Fig. 2: Architecture and operational characteristics of the nonlinear metasurface unit.
From: Multilayer nonlinear diffraction neural networks with programmable and fast ReLU activation function
a Unit structure and functional equivalence. b Front and back views of the unit. c Operational schematic. d RF detector’s output DC voltage increases with incident power density. e RF amplifier gain is controlled by DC voltages VCC and VCTRL. Gain response versus VCC (f) and VCTRL (g), both showing a cutoff region at low voltages, followed by an increase and eventual saturation. h Linearity of the output energy versus input under high VBIAS (VBIAS > 1.2 V), and gain increases with VCC. i, j Transmission coefficient rises from cutoff to saturation with incident energy; VBIAS lowers energy threshold (i), and VCC raises transmission saturation (j). k With VBIAS = 1 V and VCC = 5 V, transmission is zero below 1 mW and increases linearly above it, resembling a ReLU response. l Activation threshold decreases with VBIAS. m Gain increases with VCC.
