Microwave (MW) is applied to various fields such as microwave oven, wireless local network, and satellite broadcasting. There is great interest in microwave effects on biomolecules including proteins as the microwave technology expands. Various researches of MW effects were conducted, however such effects at molecular level of life phenomena have not been elucidated. This review summarizes some researches of MW effects on protein structures and/or enzymatic reactions.

View full abstract

In previous study, it was found that the refractive index of pure water is lower during the microwave irradiation because hydrogen bond network collapses due to the strong vibration and the rotation. In this study, refractive index of glucose aqueous solution was measured during the microwave pulse irradiation. When irradiation of pulse mode was carried out, the refractive index increased step-wisely due to the quick response of microwave. Because the temperature dependence of the refractive index of the aqueous solution is negative, the microwave effect for intermolecular structure, which is closely related with refractive index, was confirmed. In the case of the higher concentration, the refractive index increased during the irradiation because the intermolecular structure between aggregated glucose molecules and water molecules is changed. In particular, molecular structure caused by the irradiation was not fully re-constructed during the interval. For example, pulse irradiation mode can maintain molecular structure caused by microwave for a long time when the interval is 20-60 seconds.

View full abstract

Bi₂Te₃ is a thermoelectric material with the highest thermoelectric conversion efficiency near room temperature. Bi₂Te₃ has large anisotropic thermoelectric properties, which can be improved by controlling its crystal orientation. In this study, we investigated the effect of crystal growth of Bi₂Te₃ thin film by thermal annealing using microwave heating. As a result, we successfully obtained c-axis oriented Bi₂Te₃ thin films by irradiating with 900 W microwaves for only 3 seconds.

View full abstract

Conventional microwave heating methods have the problem of uneven heating due to non-uniform power density distribution. This study aims to realize uniform power irradiation over a wide area by controlling microwave beams using an array antenna. We investigated the use of orbital angular momentum (OAM) mode beam patterns generated by the uniform circular array (UCA). First, the number of antenna elements in UCA and the number of irradiated OAM modes were determined based on array factor calculation. Second, the symmetry of beam patterns was improved by using a sequentially rotated array arrangement. Electromagnetic simulation and measurement results of the designed UCA showed that the average power density distribution could be made uniform over a wide area by switching the irradiation modes appropriately. These results validate that the method of switching OAM modes is effective to realize uniform power irradiation for microwave heating.

View full abstract