Fig. 4: Experimental results.

a The fabricated sample diagram of the 5-layer SPNN for category 1 under magnified perspective. b Calculated classification accuracy of different layers. c The output amplitude distributions at four classes. d The confusion matrix of the 5-layer SPNN. Since some misidentified ports are not in the 4 categories, the complete confusion matrix of all ports is given in Supplementary Fig. S5h. e–h Measurement of transmission parameters of four categories at output ports 4, 7, 10, and 13, respectively, in which each category has the maximum transmission parameters at its respective output port at a broadband frequency range. i–k are measured amplitude distributions at different categories when the operating frequencies are 250 GHz, 265 GHz, and 280 GHz, respectively. l–n are confusion matrices for 250 GHz, 265 GHz, and 280 GHz, respectively, corresponding to 95.8%, 99.9%, and 92.4% accuracy.