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The standard of Japan Electronics and Information Technology Industries Association EM-4502, in which the shielding factor (SFo) of magnetically shielded rooms (MSRs) for the uniform magnetic field can be estimated using coils within 10% error for the extremely low-frequency region of

To shield magnetic noise, magnetically shielded rooms (MSR) are used for biomagnetic measurements, etc. To evaluate the shielding factor SF (SF=B n / B s , B n and B s are the flux densities at the center of the room without and with MSR, respectively), the magnetic noise is applied by coils. However, SF depends on the size and position of the coils, so the standard of JEITA (Japan Electronics and Information Technology Industries Association) EM-4502, in which the shielding factor (SF o ) of MSR for the uniform magnetic field in the extremely low-frequency region of less than 1 Hz without eddy current effect is estimated using coils within 10% error [1-2], has been already published [3]. Currently, a standard method for the low-frequency region, e.g. 50 Hz, with eddy current effect is being discussed. In a previous work [4], it was shown that the coil should be placed in front of the door of MSR and a much larger estimation error than 10% should be permitted for practical use in the standard to estimate SF o for the low-frequency region.

A multi-turn absolute encoder comprising a shaft angle encoder for measuring the turning angle of a rotating shaft, and a turn detector for detecting the number of turns of the rotating shaft, wherein the turn detector uses a magnetic bubble element for sequentially transferring magnetic bubbles in a pattern in accordance with a magnetic field generated by a permanent magnet turned by the shaft, and a detector to detect the number of turns of the shaft from the positions of the magnetic bubbles which are transferred in the pattern.

We investigated effective flux-to-voltage transfer function and flux noise characteristic corresponding to positive feedback parameter (beta) a on Ketchen-type dc-SQUID with additional positive feedback (APF) by comparing the experimental results with calculated results. The measurement and calculated results for the effective flux-to-voltage transfer function and white flux noise characteristic are in good agreement. We quantitatively obtained the white flux noise characteristic of dc-SQUID (dc-Superconducting Quantum Interference Device) with APF. As (beta) a approaches unity, the flux noise caused by preamplifier voltage noise is decreased and the flux noise caused by the intrinsic flux noise of dc-SQUID with APF is increased. We find that an optimum value of dc-SQUID with APF exists, determined by the trade-off between the flux noise caused by preamplifier voltage-noise and the intrinsic flux noise of dc- SQUID with APF.© (1994) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

We have constructed a multiplexed 2-channel, 2-stage superconducting quantum interference device (SQUID) amplifier using double-washer SQUIDs and a 35-SQUID series array. The biasing current of the first-stage SQUIDs is switched by a complimentary metal oxide semiconductor (CMOS) analog multiplexer at liquid helium temperature, and an on-stage SQUID transfers the signal to the second-stage SQUID. Each SQUID has an additional negative feedback circuit to enlarge the linear input region and decrease distortion. Maximum input flux at the first-stage was 0.9Φ opp and the total harmonic distortion of the overall two-stage SQUID was 1% for a sinusoidal input flux of 0.1Φ opp. The voltage swings of the two channels were 1.1 and 1.3 mV.

A 35-Series Superconducting Quantum Interference Device Array has been developed for a magnetometer with a high dynamic range. The coherence of each SQUID was observed in a double-shielded tube made of cryoperm and lead; a maximum voltage swing of 2 mV and flux noise of 0.6 µΦ0/√ Hz were obtained. The nonuniform inductance of the SQUIDs in the array, which causes Φ–V curve modulation, is decreased by using dummy SQUIDs at each end of the array. A gradiometer for biomagnetic measurement was constructed using a 35-SQUID array and a 10×10-mm planar pick-up coil. A magnetic-field sensitivity of 5.4 fT/√ Hz, a maximum slew rate of 1.9 mT/s, and a maximum feedback amplitude of ±2.23 µ T were achieved by using a direct-coupled flux-locked-loop circuit. The dynamic range of the magnetometer input field was ±4.13×108 √ Hz.

Reducing the number of loops in a Drung-type superconducting quantum interference device (SQUID) from eight to four minimally reduces the voltage swing. A four-loop SQUID, called a clover-leaf SQUID (CLS), has been designed in order to reduce the area of the SQUID chip. The CLSs are fabricated by the Nb/Al/AlO x /Nb tunnel junction process. They occupy a 4.5-mm-square area on the substrate and have high field-to-flux sensitivity (S=0.63 nT/Φ0). Typical magnetic field resolution is 4.0 fT/Hz0.5 at the white-noise level. The measured biomagnetic fields of this SQUID confirm that its performance level is acceptable.

An asymmetric bias current injection method is developed to reduce bias-caused noise in Drung-type SQUID (superconducting quantum interference devices) without adding extra coils. A measuring scheme for ∂Φ/∂I b is tested, and it is demonstrated that the reduction is from 100 to 150 times that attained by the conventional SQUID biasing method. It is revealed that the direction of APF (additional positive feedback) coil winding is important in attaining this reduction.

Ionic channels in biological membranes are one of the elementary transport elements passing specific ions across the membranes. The objective of this investigation is to design a two-microelectrode-voltage clamp system which is able to detect ionic channel noise of the membrane current in the mammalian exocrine gland acinus, an electrical unit, consisting of about 100 acinar cells. Since two high-resistance intracellular microelectrodes are used, the coupling capacitance between two electrodes makes the operation of the measurement system unstable and places a severe restriction on the experiment. In our measurement system a simple low-pass filter is inserted in the feedback system of the membrane voltage. As a result, the system operation is stabilized via the compensation of the frequency characteristic of the feedback system. If the noise inherent to the measurement system is large enough to mask the ionic channel noise of the membrane current, the channel noise below the noise level of the system cannot be detected. Since the noise of the measurement system is found to be due mainly to microelectrodes, properties of the electrode noise are analyzed in the present work. From the results, the system noise is evaluated quantitatively and the detection limit of the ionic channel noise is determined. Furthermore, the voltage is clamped for the electrically equivalent circuit to the acinar surface membrane and the operation of the voltage clamp system and the system noise level are investigated experimentally.