Note: A more polished version of this Case Study is available in PDF format as STMicroelectronics & ESEO Use ADS To Design a 2.45 GHz Wireless Power Scavenging Circuit. There is also slightly different version: Extending the Operating Life of IoT Devices with a Wireless Energy-Harvesting Circuit.
Previously I posted a Case Study about a wireless power scavenging circuit whose impedance matching circuit was built around a high Q quartz crystal resonator. This particular component works best at 24 MHz. One of the comments I received on the LinkedIn syndication of that posting asked about similar circuits, but in the microwave regime. This band is important because there is more ambient RF energy floating around at 1.8 GHz (e.g. GSM1800 from cell towers) and 2.45 GHz (from WiFi) than at 24 MHz. So I searched around and the result is this new Case Study about series of papers by Dhaou Bouchouicha and Mohamed Latrach et al. They are at ST Microelectronics and Ecole Supérieure d'Electronique de l'Ouest (ESEO) in France. The papers include An Experimental Evaluation of Surrounding RF Energy Harvesting Devices and Hybrid Rectenna and Monolithic Integrated Zero-Bias Microwave Rectifier.
To rectify the ambient RF/microwave energy, the matching circuit must put a voltage across the rectifying diode that exceeds the forward voltage drop, typically 0.3V for Schottky diode. The antenna gathers less than a microwatt of power, so we need a big impedance transformation from the antenna impedance (something on the order of the impedance of free space, 377 ohms) to several kiloohms.
The authors used ADS co-simulation of the Momentum EM field solver and Harmonic Balance circuit solver to optimize the rectenna (rectifier + antenna) design. They included diode package parasitic models, which enable them to get good correlation between simulation and measurement. By carefully tuning the distance "d" between the matching capacitor and the SMA connector (shown in their figure 3 reproduced below) they optimized the convection efficiency.
With a patch antenna with dimensions of about 20 mm on a side, they obtained a DC power of 1.3 microwatts with an input power of 10 microwatts, yielding an efficiency of 13%.
Are you working on wireless power transfer? Do you face the same challenge? Or something else? Please log in and leave a comment and/or "like" this posting!
PS Here's the link to request an ADS evaluation license if you want to try it.