Evidence of Mie scattering at terahertz frequencies in powder materials

Abstract

We present experimental results as well as modelling concerning terahertz (THz) wave scattering by powder materials with grain size of the order of the wavelength. The studied material is a mixture of high density polyethylene and fructose powders, whose grain size is varied from a sample to another one while the volume concentration is kept constant. Experimental data are recorded with a THz time-domain spectroscopy set up. The scattering contribution to the total propagation loss in such powders shows a resonant behaviour for grain size roughly equal to the THz wavelength, for which it reaches 80%–90% of the total loss. Modelling using Mie theory allows us to well describe the absorption and scattering phenomena.

Terahertz time-domain spectroscopy of chondroitin sulfate

“…where ( Within the frequency range of 0.2 THz-1.6 THz, the refractive index of pure CS is about 2.0 and the refractive index of pure PE is about 1.4, which shows good agreement with previous studies [17]. The mixed samples have the refractive indices between 1.4 and 2.0.…”

“…The results may indicate that the THz attenuation caused by CS is mainly related to the scattering of THz radiation in the granular samples [19]. Several studies have been reported regarding the effects of granular solids on THz scattering [17,[20][21][22][23]. The equation below could be used to curve-fit the experimental data relating CS K (unit: cm −1 ) and frequency f (unit: THz) [22]:…”

Study of 2,4-D Spectral Characteristics and Its Detection in Zizania Latifolia Using Terahertz Time-Domain Spectroscopy

“…Therefore, the different experimental results were probably caused by the difference of instrument components and performance. In Figure 1C, with the increase of frequency, the baseline of the absorption spectrum rose, which may have been caused by the scattering effects [36]. It can be seen that whether the frequency-domain spectrum or absorption spectrum, the usable frequency range of the sample was in the range of 0.1 to 3 THz.…”

Dielectric Losses of Paper in the THz Domain: Literature Review, Needs for Future Research, and Prospective Solutions

“…Simulations with the DEMT (Dynamic Effective Medium Theory) model show that scattering becomes significant for particles with radius >30 μm for frequencies higher than 0.5 THz . Other published results on fructose grains dispersed in HDPE matrix show similar trends . In order to reduce losses from scattering effects, it could be tempting to use nanocelluloses, which have a diameter of about of 20 nm.…”

“…[18] Other published results on fructose grains dispersed in HDPE matrix show similar trends. [20] In order to reduce losses from scattering effects, it could be tempting to use nanocelluloses, which have a diameter of about of 20 nm. However, nanocellulose films are very dense (around 1300 kg m À3 ), so that there is less air in the structure than in paper and all the measurements show that nanocelluloses have higher losses than typical paper ( Figure 3).…”