A simple magnetic shielding system for residual magnetization measurements of a motor to be used in satellites is studied. The system consists of same-sized square coils, namely three sets of Simple Cubic-3 coil system. Because the system can generate a uniform magnetic field, we investigate the uniformity of the site. With a first-order gradient coil, the geomagnetic field can be reduced to less than 100 nT in a relatively large area. Inside of the system, the residual magnetization measurements of a step motor are demonstrated. An approach to reduce the magnetic field leakage from the step motor is also presented.Keywords： Geomagnetic field canceling, step motor, magnetic moment, square coil system 1．Instructions:Satellites are supposed to be able to control their positioning and stability in space. Therefore, the equipment installed in the satellite should be measured for residual magnetization during prelaunch [1]. In order to measure residual magnetization, the Japan aerospace exploration agency (JAXA), for example, has a ferromagnetic shield with triple spherical permalloy shells [2]. Although the shielding factor is as large as 60 dB for dc fields, typical magnetic fields inside a device are 20~40 nT. The usable area is limited because of the magnetization of the inner shell. Instead of a heavy ferromagnetic shielding system, the space research facilities are considering a geomagnetic field canceling system that uses the magnetic field generation coil [3]. A geomagnetic field canceling system requires uniform magnetic field generation over a considerable volume. From the point of view of practical advantages construction and usefulness, several kinds of square coil system have already been proposed. While the number of square coils allows the axial field to have good uniformity in a large volume, the size of the entrance area is limited by coil crossing for the three orthogonal coils sets. In order to drive one power supply in one direction, the ratio of the current in the coils should be an integer, and it is relatively tolerant of small design imperfections. For the reasons mentioned above, we have proposed a Simple Cubic-3 (SC3) coil system [4]. It consists of three square coils, with same coils' distance and a simple integer ampere-turn ratio.This paper presents the results of residual magnetization measurements of a motor to be used in satellites with our proposed geomagnetic field canceling system. We chose a suitable site through the measurements of geomagnetic fields at several locations, and constructed a system with three sets of SC3. Combined with a gradient field generation coil system (G2), the geomagnetic field can be reduced to less than 100 nT in a relatively large area. Inside of the system, we demonstrate the residual magnetization measurements of a step motor. An approach to reduce residual magnetization is also presented. Geomagnetic field canceling system: Geomagnetic field measurementIn order to choose a suitable site for the system, we investigated the uniformity of a magnet...

Magnetic field is one of the essential physical parameters to study the space physics and evolution of the solar system. There are several methods to measure the magnetic field in the space by spacecraft and rockets. Fluxgate magnetometer has been most generally used out of them because it measures the vector field accurately and does not need much weight and power budgets. When we try more difficult missions such as multi-satellite observation, landing on the celestial body and exploration in the area of severe environment, we have to modify the magnetometer or develop new techniques to make the instrument adequate for those projects. For example, we developed a 20-bit delta-sigma analogue-to-digital converter for MGF-I on the BepiColombo MMO satellite, to achieve the wide-range (±2000 nT) measurement with good resolution in the high radiation environment. For further future missions, we have examined the digitalizing of the circuit, which has much potential to drastically reduce the instrument weight, power consumption and performance dependence on the temperature. Key words: Magnetometer, magnetic field, space science. Magnet Fields in the SpaceThe magnetic fields in the space are classified into three types according to the generation sources. One is the field having the source inside or on the surface of celestial body, e.g., the Sun, planets and satellites in the solar system. In the cases of the Earth, Mercury and outer planets than Mars, magnetic dynamo is working in the liquid core, and the magnetic moment is placed at the center of the planets. The area where the magnetic field is effective spreads in the range of the planetary scale and is called "magnetosphere". Meanwhile the Moon and Mars do not have significant magnetic moment. There are weakly "magnetized" parts on the surface.The second category is the magnetic field caused by the electric current carried by plasma. For example, in the Earth's magnetosphere, magnetic field lines coming from the Antarctic region or going to the Arctic region are extended in the night direction. This configuration is represented by the summation of the magnetic fields generated by the Earth's intrinsic moment and the field along the SunEarth direction. The latter field is maintained by the electric current flowing from dawn to dusk in the plasmasheet.The third is the inductive field. One of the Maxwell's equation, rotE = −(∂B)/(∂t), represents that the rotation of the electric field is accompanied by the temporal change of the magnetic field.The time scale of the magnetic fields having the source inside or on the surface of the planets is substantially long, although they are not perfectly constant. The polarity of the earth magnetic dipole is known to have changed on the time scale of million years. The magnetic fields generated by the Copyright c TERRAPUB, 2013. electrical currents vary on the relatively short time scale, although the frequency and amplitude depend on the source phenomena. The time and spatial scales of the inductive fields, those are often ob...

This paper presents a novel approach for the design of square coil system, through considerations of a conventional square coil system. This simple approach allows us to design a coil system which contains a greater number of coils. From this design method, we introduce a new structure system of same-sized square coils, Simple-Box-9. The constant coil spacing is a fourth-part of the side length of the coil, and the number of windings is 2/1/1/1/1/1/1/1/2. From numerical calculations and experiments, it is shown that Simple-Box-9 can achieve the best uniformity compared with conventional square coil systems.

In this work, we propose a data embedding scheme in MPEG-1/Audio Layer II compressed domain. Data embedding is conducted every AAU by using side information (location of sub-band allocated audio signal) as a data carrier. In general, non-zero signals concentrates in low and middle frequency bands. Therefore we utilize sub-bands that are not allocated audio signal in high frequency bands to embed information. The proposed scheme can increase payload while achieving rewritable (reversible) data embedding by choosing appropriate parameter. We verify the basic performance of our scheme through computer simulation by using some voice and music signals.1. INTRODUCTION Recently, data hiding techniques [1]- [3] have been widely investigated for various media such as still images, moving pictures, documents, audio, 3D polygonal data, and so on. The information embedded can be used for various purposes such as copyright protection, forgery detection, authentication, copy control, annotation, indexing, and so on. In this work, we focus on audio data hiding. Although many audio data hiding methods were proposed in a recent decade [4]- [7], there are few proposals for annotation and indexing purpose for audio signals. Our motivation here is to propose a method to embed information in MPEG-1/Audio Layer II compressed domain for streaming applications together with MPEG video. In this work, we design embedding method to gain payload as much as possible in rewritable (reversible) form for annotation or indexing purpose [8], while keeping complete compatibility to general audio decoder. In order to accomplish this goal, we pay attention to a statistical property of audio signals in AAU (Audio Access Unit: 1152 samples) that non-zero signals concentrates in low and middle frequency bands and the case allocated no audio signal increases in high frequency bands. We utilize sub-bands that are not allocated audio signal in high frequency bands to embed information. Consequently, the proposed scheme can increase payload (amount of embedded information) while achieving rewritable (reversible) data embedding by choosing appropriate parameter. We verify the basic performance of our scheme through computer simulation by using some voice and music signals. MPEG-1/AUDIOMPEG-1/Audio contains three kinds of coding algorithm called Layer I, Layer II, and Layer III. Higher layer algorithm achieves high audio quality and high compression ratio, but requires larger hardware configuration. In this work, we focus on Layer II algorithm, which is often used in MPEG-2 encoders for PC, HDD recorder, and DVD. Fig.1 shows the block diagram of the coding architecture of MPEG-1/Audio Layer II. The input PCM signals linearly quantized (16 bits) are decomposed into 32 pieces of frequency component in sub-band filter bank, which is implemented by PFB (Polyphase Filter Bank) with 512 taps. A scale factor is calculated for each sub-band to normalize the signals obtained. The calculation of scale factor is basically conducted every 384 samples (12 sample...