The electrical activity of the human heart and brain are noninvasively visualized and analyzed using a multi-channel superconducting quantum interference device (SQUID) system. Multi-channel SQUID systems for magneto-cardiogram (MCG) and magneto-encephalogram (MEG) procedures have been developed by improving SQUID and cryogenic technology. Recently, we have developed two types of biomagnetic systems. The SQUID system, which utilizes a low-temperature superconductor (LTS) SQUID, is capable of detecting very weak signals, because the magnetic sensor is sensitive to signals above a few fT/ (Hz)1/2; this enables even fetal heart disease to be detected within the system's scope. A specially developed display method eases the estimation of distributed current sources. Abnormalities in the current distribution for an ischemic heart and propagation pathway for an arrhythmia are thus easily detected. Moreover, cortical functional abnormalities in patients with chronic dizziness can be visualized. A high-temperature superconductor (HTS) SQUID device system is under development as a next-generation product. The device system is designed to save space and provide mobility for the overall system, including the magnetically shielded cylinder. Due to an improvement in HTS-SQUID sensitivity and the introduction of a noise reduction technique, the real-time measurement of cardio-magnetic fields has become feasible.
A SQUID system for application to the biological immunoassay process is shown. In this system, the biological binding-reaction between an antigen and its antibody is detected using a magnetic marker and a SQUID magnetometer; that is, the binding reaction is detected by measuring the magnetic field from the marker. A so-called SQUID microscope was used in order to achieve a close distance between the cooled SQUID and the room-temperature sample. Three methods have so far been developed for measurement: susceptibility, relaxation and remanence. The measurement method is chosen by the properties of the magnetic marker. It is pointed out that a marker that is optimized for the immunoassay should be developed. For this purpose, we have developed a new marker made of an Fe3O4 particle having a diameter of 25 nm. Since the new marker can keep a remanence after a field of 0.1 T is applied, we use the remanent field of the marker to detect the binding reaction. We conducted an experiment to detect an antigen called Interleukin 8 (IL8). It was shown that the present system can detect IL8 at a weight of 0.1 pg.
Scanning laser-SQUID microscopy (SLSM) is a newly developed technique. Only three groups in the world have published their experimental results. In this review paper, we provide an explanation of SLSM, and discuss the advantages of SLSM over conventional techniques including how to apply SLSM to LSI inspection (identification of bad chips) and LSI failure analysis (fault site isolation on chips). Our first SLSM machine showed a spatial resolution of 1.3 μm using a 488-nm-wavelength laser, and our second SLSM machine showed a spatial resolution of 0.89 μm when irradiating a 1,064-nm-wavelength laser from the backside of a Si wafer. Irradiation from the backside of a wafer makes it possible to irradiate all p-n junctions of an LSI, which is expected to increase the efficiency of inspection and analysis. The possibility of in-line inspections was demonstrated in a general case. The possibility of failure analysis was demonstrated in a special case.
Recently, vortices confined into micro-scale superconductors with shapes like a disk, triangle, square, etc., have attracted much attention because of the quantum phase transition of the self-organized vortex arrangement occurring within such geometrical constraints. Such a transition can be observed using a scanning SQUID microscope with high spatial resolution. We have successfully improved spatial resolution by incorporating a microfabrication technique that reduces both the size of the pick-up coil of the micro DC-SQUID and the standoff distance between the pick-up coil and the sample surface. Using this microscope, we have studied vortex arrangements in micro-scale superconductors made of Nb and YBa2Cu3O7−δ films with various sizes and geometrical shapes. A peculiar oscillating behavior of diamagnetic magnetization corresponding to the particular vortex state was observed.
An overview of a SQUID application for non-destructive testing (NDT) is given by focusing to recent highlights in the field of aeronautics. Research on NDT and non-destructive evaluation using a high-Tc SQUID is progressing at a remarkable pace. A testing procedure for extremely thick-walled structures is needed to construct megaliner aircraft. Artificial defects at a depth of up to 40 mm were measured in a bolted three-layer aluminum sample. Ferrous inclusions in aircraft turbine discs may originate cracks and eventually lead to engine failure. Detection techniques for the inclusion were developed using a high-Tc SQUID, and were then used for testing aircraft turbine discs at the aircraft engine manufacturer BMW Rolls-Royce GmbH. Aircraft wheels are subjected to enormous stress and braking-generated heat during take-off and landing. To safely detect small hidden flaws generated by the stress and heat an automated eddy-current testing system was developed using a high-Tc SQUID in combination with Joule-Thomson machine cooling mounted on a robot. The wheel testing, conducted at the Lufthansa hub at Frankfurt/M. Airport, proved the reliability and stability of the operation. Carbon-fiber composites are advanced composite materials and are used in aircraft and rockets because they are light, strong and heat-resistant. SQUID-NDT techniques applied to C/C increase the possibility of detecting defects and classifying carbon-fiber composites. Improvements in high-Tc SQUID performance and the development of a cryocooler with less magnetic noise have contributed to the progress of SQUID-NDT. Techniques to use the cryocooler without injuring the sensitivity of the high-Tc SQUID are discussed.
I report on the research and development of a data acquisition system, based on a time domain electromagnetic (TDEM) method using a highly sensitive high-temperature superconductor (HTS) SQUID vector magnetometer operating at 77 K, which is suitable for mineral exploration by the Metal Mining Agency of Japan (MMAJ). The MMAJ has achieved stable long-term operation of all three channels during field trials. The SQUID system meets high requirements for slew rate (7.3 mT/s), dynamic range (100 dB) and bandwidth (DC∼100 kHz). It offers deeper penetration of depth than the induction coil system because it is capable of recording the step response that decreases with time slower than the impulse response of the induction coil system. The MMAJ's SQUID system will perform gradient observations that can provide much better resolution of deeper conductive targets than conventional EM field component observations. We have obtained good reproducibility of SQUID data and good correlation between the output signals of the reference induction coils and the derivatives of the SQUID signals in TDEM field trials.
Beam diagnostics are an essential constituent of any accelerator. There are a large variety of beam parameters, and total current is one of the most important parameters for accelerators. A current monitor is used to operate an accelerator efficiently and to improve the performance of the machine. A Faraday cup is the most fundamental current detection process, in which charged particles are stopped in the cup. However, this destructive method cannot be applied for high-current or high-energy beams because the total energy carried by the beam can destroy and activate the intercepting material. Therefore, non-destructive beam current measurement requires the use of current transformers that detect the magnetic field produced by the pulsed or DC beam. On the other hand, a new type of beam current monitor using a low-temperature superconducting (LTS) magnetic shield and an LTS SQUID was developed to measure the faint ion beams that are below the lowest measurable limit of the DC current transformer (DCCT) for atomic-physics studies. Recently, a prototype of a highly sensitive SQUID current monitor for measuring the intensity of faint beams, such as radioisotope beams, was completed for the RIKEN RI beam factory. This monitor is composed of a high-temperature superconducting (HTS) magnetic shield and an HTS SQUID. The first measurements using ion beams were carried out in the CNS experimental hall and RIKEN Ring Cyclotron (RRC). This paper first describes the principle of the conventional current monitor such as the Faraday cup and current transformers. Second, the progress of the LTS SQUID current monitor is discussed, and finally, the present status of the prototype of the HTS SQUID current monitor at RIKEN and the results of the first beam measurement are given.