• Progress in Superconductivity
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• v.13 no.3
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• pp.139-145
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• 2012

Electric activity of cardiac muscles generates magnetic fields. Magnetocardiography (or MCG) technology, measuring these magnetic signals, can provide useful information for the diagnosis of heart diseases. It is already about 40 years ago that the first measurement of MCG signals was done by D. Cohen using SQUID (superconducting quantum interference device) sensor inside a magnetically shielded room. In the early period of MCG history, bulky point-contact RF-SQUID was used as the magnetic sensor. Thanks to the development of Nb-based Josephson junction technology in mid 1980s and new design of tightly-coupled DC-SQUID, low-noise SQUID sensors could be developed in late 1980s. In around 1990, several groups developed multi-channel MCG systems and started clinical study. However, it is quite recent years that the true usefulness of MCG was verified in clinical practice, for example, in the diagnosis of coronary artery disease. For the practical MCG system, technical elements of MCG system should be optimized in terms of performance, fabrication cost and operation cost. In this review, development history, technical issue, and future development direction of MCG technology are described.

• Progress in Superconductivity
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• v.10 no.2
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• pp.139-143
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• 2009

We have fabricated a low-noise 61-channel axial-type first-order gradiometer system for measuring fetal magnetocardiography(MCG) signals. Superconducting quantum interference device(SQUID) sensor was based on double relaxation oscillation SQUID(DROS) for detecting biomagnetic signal, such as MCG, magnetoencphalogram(MEG) and fetal-MCG. The SQUID sensor detected axial component of fetal MCG signal. The pickup coil of SQUID sensor was wound with 120 ${\mu}m$ NbTi wire on bobbin(20 mm diameter) and was a first-order gradiometer to reject the environment noise. The sensors have low white noise of 3 $fT/Hz^{1/2}$ at 100 Hz on average. The fetal MCG was measured from $24{\sim}36$ weeks fetus in a magnetically shielded room(MSR) with shielding factor of 35 dB at 0.1 Hz and 80 dB at 100 Hz(comparatively mild shielding). The MCG signal contained maternal and fetal MCG. Fetal MCG could be distinguished relatively easily from maternal MCG by using independent component analysis(ICA) filter. In addition, we could observe T peak as well as QRS wave, respectively. It will be useful in detecting fetal cardiac diseases.

• Journal of Biomedical Engineering Research
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• v.27 no.4
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• pp.154-163
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• 2006

A 64-channel magnetocardiogram (MCG) system using low-noise superconducting quantum interference device (SQUID) planar gradiometers was developed for the measurements of cardiac magnetic fields generated by the heart electric activity. Owing to high flux-to-voltage transfers of double relaxation oscillation SQUID (DROS) sensors, the flux-locked loop electronics for SQUID operation could be made simpler than that of conventional DC SQUIDs, and the SQUID control was done automatically through a fiber-optic cable. The pickup coils are first-order planar gradiometers with a baseline of 4 em. The insert has 64 planar gradiometers as the sensing channels and were arranged to measure MCG field components tangential to the chest surface. When the 64-channel insert was in operation everyday, the average boil-off rate of the dewar was 3.6 Lid. The noise spectrum of the SQUID planar gradiometer system was about 5 fT$_{rms}$/$\checkmark$Hz at 100 Hz, operated inside a moderately shielded room. The MCG measurements were done at a sampling rate of 500 Hz or 1 kHz, and realtime display of MCG traces and heart rate were displayed. After the acquisition, magnetic field mapping and current mapping could be done. From the magnetic and current information, parameters for the diagnosis of myocardial ischemia were evaluated to be compared with other diagnostic methods.

• Progress in Superconductivity
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• v.14 no.2
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• pp.106-109
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• 2012

Superconducting sensors and detectors have been applied to many fields or beginning to enter the maturing stage. The applications spread over a wide range of fields such as radio telescope, medical examination, quantum information, contamination inspection, materials analysis, etc. For users of the superconducting devices as well as developers, we have to avoid confusion of naming, graphical circuit symbols, and measurement methods for device performance. We are trying to formulate international standards under the International Electrotechnical Commission - Technical Committee 90 (IEC-TC90), which is responsible for superconductivity. The sensors and detectors to be considered are divided into two groups: coherent sensors (SQUID, SIS mixers, etc.) and direct detectors (TES, STJ, MKID, SSPD, etc.).

• 한국초전도학회:학술대회논문집
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• v.12
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• pp.43-43
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• 2002

• The Transactions of the Korean Institute of Electrical Engineers D
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• v.54 no.11
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• pp.643-649
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• 2005

A heart diagnosis system adopts Superconducting Quantum Interface Device(SQUD) sensors for precise MCG(MagnetoCardioGram) signal acquisitions. Such system needs to deal with hundreds of sensors, requiring fast signal sampling md precise analog-to-digital conversions(ADC). Our development of hardware board, processing 64-channel 12-bit in 1 ks/s speed, is built by using 8-channel ADC chips, 8-bit microprocessors, SPI interfaces, and specially designed parallel data transfers between microprocessors to meet the 1ks/s, i.e. 1 mili-second sampling interval. We extend the design into 256-channel hardware and analyze the speed .using the measured data from the 64-channel hardware. Since our design exploits full parallel processing, Assembly level coding, and NOP(No Operation) instruction for timing control, the design provides expandability and lowest system timing margin. Our result concludes that the data collection with 256-channel analog input signals can be done in 201.5us time-interval which is much shorter than the required 1 mili-second period.

• Progress in Superconductivity
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• v.9 no.1
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• pp.45-49
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• 2007

We have investigated the optimum combination of the environmental noise condition and type of SQUID pickup coil in order to obtain maximum signal-to-noise ratio (SNR). The measurement probe consists of 1st order gradiometer with pickup coils of 100 mm, 70 mm, and 50 mm baseline length, a 2nd order gradiometer with 50 mm baseline, and a magnetometer. The pickup coils are fabricated by winding Nb wire on a bobbin with 200 mm diameter. Noise and heart signal of a healthy male were measured by various SQUID sensors with different types of pickup coils in various magnetically shielded rooms (MSR), and compared to each other. The shielding factors were found to be 43 dB, 35 dB and 25 dB at 0.1 Hz for MSR-AS, MSR-BS, MSR-CS, respectively. White noises were $3.5\;fT/Hz^{1/2}$, $4.5\;fT/Hz^{1/2}$ and $3\;fT/Hz^{1/2}$ for the 1st order gradiometers, the 2nd order gradiometers, and magnetometer for all MSRs. SNR of the magnetometer was up to 56 dB in MSR-AS, while the 1st order axial gradiometer with 70 mm baseline length was up to 54 dB in MSR-BS. The 2nd order axial gradiometer with 50 mm baseline length of pickup coil was found to be up to 40 dB in MSR-CS.

• Progress in Superconductivity
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• v.6 no.1
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• pp.56-63
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• 2004

We consider design factors for a SQUID sensor array to construct a 52-channel magnetocardiogram (MCG) system that can be used to measure tangential components of the cardiac magnetic fields. Nowadays, full-size multichannel MCG systems, which cover the whole signal area of a heart, are developed to improve the clinical analysis with high accuracy and to provide patients with comfort in the course of measurement. To design the full-size MCG system, we have to make a compromise between cost and performance. The cost is involved with the number of sensors, the number of the electronics, the size of a cooling dewar, the consumption of refrigerants for maintenance, and etc. The performance is the capability of covering the whole heart volume at once and of localizing current sources with a small error. In this study, we design the cost-effective arrangement of sensors for MCG by considering an adequate sensor interval and the confidence region of a tolerable localization error, which covers the heart. In order to fit the detector array on the cylindrical dewar economically, we removed the detectors that were located at the corners of the array square. Through simulations using the confidence region method, we verified that our design of the detector array was good enough to obtain whole information from the heart at a time. A result of the simulation also suggested that tangential-component MCG measurement could localize deeper current dipoles than normal-component MCG measurement with the same confidence volume; therefore, we conclude that measurement of the tangential component is more suitable to an MCG system than measurement of the normal component.

• Proceedings of the Polymer Society of Korea Conference
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• 2006.10a
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• pp.23-24
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• 2006

Magnetic and magneto-optical properties of regioregular (>99%) poly(3-dodecylthiopenes are investigated. Faraday rotation of spin-coated films show extremely large Verdet constants, falling strongly with decreasing regioregularity. EPR spectroscopy at room temperature shows the presence of about 1 spin/190 monomers, indicative of delocalisation beyond a single polymer chain. SQUID measurements on the polymer give an effective magnetic moment of about 48900 mB, corrsponding to a S-value of 25.000. The Weiss-constant is 1.33 K indicating ferromagnetic coupling. Our experimental results show that organic polymer magnets can be prepared. Large MO effects allow the use of these materials in all-organic MO-sensors and devices.

• Korean Journal of Materials Research
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• v.8 no.3
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• pp.263-267
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• 1998

In this study, we have fabricated in-situ multilayer $YBa_2Cu_3O_{7-\delta}$/$SrTiO_{3}$/$YBa_2Cu_3O_{7-\delta}$ ramp edge type junctions by using a metal mask and pulsed laser deposition method and studied the junction properties. The junctions showed RSJ-like I-V characteristics. The normal state junction resistance R, of $18 \omega$ was nearly constant with temperature. The dc-SQUID sensors fabricated with the junctions show a sensitivity that transfer function dV/$d\Phi$)~$22\mu$V/$\Phi_{0}$, indicating that the in-situ ramp edge type junction is potentially useful for sensor application.