Investigation of Dielectric Properties of Polymers and their Discrimination Using Terahertz Time-Domain Spectroscopy with Principal Component Analysis

Abstract

Polymers are among the most commonly used materials in our everyday life. They are generally transparent to terahertz (THz) radiation, but are quite difficult to differentiate using optical techniques as few or no characteristic features exist in the spectral range of <2.0 THz for small and portable radiation systems. In this work, we report experimental measurement of refractive indices and absorption coefficients of styrene acrylonitrile (SAN) and Bakelite in the spectral range of 0.2-2.0 THz for the first time. Additionally, we demonstrate that by combining principle component analysis (PCA) with THz time-domain spectroscopy one can differentiate such polymers. In this analysis, the first three principle components PC1, PC2, and PC3 depict >94% variance with a distribution of 72.45%, 11.52%, and 9.38%, respectively.

High‐strength ceramic foams with ultralow dielectric constant and loss in terahertz frequency region

“…With the increase of sintering temperature from 700 to 900 • C, bulk density increases from 0.304 to 0.696 g/cm 3 , which results from the increase of sintering shrinkage and true density of ceramic matrix, as listed in Table 1. Given that the true densities of amorphous silica, low cristobalite, and wollastonite are 2.24, 21 2.316 (PDF 76-0935), and 2.91 (PDF 75-1396) g/cm 3 , respectively, the transition from amorphous to low cristobalite phase and the generation of wollastonite would increase the true density of ceramic matrix. The decrease of porosity from 87.3% to 72.4% is dominated by sintering shrinkage.…”

“…As for dense soda-lime glass, 𝜎 bs = 70 MPa. 25 Attila et al 26 summarized the compressive strength of foam glass with bulk density of 0.1-0.6 g/cm 3 prepared by different methods, which has lower relative compressive strength than closed-pore model. Ceramic foams sintered in 700-850 • C with a bulk density of 0.304-0.639 g/cm 3 in this study show higher relative compressive strength than closedpore model, as seen in Figure 5C.…”

“…However, few dielectric materials exhibit an ultralow relative dielectric constant (ε r ) and loss tangent (tan δ ) in terahertz frequency region to ensure ultralow signal latency and attenuation. Although dense polymers exhibit a relatively low ε r (2 < ε r < 4), they usually have a high tan δ 3 . Conversely, dense microwave dielectric ceramics exhibit a relatively high ε r (3 < ε r < 120) and moderate tan δ 4,5 .…”

“…Although dense polymers exhibit a relatively low 𝜀 r (2 < 𝜀 r < 4), they usually have a high tanδ. 3 Conversely, dense microwave dielectric ceramics exhibit a relatively high 𝜀 r (3 < 𝜀 r < 120) and moderate tanδ. 4,5 As reported, microwave dielectric ceramics are widely used in the fabrication of microwave devices such as antennas, filters, and resonators, 4,6,7 and some of them have excellent dielectric properties in terahertz frequency range.…”

Microwave and terahertz properties of porous Ba4(Sm,Nd,Bi)28/3Ti18O54 ceramics obtained by sacrificial template method

“…4 Lightweight and compact components are severely demanded for the next-generation telecommunication and Internet of Things (IoT) applications such as satellite communication and wearable devices, which require materials with a low density and relatively high r . Although polymers and polymer-based composites exhibit lower densities, the low r (mostly <15) 5,6 limits the miniaturization of devices. Conversely, conventional dense microwave dielectric ceramics usually possess high r , however, their high density can induce a heavy load on the devices.…”