Electromagnetic smart screens and applications

This project aims to develop EM smart screen (ESS) which can be adjusted or modulated by bias current or voltage. For transmission applications, when pin is turn off, the transmission coefficient, T can be 100%; when pin is on, T is adjustable from 0 to 100%. For reflection applications, the reflection coefficient, R can be adjusted from 100 to 0%. Fig. 1 shows the picture of an ESS sample and Fig. 2 shows the free space measurement system used to measure the ESS.

(1) ESS for transmission applications
HFSS and infinite array model were used to simulate a unit element of the single layer strip ESS. Measured and simulated transmission coefficients of a single layer strip ESS are shown in Fig. 3, with the diodes being switched on and off (solid lines and symbols for measured and simulated data, respectively). The resonance frequency is 6.5 GHz when diodes are switched off and 5.5 GHz when diodes are switched on. The transmission coefficient of the ESS is adjustable between 3 and 8 GHz. The difference in the transmission coefficient for the on and off states of the diodes can be taken as the tunability of the smart screen, which varies from 1 dB at 3 GHz to more than 20 dB at 6.5 GHz.

(2) ESS for reflection applications
Fig. 4 shows the measured reflection coefficient of a patch ESS. When pin diodes are switched on, the resonance frequency of the patch shifts from 4 GHz to 5 GHz, with the peak amplitude being reduced from 15 dB to about 7 dB. The effective bandwidth of the patch ESS can be more than 20% of the central frequency, meaning that it can be adjusted continuously, which is much wider than that of the metamaterials reported previously. If the thickness (< 0.6 mm) and working frequency band (4 GHz to 5 GHz) are taken into consideration, performance of the patch ESS is much better than any conventional anti-reflection composites.