Shield Room Research Articles

Optimal Design of Low-Noise Induction Magnetometer in 1 mHz–10 kHz Utilizing Paralleled Dual-JFET Differential Pre-Amplifier

The optimal design of the induction magnetometer in the frequency band from 1 mHz to 10 kHz was analytically and experimentally investigated to achieve a suitable sensor configuration under a given noise equivalent magnetic induction (NEMI) and volume limitation. The transducer model is first analyzed, and the parameters $ {R}$ , $ {L}$ , $ {C}$ , and $\mu _{\rm {app}}$ are calculated. The equivalent input voltage noise that utilizes an n-paralleled dual- Junction Field-Effect Transistor (JFET) differential pre-amplifier, was decreased by $\surd \text{n}$ times, and the equivalent input current noise was increased by $\surd \text{n}$ times. The noise calculation formulas are derived based on the mathematical principle of the flux-feedback induction magnetometer, and the NEMI was immediately calculated. A set of sensor configurations, which reached the given NEMI, were achieved by solving the NEMI equation. The optimal sensor configuration was obtained, considering the smallest coil outer diameter limitation. To verify the theoretical analysis, the optimal induction magnetometer was manufactured, and its NEMI was measured in an electromagnetic shielding room. The experimental results show good agreement with the theoretical analysis. Furthermore, the optimal induction magnetometer had a smaller volume with a similar NEMI level compared with the well-known sensor MFS-06.

Eddy current-shielded x-space relaxometer for sensitive magnetic nanoparticle characterization.

The development of magnetic particle imaging (MPI) has created a need for optimized magnetic nanoparticles. Magnetic particle relaxometry is an excellent tool for characterizing potential tracers for MPI. In this paper, we describe the design and construction of a high-throughput tabletop relaxometer that is able to make sensitive measurements of MPI tracers without the need for a dedicated shield room.

An Optimized Air-Core Coil Sensor with a Magnetic Flux Compensation Structure Suitable to the Helicopter TEM System.

The air-core coil sensor (ACS) is widely used as a transducer to measure the variation in magnetic fields of a helicopter transient electromagnetic (TEM) system. A high periodic emitting current induces the magnetic field signal of the underground medium. However, such current also generates a high primary field signal that can affect the received signal of the ACS and even damage the receiver. To increase the dynamic range of the received signal and to protect the receiver when emitting current rises/falls, the combination of ACS with magnetic flux compensation structure (bucking coil) is necessary. Moreover, the optimized ACS, which is composed of an air-core coil and a differential pre-amplifier circuit, must be investigated to meet the requirements of the helicopter TEM system suited to rapid surveying for shallow buried metal mine in rough topography. Accordingly, two ACSs are fabricated in this study, and their performance is verified and compared inside a magnetic shielding room. Using the designed ACSs, field experiments are conducted in Baoqing County. The field experimental data show that the primary field response can be compensated when the bucking coil is placed at an appropriate point in the range of allowed shift distance beyond the center of the transmitting coil and that the damage to the receiver induced by the over-statured signal can be solved. In conclusion, a more suitable ACS is adopted and is shown to have better performance, with a mass of 2.5 kg, resultant effective area of 11.6 m2 (i.e., diameter of 0.496 m), 3 dB bandwidth of 66 kHz, signal-to-noise ratio of 4 (i.e., varying magnetic field strength of 0.2 nT/s), and normalized equivalent input noise of 3.62 nV/m2.

Cross‐connection abatement in dense loosely coupled wireless charging pad environments

In a dense environment of loosely-coupled wireless charging pads to which out-of-band signalling is applied, cross-connection errors occur according to the wireless communication distance of out-of-band signalling. A cross-connect abatement technique using received-signal-strength-indicator measurement is proposed to prevent this problem and to provide stable wireless charging. To evaluate the performance of the proposed technique, two compact wireless charger environments are created in an RF shield room. The experimental results indicate that the wireless charging system using the proposed technology provides wireless charging services without cross-connection errors.

Electroencephalographic studies of eclampsia and pre-eclampsia.

To investigate eclampsia and pre-eclampsia electroencephalograms (EEGs) and related animal experiments, and to publish a Japanese article in English. A two channel EEG system constructed with a self-made vacuum tube amplifier, optical recorder, signal generator, a magic-eye signal monitor and a shield room were prepared by the author. EEGs were recorded in five admitted eclamptic and 35 pre-eclamptic cases before, during and after convulsion until clinical recovery. The hypothalami of female rabbits were stimulated with Kurotsu's electrode, and blood pressure and urinary proteins were studied before and after stimulation. The rabbits cortical and hypothalamic EEGs were studied. Frontal and occipital EEG waves synchronized immediately before and during eclamptic convulsions and during coma. Large δ waves were characteristic during the coma after convulsions. Moderately slow waves were recorded in cases of pre-eclampsia. In animal experiments, hypertension and proteinuria appeared in cases of hypothalamic sympathetic zone stimulation, while there was no change in parasympathetic stimulation. Eclamptic convulsion is evoked by synchronization of the whole cortex controlled by a heavily excited hypothalamus. Pregnancy hypertension and proteinuria is caused by the excited sympathetic center of the hypothalamus.

Flexible Microwave Antenna Applicator for Chemo-Thermotherapy of the Breast

In this letter, we propose a flexible microwave antenna applicator to induce mild hyperthermia that can be used in conjunction with chemotherapy. The antennas used were designed and tested using in vitro gels that mimic the electrical properties of human breast skin, fat, fibroglandular, and muscle tissues. Experiments show that the applicator can provide up to a 3 $\,\,^{\circ} {\hbox {C}}$ temperature increase within the breast to successfully achieve mild hyperthermia. The results obtained in this letter suggest that a cost-effective local hyperthermia treatment technology that can be widely used at local clinical cancer treatment centers is plausible without using expensive applicators and electromagnetic shielding rooms.

Assessment of uncertainties in the lung activity measurement of low-energy photon emitters using Monte Carlo simulation of ICRP male thorax voxel phantom.

Assessment of intake due to long-lived actinides by inhalation pathway is carried out by lung monitoring of the radiation workers inside totally shielded steel room using sensitive detection systems such as Phoswich and an array of HPGe detectors. In this paper, uncertainties in the lung activity estimation due to positional errors, chest wall thickness (CWT) and detector background variation are evaluated. First, calibration factors (CFs) of Phoswich and an array of three HPGe detectors are estimated by incorporating ICRP male thorax voxel phantom and detectors in Monte Carlo code 'FLUKA'. CFs are estimated for the uniform source distribution in lungs of the phantom for various photon energies. The variation in the CFs for positional errors of ±0.5, 1 and 1.5 cm in horizontal and vertical direction along the chest are studied. The positional errors are also evaluated by resizing the voxel phantom. Combined uncertainties are estimated at different energies using the uncertainties due to CWT, detector positioning, detector background variation of an uncontaminated adult person and counting statistics in the form of scattering factors (SFs). SFs are found to decrease with increase in energy. With HPGe array, highest SF of 1.84 is found at 18 keV. It reduces to 1.36 at 238 keV.

Development of high-sensitivity neutron detectors and measurements at the TPS LINAC

TPS LINAC is essentially concatenated by three consecutive sections of linear accelerators with a nominal output of 2.25 W (150 MeV, 5 nC, 3 Hz) electron beam. A 15 m long transfer line used to guide accelerated electrons from the LINAC outlet to the beam dump. For ensuring radiation safety of personnel around the area, gamma-ray and neutron dose rates outside the LINAC room were repeatedly measured and reviewed during the commissioning. If all the accelerated electrons are perfectly dumped as we wish, radiation dose rates outside the shielding should be as low as comparable to the natural background level. To be able to clearly identify radiation changes above background levels and perform reliable dose rate measurements, high-sensitivity radiation detectors are necessary. This paper presents the design and characteristics of these detectors and a data analysis of the measured results taken during a full-power LINAC operation. NSRRC is now constructing its second light source facility called Taiwan Photon Source (TPS) to meet the increasing demand for brighter synchrotron X-ray source. Focusing on a low-emittance design, the TPS will become one of the brightest synchrotron light sources in the world. The accelerator system consists of a 3.0-GeV electron storage ring with a circumference of 518.4 m, a concentric booster synchrotron with a circumference of 496.8 m, and a pre-injector of 150-MeV electron LINAC. Due to some delay of the TPS civil construction, NSRRC has built a simple rectangular shielding room made of 1 m thick concrete for the assembly and acceptance test of the outsourcing LINAC.

Comparison Between PD Inception Voltage and BD Voltage of PPLP in $\hbox{LN}_{2}$ Considering HTS Cable Insulation

With the rapid development of world economics, demand for electricity in metropolitan areas has increased dramatically. The high-temperature superconductivity (HTS) cable is one of the most promising technologies for solving the bottleneck of the transmission system. However, power system planners have not yet considered the HTS cable as a mature technology due to its weak insulation characteristics with respect to those of conventional power cables. The electrical insulation design is one of the major issues for HTS cable. It is evident that the insulation in the dc cable should be investigated further at this time. For the insulation design of the HTS cable, it is necessary to investigate the breakdown (BD) characteristics and the partial discharge (PD) inception voltage of the liquid nitrogen (LN <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> )/polypropylene laminated paper (PPLP) composite insulation system. In this paper, BD voltage and PD inception voltage of PPLP immersed in LN <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> was compared under ac and dc stresses. Various kinds of PPLP specimens considering the different layers and the butt gaps were prepared. The PD inception voltage was measured in a shield room according to IEC 60270. Consequently, it was investigated that characteristics of the PD inception voltage and the BD voltage was rather different when ac and dc voltages were respectively applied in LN <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> , and these results could be used for the insulation design of ac and dc HTS cables.

Wideband Shield Door With a Magnetic Absorber

It is necessary to secure a high shielding performance in a wide frequency range for a shield room to defend electrical equipment from high-power electromagnetic (HPEM) threat environments. We proposed a novel shield door with gaskets and magnetic absorbers. The magnetic losses of the magnetic absorbers realize the large shield effectiveness without impairing the door operability. The structures of magnetic absorbers are investigated through finite-difference time-domain (FDTD) analysis and experiments. We found that the multi-layered magnetic absorbers increase the shield effectiveness by 15 dB over a wide frequency range. Therefore, it is found that using the magnetic absorbers, high shielding performance can be achieved without impairing the door operability, which can provide an effective protection from the HPEM environments.

Characteristic Analysis of Directly Coupled HTS dc-SQUID Magnetometer With Superconducting Film Magnetic-Shield Considering Josephson-Junction Resistance

A high temperature superconducting quantum interface device (HTS SQUID) is an extremely sensitive magnetic sensor. The HTS SQUID is required to have a high robustness with respect to magnetic noise for stable operation outside a magnetic shielding room. In order to achieve the high robustness of HTS SQUID, use of a magnetic shield with a superconducting film has been proposed, and its effectiveness has been confirmed in the experiments. In this paper, an electromagnetic field simulation was performed using the 3-D edge finite element method to confirm the effectiveness of the superconducting film magnetic-shield. Since both the SQUID magnetometer and the superconducting film magnetic-shield are made of HTS, it is required to consider the HTS characteristics in the electromagnetic field simulation. Additionally, the SQUID magnetometer has Josephson junction. In this paper, the property of the Josephson junction is also considered. The simulation accuracy depending on the type of the finite element mesh is also investigated.

スリット状接続部により構成された電磁シールド室性能予測システムの開発

In this paper, a novel simulation predicting the electromagnetic wave distribution transmitted through slit-shaped joints was developed. The simulation estimates the radiated wave from the secondary source on the slits as the electromagnetic wave is transmitted through the joints. The experiment was carried out by modeling the electromagnetic shielding room with the joints. The good agreement between the predicted result and the experimental result was obtained. In addition, the electromagnetic environment inside the typical shielding room was predicted. As a result, it was shown that the simulation was able to predict a reasonable electromagnetic wave distribution transmitted through the joints.

Magnetic shield effect simulation of superconducting film shield covering directly coupled HTS dc-SQUID magnetometer

An HTS SQUID is a high sensitive magnetic sensor. In recent years, the HTS SQUID is widely used in various applications. In some applications, high robustness with respect to magnetic noise is required to realize stable operation at outside of a magnetic shielding room. The target of this paper is a directly coupled HTS dc-SQUID magnetometer. To enhance the robustness of the SQUID magnetometer, use of a superconducting thin film shield has been proposed. The magnetic field directly penetrating the SQUID ring causes the change of the critical current of Josephson junction, and then the SQUID magnetometer transitions into inoperative state. In order to confirm the magnetic shield effect of the superconducting film shield, electromagnetic field simulation with 3D edge finite element method was performed. To simulate the high temperature superconductor, E–J characteristics and c-axis anisotropy are considered. To evaluate the effect of the superconducting film shield, an external magnetic field which is supposed to be a magnetic noise is applied. From the simulation results, the time transition of the magnetic flux penetrating the SQUID ring is investigated and the effect of the superconducting film shield is confirmed. The amplitude of the magnetic flux penetrating the SQUID ring can be reduced to about one-sixth since the superconducting film shield prevents the magnetic noise from directly penetrating the SQUID ring.

A simple 5-DoF MR-compatible motion signal measurement system

The purpose of this study was to develop a simple motion measurement system with magnetic resonance (MR) compatibility and safety. The motion measurement system proposed here can measure 5-DoF motion signals without deteriorating the MR images, and it has no effect on the intense and homogeneous main magnetic field, the temporal-gradient magnetic field (which varies rapidly with time), the transceiver radio frequency (RF) coil, and the RF pulse during MR data acquisition. A three-axis accelerometer and a two-axis gyroscope were used to measure 5-DoF motion signals, and Velcro was used to attach a sensor module to a finger or wrist. To minimize the interference between the MR imaging system and the motion measurement system, nonmagnetic materials were used for all electric circuit components in an MR shield room. To remove the effect of RF pulse, an amplifier, modulation circuit, and power supply were located in a shielded case, which was made of copper and aluminum. The motion signal was modulated to an optic signal using pulse width modulation, and the modulated optic signal was transmitted outside the MR shield room using a high-intensity light-emitting diode and an optic cable. The motion signal was recorded on a PC by demodulating the transmitted optic signal into an electric signal. Various kinematic variables, such as angle, acceleration, velocity, and jerk, can be measured or calculated by using the motion measurement system developed here. This system also enables motion tracking by extracting the position information from the motion signals. It was verified that MR images and motion signals could reliably be measured simultaneously.

E-1-1 体内埋込型人工心臓のEMC : 生体から導線が伸びている場合の生体への電磁的影響の検討(E-1 生体治療・計測,口頭発表:生体治療・医療,バイオ操作・検査)

This paper addresses EMC of an implantable artificial heart connected by a conducting wire (drive line) and influence of the emitted electromagnetic noise on the human body. Conducting wire length and human height may cause electrical resonance. At such times, the current through the conducting wire and the human body could increase conspicuously. We determined the current passing through the human body attached the conducting wire by both FDTD electromagnetic simulation and experimental observation. A cylinder model was used to imitate the human trunk. It was placed at the center of a shield room and subjected to electromagnetic plane waves with wavelengths ranginge from 80 MHz to 1 GHz. Experimental results show that the current through the human body was generally in the range of 0.25-2.3 mA (100-400MHz) with three remarkable current peaks. Simulation results show higher average current and lower peak frequency compared to the experimental results.

직렬 아크 및 코로나 방전의 주파수 스펙트럼 분석

In this paper, we analyzed the frequency spectrum of radiated electromagnetic pulses generated by series arc- and corona- discharges as a basic study to develop an on-line diagnostic technique for power facilities installed inside closed-switchboards. To simulate series arc and corona discharges, five types of electrode system which consists of needle and plane electrodes were arranged. The experiment was carried out in an electromagnetic shielding room, and the measurement system consists of an ultra log antenna and an EMI receiver. From the experimental results, the frequency spectrum exists in ranges from 30 MHz to 2 GHz for a series arc discharge and 30 MHz to 1.2 GHz depending on defects for a corona discharge. The peak frequency of the series arc- and corona- discharges were 100 MHz to 160 MHz and 40 MHz to 80 MHz, respectively.

Three-Dimensional Magnetic Field Numerical Calculation by Equivalent $B\hbox{–}H$ Method for Magnetic Field Mitigation

The 3-D magnetic field numerical analysis of a full-scale magnetic shielding room is advantageously performed by using the equivalent B-H method. In the proposed numerical method, the magnetic anisotropy and the nonlinearity due to material magnetic saturation are taken into account, by directly introducing the magnetization characteristics of the considered materials. An equivalent element, which substitutes the plural finite elements having different material properties for a homogeneous one, is introduced to reduce the number of unknowns. When the equivalent B-H method is applied to a full-scale magnetic shielding room (length 5.8 m, width 3.3 m, height 3.3 m), the measured leakage magnetic flux density distribution is found to be in good agreement with the calculated one, proving the reliability of the proposed approach, which can be adopted in many large-scale electromagnetic field problems.

Development of a low noise MREIT current source

In MREIT conductivity imaging experiments of animal and human subjects, we should minimize the noise level in measured magnetic flux density data induced by injection currents with low amplitude. Since noise and artifact from an MREIT current source directly affect the quality of the data, a low-noise current source is desirable. In order to be compatible with various MREIT pulse sequences, it should be also programmable. We have developed a new MREIT current source, which is controlled by a PC program for flexibility. We designed it in such a way that it is located inside the shield room of an MRI system. To minimize noise and artifact, we adopted an optical link for the connection to the PC outside the shield room. The enclosure of the new current source provides a magnetic as well as electric shielding to prevent high frequency switching noise of the current source from interfering with the scanner. It is powered by a rechargeable battery so that the entire current source is isolated from the ground. Equipped with automatic lead switching capability, it simplifies and automates MREIT imaging experiments. Our experimental results show that its performance is superior to the previous version, which is located outside the shield room.

Study of encapsulated T170m sources for their potential use in brachytherapy

High dose-rate (HDR) brachytherapy is currently performed with 192Ir sources, and 60Co has returned recently into clinical use as a source for this kind of cancer treatment. Both radionuclides have mean photon energies high enough to require specific shielded treatment rooms. In recent years, 169Yb has been explored as an alternative for HDR-brachytherapy implants. Although it has mean photon energy lower than 192Ir, it still requires extensive shielding to deliver treatment. An alternative radionuclide for brachytherapy is 170Tm (Z=69) because it has three physical properties adequate for clinical practice: (a) 128.6 day half-life, (b) high specific activity, and (c) mean photon energy of 66.39 keV. The main drawback of this radionuclide is the low photon yield (six photons per 100 electrons emitted). The purpose of this work is to study the dosimetric characteristics of this radionuclide for potential use in HDR-brachytherapy. The authors have assumed a theoretical 170Tm cylindrical source encapsulated with stainless steel and typical dimensions taken from the currently available HDR 192Ir brachytherapy sources. The dose-rate distribution was calculated for this source using the GEANT4 Monte Carlo (MC) code considering both photon and electron 170Tm spectra. The AAPM TG-43 U1 brachytherapy dosimetry parameters were derived. To study general properties of 170Tm encapsulated sources, spherical sources encapsulated with stainless steel and platinum were also studied. Moreover, the influence of small variations in the active core and capsule dimensions on the dosimetric characteristics was assessed. Treatment times required for a 170Tm source were compared to those for 192Ir and 169Yb for the same contained activity. Due to the energetic beta spectrum and the large electron yield, the bremsstrahlung contribution to the dose was of the same order of magnitude as from the emitted gammas and characteristic x rays. Moreover, the electron spectrum contribution to the dose was significant up to 4 mm from the source center compared to the photon contribution. The dose-rate constant lamda of the cylindrical source was 1.23 cGy h(-1) U(-1). The behavior of the radial dose function showed promise for applications in brachytherapy. Due to the electron spectrum, the anisotropy was large for r <6 mm. Variations in manufacturing tolerances did not significantly influence the final dosimetry data when expressed in cGy h(-1) U(-1). For typical capsule dimensions, maximum reference dose rates of about 0.2, 10, and 2 Gy min(-1) would then be obtained for 170Tm, 192Ir, and 169Yb, respectively, resulting in treatment times greater than those for HDR 192Ir brachytherapy. The dosimetric characteristics of source designs exploiting the low photon energy of 170Tm were studied for potential application in HDR-brachytherapy. Dose-rate distributions were obtained for cylindrical and simplified spherical 170Tm source designs (stainless steel and platinum capsule materials) using MC calculations. Despite the high activity of 170Tm, calculated treatment times were much longer than for 192Ir.

INVESTIGATION OF ELECTROMAGNETIC SHIELDING ROOMS WITH METAL CABINET AND APERTURE

In this paper, a fast and e-cient method has been proposed to analyze the electromagnetic shielding rooms with electrical large sizes and arbitrary shapes. The ray-tracing method is used to predict the Shielding Efiectiveness (SE) of the electromagnetic shielding rooms. The proposed method is based on speeding up the ray tracing algorithm. The performance of the proposed method is verifled by a comprehensive example. The efiect of additional metal cabinet in the shielding efiectiveness of shielding room has been investigated. Also the position of it has been found optimally to produce a \best performance for the shielding room.