• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2004.05a
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• pp.153-158
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• 2004

The coupling phenomenon between stress and magnetic induction, known as magnetostriction, has been successfully applied to generate and measure elastic waves. Most applications of this phenomenon thus far, however, are rather limited to cylindrical ferromagnetic waveguides. The main objective of this work is to develop a new patch-type, orientation-adjustable magnetostrictive transducer that is applicable for non-cylindrical, non-ferromagnetic waveguides. The existing patch-type transducer consisting of a ferromagnetic patch and a racetrack coil is useful to generate elastic waves only in one specific direction once the patch is bonded to a test specimen. However, the proposed transducer can transmit and receive elastic waves in any direction only with one patch at a given location. The proposed magnetostrictive transducer consists of a circular nickel patch, a figure-of-eight coil, and a couple of bias permanent magnets. Because of the unique configuration of the transducer, the propagating direction of the generated waves can be freely controlled since the set of bias magnets and the coil is not bonded to the magnetostrictive patch. In this work, the characteristics of the proposed transducer were investigated experimentally.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2006.05a
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• pp.1159-1164
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• 2006

Torsional vibration is an important vibration mode when shafts, cylinders and pipes are considered. However, the modal testing of torsional vibrations is not an easy job to carry out because of the lack of proper transducers. This work presents a new torsional vibration transducer based on the magnetostrictive principle and its application to torsional modal testing. The transducer is so designed as to generate/measure only torsional vibrations excluding other vibration modes such as longitudinal and bending vibrations. The transducer is composed of ferromagnetic patches bonded to a test structure, permanent magnets, and a solenoid. Though patches and magnets are bonded to a structure, torsional vibrations are generated and measured wirelessly by a solenoid encircling a test structure. The proposed transducer works even at considerably high frequencies, say, tens of kilohertz. Furthermore, the transducer can be manufactured at a low price. To check the performance of the proposed method, the torsional modal testing on a hollow aluminum shaft was conducted. The results, such as eigenfrequencies, obtained by the proposed transducer agreed favorably with theoretical results.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.16 no.8 s.113
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• pp.879-885
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• 2006

Torsional vibration is an important vibration mode when shafts, cylinders and pipes are considered. However, the modal testing of torsional vibrations is not an easy task to carry out because of the lack of proper transducers. This work presents a new torsional vibration transducer based on the magnetostrictive principle and its application to torsional modal testing. The transducer is so designed as to generate/measure only torsional vibrations excluding other vibration modes such as longitudinal and bending vibrations. The transducer is composed of ferromagnetic patches bonded to a test structure, permanent magnets, and a solenoid. Though patches and magnets are bonded to a structure, torsional vibrations are generated and measured wirelessly by a solenoid encircling a test structure. The proposed transducer works even at considerably high frequencies, say, tens of kilohertz. Furthermore, the transducer can be manufactured at a low price. To check the performance of the proposed method, the torsional modal testing on a hollow aluminum shaft was conducted. The results, such as eigenfrequencies, obtained by the proposed transducer agreed favorably with theoretical results.

• Korean Journal of Metals and Materials
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• v.49 no.1
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• pp.85-91
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• 2011

Alnico magnets can be used as magnetic bearings for the precise electric power measuring instruments such as watt-hour meters because they have high remanence ($B_r$), relatively high maximum energy product ($(BH)_{max}$), and excellent temperature stability. In this study, Alnico composite magnets were fabricated by appropriately mixing alnico alloy powders with epoxy resin and binder. The Alnico powders mixed with epoxy resin and a hardening agent with a mixing ratio of 96:4 were pressed and then cured to be a toroid-type ring magnet with an outer diameter (${\Phi}_{out}$) of 15 mm, an inner diameter (${\Phi}_{in}$) of 6.5 mm and a thickness (t) of 2.5 mm, respectively. The magnetic properties of the Alnico ring magnets were varied with the mixing ratio of Alnico powders that possess different average particle sizes. The Alnico ring magnet prepared by mixing 5 wt% of $50{\mu}m$ (small size) powder, 15~20 wt% of $150{\mu}m$ (medium size) powder, and 75~80 wt% of $300{\mu}m$ (large size) powder showed the best magnetic properties (remanent induction, coercive force, maximum energy product, and surface flux density). In addition, measurements of temperature and moisture characteristics for the Alnico ring magnets showed that the surface flux densities of the N and S poles decreased little and the repulsive distance between the magnets decreased as small as 0.05 mm after 10 days.

• Journal of Magnetics
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• v.4 no.2
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• pp.52-54
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• 1999

Injection molding is one of the methods to prepare dielectromagnets-permanent magnets made from hard magnetic powder (or from mixture of powders) bonded by dielectric materials. Magnetic properties of dielectromagnets are worse than those of sintered magnets made from the same hard magnetic powders, but this type of the permanent magnet has many advantages. One of them is simpler technology-easier in comparison to the technology of sintered magnets. The injection molded dielectromagnets do not need any final treatment. This technology permits to control magnetic, thermal and mechanical properties of dielectromagnets. The main chracteristics of dielectormagnets are magnetic properties, however mechanical properties have serious influence onto a range of their applications. The main factors shaping mechanical properties have serious influence onto a range of their applications. The main factors shaping mechanical properties of dielectromagnets are the kind and quantity of resin and the technology. The purpose of this investigateion was to find the correlation between infection conditions and the mechanical properties of dielectromagnets. Influence of two parameters of injection, temperature and pressure on mechanical and magnetic properties of dielectromagnets were not significantly changed. Increasing of pressure of injection also does not influence on mechanical properties of analysed samples, however increasing of temperature of injection significantly improved both compression and bending strength.

• Journal of the Korean Magnetics Society
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• v.5 no.5
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• pp.824-827
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• 1995

Dielectromagnets are permanent magnets made from resin-bonded hard magnetic powders. Magnetic properties of dielectromagnets depend on kind of used hard magnetic materials as chemical compound, shape, size of grain and applied technology. Comparison of advantages and disadvantages of dielectromagnets made from different kind of magnetic powders induced us to try to prepare dielectromagnets from mixture of hard magnetic powders, not only one of them. The purpose of investigation on this kind of dielectromagnets is to find formula to prepare permanent magnets with properties adequate to different kind of electrical motors requirements. As hard magnetic materials we used powders of ferrite, melt-spun ribbon Nd-Fe-B and Alnico. Papers present results of investigation on technology of this kind of dielectromagnets. It shows also influence of kind of mixture and used technology on magnetic properties of dielectromagnets.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 1994.11a
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• pp.65-66
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• 1994

This paper describes study on the preparation of ferrite powder for bonded mallets. The specimen which has the basic composition of SrO$.$nF$_2$O$_3$ with n=5.9 is in nonstoichiomatric region. Calcination is performed under N$_2$ atmosphere 1175$^{\circ}C$, 1200$^{\circ}C$, 1225$^{\circ}C$, 1250$^{\circ}C$ and 1275$^{\circ}C$ respectively. Then, Cooling is carried out in the furnace. In order to increase coecivity and obtain uniform grain size, we add to the specimen 0.7wt%CaCO$_3$, 0.3wt % SiO$_2$, 0.5wt%Na$_2$SiO$_3$ and 0.5wr% Al$_2$O$_3$. Also, in order to increase milling effect, carbon coating on sample particles is tried. As the result, single magnetic domain partic1e with Size of 1$\mu\textrm{m}$ in obtained and magnetic properties are improved.

• Proceedings of the Korean Powder Metallurgy Institute Conference
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• 2006.09b
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• pp.1286-1287
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• 2006

[ $Nd_2Fe_{14}B/{\alpha}-Fe$ ] nanocomposite powders with a nominal composition of $Nd_{12}Fe_{82}B_6$ were prepared by HDDR combined with mechanical milling. The microstructure was studied by Mossbauer spectrometry and TEM. The magnetic properties were investigated by VSM using bonded magnet samples. The results showed that the annealing temperature had significant influence on both the recombination kinetics and the grain size of the $Nd_2Fe_{14}B$ and ${\alpha}-Fe$ phases, and the bonded magnets presented the best magnetic properties when the nanocomposite powders were prepared by annealing at $760^{\circ}C$ for 30 min.

• Journal of Powder Materials
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• v.16 no.1
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• pp.1-8
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• 2009

• Journal of the Korean Magnetics Society
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• v.4 no.3
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• pp.219-225
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• 1994

The alignment of Sr-ferrite magnetic powders, which is usually related to the fluidity and the applied magnetic field, is investicated in the anisotropic Sr-ferrite / resin-bonded permanent magnets. The magnetic powder alignment is observed to increase with the applied magnetic field and the fluidity which is a function of molding temperature and powder packing ratio. The best magnetic powder alignment is achieved at the following conditions; Sr-ferrite packing ratio of 56vol%, apparent viscosity of about 3000 poise in $1000sec^{-1}$ shear rate, and applied magnetic field of about 5kOe. The degree of preferred orientation of the magnetic powders in the field direction, as determined by the dc hysterisis graphs, is 84~85% (0.84~0.85). This result is in agreement with the value of 0.85 obtained by the X-ray experiments in the $2{\theta}$ range of ${23~40}^0$. The best magnetic properties obtained are:2.2kG of remanent flux density, 2.2MGOe of maximum energy product.