Fig. 1. Foreign bodies sample
(a): Cricket; (b): Worm

Fig. 2. THz time-domain spectroscopy transmission experimental setup

Fig. 3. THz spectral absorption coefficient (a) and dielectric loss (b) of tea and foreign matters

Fig. 4. Analysis of response of spectroscopy to insect foreign bodies hidden in tea, absorption coefficient (a) and dielectric loss (b)

Fig. 5. Principal component analysis scores plot of black tea and foreign body samples
(a) : Absorption coefficient; (b): Dielectric loss