Keiji Tsukada

Multichannel SQUID system detecting tangential components of the cardiac magnetic field

The 32‐channel SQUID system described here is used for diagnosing heart disease by measuring the x and y components of the cardiac magnetic field. To detect a magnetic field parallel to the body surface, it uses a compact hybrid superconducting quantum interference device (SQUID) gradiometer consisting of a planar pickup coil (fabricated using thin‐film techniques) and a square double‐washer dc‐SQUID having large voltage‐flux transfer function. The SQUIDs are operated in a flux‐locked mode using simple readout circuits connected directly to the preamplifier without additional positive feedback. The system is installed in a magnetically shielded room in a hospital. A low noise characteristics lower than 10 ft/√ Hz in a white noise is obtained in the hospital. Examples of tangential magnetocardiogram (MCG) measurements presented here show that the MCG obtained using this gradiometer makes it easy to visually estimate the electrophysiological behavior of the heart.

Development of multisample biological immunoassay system using HTSSQUID and magnetic nanoparticles

We developed a prototype magnetic immunoassay system using a high temperature superconductor (HTS) superconducting quantum interference device (SQUID) to investigate the performance and usability of the magnetic immunoassay. The system is designed to measure multiple samples and liquid samples, and it can work in an unshielded environment at a medical facility. To reduce the disturbance from environmental noise, the SQUID and samples are covered with three-layers of permalloy magnetic shield. The SQUID and magnetic shield are set in an aluminum box which acts as an RF shield. A gradiometer with a 5 /spl times/ 10 mm pickup coil, which is cooled by liquid nitrogen through a sapphire/Cu rod, is used as a sensor. We also developed a nonmagnetic sample disk with 12 reaction cells and examined 12 samples in one measurement sequence. The measurement process is controlled by a computer, which perform data averaging. Fe/sub 3/O/sub 4/ nanoparticles with a 25-nm diameter were used as test samples. After applying a magnetic field of about 0.1 T, we measured the remanent magnetic field from the Fe/sub 3/O/sub 4/ nanoparticles. The present system could detect 30 pg of Fe/sub 3/O/sub 4/ nanoparticles. This result was obtained by averaging 100 trials under an unshielded laboratory environment. The measurement time for 100 trials was only 100 s.

Quantitative magnetic detection of finger movements in patients with Parkinson’s disease

To develop a new measurement tool for quantitatively detecting the finger movement of a patient with Parkinsons disease (PD), we designed a magnetic sensing system consisting of a magnetic induction coil, a sensing coil, and a circuit unit. The sensing coil detects the inducted magnetic field that varies with the distance between the two coils, and the detected signals are demodulated in the circuit unit in order to obtain the variation voltage from the oscillation frequency. To obtain a coefficient for converting voltage to distance, we measured the output voltages for seven fixed finger positions of 12 normal volunteers. The voltage differences corresponding to the finger movement in 20 PD patients, six age-matched controls, and 12 normal volunteers were then recorded for 30s. To investigate the velocity and acceleration of the finger movement, we calculated their waveforms from the measured displacement waveform. We also detected the main frequency of the tapping rhythm by using a fast Fourier transform (FFT). The averaged amplitude of each waveform decreased with the disorder in the Hoehn-Yahr (HY) stage, while the averaged tapping frequency of PD patients did not have any correlation with this stage. It can be concluded that this magnetic sensing system can assess finger movement quantitatively.

Chemical sensing plate with a laser-terahertz monitoring system

A new type of laser-terahertz emission system for noncontact investigations of chemical solutions has been developed. The system monitors terahertz emission from a sensing plate, which consists of silicon oxide and silicon thin film layers on a sapphire substrate. Sensing of chemical solutions with pH values between 1.68 and 10.01 was demonstrated. The amplitude of the terahertz emission from the sensing plate increased with increasing pH value. This change in the amplitude was caused by a change in the depletion layers of the silicon thin film when protons were adsorbed on the surface of the sensing plate. This study demonstrates that full noncontact monitoring of chemical solutions is possible using the laser-terahertz emission system.

A Terahertz Chemical Microscope to Visualize Chemical Concentrations in Microfluidic Chips

Here, a new type of terahertz chemical microscope (TCM) is proposed and developed, and the first demonstration of imaging the chemical concentration in fluid channels is reported. Fluid samples flow through channels possessing a semiconductor sensing plate as a bottom wall. Terahertz (THz) waves are radiated from the sensing plate as a result of femtosecond laser illumination. Because the amplitude of the THz radiation depends on the concentration of ions adsorbed on the surface of the plate, the ion distribution in the fluid channels can be visualized by scanning the laser across the plate. An image showing separated solutions with two different proton concentrations is successfully observed as the first demonstration of this instrument.

Laser terahertz emission system to investigate hydrogen gas sensors

A laser terahertz emission system is proposed to investigate the catalytic metal/semiconductor interfaces of hydrogen sensors. Samples were fabricated by depositing a catalytic metal thin film on a semi-insulating silicon substrate. A femtosecond laser was used to radiate terahertz waves from the sample in a gas cell filled with a hydrogen and nitrogen gas mixture. The peak amplitude of the terahertz waves decreased with increasing hydrogen concentration. We also fabricated a metal-oxide-semiconductor field effect transistor hydrogen sensor, and compared its properties with the terahertz radiation properties. These results suggest that the laser terahertz emission system is a potential tool to investigate catalytic metal/semiconductor interfaces.

Hydrogen gas detection system prototype with wireless sensor networks

We fabricated a prototype for detecting hydrogen gas leaks in hydrogen filling stations. The prototype is composed of a wireless network with ten sensor nodes that can monitor the spatial distribution of hydrogen gas leakage. To enable each sensor node to be driven by a battery, field-effect-transistor sensors and a microprocessor with low power consumption have been adopted. Additionally, a function to consume minimal levels of power has been developed and installed in the microprocessor in each node. The use of batteries and wireless communications enables the nodes to be placed at optimal sensing locations without regard to the wiring needed with existing gas sensors

Magnetic property mapping system for analyzing three-dimensional magnetic components

A magnetic measurement system utilizing a vector magnetic sensor for analyzing and mapping low frequency magnetic properties of metals has been developed for nondestructive evaluation. The measurement system consists mainly of an induction coil which can expose a large sample area, a vector magnetic sensor for detecting magnetic fields emanating from a sample, a lock-in amplifier, and a two-dimensional scanning stage. The system was determined to have a high magnetic sensitivity corresponding to less than 1nT in the locked-in state. The magnetic field strength change was detected in a sample that contained a slit of width greater than 1mm. Time sequential vector component (normal and tangential) maps were developed. An iron plate as an example of a ferromagnetic metal and an aluminum plate as an example of a good conducting and nonferromagnetic material were compared using this system. Analyzing the vector component maps could differentiate differences in the magnetic properties, such as permeability, edd...

Development of a compact DC magnetometer using HTS-SQUID and a rotating sample

We developed a compact DC magnetometer using a high-temperature superconductor (HTS) superconducting quantum interference device (SQUID) to measure very weak magnetic signals from samples such as paramagnetic and diamagnetic materials. The samples were rotated in the DC magnetic field that was detected by a normal conductive pick-up coil. The detected signal was transferred to an input coil that was inductively coupled to the SQUID. To clarify the basic characteristics of this system, the magnetic signal from a magnetic material was measured by varying the sample position and rotation speed. Then, the magnetic signal from pure water was measured under the optimized condition and a very weak magnetic signal from pure water was successfully detected. Therefore, the developed system could be applied to various non-destructive evaluation systems.

Low-Frequency Eddy Current Imaging Using MR Sensor Detecting Tangential Magnetic Field Components for Nondestructive Evaluation

An eddy-current distribution imaging system with wide area magnetic field exposure, which can be applied to the detection of deep crack of the metal using a magnetic resistive (MR) sensor is developed. This eddy current image is obtained by the developed system detecting perpendicular components to the magnetic filed exposure. By using very low frequency magnetic field exposure, detection of the opposite side slit of the metal substrate is enabled.An eddy-current distribution imaging system using a wide-area magnetic field exposure has been developed. This system can be employed to detect deep metal cracks using a magnetic resistive (MR) sensor. The measuring system consists of the exposure coil, MR sensors, measuring circuits, lock-in amplifier, xy stage, and a personal computer. To detect the eddy current distribution, the imaging system uses a pair of MR sensors that detect the x and y magnetic field components parallel to the metal surface. The system operates at a low-frequency range in order to obtain depth of penetration. An artificial defect consisting of a multilayer Al substrate sample with a bottom half slit was measured to test the system. The change in the eddy current distribution image due to the presence of the flaw was obtained. In particular, it was determined that the detection of the slit depth was improved by this lower exposure frequency