影响松耦合变压器性能的参数分析

影响松耦合变压器性能的参数分析

摘 要

传统的电能传输主要通过导线直接进行，在一般环境下这种方式合理有效，被广泛采

用。但是在一些特殊场合，如易燃易爆场合和水下系统，这种电能传输方式的安全性难以得到保证。非接触电能传输系统利用电磁感应耦合技术与电力电子技术，避免了电能传输过程中裸露导体或产生电火花的问题，实现了电能的安全传输。

松耦合变压器是非接触电能传输系统中的关键部分。在简单地介绍松耦合变压器的基本结构及工作原理的基础上，给出了松耦合变压器的互感等效模型。由松耦合变压器的特点，对影响松耦合变压器耦合系数的磁芯材料、绕组位置、气隙大小等因素进行了分析。

装 订 线

针对不同的应用场合，对原副边进行了补偿设计，提高了电能传输效率和减小了供电电源的电压电流定额。

关键词：非接触能量传输；松耦合变压器；耦合系数；原副边补偿

The analysis of the parameters for affecting the loosely coupled

transformer performance

ABSTRACT

Most electrical equipment get the energy through plugs from source, this kind of energy transmission system is efficient and accepted widely. But it is unsafe at the special circumstance such as undersea applications and flammable environments. This paper describes a contact less power transmission system using isolation transformer, which is spark free and no uncovered conduct being exposed to the environments.

Loosely coupled transformer is a key part in contact less in ductile power transfer system. For this reason, the fundamental structure and work principle of the loosely coupled transformer are introduced, and the circuit model of mutual inductance is established. Factors that affect the coupling coefficients of the loosely coupled transformer are studied, including magnetic material, location of windings and the width of air gap. Due to the leakage inductances, compensation is necessary to achieve the required power transfer capability. The level of compensation and compensation to apologies are discussed. The design proposal for main parameters of the loosely coupled transformer is suggested.

Key words: inductive power transfer; loosely coupled transformer ; coupling coefficient; primary and secondary compensation

1 绪论

从1840年发现利用电磁感应原理和导线可以传输电能至今，电能的传输主要通过导线直接进行，但是这种传统的电能传输方式存在很多弊端，例如，水下工作系统、化工、矿业、石油领域等，在传统的电能传输过程中，由于导线的裸露，故存在摩擦、磨损、漏电、火花等不安全因素，极易引起短路或者爆炸；移动设备如电车采用的是滑动接触，在其充电时会存在滑动磨损、积碳、导体裸露和接触火花等问题[1-5]。因此，传统的接触式电能能传输系统已经不能满足现实生活及生产的需要，新型的电能传输技术急需产生。

非接触电能传输系统应用电磁感应耦合技术、现代电力电子能量变换等新技术，通过存有较大气隙的松耦合变压器将电能从电源侧传输至负载侧。这种无导线连接的电能传输新技术有效地解决了传统的电能传输系统中存在的滑动磨损、电火花、导体裸露、短路等问题，从而安全有效灵活地实现了电能的传输。

非接触电能传输系统核心组成部件是松耦合变压器。松耦合变压器是将其原边和副边分开一定距离，通过电磁耦合实现电能的传输。图1-1为松耦合变压器的试验样机(a)和绕组接线图(b)

图1-1 松耦合变压器试验样机及绕组位置

普通的变压器原副边之间的气隙接近为零，原边传送至副边的能量可通过原副边匝数比计算得到，而松耦合变压器原副边之间存在有较大的气隙，气隙对松耦合变压器的参数影响较大，尤其对松耦合变压器的漏感和耦合系统影响最为明显，进而影响了松耦合变压器的功率传输。本文将在介绍了非接触电能传输系统的工作原理及功率传输问题的基础上，针对影系统的核心部件—松耦合变压器性能的各种初、次级补偿拓扑及运行参数进行详细地分析，同时对非接触电能传输系统的应用做简单的介绍。

2 非接触电能传输系统的构成及工作原理

图2-1 为非接触电能传输系统构成原理图，该系统主要由能量发送器、松耦合变压器和能量接收器组成，能量发送器主要包括工频整流和高频逆变部分，能量接收器主要由高频整流和能量调节部分组成。系统工作时电源侧将工频交流电经整流和滤波进入高频逆变装置，从而转变为高频交流电供给松耦合变压器原边绕组，通过电磁耦合后，副边绕组输出了高频电流，若负载需要直流电，则副边的高频电流经整流滤波后输送至负载；若需交流电，则需对整流后的直流再逆变为交流电。接收器的控制电路还具有保持传输能量稳定性的作用，此外的辅助环节这里不做描述。

图2-1 非接触电能传输系统构成原理图

3 松耦合变压器的分析

3.1 物理结构

松耦合变压器是实现电能非接触传输的关键部件，松耦合变压器是将常规的变压器磁芯的原副边分离，因而具有较大的空气间隙，当原边输入高频交流电时，原边磁芯中产生了交变磁场，这个磁场经过空气间隙传到副边磁芯中，副边线圈有交变磁场穿过，由电磁感应原理可知，此时副边线圈将产生感应电动势，从而实现电能的非接触传输。

根据应用对象的不同，松耦合变压器中可采用高磁导率的磁芯，也可采用空心线圈，根据原副边线圈之间的相对运动关系可分为相对运动型和相对静止型。

3.2 等效电路模型分析

（a） 互感电路 (b) 等效电路

图3-1 松耦合变压器及其等效电路

作为非接触电能传输系统的关键组成部分，松耦合变压器在系统中发挥着重要的作用，其工作原理与原副边相互分离的空心变压器[6][7]相似，基于互感的等效电路模型可使系统简化，便于分析系统电路参数及传输功率。

图3-1为松耦合变压器的模型，图中r1和r2为原副边线圈的等效内阻；ip和is为原副边电流；LP和LS为原副边线圈的自感；RL为系统的等效负载；w为电源角频率；M为原副边线圈之间的互感；Ui和Uo分别为原边输入电压和负载端电压。

由上图可得到

Ui(r1jwLP)iPjwMis 3—1 0jwMip(r2jwLSRL)iS 3—2

由①和②得到

Uiw2M2 r1jwLPiPr2jwLSRL副边对原边的反映阻抗为

w3M2LSw2M2(r2RL)w2M2ZrjRrjXr 222222r2jwLSRL(r2RL)wLS(r2RL)wLS其中，Rr为反映电阻，Xr为反映电抗。

在忽略线圈损耗的情况下，系统从原边传输到副边的功率

POiPRe(Zr)iPRr 3—3

22由此可知，反应电阻反映了非接触电能传输系统将电能从原边线圈传到副边线圈的传输能力，且Rr越大，电能传输能力越强。

由于松耦合变压器存在较大的空气间隙，电能传输时，其磁动势主要降落在空气磁路部分，因而具有很大的漏感，导致松耦合变压器的传输效率下降。因此必须对影响松耦合变压器性能的参数进行研究，从而有效地提高传输效率。

4 影响松耦合变压器性能的参数分析

在非接触电能传输系统中，原副边电路的工作依赖性大，原副边电能的传输关系由多个参数共同决定，这些参数之间都存在着相互制约的关系，而松耦合变压器的性能优劣是系统电能传输效率高低的关键，因此，对影响松耦合变压器性能的参数分析很有必要。

将互感M用耦合系数K和线圈匝数比n代替，即MnKLS 代入到Rr的表达式中有

Rr(nK)2w2LSZS22(r2RL) 4—1

其中ZS为包含负载电阻RL和副边线圈内阻在内的副边等效阻抗。

反应电阻Rr直接反映了系统将电能从原边线圈传输到副边线圈的传输能力，因而由上式④可知，提高反应电阻的方法除了提高耦合系数K和工作频率w外，还可增加原副边的匝数比n。

提高松耦合变压器的电能传输效率，主要可以从两方面入手：①改进松耦合变压器内部结构，提高耦合系数K；②改进外部电路结构，选取合适频率，增加原副边补偿电路。下面通过利用ANSYS软件对非接触电能传输系统进行仿真，得到以上参数和效率之间的关系，可为非接触电能传输系统的设计给出一定的指导。

4.1 耦合系数K

耦合系数KML1L2是由松耦合变压器内部结构所决定的，其决定因素主要有原副边

线圈之间的气隙大小、磁芯材料、绕组位置等。

4.1.1 气隙

由于松耦合变压器原副边之间存在较大的空气间隙，致使磁动势主要降落在气隙的磁阻上，因此，松耦合变压器的传输效率就大大降低，故气隙是影响松耦合变压器传输性能的主要因素。

松耦合变压器设计的关键在于让气隙在规定的范围内保证耦合系数变化较小，从而有利于系统的优化设计和效率的提高。

图4-1给出了样机耦合系数K和气隙的关系，由图可知，当气隙的大小在70mm之外时耦合系数的变化趋于稳定，变化较小，所以这段距离范围是比较适合的气隙选取范围。

图4-1 耦合系数与气隙的关系图

4.1.2 磁芯材料

选取合适的磁芯材料主要是为了降低能量传输过程中的能量损耗，提高性价比。对于松耦合变压器磁芯材料的选取，一般有以下几个要求：①磁导率高②具有很小的矫顽力③电阻率高④饱和磁感应强度大⑤磁损率小⑥居里温度高。

具有高磁导率材料的磁芯激励存储能量小，而激励电流只提供能量传输的条件，不参与能量传输，因此，磁芯磁导率越高越好。下图为磁芯在气隙为0.2mm时磁芯相对磁导率与耦合系数K的关系图。

图4-2 磁芯相对磁导率与耦合系数关系

由图4-2 可知，随着相对磁导率的提高，耦合系数K也在不断提高，但是提高的幅度很小，气隙大小的改变对K影响比较大。虽然磁芯材料对耦合系数的影响较小，但是为了铁损，磁芯材料应选取较高电阻率的导磁材料。

4.1.3 绕组位置

传统的变压器绕组缠在了磁芯的底部即中心绕组，而新型的松耦合变压器的绕组则缠在了磁芯的端部，如图4-3所示，(a)所示的是传统变压器的绕组缠绕方式(b)为松耦合变压器的绕组缠绕方式，在相同的气隙下，（a）的绕组方式漏磁较多，耦合系数比较小，而（b）的绕组方式使绕组线圈紧密接触，更多的磁力线在原副边绕组之间垂直通过，漏磁少，耦合系数较高。

图4-4为在不同绕组位置下耦合系数随气隙的变化图，从图中可以看出，随着气隙的增大，两种绕组方式下的耦合系数均在减少，但是端置绕组变压器的耦合系数较中心置变压器的耦合系数明显偏高，在气隙较大时，端置绕组比中心绕组更有有优势。

图4-3 两组不同绕组位置的变压器

图4-4 不同绕组下耦合系数随气隙变化关系

4.2 漏感

松耦合变压器原副边耦合存在漏感，漏感不参与能量的传输，也即存储在漏感中的能量不能被传输到次级。漏感是变压器的寄生参数，越小越好，但是随着气隙的增加，变压器中漏感会随之增加，漏感的增加会使穿过次级线圈的磁通量减少，由电磁感应原理可知，次级的感应电动势也会减小，进而降低了系统的传输效率。

由uNddt可知，为了增加感应电动势，则需要增加磁通量的变化率，也即提高原边

输入电流的变化频率。

4.3 外部电路结构参数

在非接触电能传输系统中，因为存在着较大的漏感致使传输功率受到了。为了提高系统的传输功率，通常采用补偿容抗来平衡电路中的感抗。

原边的补偿电容可以平衡原边的漏感和副边的反映感抗，从而可以减少感应电源的视在功率，提高感应电源的功率因数。副边的补偿电容可以减小副边的无功功率，增大系统的输出功率。

图4-5 原副边补偿拓扑

最基本的补偿拓扑有电容串联和电容并联补偿两种方式。若原副边分别采用串联或者并联补偿的方式，那么系统的补偿拓扑方式一共有4种：串联-串联补偿拓扑、串联-并联补偿拓扑、并联-串联补偿拓扑和并联-并联拓扑补偿，见图4-5所示。

4.3.1 副边补偿

在非接触电能传输系统中，由于漏感的存在，副边线圈直接与负载连接，系统副边的输出电压与电流随负载变化而变化，从而了功率的传输，输出功率：

RUOCP22R(wL2)22 4—2

其中，P为输出功率，R为等效负载，UOC为副边开路电压，w为原边的谐振频率，L2为副边的电感。

因此，必须对副边进行补偿设计从而减小副边的无功功率，增大系统的输出功率，其补偿如图4-6所示。

图4-6 副边补偿拓扑

在副边的电容串联补偿电路中，副边阻抗

Z2RjwL21 4—3 jwC2输出功率为

P2RUOC212R2(wL2)wC2 4—4

当副边补偿电容C2与副边电感L2在系统的工作频率下处于谐振状态的时候，副边的容抗与感抗互消，阻抗等效为纯的电阻,输出电压等效为开路电压，与负载无关，从理论上讲电能的传输不受，此时输出功率

2UP2OC 4—5

R适用于需要直流母线电压的场合。 在副边电容并联补偿的电路中，副边导纳

Y211jwC2 4—6 RjwL2输出功率

12ISCRP2211wC2wL2R2 4—7

其中ISC为副边短路电流。

当副边补偿电容C2与电感L2在系统的工作频率下处于谐振状态时，副边容纳与感纳相互抵消，导纳等效为纯电导，输出电流等效为副边的短路电流ISC，与负载无关，在理论上讲，电能的传输不受，输出功率为

2P2ISCR 4—8

适用于充电器场合。

w2M2副边电路反应到原边的反映阻抗为,现将其结果列于表1中。 2Z表4-1 副边补偿电容与反映阻抗

副边补偿拓扑 电容串联补偿 副边补偿电容值 电阻 反映阻抗 电抗 1 w2L2w2M2 R0 wM2 L2电容并联补偿 1 2wL2M2RL22

4.3.2 原边补偿

在非接触电能传输系统中，原边的补偿电容目的在于平衡原边的漏感抗和副边的映射

感抗，减小视在功率，从而提高感应电源的功率因数。原边通过通过变换器得到了高频电流，而变换器的电压和电流定额高，使系统成本较高，因此，有必要采取措施使变换器电压电流定额降低。

对原边的补偿设计也称为原边谐振问题，其补偿方式有串联和并联两种方式，其补偿电路图如图4-7所示。

图4-7 原边补偿拓扑

在原边电容的串联补偿电路中，原边阻抗

Z1jwL11Zr （4—9） jwC1其中，Z1为副边到原边的反应阻抗。

电容电压补偿了原边绕组的电压，降低了变换器的电压定额，从而适用于原边绕组较长且分散的场合。

在原边的电容并联补偿电路中，原边导纳

Y1jwC11 4—10

jwL1Zr电容电流补偿了原边绕组上的电流，从而降低了变换器的电流定额，故适用于集中绕组的场合。

表4-2 原边的补偿电容值

副边补偿拓扑 串联补偿 原边补偿拓扑 串联补偿 原边补偿电容C1 串联补偿 并联补偿 并联补偿 串联补偿 并联补偿 并联补偿

4.4 谐振频率wo

为提高非接触电能传输系统的输出功率和效率，系统的工作角频率wo应大于副边的谐振角频率及原边的零相位角频率[8]。当系统在谐振状态下工作并且原副边的各个参数不变时，工作频率wo越高，副边对原边的映射电抗Zr就越大，在满足足够的输出功率下，wo越高，原边电流越小，系统损耗越小，电流的应力也就越小，因此，松耦合感应电源适合在高频条件下工作。

5 发展及应用

感应耦合电能传输作为一种新型无接触电能传输系技术，由于电能供应端与电能接收端靠感应耦合来传输能量，没有直接的金属导体接触，无需电缆连接，从而提高了供电的灵活性。学术界已经对非接触能量传输技术进行了广泛的研究，国外对非接触电能传输技术的研究比较早，在2001年5月，法国国家科学研究中心的G.Pignolet利用微波无线传输电能点亮40mm外的一个灯泡；2006年，物理学教授马林.索尔贾希克为首的研究团队试制出了无线供电装置，可以点亮7英尺远的灯泡，能量传输效率达到了40%；2008年8月的英特尔信息技术峰会上演了无线供电方式点亮一个灯泡并且可在一米范围内给灯泡无线提供电力，效率达到75%，此外还有内植式医疗装置，移动设备无接触充电装置及便携式携带等，国内的研究起步较国外晚，主要集中于对非接触电能传输技术的系统建模，频率稳定及电路补偿技术的研究。西安石油学院的李宏最先地对非接触电能传输系统做了介绍[9]，中国科学院已经研制出传输功率达到25W的试验样机[10]，西安交通大学搭建了采用可分离变压器的非接触电能传输实验系统，效率高达87.6%[11]，但是，很少有非接触电能传输技术的应用的报道。目前，非接触电能传输技术正向大功率电气设备的无接触供电、小功率便携式电子装置的非接触充电和工作于特殊环境下的电气设备无接触供电等方面发展，其具有无磨损。便于维护、安全性高、自动化程度高等优点，在以下领域具有广阔的应用前景[12][13]

1）为水下设备、工矿设备提供电能供应

非接触电能传输技术应用于水下设备，目前多数水下设备都使用电池供电,也有部分通过电缆传输电能。非接触电能传输技术以无电缆连接实现能量传输，减少对设备的束缚，配合水下无接触式耦合信息传输，实现“无线”水下设备,为海洋科考实验提供更加优越的实验环境。同时,非接触电能传输可以有效地避免因为电源插口外露、电线断裂而带来的安全隐患，提高系统的安全性。

在目前我国的水下设备大多数采用的是有线的电能传输来为设备提供电能，随着我国对海洋领域的重视与开发，将需要大量的水下救生，探测以及考古等各种装置，能源问题急需解决，尤其对充电方式方面缺少充分的研究。非接触电能传输技术不存在电路的直接耦合，从而避免了普通方式充电所带来的充电麻烦和维护困难的问题。

在矿工业，由于非接触电能传输技术消除了传统的接触式供电方式中所产生的摩擦、磨损、电火花，适合于各种充满易燃易爆物体、气体、粉尘的地下矿业、生产车间中的电气设备的电能供应，同时非接触电能传输技术由于具有免维护的特性，也适应于危险环境下电气设备的供电。

2）内植式医疗电子设备电能的供应

新型非接触电能传输技术可以为人体内植式医疗电子装置如心脏起搏器等提供稳定的电能，避免了患者定期通过手术来更换装置电池的痛苦。

3）为移动设备供电

由于社会的发展与进步，电动火车、电动汽车等电动交通工具越来越多的得到了应用，而采用非接触电能传输技术为电动交通工具充电则将扩大了他们的应用范围，也适应了节能减排的环境需求。

4）构建便携式小功率电子设备非接触充电平台

现在电子产品越来越多，每一个电子产品都有与之相匹配的充电器，且通过导线连接来实现电能的传输，对使用者而言，有线充电显得相当麻烦，以非接触电能传输技术为支持的无线充电器便应运而生。该充电系统通过新型耦合传能线圈将电能无线传输至负载端，负载端可以为电池也可直接为用电设备。只需把手机、笔记本电脑或者其他电子产品放在充电平台上即可不需要物理连接而实现充电。利用感应耦合原理构建的新型无接触充电平台，可同时为多个电子设备提供无接触充电，受电设备可以不分方位置于充电平台上获取电能，而且在工作过程中，多个设备间不存在相互干扰的问题，提高了充电的灵活性。

近来年的科技发展表明，在无线数据传输技术日益普及之时，无线电力传输的研究也取得了很大的突破，在未来的生活中我们可以摆脱充电器上的电源线而达到简单方便的电能传输。

6 结论

非接触电能传输技术是一种新型的电能传输技术，该技术消除了传统的采用电缆方式进行电能传输的固有缺点，没有导线裸露，接触电火花，供电端与用电负载可以先对移动，极大地提高了供电的安全性可靠性及灵活性。在各种移动设备供电、电动交通运输工具的供电、内植式医疗设备的供电及便携式电子产品的供电以及工作于特殊环境下的电气设备的供电等方面都具有广阔的应用前景。目前，在非接触电能传输系统的结构设计以及控制方法上已经取得了一定的进展。非接触电能传输技术已经在多个领域得到了应用，其基本的性能已经进过了分析和验证。但是，作为一门新兴的技术，非接触电能传输技术还处于发展阶段，对非接触电能传输系统的相关问题进行深入的研究有利于提高系统的综合传输能力，提高电能的传输效率，降低制造成本，拓宽应用范围，为各类移动电气设备提供高效安全的供电模式。因此，对非接触电能传输技术的研究具有重要的理论意义和实际应用价值。

参考文献

[ 1 ] Klontz K W, Divan D W, Novotnoy D W, et al. Contactless power delivery system for mining appli-

cations [ J] . IEEE Transaction on Industry Applications, 1995, 31( 1) : 27-35.

[ 2 ] Heeres B J, Novotny D W, Divan D W, et al. Contactless underwater power delivery [ C] . IEEE

Annual Power Electronics Specialists Conference,1994: 418-423.

[ 3 ] Boys J T, et al. Inductive power distribution system[ P] . Patent Number: 5, 293, 308. March 8, 1994. [ 4 ] Pedder D A G, Brown A D, Skinner J A. A contactless electrical energy transmission system [ J ] .

IEEE Transaction on Industrial Electronics, 1999,46( 2) : 23-30.

[ 5 ] Boys J T, Hu A P, Covic G A. Critical Q analyze is of a current-fed resonant converter for ICPT

applications [ J ] . Electronics Letters, 2000, 36 ( 17 ) :1440-1442.

[6] KAWAMURA A，ISHIOKA K，HIRAI J. Wireless transmission of power and information through

one high-frequency resonant AC link inverter for robot manipulator applications[J]. IEEE Transactions on Industrial Electronics,1996, 32（3）：503-508.

[7] Don PEDDER A G,BROWN A D,SKINNER J A. A contactless electrical energy transmission

system［J］. IEEE Transactions on Industrial Electronics，1999，46（1）:23-30.

[8] Wang C S, Covic G A, Stielau O H . Load models and t heir application in the design of loosely

coupled inductive power transfer systems [ A] . Proc. 2000 Int. Conf. Power System Technology [ C] . Nelson: IEEE, 2000.

[9] 李宏. 感应电能传输 电力电子及电气自动化的新领域[ J].电气传动, 2001, ( 2) : 62- . [10] 武瑛, 严陆光, 黄善纲. 新型无接触电能传输系统的性能分析[ J].电工电能新技术, 2003,

22( 4) : 10-13.

[11] 韩腾,卓放,刘涛.可分离变压器实现的非接触电能传输系统研究[ J].电力电子技术

2004,38( 5) :28- 29.

[12] 李宏. 感应电能传输－电力电子及电气自动化的新领域[ J].电气传动, 2001( 2) : 62－. [13] 武瑛, 严陆光, 徐善纲. 新型无接触能量传输系统[ J].变压器, 2003, 40( 6) : 1－6.

致 谢

本研究及学位论文是在我的导师亲切关怀和悉心指导下完成的。她严肃的科学态度，严谨的治学精神，精益求精的工作作风，深深地感染和激励着我。从课题的选择到项目的最终完成，刘老师都始终给予我细心的指导和不懈的支持。在此谨向刘老师致以诚挚的谢意和崇高的敬意。

在此，我还要感谢在一起愉快的度过大学生活的老师们和同学们，正是由于你们的帮助和支持，我才能克服一个一个的困难和疑惑，直至本文的顺利完成。

在论文即将完成之际，我的心情无法平静，从开始进入课题到论文的顺利完成，有多少可敬的师长、同学、朋友给了我无言的帮助，在这里请接受我诚挚的谢意!最后我还要感谢培养我长大含辛茹苦的父母，谢谢你们!

附 录 Wireless energy transfer

From Wikipedia, the free encyclopedia

Wireless energy transfer or wireless power is the transmission of electrical energy from a power source to an electrical load without a conductive physical connection. Wireless

transmission is useful in cases where interconnecting wires are inconvenient, hazardous, or impossible. The problem of wireless power transmission differs from that of wireless

telecommunications, such as radio. In the latter, the proportion of energy received becomes critical only if it is too low for the signal to be distinguished from the background noise.[1] With wireless power, efficiency is the more significant parameter. A large part of the energy sent out by the generating plant must arrive at the receiver or receivers to make the system economical. The most common form of wireless power transmission is carried out using direct induction followed by resonant magnetic induction. Other methods under consideration include electromagnetic radiation in the form of microwaves or lasers.[2]

Contents

•

• • • • •

1 Electric energy transfer

o 1.1 Electromagnetic induction

▪ 1.1.1 Electrodynamic induction method ▪ 1.1.2 Electrostatic induction method

o 1.2 Electromagnetic radiation

▪ 1.2.1 Beamed power, size, distance, and efficiency ▪ 1.2.2 Microwave method ▪ 1.2.3 Laser method

o 1.3 Electrical conduction 2 Timeline of wireless power 3 See also

4 Further reading 5 References 6 External links

Electric energy transfer

Main article: Coupling (electronics)

An electric current flowing through a conductor carries electrical energy. When an electric current passes through a circuit there is an electric field in the dielectric surrounding the

conductor; magnetic field lines around the conductor and lines of electric force radially about the conductor.[3]

In a direct current circuit, if the current is continuous, the fields are constant; there is a condition of stress in the space surrounding the conductor, which represents stored electric and magnetic energy, just as a compressed spring or a moving mass represents stored energy. In an alternating current circuit, the fields also alternate; that is, with every half wave of current and of voltage, the magnetic and the electric field start at the conductor and run outwards into space with the speed of light.[4] Where these alternating fields impinge on another conductor a voltage and a current are induced.[3]

Any change in the electrical conditions of the circuit, whether internal[5] or external[6] involves a readjustment of the stored magnetic and electric field energy of the circuit, that is, a so-called transient. A transient is of the general character of a condenser discharge through an inductive circuit. The phenomenon of the condenser discharge through an inductive circuit therefore is of the greatest importance to the engineer, as the foremost cause of high-voltage and high-frequency troubles in electric circuits.[7]

Electromagnetic induction is proportional to the intensity of the current and voltage in the conductor which produces the fields and to the frequency. The higher the frequency the more intense the induction effect. Energy is transferred from a conductor that produces the fields (the primary) to any conductor on which the fields impinge (the secondary). Part of the energy of the primary conductor passes inductively across space into secondary conductor and the energy decreases rapidly along the primary conductor. A high frequency current does not pass for long distances along a conductor but rapidly transfers its energy by induction to adjacent conductors. Higher induction resulting from the higher frequency is the explanation of the apparent

difference in the propagation of high frequency disturbances from the propagation of the low frequency power of alternating current systems. The higher the frequency the more preponderant become the inductive effects that transfer energy from circuit to circuit across space. The more rapidly the energy decreases and the current dies out along the circuit, the more local is the phenomenon.[3]

The flow of electric energy thus comprises phenomena inside of the conductor[8] and phenomena in the space outside of the conductor—the electric field—which, in a continuous current circuit, is a condition of steady magnetic and dielectric stress, and in an alternating current circuit is alternating, that is, an electric wave launched by the conductor[3] to become far-field electromagnetic radiation traveling through space with the speed of light.

In electric power transmission and distribution, the phenomena inside of the conductor are of main importance, and the electric field of the conductor is usually observed only incidentally.[9] Inversely, in the use of electric power for radio telecommunications it is only the electric and magnetic fields outside of the conductor, that is electromagnetic radiation, which is of

importance in transmitting the message. The phenomenon in the conductor, the current in the launching structure, is not used.[3]

The electric charge displacement in the conductor produces a magnetic field and resultant lines of electric force. The magnetic field is a maximum in the direction concentric, or approximately so, to the conductor. That is, a ferromagnetic body[10] tends to set itself in a direction at right angles to the conductor. The electric field has a maximum in a direction radial, or approximately so, to the conductor. The electric field component tends in a direction radial to the conductor and dielectric bodies may be attracted or repelled radially to the conductor.[11]

The electric field of a circuit over which energy flows has three main axes at right angles with each other:

1. The magnetic field, concentric with the conductor. 2. The lines of electric force, radial to the conductor. 3. The power gradient, parallel to the conductor.

Where the electric circuit consists of several conductors, the electric fields of the conductors superimpose upon each other, and the resultant magnetic field lines and lines of electric force are not concentric and radial respectively, except approximately in the immediate neighborhood of the conductor. Between parallel conductors they are conjugate of circles. Neither the power consumption in the conductor, nor the magnetic field, nor the electric field, are proportional to the flow of energy through the circuit. However, the product of the intensity of the magnetic field and the intensity of the electric field is proportional to the flow of energy or the power, and the power is therefore resolved into a product of the two components i and e, which are chosen proportional respectively to the intensity of the magnetic field and of the electric field. The

component called the current is defined as that factor of the electric power which is proportional to the magnetic field, and the other component, called the voltage, is defined as that factor of the electric power which is proportional to the electric field.[11]

In radio telecommunications the electric field of the transmit antenna propagates through space as a radio wave and impinges upon the receive antenna where it is observed by its magnetic and electric effect.[11] Radio waves, microwaves, infrared radiation, visible light, ultraviolet radiation, X rays and gamma rays are shown to be the same electromagnetic radiation phenomenon, differing one from the other only in frequency of vibration.[3][12]

[edit] Electromagnetic induction

Energy transfer by electromagnetic induction is typically magnetic but capacitive coupling can also be achieved.

Electrodynamic induction method

Main articles: Inductive coupling, Electrodynamic induction, and Resonant inductive coupling

The electrodynamic induction wireless transmission technique is near field over distances up to about one-sixth of the wavelength used. Near field energy itself is non-radiative but some radiative losses do occur. In addition there are usually resistive losses. With electrodynamic induction, electric current flowing through a primary coil creates a magnetic field that acts on a secondary coil producing a current within it. Coupling must be tight in order to achieve high efficiency. As the distance from the primary is increased, more and more of the magnetic field misses the secondary. Even over a relatively short range the inductive coupling is grossly inefficient, wasting much of the transmitted energy.[13]

This action of an electrical transformer is the simplest form of wireless power transmission. The primary and secondary circuits of a transformer are not directly connected. Energy transfer takes place through a process known as mutual induction. Principal functions are stepping the primary voltage either up or down and electrical isolation. Mobile phone and electric toothbrush battery chargers, and electrical power distribution transformers are examples of how this principle is used. Induction cookers use this method. The main drawback to this basic form of wireless

transmission is short range. The receiver must be directly adjacent to the transmitter or induction unit in order to efficiently couple with it.

The application of resonance increases the transmission range somewhat. When resonant

coupling is used, the transmitter and receiver inductors are tuned to the same natural frequency. Performance can be further improved by modifying the drive current from a sinusoidal to a nonsinusoidal transient waveform.[14] Pulse power transfer occurs over multiple cycles. In this way significant power may be transmitted between two mutually-attuned LC circuits having a relatively low coefficient of coupling. Transmitting and receiving coils are usually single layer solenoids or flat spirals with series capacitors, which, in combination, allow the receiving element to be tuned to the transmitter frequency.

Common uses of resonance-enhanced electrodynamic induction are charging the batteries of portable devices such as laptop computers and cell phones, medical implants and electric

vehicles.[15][16][17] A localized charging technique[18] selects the appropriate transmitting coil in a multilayer winding array structure.[19] Resonance is used in both the wireless charging pad (the transmitter circuit) and the receiver module (embedded in the load) to maximize energy transfer efficiency. This approach is suitable for universal wireless charging pads for portable electronics such as mobile phones. It has been adopted as part of the Qi wireless charging standard. It is also used for powering devices having no batteries, such as RFID patches and contactless smartcards, and to couple electrical energy from the primary inductor to the helical resonator of Tesla coil wireless power transmitters.

Electrostatic induction method

Main article: Capacitive coupling

The Tesla effect[20][21][22] is shown with the illumination of two exhausted tubes by means of a powerful, rapidly alternating electrostatic field created between two vertical metal sheets suspended from the ceiling on insulating cords. It utilizes the physics of electrostatic induction.

Electrostatic or capacitive coupling is the passage of electrical energy through a dielectric. In practice it is an electric field gradient or differential capacitance between two or more insulated terminals, plates, electrodes, or nodes that are elevated over a conducting ground plane. The electric field is created by charging the plates with a high potential, high frequency alternating current power supply. The capacitance between two elevated terminals and a powered device form a voltage divider.

The electric energy transmitted by means of electrostatic induction can be utilized by a receiving device, such as a wireless lamp.[23][24][25] Tesla demonstrated the illumination of wireless lamps by energy that was coupled to them through an alternating electric field.[26][27][20]

\"Instead of depending on electrodynamic induction at a distance to light the tube . . . [the] ideal way of lighting a hall or room would . . . be to produce such a condition in it that an illuminating device could be moved and put anywhere, and that it is lighted, no matter where it is put and without being electrically connected to anything. I have been able to produce such a condition by creating in the room a powerful, rapidly alternating electrostatic field. For this purpose I suspend a sheet of metal a distance from the ceiling on insulating cords and connect it to one terminal of the induction coil, the other terminal being preferably connected to the ground. Or else I suspend two sheets . . . each sheet being connected with one of the terminals of the coil, and their size being carefully determined. An exhausted tube may then be carried in the hand anywhere between the sheets or placed anywhere, even a certain distance beyond them; it remains always luminous.\"[28]

The principle of electrostatic induction is applicable to the electrical conduction wireless transmission method.

“In some cases when small amounts of energy are required the high elevation of the terminals, and more particularly of the receiving-terminal D', may not be necessary, since, especially when the frequency of the currents is very high, a sufficient amount of energy may be collected at that terminal by electrostatic induction from the upper air strata, which are rendered conducting by the active terminal of the transmitter or through

which the currents from the same are conveyed.\"[29]

Electromagnetic radiation

Far field methods achieve longer ranges, often multiple kilometer ranges, where the distance is much greater than the diameter of the device(s). The main reason for longer ranges with radio wave and optical devices is the fact that electromagnetic radiation in the far-field can be made to match the shape of the receiving area (using high directivity antennas or well-collimated Laser Beam) thereby delivering almost all emitted power at long ranges. The maximum directivity for antennas is physically limited by diffraction.

Beamed power, size, distance, and efficiency

The size of the components may be dictated by the distance from transmitter to receiver, the wavelength and the Rayleigh criterion or diffraction limit, used in standard radio frequency antenna design, which also applies to lasers. In addition to the Rayleigh criterion Airy's diffraction limit is also frequently used to determine an approximate spot size at an arbitrary distance from the aperture.

The Rayleigh criterion dictates that any radio wave, microwave or laser beam will spread and become weaker and diffuse over distance; the larger the transmitter antenna or laser aperture compared to the wavelength of radiation, the tighter the beam and the less it will spread as a function of distance (and vice versa). Smaller antennae also suffer from excessive losses due to side lobes. However, the concept of laser aperture considerably differs from an antenna.

Typically, a laser aperture much larger than the wavelength induces multi-moded radiation and mostly collimators are used before emitted radiation couples into a fiber or into space.

Ultimately, beamwidth is physically determined by diffraction due to the dish size in relation to the wavelength of the electromagnetic radiation used to make the beam. Microwave power

beaming can be more efficient than lasers, and is less prone to atmospheric attenuation caused by dust or water vapor losing atmosphere to vaporize the water in contact.

Then the power levels are calculated by combining the above parameters together, and adding in the gains and losses due to the antenna characteristics and the transparency and

dispersion[disambiguation needed ] of the medium through which the radiation passes. That process is known as calculating a link budget.

Microwave method

Main article: Microwave power transmission

An artist's depiction of a solar satellite that could send electric energy by microwaves to a space vessel or planetary surface.

Power transmission via radio waves can be made more directional, allowing longer distance power beaming, with shorter wavelengths of electromagnetic radiation, typically in the

microwave range. A rectenna may be used to convert the microwave energy back into electricity. Rectenna conversion efficiencies exceeding 95% have been realized. Power beaming using microwaves has been proposed for the transmission of energy from orbiting solar power

satellites to Earth and the beaming of power to spacecraft leaving orbit has been considered.[2][30] Power beaming by microwaves has the difficulty that for most space applications the required aperture sizes are very large due to diffraction limiting antenna directionality. For example, the 1978 NASA Study of solar power satellites required a 1-km diameter transmitting antenna, and a 10 km diameter receiving rectenna, for a microwave beam at 2.45 GHz.[31] These sizes can be somewhat decreased by using shorter wavelengths, although short wavelengths may have

difficulties with atmospheric absorption and beam blockage by rain or water droplets. Because of the \"thinned array curse,\" it is not possible to make a narrower beam by combining the beams of several smaller satellites.

For earthbound applications a large area 10 km diameter receiving array allows large total power levels to be used while operating at the low power density suggested for human electromagnetic exposure safety. A human safe power density of 1 mW/cm2 distributed across a 10 km diameter area corresponds to 750 megawatts total power level. This is the power level found in many modern electric power plants.

Following World War II, which saw the development of high-power microwave emitters known as cavity magnetrons, the idea of using microwaves to transmit power was researched. By 19 a miniature helicopter propelled by microwave power had been demonstrated.[32]

Japanese researcher Hidetsugu Yagi also investigated wireless energy transmission using a directional array antenna that he designed. In February 1926, Yagi and Uda published their first paper on the tuned high-gain directional array now known as the Yagi antenna. While it did not prove to be particularly useful for power transmission, this beam antenna has been widely adopted throughout the broadcasting and wireless telecommunications industries due to its excellent performance characteristics.[33]

Wireless high power transmission using microwaves is well proven. Experiments in the tens of kilowatts have been performed at Goldstone in California in 1975[34][35][36] and more recently (1997) at Grand Bassin on Reunion Island.[37] These methods achieve distances on the order of a kilometer.

Laser method

With a laser beam centered on its panel of photovoltaic cells, a lightweight model plane makes the first flight of an aircraft powered by a laser beam inside a building at NASA Marshall Space Flight Center.

In the case of electromagnetic radiation closer to visible region of spectrum (10s of microns (um) to 10s of nm), power can be transmitted by converting electricity into a laser beam that is then pointed at a solar cell receiver. This mechanism is generally known as \"powerbeaming\" because the power is beamed at a receiver that can convert it to usable electrical energy. Advantages of laser based energy transfer compared with other wireless methods are:[38]

1. collimated monochromatic wavefront propagation allows narrow beam cross-section area for energy

transmission over large ranges.

2. compact size of solid state lasers-photovoltaics semiconductor diodes fit into small products. 3. no radio-frequency interference to existing radio communication such as Wi-fi and cell phones. 4. control of access; only receivers illuminated by the laser receive power.

Its drawbacks are:

1. Conversion to light, such as with a laser, is inefficient

2. Conversion back into electricity is inefficient, with photovoltaic cells achieving 40%–50%

efficiency.[39] (Note that conversion efficiency is rather higher with monochromatic light than with insolation of solar panels).

3. Atmospheric absorption causes losses.

4. As with microwave beaming, this method requires a direct line of sight with the target.

The laser \"powerbeaming\" technology has been mostly explored in military weapons[40][41][42] and aerospace[43][44] applications and is now being developed for commercial and consumer electronics Low-Power applications. Wireless energy transfer system using laser for consumer space has to satisfy Laser safety requirements standardized under IEC 60825.

To develop an understanding of the trade-offs of Laser (\"a special type of light wave\"-based system):[45][46][47][48]

1. Propagation of a laser beam[49][50][51] (on how Laser beam propagation is much less affected by

diffraction limits)

2. Coherence and the range limitation problem (on how spatial and spectral coherence characteristics of

Lasers allows better distance-to-power capabilities[52])

3. Airy disk (on how wavelength fundamentally dictates the size of a disk with distance)

4. Applications of laser diodes (on how the laser sources are utilized in various industries and their sizes

are reducing for better integration)

Geoffrey Landis[53][][55] is one of the pioneers of solar power satellite[56] and laser-based transfer of energy especially for space and lunar missions. The continuously increasing demand for safe and frequent space missions has resulted in serious thoughts on a futuristic space elevator[57][58] that would be powered by lasers. NASA's space elevator would need wireless power to be beamed to it for it to climb a tether.[59]

NASA's Dryden Flight Research Center has demonstrated flight of a lightweight unmanned model plane powered by a laser beam.[60] This proof-of-concept demonstrates the feasibility of periodic recharging using the laser beam system and the lack of need to return to ground.

Electrical conduction

The Tesla coil wireless power transmitter

U.S. Patent 1,119,732

Means for long conductors of electricity forming part of an electric circuit and electrically connecting said ionized beam to an electric circuit. Hettinger 1917 -(U.S. Patent 1,309,031) Main article: World Wireless System

Nikola Tesla proposed transmission of high-potential, high-frequency alternating current through the earth with an atmospheric return circuit for transmission of power and signals. Tesla's method relied on alternating current to be transmitted through atmospheric strata having a barometric pressure even greater than 130 millimeters of mercury.[61] Tesla proposed to induce current flows by means of electrostatic induction through the lower atmosphere up to about two or three miles above the Earth's surface. [62] [63] Electrical conduction through atmospheric strata is made possible by the creation of capacitively coupled discharge plasma through the process of atmospheric ionization.[][65][66]

Tesla theorized that electrical energy can be transmitted through the earth and the atmosphere. In the course of his research he successfully lit lamps at moderate distances and was able to detect the transmitted energy at much greater distances. The Wardenclyffe Tower project was a

commercial venture for trans-Atlantic wireless telephony and proof-of-concept demonstrations of global wireless power transmission. The facility was not completed because of insufficient funding.[67]

The same transmitter used for the atmospheric conduction method is used for the terrestrial single-conductor earth resonance method.[68][69]

Timeline of wireless power

• • • •

1820: André-Marie Ampère develops Ampere’s law showing that electric current produces a magnetic field.

1831: Michael Faraday develops Faraday’s law of induction describing the electromagnetic force induced in a conductor by a time-varying magnetic flux. 1836: Nicholas Callan invents the electrical transformer.

18: James Clerk Maxwell synthesizes the previous observations, experiments and equations of electricity, magnetism and optics into a consistent theory and mathematically models the behavior of electromagnetic radiation.

• • • • • • • • • • •

• • •

•

• • • •

1888: Heinrich Rudolf Hertz confirms the existence of electromagnetic radiation. Hertz’s \"apparatus for generating electromagnetic waves\" was a VHF or UHF \"radio wave\" spark gap transmitter. 11: Tesla was one of the first to patent a means to reliably produce radio frequencies (e.g., U.S. Patent 447,920, \"Method of Operating Arc-Lamps\" (March 10, 11)).

13: Tesla demonstrates the wireless illumination of phosphorescent lamps of his design at the World's Columbian Exposition in Chicago.[70]

13: Tesla publicly demonstrates wireless power and proposes the wireless transmission of signals before a meeting of the National Electric Light Association in St. Louis.[25][71][72][73]

14: Tesla lights incandescent lamps wirelessly at the 35 South Fifth Avenue laboratory in New York City by means of \"electro-dynamic induction\" or resonant inductive coupling.[74][75][76]

14: Hutin & LeBlanc, espouse long held view that inductive energy transfer should be possible, they received U.S. Patent # 527,857 describing a system for power transmission at 3 kHz.[77]

14: Jagdish Chandra Bose rings a bell at a distance using electromagnetic waves and also ignites gunpowder, showing that communications signals can be sent without using wires.[78][79]

15: Marconi was the first scientist to achieve successful radio transmission.[80] In summer 15, Marconi sent signals 1.5 miles.[81] Developed Marconi's Law.

16: Tesla demonstrates wireless transmission over a distance of about 48 kilometres (30 mi).[82] 17: Tesla files his first patent application dealing specifically with wireless transmission. 1904: At the St. Louis World's Fair, a prize is offered for a successful attempt to drive a 0.1

horsepower (75 W) airship motor by energy transmitted through space at a distance of at least 100 feet (30 m).[83]

1926: Shintaro Uda and Hidetsugu Yagi publish their first paper on Uda's \"tuned high-gain directional array\"[33] better known as the Yagi antenna.

1961: William C. Brown publishes an article exploring possibilities of microwave power transmission.[84][85]

19: Brown demonstrates on CBS News with Walter Cronkite a model helicopter that receives all of the power needed for flight from a microwave beam. Between 1969 and 1975, Brown is technical director of a JPL Raytheon program that beams 30 kW over a distance of 1600 meters (1 mile) at 84% efficiency.[citation needed]

1968: Peter Glaser proposes wirelessly transmitting solar energy captured in space using

\"Powerbeaming\" technology.[86][87] This is usually recognized as the first description of a solar power satellite.

1971: Prof. Don Otto develops a small trolley powered by induction at The University of Auckland, in New Zealand.[citation needed]

1973: The world's first passive RFID system is demonstrated at Los-Alamos National Lab.[88] 1975: Goldstone Deep Space Communications Complex does experiments in the tens of kilowatts.[34][35][36]

1988: A power electronics group led by Prof. John Boys at The University of Auckland in New

Zealand, develops an inverter using novel engineering materials and power electronics and conclude that power transmission by means of electrodynamic induction should be achievable. A first prototype for a contact-less power supply is built. Auckland Uniservices, the commercial company of The University of Auckland, patents the technology.[citation needed]

•

•

•

• • •

•

•

•

•

• •

•

19: Daifuku, a Japanese company, engages Auckland Uniservices Ltd. to develop technology for car assembly plants and materials handling providing challenging technical requirements including multiplicity of vehicles.[citation needed]

1990: Prof. John Boys team develops novel technology enabling multiple vehicles to run on the same inductive power loop and provide independent control of each vehicle. Auckland UniServices Patents the technology.[citation needed]

1996: Auckland Uniservices develops an Electric Bus power system using electrodynamic induction to charge (30–60 kW) opportunistically commencing implementation in New Zealand. Prof John Boys Team commission 1st commercial IPT Bus in the world at Whakarewarewa, in New Zealand.[citation needed]

1998: RFID tags are powered by electrodynamic induction over a few feet.

1999: Dr. Herbert L. Becker powers a lamp and a hand held fan from a distance of 30 feet.[citation needed] 1999: Prof. Shu Yuen (Ron) Hui and Mr. S.C. Tang file a patent on \"Coreless Printed-Circuit-Board (PCB) transformers and operating techniques\with \"vertical flux\" leaving the planar surface. The circuit uses resonant circuits for wireless power transfer. EP(GB)0935263B

2000: Prof. Shu Yuen (Ron) Hui invent a planar wireless charging pad using the \"vertical flux\"

approach and resonant power transfer for charging portable consumer electronic products. A patent is filed on \"Apparatus and method of an inductive battery charger,” PCT Patent PCT/AU03/00 721, 2000.

2000: Based on the coreless PCB transformer developed by Prof. Ron Hui, Prof. B. Choi and his team at Kyungpook National University publish a paper on “A new contactless battery charger for portable telecommunication/computing electronics,” in Proc. ICCE’00 Int. Conf. Consumer Electron., 2000, pp. 58–59. The coreless PCB transformer is used to wirelessly charge a mobile phone.

2001 Prof. Shu Yuen (Ron) Hui and Dr. S.C. Tang file a patent on \"Planar Printed-Circuit-Board Transformers with Effective Electromagnetic Interference (EMI) Shielding\". The EM shield consists of a thin layer of ferrite and a thin layer of copper sheet. It enables the underneath of the future wireless charging pads to be shielded with a thin EM shield structure with thickness of typically 0.7mm or less. Patent: US6,501,3.

2001: Prof. Ron Hui's team demonstrate that the coreless PCB transformer can transmit power close to 100W in ‘A low-profile low-power converter with coreless PCB isolation transformer, IEEE Transactions on Power Electronics, Volume: 16 Issue: 3 , May 2001. A team of Philips Research Center Aachen, led by Dr. Eberhard Waffenschmidt, use it to power an 100W lighting device in their paper \"Size advantage of coreless transformers in the MHz range\" in the European Power Electronics Conference in Graz.

2001: Splashpower formed in the UK. Uses coupled resonant coils in a flat \"pad\" style to transfer tens of watts into a variety of consumer devices, including lamp, phone, PDA, iPod etc.[citation needed] 2002: Prof. Shu Yuen (Ron) Hui extends the planar wireless charging pad concept using the vertical flux approach to incorporate free-positioning feature for multiple loads. This is achieved by using a multilayer planar winding array structure. Patent were granted as \"Planar Inductive Battery Charger\GB23720 and GB 23767.

2004: Electrodynamic induction used by 90 percent of the US$1 billion clean room industry for materials handling equipment in semiconductor, LCD and plasma screen manufacture.[citation needed]

•

• •

•

• • •

•

• •

2005: Prof. Shu Yuen (Ron) Hui and Dr. W.C. Ho publish their work in the IEEE Transactions on a planar wireless charging platform with free-positioning feature. The planar wireless charging pad is able to charge several loads simultaneously on a flat surface.

2005: Prof Boys' team at The University of Auckland, refines 3-phase IPT Highway and pick-up systems allowing transmission of power to moving vehicles in the lab.[citation needed]

2007: A localized charging technique is reported by Dr. Xun Liu and Prof. Ron Hui for the wireless charging pad with free-positioning feature. With the aid of the double-layer EM shields enclosing the transmitter and receiver coils, the localized charging selects the right transmitter coil so as to minimize flux leakage and human exposure to radiation.

2007: Using electrodynamic induction a physics research group, led by Prof. Marin Soljacic, at MIT, wirelessly power a 60W light bulb with 40% efficiency at a 2 metres (6.6 ft) distance with two 60 cm-diameter coils.[]

2008: Bombardier offers a new wireless power transmission product PRIMOVE, a system for use on trams and light-rail vehicles.[90]

2008: Industrial designer Thanh Tran, at Brunel University make a wireless lamp incorporating a high efficiency 3W LED.[citation needed]

2008: Intel reproduces Tesla's original 14 implementation of electrodynamic induction and Prof. John Boys group's 1988 follow-up experiments by wirelessly powering a nearby light bulb with 75% efficiency.[91]

2008: Greg Leyh and Mike Kennan of the Nevada Lightning Laboratory publish a paper on Tesla's disturbed charge of ground and air method of wireless power transmission with circuit simulations and test results showing an efficiency greater than can be obtained using the electrodynamic induction method.[92]

2009: Palm (now a division of HP) launches the Palm Pre smartphone with the Palm Touchstone wireless charger.

2009: A Consortium of interested companies called the Wireless Power Consortium announce they are nearing completion for a new industry standard for low-power (which is eventually published in August 2010) inductive charging.[93]

2009: An Ex approved Torch and Charger aimed at the offshore market is introduced.[94] This product is developed by Wireless Power & Communication, a Norway based company.

2009: A simple analytical electrical model of electrodynamic induction power transmission is proposed and applied to a wireless power transfer system for implantable devices.[95]

2009: Lasermotive uses diode laser to win $900k NASA prize in power beaming, breaking several world records in power and distance, by transmitting over a kilowatt more than several hundred meters.[96]

2009: Sony shows a wireless electrodynamic-induction powered TV set, 60 W over 50 cm[97]

2010: Haier Group debuts “the world's first” completely wireless LCD television at CES 2010 based on Prof. Marin Soljacic's follow-up research on Tesla's electrodynamic induction wireless energy transmission method and the Wireless Home Digital Interface (WHDI).[98]

2010: System On Chip (SoC) group in University of British Columbia develops a highly efficient wireless power transmission systems using 4-coils. The design is optimized for implantable applications and power transfer efficiency of 82% is achieved.[99]

2012: \"Bioelectromagnetics and Implantable Devices\" group in University of Utah, USA develops an efficient multi-Coil telemetry system for power and data transfer in biomedical Implants. Design

• • •

• •

•

•

approach is extendable to other industrial \"smart\" wireless power transfer system. Proposed multi-coil based telemetry system achieves more than twice power transfer efficiency and higher tunable

frequency bandwidth as compared to its equivalent two-coil design. Based on circuit theory, analytical formulation is proposed to optimize the design for maximum power transfer, frequency bandwidth and power transfer efficiency. [100]

See also

• • • • • • • • • • • • • •

Beam-powered propulsion

Beam Power Challenge – one of the NASA Centennial Challenges Differential capacitance Distributed generation Electricity distribution

Electric power transmission Electromagnetic compatibility Energy harvesting

Friis transmission equation Microwave power transmission Resonant inductive coupling Thinned array curse Transmission medium Wardenclyffe Tower

Further reading

Books

• • • •

• • •

•

Walker, J., Halliday, D., & Resnick, R. (2011). Fundamentals of physics. Hoboken, NJ: Wiley.

Hu, A. P. (2009). Wireless/Contactless power supply: Inductively coupled resonant converter solutions. Saarbrücken, Germany: VDM Verlag Dr. Müller.

Valone, T. (2002). Harnessing the wheelwork of nature: Tesla's science of energy. Kempton, Ill: Adventure Unlimited Press.

General Electric Co. (1915). General Electric review, Volume 18. \"Wireless Transmission of Energy\" By Elihu Thomson. General Electric Company, Lynn. (ed. Lecture by Professor Thomson, National Electric Light Association, New York.)

Steinmetz, C. P. (1914). Elementary lectures on electric discharges, waves and impulses, and other transients. New York: McGraw-Hill book co., inc.

Louis Cohen (1913). Formulae and tables for the calculation of alternating current problems. McGraw-Hill.

Kennelly, A. E. (1912). The application of hyperbolic functions to electrical engineering problems: Being the subject of a course of lectures delivered before the University of London in May and June 1911. London: University of London Press.

Orlich, E. M. (1912). Die Theorie der Wechselströme.

• • •

Fleming, J. A. (1916) The principles of electric wave telegraphy and telephony. London: Longmans, Green and Co.

Fleming, J. A. (1911). Propagation of electric currents in telephone & telegraph conductors. New York: Van Nostrand.

Franklin, W. S. (1909). Electric waves: An advanced treatise on alternating-current theory. New York: Macmillan Co.

Patents

• • • •

U.S. Patent 4,955,562, Microwave powered aircraft, John E. Martin, et al. (1990).

U.S. Patent 3,933,323, Solid state solar to microwave energy converter system and apparatus, Kenneth W. Dudley, et al. (1976).

U.S. Patent 3,535,3, Microwave power receiving antenna, Carroll C. Dailey (1970).

U.S. Patent 9,621, Apparatus for Transmission of Electrical Energy, Nikola Tesla (1900).

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能量无线传输

能量的无线传输或者电能的无线传输是一种电能直接从电源侧传输到负载侧的无导线连接的系统。在一些导线会带来不便、危险或者不允许导线存在的情况下，无线传输是相当有用的。电能的无线传输不同于无线通信，比如说收音机。对于无线通信而言，从噪声中过滤得到的有用信号非常少，得到有用信号能量的比重的大小是非常重要的[1]。对于无线电能传输，效率是更重要的参数。一个发电厂所发出的能量必须将大部分输送到接收器，使系统经济。

能量的无线传输最常见的形式是直接采用磁共振感应，正在考虑的其他方法包括微波或激光形式的电磁辐射[2]。

内容 1.电能的传输

1.1 电磁感应 1.1.1电动感应法 1.1.2 静电感应法 1.2电磁辐射

1.2.1 定向的功率、大小、距离、效率 1.2.2 微波法 1.2.3 激光法 1.3 电能的传导

1.3.1地面和空气之间传输的方式① 1.3.1.1地面与大气传输线路间的回返 1.3.1.2 地面单导体电磁波传输方向

2.电能无线传输发展的时间轴 3.参见 4.引申阅读 5.参考文献 6.外部链接

主要文章：耦合（电子）

一束电子流流经导体便产生电能。当流过电路的电流穿过一个电场 ，该电场处于围绕在导体周围的介质中，那么导体周围的磁场线和电场线会呈辐射状发散[3]。

在直流电路中，如果电流是连续的，那么导体周围不会产生磁场；有一个在导体周围产生应力的状态，这种状态是指在电场或者磁场中所存储的能量，类似于压缩弹簧或者运动的物体所具有的能量。在交流电路中，导体周围会产生交变的磁场。也就是说，每半波

的电流和电压变化，导体周围便产生了电场和磁场并且以光速变化[4]。当另外一导体处在交流的磁场中也会产生电流和电压[3]。

任何电路电气状态的改变，无论是在存储磁场和电场的电路的内部和外部[5][6]，都称为瞬态磁场能量的调整。 瞬态是电容器通过一电感电路放电具有的一般性质。电容通过一电感电路放电的现象对研究者来说是非常重要的，因为这是电路在高频率和高压下作用所产生的[7]。

交变的电场产生磁场，电磁感应与电流或者电压在电场中变化的频率和强度成正比，频率越高，产生的磁场越强。产生的电磁能可从产生磁场的导体（初级导体）转移至在磁场中的任何导体（第二导体），同时，在传递过程中，电磁能会沿着磁场线迅速减小。高频率的交变电流虽不沿初级导体长距离的传送，但其产生的电磁能却迅速感应到初级导体周围的导体。交流电频率越高越有利于电路与电路间电磁能的转移。能量减小的越迅速并在导体中消失，在导体中产生电磁感应现象越强[7]。

在电力输送与分配过程中，内部导体的现象是最主要的，导体的电场是次要的[9]。在无线电通信中，导体产生的磁场或者电场是最重要的[3]。

导体中的由于电荷的移动而产生了磁场和由此而产生的电场线，磁场是呈中心辐射状的发散。

电场的能量流向路径主要有三个彼此垂直的轴线： 1.与导体同心的磁场； 2.导体径向的电场线； 3.与导体平行的功率梯度；

在由几个导体组成的电路中，每个导体产生的电场和磁场及磁力线和电场线相互叠加，除了在导体附近外，在其他地方这些都不属于同心或者径向的关系。导体中的功耗总是与流过导体的能量成正比，然而，磁场或者电场能量强度的大小取决于通过磁场或者电场的能源的流量大小有关。电流和电压是电场与磁场成比例关系的关系因素[11]。

在无线电通信中，通过无线电波的空间和发射天线传播电场撞击后观察其磁电效应

[11]

。无线电波，微波，红外辐射，可见光，紫外线辐射，X射线和伽玛射线显示的是相同电磁感应

通过电磁感应的能量转移通常是磁性的，但也可以实现电容耦合。 电动感应方法

主要文章：电感耦合，电动感应，共振电感耦合

电动感应无线传输技术适用于近场距离为所用波长约六分之一。近场能量本身是无辐

的电磁辐射现象，不同于其他只在振动频率[3][12]。

射的，但是确实发生了一些辐射损耗，此外还有通常的电阻损耗。电动感应电流流经初级线圈产生磁场，在二次线圈产生了电流所产生的作用。耦合必须拧紧，以提高传输效率。由于从小距离开始增加，随着距离的增加越来越多的磁场能量在传输至二次线圈时被损耗了，导致传输能量的浪费[13]。

电力变压器的工作过程是最简单的无线能量传输形式。变压器的初级和次级电路没有直接连接。能量的传输是通过互感来进行的，主要职能是加强初级电压向上或者向下的电气隔离。手机和电动牙刷的电池充电器、配电变压器是使用这个原则的最好的例子，电磁炉也是使用此种方法的，但是，这种无线传输的方式主要缺点是短距离传送，接收器必须与发射器或感应装置直接相邻，以便有效地感应。

共振技术的应用增加了无线传输的范围，当发射器和接收电感器调整到相同的自然频率时便发生了共振耦合。性能可以进一步改善非正弦瞬态波形正弦电流通过的驱动器[14]。脉冲功率传输有多个周期，发射和接受线圈通常是单层线圈或平面螺旋系列电容器，允许接受单元进行调整发射频率。

共振增强的电动感应常见的用途是便携设备，如笔记本电脑和手机，医疗植入式和电动汽车的充电电池[15][16][17]。传统的充电技术[18]选择适当的发射线圈在一个多层缠绕的阵列结构[19]。共振是用于无线充电垫（发射电路）和接受模块（嵌入在负载），以最大限度地提高能源转换效率。这种方法适合便携式电子产品如手机通用的无线充电垫，它已被采纳为无线充电标准的一部分。

它也可用于螺旋谐振器的特斯拉线圈无线功率发射机的电池，如REID补丁和非接触式智能卡，以及从初级电感耦合电能的供电设备。

静电感应法

主要文章：电容耦合

静电或电容耦合是电能通过介质的途径，在实践中，它是一个或者两个或者两个以上的绝缘端子，板，电极，或升高超过地面进行节点之间的电场梯度差分电容。电场创建高容量高频率的交流电电源充电板，两个高架终端和供电设备之间的电容构成一个分压器。

电能通过静电感应可实现无线传输至接受设备，如无线灯[23][24][25]。特斯拉展示了能源无线照明灯通过交变领域实现了能量无线传输[26][27][28]。

“相反，在距离上取决于电动感应光管……一个大厅或者房间照明的理想方式会产生这样的条件，可移动的照明设备，可随时随地的被点亮，没有任何的电气连接。我已经能够产生这样的情况，在房间里产生一个强大的静电场。为此，我将电灯连接到一个感应线圈的终端，其他终端最好连接到地面。不然我暂停……电灯被放置在任意位置均可发光，当然要在一定的距离范围内[28]。”

静电感应原则是适用于电能无线传输的一种方法[29]。

电磁辐射

远场方法实现了更长的范围，通常为数公里，这里的距离要比设备（S）的直径大的多。无线电波和光学器件需要大范围的主要原因是在远场的电磁辐射必须有与之相匹配的接受面积的形状（使用高方向性的天线或准直激光束），从而提供提供几乎所有在远场距离的发射功率。 发射功率，大小，距离和效率

元件的大小可以从发射器到接受器，波长和瑞利判据或标准的射频天线来设计，这也适用于以激光衍射的极限和距离所决定。此外，瑞利判据艾里的衍射极限也经常被用来确定在任意距离的光圈近似的光斑大小。

根据瑞利判据描述，任何无线电波，微博或者激光束都在超过一定距离后变得越来越弱，激光孔径的概念不同于天线。通常状况下要比较大的波长激光孔径辐射大。

微波法

主要文章：微波功率传输

通过无线电波进行的能量传输可更加定向的长距离的传送功率，电磁辐射的波

长较短，通常为微波范围内。一个整流天线，可用于微波能量转换为电能。现在已经实现了整流天线转换效率为95%。现在已经提出了用微波发送的能量作为能量的传输方式[2][30]。

微波发射的功率的难题在于大部分空间应用所需的光圈大小是非常大的，这是由于衍射具有方向性。例如，1978年美国宇航局的太阳能发电卫星研究需要直径为1公里的发射天线，接受整流天线直径10公里，在2.45GH为微波束。这些尺寸可是更短的波长有所下降，虽然短的波长可能会被大气吸收了或者是被雨水吸收。

对地球上的应用，大面积的10公里直径接收阵列允许在低功率密度人体电磁暴露安全建议操作时要使用大型的总功率水平。 1 mW/cm2的人类安全的功率密度分布在整个直径10公里的区域，相当于750兆瓦的总功率水平。这是发现在许多现代的发电厂的功率水平。

继第二次世界大战，它看到了高功率微波发射器，称为腔磁控管的发展，利用微波发射功率的想法进行了研究。微波功率推动一个微型直升机，到19年已被证明[31]。

日本的研究员Hidetsugu Yagi也探讨使用他设计的定向天线阵列的无线能量传输技术。

在1926年2月，Yagi 和 Uda发表了他们的第一篇论文上的高增益定向调整现在的天线阵列。虽然它没有被证明对电力传输特别有用，但这束天线已被广泛采用在整个广播和无线电信行业，因为其具有性能优良的特点[32]。

高功率无线传输技术在使用微波炉上得到了很好的证明。在最新千瓦的实验已经在加州于1975年在戈德斯通[33][34][35]，最近（1997年）在大盆地留尼汪冰岛[36]，这些方法可在一公里的距离内实现。

激光法

在电磁辐射接近可见光谱区（10微米（微米）的纳米10S）的情况下，功率可转换成太阳能电池接收器，然后指出了激光束的电力传输。这种机制是基因集会称为

“powerbeaming”，因为电源在横梁一个接收器，可以将其转换为可用的电能。 基于激光的能量转移与其他无线方法相比的优点是[37]：

1.平行单色光波正面的传播允许电能长距离传输中光束具有窄的横截面。 2.可以将小型的光电固态激光器，半导体二极管放入小的产品中。 3.在现有的无线电通信中没有无线电频率的干扰，比如Wi-Fi和手机。 4.可控制访问；仅接受激光器的照射。 其主要缺点：

1.必须转换为光，比如用激光测试，效率比较低；

2.转换为电能是低效的，光伏电池仅达到了40%-50%的效率[38]。（注意，比起日晒的太阳能电池板转换效率要高得多）

3.大气吸收造成损失。

4.随着微波的传输，这种方法需要有直接的目标线。

激光“能量发射”技术大多已探索[39][40][41]并应用在航天和军事武器上[42][43]，并正在为商业和消费类电子产品的低功耗的应用进行开发。无线能量传输系统使用激光器的消费空间，满足激光根据IEC 60825标准的安全要求。

要发展激光权衡的理解（基于系统“特殊类型的光波”）[44][45][46][47]： 1.激光束的传播[48][49][50]（激光束的传播如何较小地受衍射极限的影响）。

2.连贯性和范围问题（空间和光谱相干激光特性允许更好的距离—功率的能力[51]）

3.通风盘（波长如何从根本上决定磁盘的大小与距离）。

4.激光二极管（如何让激光光源在各个行业应用并且其尺寸要减小以利于更好地整合）。

Geoffrey Landis是太阳能发电卫星和基于激光能量转移特别是针对月球和空间的先驱之一。随着太空任务的愈加频繁及对安全性的要求不断增加，在认真思考之下，未来的

太空电梯[56][57]将通过激光器供电。美国宇航局的太空电梯将通过无线传输能量来供电[58]。

美国宇航局德莱顿飞行研究中心已经删除了采用激光束供能的轻量级无人机模型的航空旅行。这个概念证明演示了使用激光系统缺乏返回地面定期充电的可行性。

电动传导

主要文章：世界无线通讯系统

特拉斯提出的高潜力高频率的传输是指返回到大气中的电能和信号的传输。特拉斯的方法依赖于交流电的传输要通过有一个气压大于130毫米的大气阶层，特拉斯建议所引起的静电感应电流流经大约两三公里以上的地球表面的低层大气[60][61][62]。

通过大气阶层的电气传导是由通过对大气电离过程中创造的电容耦合放电等离子体实现的[63][][65]。

在特拉斯的理论中，他提出可以通过地球和大气来实现电能的传输，在他的研究过程中，他成功地点燃了中等距离远的灯并能够探测到更远距离的电能传输。Wardenclyffe Tower项目是跨大西洋的无线电话商业企业，它是全球无线电传输发展的好的例证，但是该项目由于资金不足而为完成[66]。用于大气传导的相同的发射机用于地面单导体共振

[67][68]

。

无线供电时间表

1820年：André-Marie Ampère 应用安培定律展示了电流产生磁场。

1831年：迈克尔·法拉第应用法拉第电磁感应定律描述电磁力随时间变化的磁诱导导体。 1836年：尼古拉斯·卡伦发明的电力变压器。

18年：詹姆斯·克拉克·麦克斯韦综合成一个电磁辐射行为以前的观察，实验和电磁及光学方程一致的理论和数学模型。

1888年：海因里希·鲁道夫·赫兹证实了电磁辐射的存在。赫兹的“产生电磁波的仪器”VHF或UHF是“无线电波”火花隙发射机。

13年：特斯拉在芝加哥的世界哥伦比亚博览会上展示了他设计的磷光灯照明 [69]。 13：特斯拉在圣路易斯的全国电灯协会[25] [70][71]上展示了无线电源。

14年：特斯拉在纽约第五大道的35家实验室展示了无线灯白炽灯“电动力感应”或谐振电感耦合的方式 [72][73][74]。

14年：Hutin和勒布朗，信奉长期持有的观点，应该是可能的电感能量转移，他们收到了美国专利＃527.857描述输电系统在3 kHz[75]。

14年：贾格迪什·钱德拉·鲍斯环在使用距离的电磁波的钟声，从而点燃了火药，表明可以发送无需使用电线通信信号[76][77]。

15年：马可尼是第一个科学家成功实现无线传输[78]在15夏天，马可尼发送信号1.5公里[79]马可尼的“...

16年：特斯拉实现了距离约48公里（30英里）的无线传输[80]。 17：特斯拉他的第一个专利申请文件，专门处理与无线传输。

1904年：在圣路易斯世界博览会，奖品是一个成功的尝试，带动0.1马力（75瓦）能源英尺的距离至少有100（30米）[81]通过空间传播的飞艇电机提供。

1926年：晋太郎宇田和Hidetsugu公布的“调谐高增益定向阵列的第一篇论文”[32]。 1961年：威廉·C·布朗发表了一篇文章，探讨微波输电的可能性[82][83]。

19年：布朗演示了在 CBS新闻与沃尔特·克朗凯特接收所有从微波束的飞行所需的功率模型直升机。布朗是在1969年和1975年之间，横梁距离1600米（1英里），84％的效率超过30千瓦的喷气推进实验室的雷神方案的技术总监。[需要的引证]

1968年：彼得·格拉泽建议使用“Powerbeaming”技术，在太空中捕获的太阳能无线传输[84][85]这通常是公认的太阳能发电卫星的第一次描述。

1971年：唐·奥托教授开发了一个感应小推车，新西兰奥克兰大学[需要的引证] 1973年：世界上第一个无源RFID系统中，在洛斯阿拉莫斯国家实验室[86]。 1975年：斯通深空通信综合大楼确实千瓦的最新实验[33][34][35]。

1988年在新西兰奥克兰大学电力电子学教授约翰·男孩在A组，开发中使用新型工程材料和电力电子逆变器和结束，输变电，电动感应应该是可以实现的。是建立一个非接触式电源的第一架原型机。 uniservices奥克兰，奥克兰大学，专利技术的商业公司。[需要的引证]

19年：大福，一家日本公司，从事奥克兰有限公司Uniservices。发展汽车组装厂和处理提供具有挑战性的技术要求，包括车辆的多重材料的技术。[需要的引证]

1990年：约翰教授男孩团队开发新技术，使多个车辆上运行相同的感应式电源回路，并提供每辆车的控制。奥克兰专利技术。[引证需要]

1996年：奥克兰开发的电动客车动力系统，使用电动感应充电（30-60千瓦）的时机开始在新西兰实施。教授约翰男孩小组委员会1日在世界商业的IPT巴士在新西兰在华卡雷瓦雷瓦[引文需要]

1998年：RFID标签是电动感应供电超过几英尺。

1999年：赫伯特博士贝克尔权力从一个30英尺的距离通过手持风扇发电的一盏灯[引文需要]。

1999年：教授舒元朗区（RON）辉先生及资深大律师唐文件“无芯印刷电路板（PCB）的变压器和操作技术，形成平面为未来充电”垂直通量“留下的平面表面的基础专利。无线电力传输电路采用谐振电路。 EP“（GB）0935263B

2000年：教授舒元（罗恩）辉发明了一种无线充电垫使用平面垂直通量“的方针和便携式消费电子产品充电的谐振权力移交。专利申请“仪器和方法的感应电池充电器，”721 PCT专利PCT/AU03/00的，2000年。

2000年：基于蔡教授，B.教授罗恩·许和他的团队在庆北国立大学发布一纸“无芯PCB变压器”一个新的便携式电子电信/计算的非接触式电池充电器，“在PROC。 ICCE'00国际。 CONF。消费电子，2000年，P. 58-59.的无芯PCB变压器用于无线手机充电。 2001年舒教授元朗区（RON）辉博士和南卡罗来纳唐文件对专利“平面印刷电路板变压

器的电磁干扰（EMI）的有效屏蔽。”电磁屏蔽板组成的铁素体的一层薄薄的铜。它使未来的无线充电垫厚度为0.7mm或更少通常用薄的电磁屏蔽结构屏蔽下方。专利号：US6，501.3。

2001：教授罗恩·许的团队恶魔trate，“无芯印刷电路板变压器可以传送无芯印刷电路板隔离变压器电源”一个低调的低功率转换接近100W的，电力电子，卷IEEE交易：16期：3，二○○一年五月。飞利浦研究中心亚琛埃伯哈德博士率领的一个团队，用它的功率在100W的照明设备在他们的论文在格拉茨在欧洲电力电子会议“空心变压器的大小在MHz范围内的优势”。

2001年：在英国Splashpower的形成。一个单位的“垫”的风格，在使用最新的瓦转移到各种消费电子设备，包括灯，手机，掌上电脑，IPOD等[需要的引证]耦合谐振线圈 2002：教授舒元（RON）回族无线充电垫延伸平面的概念，使用垂直通量的方法来整合多个负载的自由定位功能。这是通过使用一种多层平面绕组阵列结构。专利被授予“平面感应式充电器”，GB23720和GB 23767。

2004年：电子动态感应的10亿美元的洁净室行业的90％用于处理[引文需要]在半导体，液晶和等离子屏幕制造设备的材料。

2005年：舒源（教授罗恩）辉和博士W.C.发布他们的工作平面自由定位功能的无线充电平台上，在IEEE交易。平面无线充电垫能同时在一个平面上收取多个负载。

2005年：教授男童在奥克兰大学，细致的IPT公路和接机系统，使传输功率在3个阶段的实验室[需要的引证]移动车辆团队。

2007年：一个本地化的充电技术是由博士鲁迅刘和辉教授罗恩·自由定位功能的无线充电垫。双层封闭的发射器和接收线圈的电磁屏蔽的援助，本地化的收费权选择发射线圈作为太阳和人类暴露在辐射中，以尽量减少漏磁。

2007年：使用电动感应物理研究小组，由马林·索尔亚契奇教授率领，在麻省理工学院，在2米（6.6英尺）的距离无线功率60W灯泡40％的效率，有两个直径60厘米的线圈[87]。 2008年：庞巴迪提供了一个新的无线电力传输产品PRIMOVE，有轨电车和轻轨车辆[88]使用的系统。

2008年：工业设计师槟城陈德良在布鲁内尔大学纳入一个高效率的无线灯3W LED [引文需要]。

2008年：英特尔再现特斯拉的原甲午电动感应执行情况和1988年教授约翰少年组的后续实验，通过无线电灯泡附近的光效率达到75％[]。

2008：格雷格Leyh和迈克在内华达州的闪电实验室凯南发布一份对特斯拉的不安地下水和空气与电路模拟和效率可以将获得的电动感应方法[90]显示测试结果的无线电力传输的方法收费的文件。

2009年：棕榈（现在惠普的一个部门）推出的Palm Pre智能手机与Palm的Touchstone无线充电器。

2009：感兴趣的公司组成的财团被称为无线电源联盟宣布，他们已接近完成低功率充电的

一个新的行业标准（这是最终在2010年8月出版）[91]。

2009年：前批准的火炬和充电器，针对境外市场。介绍[92]该产品是由无线电力和通讯挪威公司开发。

2009年：一个简单的电动感应电力传输分析模型，提出并应用于植入式装置的无线电力传输系统[93]。

2009年：激光二极管激光器使用的图案，打破多项世界纪录，在距离上发射超过数百位米超过千瓦[94]，赢得$ 900K在美国宇航局的功率奖。

2009年：索尼电动感应无线供电的电视机，超过50厘米[95] 60 W。

2010：。海尔集团推出“世界上第一个”完全无线液晶电视在2010年国际消费电子展，根据教授马林·索尔亚契奇的后续研究特斯拉的电动感应无线能量传输方法，并应用在无线家庭数字接口（WHDI）[96]

2010：系统芯片（SOC）在不列颠哥伦比亚大学的小组开发优化设计的高效无线电力传输

[97] 系统使用多个线圈的工具。实现了植入式的应用程序和82％的电力传输效率优化设计。

2012年：美国在犹他州立大学“生物电磁学和植入装置”组，发展了电源和数据传输的高效多线圈遥测系统，应用在生物医学植入式装置上。建议基于多线圈遥测系统达到超过两次电源转换效率和更高的可调谐频带宽相比，它具有等效双线圈的设计 [98]。

参见

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Beam-powered propulsion

Beam Power Challenge – one of the NASA Centennial Challenges Differential capacitance Distributed generation Electricity distribution Electric power transmission Electromagnetic compatibility Energy harvesting

Friis transmission equation Microwave power transmission Resonant inductive coupling Thinned array curse Transmission medium Wardenclyffe Tower

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56