andits antibody was performed by using a magnetic marker and a high Tc superconducting quantum interference device (SQUID) magnetometer. In this method, the binding reaction is detected by measuring the magnetic field from the marker. A new marker made of Fe3O4 particle with diameter of 25 nm was developed, and the remanent field of the marker was used for the detection of the antigen called Interleukin 8 (IL8). It was shown that the present system can detect 0.1 pg weight of IL8.

SQUID magnetometer utilizing normal pickup coil and resonant-type coupling circuit

Abstract We have developed a high T c superconducting quantum interference device (SQUID) magnetometer utilizing a Cu pickup coil cooled to T =77 K and a resonant-type coupling circuit. The thermal noise can be decreased by cooling the pickup coil, while the signal transferred to the SQUID can be increased by using the resonant-type coupling circuit. Four pickup coils with different radii were used in the experiment. For the pickup coil with a radius r =15 mm and the number of turns n =150, we obtained the magnetic field noise of S B 1/2 =26 fT/Hz 1/2 at the resonant frequency of f r =6.37 kHz.

Suppression of thermally activated flux entry through a flux dam in high Tc superconducting quantum interference device magnetometer

Thermally activated magnetic-flux entry into a pickup coil through a flux dam in high-Tc superconducting quantum interference device (SQUID) magnetometer is studied. Since the thermally activated flux entry strongly depends on the circulating current in the pickup coil, the behavior of the circulating current is studied with numerical simulation when an external field is applied. It is shown that the circulating current becomes near the critical current of the flux dam after the large external field is applied. In this case, thermally activated flux entry becomes large, and degrades the SQUID performance. In order to suppress the thermal activation, the circulating current must be much below the critical current. For this purpose, two methods are proposed. One is to use a compensation field in the case of the flux dam, and the other is to use a switch instead of the flux dam. Numerical simulation shows that we can rapidly decrease the circulating current much below the critical current, and hence, can sup...

Magnetometer Utilizing Cooled Normal Pickup Coil and High-Tc Superconducting Quantum Interference Device Picovoltmeter for Nondestructive Evaluation

A magnetometer utilizing a cooled normal pickup coil and a high-Tc superconducting quantum interference device (SQUID) picovoltmeter was applied to nondestructive evaluation in an unshielded environment. The pickup coil of copper wire was cooled to T=77 K in order to decrease thermal noise from resistance. The magnetic field noise of the magnetometer was 130 pT/Hz1/2 and 10 pT/Hz1/2 at 100 Hz and 1 kHz, respectively, for the pickup coil with a 4.4 mm diameter. It was shown that the magnetometer could be moved in an unshielded environment without degradation of its performance. By moving the cooled pickup coil, we successfully detected a small crack on the backsurface of the Cu plate in an unshielded environment.

Eddy Current Testing Utilizing Cooled Normal Pickup Coil and Superconducting Quantum Interference Device Picovoltmeter: Comparison between Experiment and Analysis

Eddy current testing utilizing a cooled normal pickup coil and a high-Tc superconducting quantum interference device (SQUID) picovoltmeter was performed both experimentally and analytically. In the experiment, we successfully detected a small crack on the back surface of a Cu plate by moving the coil in an unshielded environment. First, we developed a method of avoiding the drift of the detected signal that was caused by the variance of lift-off. Next, we clarified the dependences of the detected signal on the excitation frequency and the thickness of the Cu plate. It was shown that an optimum frequency that maximizes the detected signal exists. Because this frequency changed with the thickness of the Cu plate, the frequency dependence could be used to estimate the depth of the crack from the surface of the Cu plate. The experimental results were analyzed taking into account the phase and amplitude of the signal field caused by the crack. Good agreement was obtained between experiment and analysis.

Eddy Current Testing Utilizing Cooled Normal Pickup Coil and Superconducting Quantum Interference Device Picovoltmeter

An eddy current probe utilizing a cooled normal pickup coil and a high-Tc superconducting quantum interference device (SQUID) picovoltmeter was developed. The pickup coil could be moved in an unshielded environment, during which the signal voltage across the pickup coil was transferred to the SQUID picovoltmeter, which was fixed in a cylindrical magnetic shield. By moving the pickup coil, we successfully detected a small crack on the back surface of a Cu plate in the unshielded environment. The dependences of the detected signal on the excitation frequency and thickness of the Cu plate were clarified. The frequency dependence could be used to estimate the depth of the crack from the surface of the Cu plate.