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In this paper, we propose a new design of a piezoelectric transformer (PT) for low-profile DC/DC converter applications, which increases the output power by using heat transfer equipment. We examined several parameters, which allow us to produce a piezoelectric transformer with optimal efficiency. Instead of looking at the typically optimal loading condition of the PT, we consider the influence of the temperature rise on losses. When the vibration velocity is too large, the piezoelectric transformer generates heat unstably until it cracks. By maintaining the vibration mode and limiting the heat produced by the PT, this design can enhance the power capacities of the PT and thus increase the output power of the DC/DC converter. A finite element analysis (FEA) approach with COMSOL Multiphysics was made to predict PT's working temperature. A theoretical-phenomenological model was also developed to explain the relationship between the equivalent losses resistances and the input voltage at different temperatures. It will be shown that the vibration velocity as well as the heat generation increases the losses. A large vibration velocity and generated heat may cause the temperature feedback loop to enter into an unstable state. We began by modeling a piezoelectric transformer in a DC/DC converter configuration in order to determine the design constraints and variables such as the maximum mechanical current, the temperature distribution, the PT geometrical configuration and the energy balance. In our design, the PT power capacity increases 3 times (i.e. from 4.54 W to 13.29 W) at specific temperature and the effects of the different cooling methods of the system were verified. The study comprises of a theoretical part and experimental proof-of-concept demonstration of the proposed design method. [ABSTRACT FROM AUTHOR]

We present the results of an international comparison regarding the magnetic properties of hard magnets, measured using the Vibrating Sample Magnetometer. The comparison involved eight different international laboratories, plus two laboratories using the SQUID magnetometer. It was directed, in particular, at the determination of the hysteresis loop parameters of hard ferrite and magnetic tape samples. It was carried out in the framework of the activity of the IEC TC68 Working Group 2. The statistical analysis of the obtained results was performed according to standard rules (e.g. ISO and EURAMET guidelines). The standard deviation around the mean of the laboratories best estimates is found to be s ∼⃒ 1% in anisotropic ferrites for all the measured quantities: coercive fields H_{cJ} and H_{cB}, high-field polarization J_{800 k}, polarization at remanence J_r, maximum energy product (BH)_{max}. Isotropic ferrites show larger dispersion of the best estimates of J_r and H_{cB} (∼⃒ 3%) and (BH)_{max} (∼⃒6%). For the quantities measured in the magnetic tapes (magnetic moment under applied field H=400 kA/m m_{400 k} and at remanence m_r, squareness S = m_{400 k}/m_r, H_{cJ}) s is found to fluctuate around 2%. In all cases, the relative expanded uncertainty of the reference value (weighted mean), associated with a 95% confidence level, is at most ± 1.5%. [ABSTRACT FROM AUTHOR]