從無線電波中獲取能量

　　電力的無線傳輸常常帶來一個世紀(jì)前尼古拉特斯拉及其無線輸電技術(shù)的圖像。William C. Brown，微波功率傳輸?shù)?a target='_blank' class='arckwlink_none'>知名整流天線的發(fā)明者，寫了一本極好的歷史回顧的技術(shù)可以追溯到海因里希赫茲，實際上早于特斯拉的工作。1雖然特斯拉的電網(wǎng)愿景是從來沒有通過，其他應(yīng)用程序更適合有用功率無線傳輸和收集軍事和航天現(xiàn)在正在實施的。

　　對于能量收集，人們可以考慮兩種方法——寬或窄波段。任何熟悉RF技術(shù)的人都會明白，在盡可能窄的頻帶范圍內(nèi)進(jìn)行大量的調(diào)整通常會消耗大量的精力。對于無線電通信信號的典型使用，主要的好處是減少噪聲和拒絕其他信號以外的通信信道。窄帶設(shè)計有兩個好處，特別是在能源收獲的好處。聚焦在一個小范圍的頻率通常會產(chǎn)生增益的天線或電路，以及改進(jìn)的功率傳輸通過匹配調(diào)諧所有的電路元件。

　　However， narrowing the band of collected frequencies has the deleterious effect of rejecting other ambient energy that could otherwise be scavenged. Ultra-wideband （UWB） is a communications protocol that exploits a larger range of frequency to improve performance for certain applications. Wideband techniques are also employed for energy-harvesting applications to collect the widest possible array of frequencies in the bands with the greatest energy density available.

　　As one may expect， most off-the-shelf antennas are designed with specific tuning for narrow band reception of RF signals. In some cases， especially for mobile phone applications， antennas are available that cover several bands. For antennas in the cellular GSM band， designers should consider the Taoglas 931-1052-ND Penta-band antenna （Figure 1） covering five major cellular bands near both 900 MHz and 1.9 GHz. Another pentaband antenna is available from Ethertronics. The 939-1022-1-ND（Figure 2） offers high gain of 2.5 dBi for the 2-GHz band and is shorter than the Taoglas design.