大森 達也

Abstract This paper proposes a high-sensitive measuring method for nonlinear harmonic responses in radio frequency (RF) SAW/BAW devices using a lock-in amplifier. The proposed system could detect the nonlinear complex harmonic responses generated in an RF SAW resonator, even if the responses are weaker than −140 dBm. The detection limit is extended by around 10 dB compared with the conventional technique using a cross-domain analyzer.

Herein, a time-resolved electrical measurement is developed to observe the transient impedance of organic photovoltaics (OPV) and traced the initial photocarrier generation dynamics with the time region from 10 ns to 190 μs. A light-triggered time-domain reflectometry is adopted to observe the initial carrier dynamics in OPV by synchronizing rectangular light pulses from LED with a transient impedance probe pulse. Both the rising and recovery processes of OPV are observed in detail. The time evolution of the photocarrier distribution is calculated based on the diffusion–recombination scheme and is discussed in the initial process of photocarrier generation.

SUMMARY The massive explosive eruption of the Hunga volcano on 15 January 2022 generated atmospheric waves that were recorded around the globe and affected the ionosphere. The paper focuses on observations of atmospheric waves in the troposphere and ionosphere in Europe, however, a comparison with observations in East Asia, South Africa and South America is also provided. Unlike most recent studies of waves in the ionosphere based on the detection of changes in the total electron content, this study builds on detection of ionospheric motions at specific altitudes using continuous Doppler sounding. In addition, much attention is paid to long-period infrasound (periods longer than ∼50 s), which in Europe is observed simultaneously in the troposphere and ionosphere about an hour after the arrival of the first horizontally propagating pressure pulse (Lamb wave). It is shown that the long-period infrasound propagated approximately along the shorter great circle path, similar to the previously detected pressure pulse in the troposphere. It is suggested that the infrasound propagated in the ionosphere probably due to imperfect refraction in the lower thermosphere. The observation of infrasound in the ionosphere at such large distances from the source (over 16 000 km) is rare and differs from ionospheric infrasound detected at large distances from the epicenters of strong earthquakes, because in the latter case the infrasound is generated locally by seismic waves. An unusually large traveling ionospheric disturbance (TID) observed in Europe and associated with the pressure pulse from the Hunga eruption is also discussed. Doppler sounders in East Asia, South Africa and South America did not record such a significant TID. However, TIDs were observed in East Asia around times when Lamb waves passed the magnetically conjugate points. A probable observation of wave in the mesopause region in Europe approximately 25 min after the arrival of pressure pulse in the troposphere using a 23.4 kHz signal from a transmitter 557 km away and a coincident pulse in electric field data are also discussed.