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A novel Vivaldi rectenna operated at 35 GHz with high millimeter wave to direct current (MMW-to-DC) conversion efficiency is presented and the arrays are investigated. The measured conversion efficiency is 51.6% at 35 GHz and the efficiency higher than 30% is from 33.2 GHz to 36.6 GHz when the input MMW power is 79.4 mW. The receiving Vivaldi antenna loaded with metamaterial units has a high gain of 10.4 dBi at 35 GHz. A SIW- (substrate integrated waveguide-) to-microstrip transition is designed not only to integrate the antenna with the rectifying circuit directly but also to provide the DC bypass for the rectifying circuit. When the power density is 8.7 mW/cm2, the received MMW power of the antenna is 5.6 mW, and the maximum conversion efficiency of the rectenna element is 31.5%. The output DC voltage of the element is nearly the same as that of the parallel array and is about half of the series array. The DC power obtained by the 1 × 2 rectenna arrays is about two times as much as that of the element. The conversion efficiencies of the arrays are very close to that of the element. Large scale arrays could be expended for collecting more DC power.

In the use of traditional mechanical or electronic handheld anemometer, surveyors must measure wind speed in the prescribed measuring route, so it is easy to miss part of measurement or records, etc. The monitoring system uses CC2530 as the master controller, and calculates the value of wind speed by means of optical pulse emitted by an optical coupler. Different nodes are arranged on the wall of roadway, to set up a Zigbee network. When the surveyor's anemometer node transmit the measured value of wind speed to the fixed nodes of the roadway, the system will make use of the RSSI to calculate the coordinates of the surveyor, and data package be sent to the network coordinator and to the upper computer with the aid of optical fiber. The system can rapidly and accurately record the value of wind speed and the position of surveyors, to ensure the safety of surveyors. [ABSTRACT FROM AUTHOR]