Broadband Polarization-Insensitive Rectifying Metasurface Toward Battery-Free Sensors

In this letter, a broadband polarization-insensitive rectifying metasurface unit with wide-reception-angle is proposed for powering battery-free sensors. To extend the bandwidth, two orthogonal stair-shaped dipoles (SS-dipole) with a wide impedance bandwidth are proposed as the unit. The vertical SS-dipole operates as dominating dipole to generate a resonant frequency of 5 GHz, while the horizontal one works as the parasitic one to excite 6.7 GHz. Thereby the operation band is from 4.6 to 7 GHz (41%), which covers the n79, LTE band46, and Wi-Fi band. An equivalent circuit is established to reveal the broadband operation principle. Furthermore, two SS-dipoles interact as the dominating and parasitic dipoles at two orthogonal polarizations, so polarization-insensitive performance is realized. By conjugate matching the unit with the rectifying diode, the rectifying metasurface is designed. A 5 x 5 array is fabricated and the measured harvesting-rectifying efficiency is higher than 45% within the operation band with the peak one of 63% at 5 GHz. The efficiency is higher than 50% when the incident angle is 48 degrees.