It is essential to acquire complex permittivity spectra in a wide frequency range, such as from 10 mHz to 10 THz, to examine the dielectric properties of a substance. For example, the relative dielectric constant of polyamide, nylon 6, becomes as high as 10⁶ at 200 ℃ when measured at a low frequency of 10 mHz. Its dielectric loss also becomes an incredibly high value, as high as 10⁷ at 200 ℃ and 10 mHz. The increase in dielectric constant is due to the so-called electrode polarization. That is to say, if electric charge carriers, with the polarity opposite to that of the facing electrode, accumulate in the dielectric substance near the electrode, they induce electric charges on the electrode. This phenomenon is due to simple electrostatic induction, and the power source supplied the charges to the electrode. On the other hand, the increase in dielectric loss is due to the Joule heating or conduction loss caused by the transport of charge carriers. These facts indicate that we can know about the transport and accumulation processes of charge carriers from the behavior of the complex permittivity at very low frequencies. Although we do not use nylon 6 for electrical insulation, we observe similar phenomena in many superior polymeric insulating materials. Compared to the above low-frequency range, if we measure complex permittivity spectra in a high-frequency range, we can obtain information on molecular motions in the dielectric material.

   If we pay attention to the electric modulus, we can analyze the above dielectric properties very clearly. The electric modulus is a reciprocal of complex relative permittivity, and its imaginary part provides us with an especially powerful tool to analyze the dielectric behavior. The keynote lecture presentation will include easy-to-understand mathematical developments to demonstrate that the complex permittivity and electric modulus obey the same or mirror relations. If we show one example, when the complex permittivity of a material obeys the Cole-Cole relation, its electric modulus also satisfies the same relation.

   In this presentation, the author will explain the above while exhibiting abundant examples acquired by his laboratory. Namely, he will show complex permittivity spectra of many polymers in broadband frequency ranges, including THz frequencies from 0.1 to 10 THz, from which we can analyze many dielectric relaxation phenomena of the polymers. The THz spectroscopy is an emerging technology since THz waves are intermediate between radio frequencies and infrared light, with no oscillating or receiving devices available until recent years. You will find several THz absorption spectra of insulating polymers, by which you can understand their versatility. He will also show ample examples of the importance of electric modulus analyses for the research on the dielectric behavior of insulating polymers.

   In addition, as mentioned above, the accumulation of so-called hetero space charge causes electrode polarization. This fact means that the space charge accumulation in a dielectric material is not an event that occurs only when we apply a high voltage, but it also appears often at low voltages as several volts or so.