Terahertz time-domain spectroscopy for discrimination of common plastic types found in household waste

We present a study of common plastic types found in household waste using terahertz time-domain spectroscopy (THz-TDS). We measure in transmission geometry to create a database and make a 2D map of all plastic types spanned by the mean refractive index and absorption growth obtained in the range from 0.4 to 1.0 THz. Additionally, we measure samples on a conveyor belt at a speed of 3 cm/s in a reflection geometry feasible for industrial sorting facilities, where the refractive index, absorption coefficient and sample thickness are obtained independently from the reflected pulses. The total detection and algorithm processing time for plastic type determination is less than 1 second, which is acceptable for a subsequent sorting in an industrial facility.