Figure 2. Experiment demonstration of unidirectional transparency of the PT symmetric system at 5.3 kHz.

(a) The photo of an experimental sample including loss and gain units. (b,c) The calculated (solid curves) and measured (marked dots) transmissions and reflections when the incident wave is coming from the loss side. (d,e) Similar representation to b and c) when the incident wave is from the gain side. Black, green, red, blue and grey colours denote the incidence, reflection from the loss side, the reflection from the gain side, the transmission and the reflection from the end of the waveguide, respectively. All results have been normalized with the amplitude of incidence. The two calibrated unidirectional microphones are mounted at l₁=15.5 cm and l₂=13 cm away from the boundaries of our PT symmetric materials. The spacing between the loss and gain materials is L=1.24 cm. No reflection is observed from the loss side (green curve and dots in b), ∼330% reflection is observed from the gain side (red curve and dots in d), and total transmissions (|t|=1) have been observed on both sides, resulting in unidirectional transparency from the loss side.