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We developed a low-vibrational-noise cooling configuration using continuous liquefaction of evaporated helium gas from a multi-channel SQUID gradiometer system for whole-head magnetoencephalography (MEG) measurements. The initial reduction of the vibration of the cryocooler was done by rigidly mounting the remote motor and cold head chamber on a concrete wall. This significantly reduces transmission of vibrations to the transfer tube, especially compared with mounting them on vertical aluminum frames. In addition, to reduce vibrations from a mechanical SQUID array insert, we completely eliminated it by mounting each SQUID gradiometer separately on the helmet surface within the vacuum space. Thus, vibrations from the boiling liquid helium and transmission from the transfer tube were both greatly reduced. Magnetic field noise of the 150-channel SQUID gradiometer system showed that the vibration-induced interference peaks are comparable in amplitude to those from a conventional MEG system without helium reliquefaction.

We have developed a biomagnetic measurement system for mouse by using high-TC SQUID magnetometer. The system consists of a high-TC SQUID magnetometer, a table-top magnetically shielded box, and a nonmagnetic dewar with a warm-to-cool distance of about 4 mm. Mice with weights of about 27 g were anesthetized and fixed in supine position on a plastic xyz-stage inside the shield box. The SQUID readout signal was digitized in 24-bit and recorded with sampling rate of 1280 Hz. We carried out a scanning measurement by changing x- and y-position of the subject inside the shield box. Finally, we could obtain clear mouse MCG waveforms of about 20 pT in peak amplitude with well defined P-, QRS-, and T-wave. We demonstrated the high-TC SQUID magnetometer based biomagnetic measurement system is useful for monitoring mouse MCG signals with sufficient noise-to-signal ratio.

In this paper, we fabricated a low-TC second-order superconducting quantum interference device gradiometer (SQUID) to measure magnetocardiography (MCG) in unshielded environment. The second-order gradiometer consists of the pickup coil and the SQUID. The pickup coil is formed with two single-turn coils and one double-turn coil. The three coils are connected in order of single-, double-, and single-turn coil. The coupling polarity of two single coils is opposite to the double-turn coil. The SQUID is based on double relaxation oscillation SQUID (DROS), which consists of a hysteretic signal SQUID, a reference junction, and shunted a relaxation circuit with a resistor and an inductor. The DROS has ten times larger flux-to-voltage transfer coefficient (~ 1 mV/Phi0) than that of the conventional SQUID. Therefore, DROS could be operated with a simple flux-locked loop circuit. The pickup coil and the SQUID were fabricated on the independent wafers and connected superconductively using an Nb wire. The overall size of the second-order gradiometer is 94 times 12 mm2 with a baseline of 35 mm. The average field noise was about 8 fT /radicHz at 100 Hz with the second-order gradiometer in shielded or unshielded environment. The noise level is low enough to measure MCG signals in the unshielded environment. Finally, we measure the MCG in shielded and unshielded environments by using the second-order gradiometer and compared the signal characteristics measured in both environments.

Magnetocardiography (MCG) using a superconducting quantum interference device (SQUID) sensor has been known for a noninvasive, noncontact, and safe diagnostic tool to detect ischemic heart disease such as angina and myocardial infarction. The magnetic distribution generated by the electrical activation of the heart reveals the abnormality of the myocardial status. The bust depth of people in 20s and 70s are much different, and the greatest difference is up to 154 mm. The purpose of this study is to identify whether MCG signals and parameter values are changed at the different locations of the SQUID sensor assembly. It would be an important reference for the standard measurement. Four healthy male subjects (33.3 plusmn 6.3 years) participated in this study. The distance between the chest surface and the bottom of the sensor assembly was 20, 40, 60, and 80 mm. Recording was made using 64-channel MCG system (axial type, first-order gradiometer) developed by Korea Research Institute of Standards and Science (KRISS). MCG were recorded for 30 s in a magnetically shielded room. As the sensor location is getting away from the chest surface, the each mean amplitude of R- and T-wave peak decreases to 70% (at 40-mm distance), 51% and 50% (at 60 mm), and 38% and 35% (at 80 mm) of the reference amplitude measured at 20-mm distance (y = -0.000002*x 3 + 0.0003*x 2 - 0.0308*x + 1.4961, R 2=1.00; where y= average amplitude remained after reduction}, x = distance between the chest surface and sensor location). Interindividual difference was less than 5%. The regression equations may be used as a good reference to calculate how much strength will be decreased by the distance. In MCG parameters, most parameters decreased when the distance increased. As an example, the current moment at T-wave peak reduced to 52% (at 40-mm distance), 33% (at 60 mm), and 19% (at 80 mm). Results showed how MCG signal and parameter values decreased rapidly when the sensor assembly was located far from the signal source. The study results may be used as a useful reference to design MCG system and analysis program.

Magnetocardiography (MCG) is a device to measure the weak magnetic fields generated from the heart using a superconducting quantum interference device sensor which converts magnetic flux to voltage and is the most sensitive sensor to detect magnetism. In the previous study, authors found that the values of MCG parameters of patients with non-ST-segment myocardial infarction were greater than those of age-matched controls (AMCs). In this study, we selected five different groups of patients considering their severity. We compared 10 MCG parameters recorded from 19 healthy young subjects (26.8plusmn13.4 years), 19 age-matched healthy subjects (55.4plusmn10.7), 23 stable angina patients (56.4plusmn7.6 years) with no stenosis (=0% on coronary angiogram) and normal echocardiogram, 24 unstable angina patients (61.9plusmn9.8 years) with severe stenosis (ges70%), and 20 Q-wave myocardial infarction (QMI) patients (57.3plusmn11.2 years) with severe stenosis (ges70%). To record the magnetic signals from a heart with minimal noise, a magnetically shielded room was used. The number of abnormal parameters was counted and magnetic field map (MFM) patterns were compared. As a result, young healthy subjects showed the smallest values in all 10 MCG parameters and QMI subjects showed the greatest values. Significant difference was found from dynamics parameters such as current angle, map angle, and distance dynamics between young healthy controls and AMC groups (p>0.05). No significant difference was found from AMC and stable angina groups even though parameter values of stable angina were slightly greater than those of AMC. Significant difference was found from five parameters between AMC and QMI subjects. These results are supportive to the previous analysis. In addition, the abnormal MCG parameters increased when the ischemic disease was worsened. Abnormal MFM patterns were easily found from QMI patients than stable angina pectoris. It is clear that abnormal MFM and parameters increase when the status of ischemic heart disease patients are getting worse.

In this paper, the effects of electromagnetic fields from the frequency band of digital wireless telephones on a superconducting quantum interference device (SQUID) were experimentally investigated. A first-order planar gradiometer based on the double relaxation oscillation SQUID (DROS) was operated without low-frequency magnetic shielding, and was exposed to radiated electromagnetic fields in the frequency range of 300 MHz-2 GHz. The experiments have been performed in a fully anechoic chamber to minimize reflected waves in the chamber. The flux-to-voltage transfer and the field sensitivity of the gradiometer have been observed under the irradiation of fields. Results show that the performance of the gradiometer was significantly affected at a typical power level of the digital wireless telephones for both horizontally and vertically polarized electromagnetic waves. The noise level of the DROS output voltage also increases as the strength of the external fields becomes higher.

A double relaxation oscillation SQUID with a reference junction (RJ-DROS) already has a fixed reference current, so that it holds a fixed flux-to-voltage characteristics when fabricated. When an additional current flows through the reference junction but not through the signal junction in the RJ-DROS, we have obtained the variation of its characteristics. The additional reference current has an effect on reducing the fixed reference current, which results in changing averaged relaxation voltage and transfer coefficient. In particular, while the critical current of the signal SQUID exceeds the reference current, the averaged relaxation voltage at the reference junction is enlarged by the added bias current combined with an additional current and an initial bias current. Therefore the additional reference current can provide the RJ-DROS with variable modulation depth and width within the operating range. Although the characteristics of RJ-DROSs are fixed differently each to each when they are fabricated, the additional current can adjust their characteristics to the same one, which is useful for controlling DROSs in a multichannel DROS system. However, an input-bias current in the preamplifier detecting the outputs at the reference junction, acts as an additional current, and then makes the reference current shift from the optimum current or deviate from the operating range, the input-bias current needs to be regulated within the operating range

This paper investigates the origins of localization errors when cortically distributed source approach is applied to magnetoencephalography (MEG) and electroencephalography (EEG) focal source reconstruction problems. It was revealed from simulations that the errors mainly stem from 1)Asymmetric distribution of crosstalk and 2)Large noises at some time slices. To enhance the localization accuracy, a new algorithm named cortical surface scanning (CSS) method is presented. The proposed algorithm was applied to realistic simulations and more accurate and robust source estimates could be obtained

We present a 62-channel double relaxation oscillation SQUID (DROS) planar gradiometer system to measure magnetocardiogram (MCG) signals tangential to the chest surface. The DROSs were fabricated using Nb/Al-oxide/Nb junctions, and provided flux-to-voltage transfers of larger than 1 mV//spl Phi//sub 0/ typically, which is large enough for direct readout by room-temperature flux-locked loop (FLL) circuits. The analog FLL circuits and digital control circuits are made in a single printed circuit board. The planar gradiometers are integrated, series-connected first-order pickup coils with a baseline of 4 cm. White noise level of the planar gradiometer is about 1.5 (fT/cm)//spl radic/Hz or 6 fT//spl radic/Hz, operated inside a magnetically shielded room. The planar gradiometers were arranged to measure dB/sub x//dz and dB/sub y//dz simultaneously. The covering area of the 62 channel system is 162 mm /spl times/ 162 mm, which is smaller than the sensor coverage area of vertical measurement systems, but large enough to measure the essential MCG field distribution in a single position measurement.

Compact and low-cost SQUID electronics to operate double relaxation oscillation SQUIDs (DROSs) has been constructed for detecting magnetocardiogram (MCG) fields. SQUID electronics consists of low-noise preamplifier with a white noise of 0.6 nV//spl radic/Hz, flux-locked loop (FLL) circuit with auto-reset, and interface circuit to control FLL using 3 digital lines from a computer. The automatic control software adjusts SQUID parameters to the optimum operating condition within 15 seconds for 62 channels. Outputs of FLL circuits are passed through the hardware filter box to the 64-channel data acquisition board. Each SQUID electronics for FLL and digital control is built together on a printed circuit board of 45 mm /spl times/ 95 mm. When SQUID electronics is connected to DROS gradiometer with typical flux-to-voltage transfers of 1 mV//spl Phi//sub o/, the noise contribution of FLL circuit is about 0.6 /spl mu//spl Phi//sub o///spl radic/Hz or 0.6 fT//spl radic/Hz at 100 Hz, low enough to measure MCG fields.

This paper proposes a novel approach to enhancing results of magnetoencephalography cortical source imaging. The proposed approach utilizes bell-shaped functions defined on an inflated cortical surface, which has one-to-one correspondence with original tessellated cortical surface. The coefficients of the functions are then determined using sensitivity analysis with conjugate gradient updating scheme. Applications of the approach to a simulation study and a practical experiment have resulted in more stable and smoother brain source distribution, compared to conventional linear inverse approach.

In this paper, an improved technique for multiresolutive reconstruction of magnetoencephalography source distribution is proposed. Using the proposed technique, focal source distribution with higher energy density can be reconstructed. Moreover, the proposed approach is very easy to implement compared with conventional ones. The usefulness of the proposed technique is verified using a cortical patch test for a realistic brain model.

A multidipole searching technique using a moving dipole concept is proposed for magnetoencephalography (MEG) source localization. The proposed method can be a promising method to resolve a critical disadvantage of conventional equivalent current dipole (ECD) method-the number of current dipoles should be given a priori. From several simulation results, the accuracy and effectiveness of the method will be verified.

We constructed a multichannel superconducting quantum interference device (SQUID) magnetometer system for magnetoencephalogram measurements. The SQUID is based on the double relaxation oscillation SQUID (DROS), which consists of a hysteretic signal SQUID and a reference junction, and shunted by a relaxation circuit of a resistor and an inductor. With the high flux-to-voltage transfers, usually larger than 1 mV//spl Phi//sub 0/, simple flux-locked loop circuits could be used for SQUID operation. The SQUID system consists of 37 integrated magnetometers, distributed on a hemispherical surface, and external feedback scheme was used to eliminate magnetic coupling with the adjacent channels. In addition to the 37 signal channels, 8 reference channels were installed to pickup background noise and to apply software gradiometer. The average noise level of the magnetometers is about 3 fT//spl radic/Hz at 100 Hz, operated inside a magnetically shielded room. The magnetometer system was applied to measure auditory-evoked fields.

We have fabricated a single-stage superconducting quantum interference device (SQUID) current amplifier for detecting pulse outputs of a superconducting microcalorimeter. The current amplifier is made of a double relaxation oscillation SQUID (DROS) that provides a high flux-to-voltage transfer of about 1mV//spl Phi//sub 0/ and a large modulation depth of 80 /spl mu/V. Due to the high flux-to-voltage transfer, the voltage output of the DROS is measured directly with a room-temperature dc preamplifier. The bandwidth of the current amplifier is measured to be 1.2 MHz. Typical noise of the DROS current amplifier is about 6 pA//spl radic/Hz.

We have fabricated thermal-induced wavelength- tunable vertical-cavity surface-emitting lasers with a 780-nm emission wavelength that is tunable by using an internal device heater. A 5.36-nm tuning range was achieved by means of a 70-mA tuning current and a 3.5-mA driving current while maintaining continuous single-mode operation and the optical power variation is less than 2.5 dB in the tuning range. In addition, a multimode tuning range of 9.1 nm was achieved with a 90-mA tuning current and a 7-mA driving current.

Presents a compact and reliable planar gradiometer for a multichannel system measuring tangential components of biomagnetic fields. The readout electronics was simplified by using a double relaxation oscillation SQUID (DROS) which provides very large flux-to-voltage transfer of typically 3 mV//spl Phi//sub 0/, enabling direct readout by a DC preamplifier with modest voltage noise. The DROS was made from hysteretic Nb/AlO/sub x//Nb junctions. To realize a compact and reliable gradiometer, the planar pickup coil is integrated on the same wafer with the SQUID. The planar pickup coil consists of two 10 mm/spl times/10 mm coils connected in series to form a first-order gradiometer and has a baseline of 30 mm. The field gradient noise is 9 fT/cm/spl radic/Hz at 1 Hz inside a magnetically shielded room. The gradiometers were arranged to measure simultaneously x and y components of biomagnetic fields.

By using the selective niobium anodization process (SNAP) an all refractory 210-junction array was fabricated at KRISS. The array consists of Nb/Al-oxide/Nb junctions that have A=20 mu m*40 mu m. V/sub g/=2.8 mV, an average critical current approximately=650 mu A, and the spread of critical currents approximately=+or-5%. When operated at 94 GHz, the array generated zero-crossing steps up to 240 mV with stability times of more than 1 h. >

The giant magnetoimpedance (GMI) is studied as function of annealing-field angle /spl theta//sub k/ in Co/sub 66/Fe/sub 4/NiB/sub 14/Si/sub 15/ ribbon with respect to transverse direction. The GMI profile at 10 kHz shows two peaks located at negative and positive external field H. The interval between two peaks, about 2.1 Oe for /spl theta//sub k/=0/spl deg/, slightly increases with /spl theta//sub k/ up to /spl theta//sub k/=30/spl deg/ and then decreases down to 1.0 Oe for /spl theta//sub k/=90/spl deg/. However, two peaks are asymmetric and hysteresis exists during cyclic magnetization. The asymmetry ratio, fractional difference of two peaks, is maximum about 2% for /spl theta//sub k/=10/spl deg/ and its sign is reversed from /spl theta//sub k/=40.

An user-friendly and economical hysteresis loop tracer that permits to measure four-quadrant J-H loop of Nd based high coercivity magnet is constructed. An alternate pulse magnetic field with a peak value of about 10 T is generated by a way of connecting 3 monopolar pulse generators to an air solenoid magnet by using a sequential ignition circuit and a magnet exciting circuit. The J-H loops with initial magnetization curves are then obtained for rod type Nd based magnets (length of 5 mm and diameter of 5 mm) with an electronic fluxmeter. The increase of apparent coercivity of the magnets due to the eddy current effect is calculated, considering eddy current loss by analyzing a wave of generating magnetic field. The results are calibrated with pure Ni rods with the dimension identical to the Nd magnets.

Dependences of magnetoresistance and morphology upon the insertion of very thin magnetic layers at interfaces between magnetic and nonmagnetic layers in Co/Cu and Ni/sub 81/Fe/sub 19//Cu multilayers have been investigated. The Co/Cu multilayers with inserted Fe thickness of 0.5/spl sim/1.0 /spl Aring/ have the MR ratio of about 18% more than the noninserted multilayers, and the MR ratio in the NiFe/Cu multilayers with inserted Co of thickness of 3 /spl Aring/ was found to be significantly increased. These results can be explained by the enhanced interlayer antiferromagnetic coupling and spin-dependent scattering phenomena at the interface. Of particular interest, the "Clustered out-growth" in the surface morphology of these multilayers was observed.

An economic and versatile magnetometer for measuring basic magnetic characteristics such as hysteresis loops, magnetic anisotropy and magnetostriction with a single system was built. It is based on the principle that most magnetic characteristics could be obtained by analyzing the torque acting on a sample under an appropriate magnetic field. A capacitive torque sensor with 0.1 nJ resolution measures such torque. By limiting the duration of electromagnetic excitation only to the measuring period (about 4 s), temperature rise of the magnet becomes negligible so that a very compact and economic electromagnet and power supply (10 kg weight, 25 mm air gap, 350 W power consumption, and 480 kA/m of generated field) is realized.

The authors have fabricated superconductor-insulator-normal metal (SIN) tunnel junctions with c-axis-oriented YBCO thin films as the superconducting electrodes and studied the tunneling characteristics of the junctions by measuring the zero-bias junction resistance as a function of temperature and dI/dV as a function of the bias voltage. Measured junction resistance showed characteristic tunneling properties with a strong semiconducting background, which is ascribed to the imperfect tunnel barrier. dI/dV curves indicated gap structures at 27 mV and 4.5 mV, respectively, with a parabolic background. >

A novel approach for the measurement of magnetic anisotropy is introduced, and a preliminary small-scale system is described. In order to create a rotating magnetic field without mechanical rotation of the electromagnet, two pairs of electromagnets are placed so that their axes are mutually perpendicular. One of the pairs of electromagnets is excited with a sinusoidal current and the other with a cosine current. Thus, the net magnetic field vector rotates. The exciting currents are intermitted by a zero crossing analog switch to minimize power loss in the electromagnets and power supplies. The rotating magnetic field generates a torque on the magnetically anisotropic sample placed in the center of the field. The torque is measured with a piezoelectric sensor. In a preliminary experiment, a rotating field intensity of 0.2 T was obtained with a 1-kg electromagnet and a 20-W power amplifier. The calibration for the measurement was carried out with pure nickel wire. The anisotropy constants of several amorphous ribbons were measured. >

A new measurement system to obtain a proper value of disaccommodation intensity D was devised and applied to Metglas 2605SC and Fe 5 Co 7 Si 15 B 10 amporphous ribbons as received. The initial susceptibility χ, the stabilization field H o and the effective domain wall thickness δ were obtained from analysis of minor hysteresis loops at room temperature. The effects of a tensile stress σ along the long axis of the ribbons on χ, H o , D and δ were investigated. The inverse of susceptibility r and H o increased linearly with log t where t is the time after demagnetization δ was almost constant with t except at small σ. The disaccommodation intensity defined as D=Δχ/χ(t 1 ) was much greater than reported previously and was enhanced by σ.