Kan-ichi Kamiyoshi

Bio: Kan-ichi Kamiyoshi is an academic researcher. The author has contributed to research in topics: Dielectric & Ammonium sulfate. The author has an hindex of 5, co-authored 11 publications receiving 59 citations.

The dielectric constant of sandstones, 60 kHz to 4 MHz

Abstract: Complex impedance data were collected for eight sandstones at various levels of water saturation (Sw) in the frequency range of 5 Hz to 4 MHz. The measurements were made using a two‐electrode technique with platinum electrodes sputtered onto the flat faces of disk‐ shaped samples. Presentation of the data in the complex impedance plane shows clear separation of the response due to polarization at the sample‐electrode interface from the bulk sample response. Electrode polarization effects were limited to frequencies of less than 60 kHz, allowing us to study the dielectric constant κ′ of the sandstones in the frequency range of 60 kHz to 4 MHz. κ′ of all samples at all levels of saturation shows a clear power‐law dependence upon frequency. Comparing the data from the eight sandstones at Sw=0.36, the magnitude of the frequency dependence was found to be proportional to the surface area‐to‐volume ratio of the pore space of the sandstones. The surface area‐to‐volume ratio of the pore space of each sandstone wa...

Giant barocaloric effects at low pressure in ferrielectric ammonium sulphate

Abstract: Caloric effects are currently under intense study due to the prospect of environment-friendly cooling applications. Most of the research is centred on large magnetocaloric effects and large electrocaloric effects, but the former require large magnetic fields that are challenging to generate economically and the latter require large electric fields that can only be applied without breakdown in thin samples. Here we use small changes in hydrostatic pressure to drive giant inverse barocaloric effects near the ferrielectric phase transition in ammonium sulphate. We find barocaloric effects and strengths that exceed those previously observed near magnetostructural phase transitions in magnetic materials. Our findings should therefore inspire the discovery of giant barocaloric effects in a wide range of unexplored ferroelectric materials, ultimately leading to barocaloric cooling devices.

Dielectric Properties of and Conductivity in Ferrites

Abstract: The dielectric properties of ferrites are dependent upon their methods of preparation. Low resistivity ferrites in which the individual grains are separated by air gaps or are coated with films that have high resistivities behave as inhomogeneous dielectric materials. Such low resistivity grains covered by high resistivity films are formed upon cooling slightly reduced ceramic ferrites in an oxygen containing atmosphere. Apparent low-frequency dielectric constants as high as 105 are found as a consequence of this. Ferrites with dc resistivities of 109 ? cm or higher, in general, have dielectric losses which are low enough to meet the requirements of microwave applications. Resistivities of this order can be obtained in modified magnesium and nickel ferrites. The effects on conduction of varying composition and temperature are discussed in some detail.

Physical Properties of Ferrites

Abstract: Publisher Summary This chapter discusses the physical properties of ferrites. Ferrites are used in a number of applications—such as in coils of high quality and transformers in radio, television, and telecommunication engineering; in aerial rods; in accelerators for elementary particle; and in digital computers. The ferrites with the general formula MO·Fe 2 O 3 have the cubic spinel structure, named after the mineral spinel MgA1 2 O 4 . The structure may be considered as a cubic close-packed arrangement of the large oxygen ions, in the interstices of which the much smaller metal ions are situated. A closer inspection shows that not all interstices are the same, but two types can be distinguished—namely, tetrahedral (A) and octahedral (B) interstices that are surrounded by four and six oxygen ions, respectively. This chapter discusses those fundamental properties of the ferrites that are not influenced by the imperfections due to the manufacturing processes and that may be of importance for the explanation of their physical properties as met in practice. The concepts of saturation magnetization and its variation with temperature are discussed in the chapter. The applications of ferrites are also elaborated in the chapter.