磁共振和磁感應(yīng)技術(shù)：哪一個(gè)才是我們最好的應(yīng)用選擇？

Architects of wireless power transfer systems face a couple of choices in the configurations of coils and the magnetic transfer technique. The best choice depends on the application:

無線充電系統(tǒng)的設(shè)計(jì)構(gòu)造有幾個(gè)部分需要作出選擇，即線圈參數(shù)設(shè)置和磁場轉(zhuǎn)換技術(shù)選擇。但是具體方案還是要根據(jù)不同的設(shè)備來確定：

選擇1：發(fā)射線圈和接收線圈之間是使用松耦合還是緊耦合？

Inductive power transfer works by creating an alternating magnetic field (flux) in a transmitter coil and converting that flux into an electrical current in the receiver coil. Depending on the distance between the transmit and receive coils, only a fraction of the magnetic flux generated by the transmitter coil penetrates the receiver coil and contributes to the power transmission. The more flux reaches the receiver, the better the coils are coupled.

磁感應(yīng)能量轉(zhuǎn)換是通過在發(fā)射線圈里創(chuàng)造一個(gè)變化的磁場實(shí)現(xiàn)的，接收線圈將變化的磁場轉(zhuǎn)換為電流。由于發(fā)射線圈和接收線圈之間的距離不同，只有一部分發(fā)射線圈產(chǎn)生的磁場能夠被接收線圈吸收并轉(zhuǎn)化為電能。在整個(gè)過程中，接收線圈收到的磁通量越大，則兩個(gè)線圈耦合性越好。

A higher coupling factor improves the transfer efficiency, and reduces losses and heating. Applications with a larger distance between the transmit and receive coils operate, by definition, as a loosely coupled system. In loosely coupled systems, only a fraction of the transmitted flux is captured in the receiver. That means that loosely coupled systems have higher electromagnetic emissions, making them less suitable for applications with tight EMI or EMF requirements.

耦合性越高，線圈之間傳輸能量的效率越高，并且會(huì)減少漏磁和線圈的發(fā)熱。在應(yīng)用過程中，若發(fā)射線圈與接收線圈相距較遠(yuǎn)，則被稱為松耦合系統(tǒng)（loosely coupled system）。在松耦合系統(tǒng)中，只有一小部分變化的磁場能被接收線圈接收，這就意味著松耦合系統(tǒng)會(huì)產(chǎn)生更多的電磁泄漏，因此不適用于對(duì)EMI和EMF高要求的應(yīng)用場景。

Loosely coupled systems trade-off larger distance at the cost of lower power transfer efficiency and higher electromagnetic emissions. This may be suitable choice in applications where tightly aligned coils is impractical, but less suitable for applications with tight EMI or EMF of efficiency requirements.

松耦合系統(tǒng)可以調(diào)節(jié)長距離，低效率和高電磁泄漏三者之間的關(guān)系。這使松耦合系統(tǒng)可適用在“緊耦合的線圈陣列”不可行的應(yīng)用場景，但是對(duì)于EMI和EMF要求過高或者對(duì)效率要求過高的應(yīng)用場景，松耦合系統(tǒng)則很不適用。

Tightly coupled systems, because of their higher efficiency, tend to produce less heat which is an advantage is products with tight thermal budgets such as modern smartphones.

緊耦合系統(tǒng)，由于能量傳遞更高效，因此產(chǎn)生熱量較少，適合對(duì)發(fā)熱控制要求較高的設(shè)備，例如我們常用的手機(jī)等。

For the definition of coupling factor see:

另外關(guān)于耦合相關(guān)系數(shù)的解釋請(qǐng)參見以下網(wǎng)頁：http://www.wirelesspowerconsortium.com/technology/coupling-factor.html

The transmit and receive coils are tightly coupled when (a) the coils have the same size, and (b) the distance between the coils is much less than the diameter of the coils.

當(dāng)發(fā)射線圈和接收線圈大小相同，并且線圈之間的距離遠(yuǎn)遠(yuǎn)小于線圈直徑時(shí)，就會(huì)產(chǎn)生緊耦合。

Loosely coupled coils or operate with significantly different coil sizes, or operate at larger distance.

當(dāng)發(fā)射線圈和接收線圈尺寸有明顯差距或者距離很遠(yuǎn)時(shí)，會(huì)產(chǎn)生松耦合。

Choice 2: Operate the coils at resonance or off-resonance?

選擇2：使線圈處于磁共振狀態(tài)，還是非磁共振狀態(tài)?

From the beginning of inductive power transmission, resonant circuits have been used to enhance the efficiency of power transmission. As early as 1891, Nicola Tesla used resonance techniques in his first experiments with inductive power transmission. Systems with a low coupling factor generally use a resonant receiver and resonant transmitter to improve power transfer efficiency.

在早期的磁感應(yīng)能量傳輸系統(tǒng)中，共振電路就被用來提高能量傳輸?shù)男?。早?891年，尼古拉-特斯拉就將磁共振技術(shù)應(yīng)用在磁感應(yīng)能量傳輸中。通常在弱耦合系統(tǒng)中，使用共振的接收器和共振的發(fā)射裝置以提高傳輸效率。

For technical details see:

技術(shù)背景請(qǐng)參考以下網(wǎng)頁：http://www.wirelesspowerconsortium.com/technology/resonant-coupling.html

You might expect that operating tightly coupled coils at resonance offers the best performance. That combination, however, is not used in practice because two tightly coupled coils cannot be both in resonance at the same time. This is one of the counter-intuitive effects that make power electronics such an interesting subject.

你可能十分期待，將緊耦合技術(shù)與共振原理相結(jié)合以得到最好的能量傳輸效率。但是，緊耦合+磁共振，并沒有在實(shí)際中應(yīng)用，因?yàn)榫o耦合線圈不能同時(shí)產(chǎn)生共振。這是電力電子科學(xué)中一個(gè)比較有趣的反直覺效應(yīng)。

Most Qi transmitters use tight coupling between coils. In that configuration, the best results are achieved by operating the transmitter at a frequency that is slightly different from the resonance frequency of the Qi receiver. Off-resonance operation gets you the highest amount of power at the best efficiency.

大多數(shù)Qi充電器通過線圈之間產(chǎn)生的緊耦合運(yùn)轉(zhuǎn)。在這樣的前提下，最好的結(jié)果就是調(diào)節(jié)發(fā)射端的工作頻率，使其與接收端的共振頻率有一點(diǎn)細(xì)微的差別。因?yàn)闊o法達(dá)到共振頻率，只能無限接近。非共振傳輸會(huì)提供最強(qiáng)最高效的表現(xiàn)。

chioce3: Single coil or multi-coil?

選擇3：單線圈還是多線圈？

Tightly coupled coils are sensitive to misalignment. That’s why most Qi transmitters use multiple coils. This increases the complexity of the transmitter design, but improves the horizontal (X, Y) freedom of positioning. Coil arrays can cover large areas. See, for example, ConvenientPower’s WoW5 transmitter.

緊耦合線圈對(duì)線圈之間的對(duì)準(zhǔn)程度要求很高。這就是為什么大多數(shù)Qi充電器使用多線圈的原因。多線圈極大地增加了充電器的設(shè)計(jì)要求，但是接收端就有了更強(qiáng)的平面自由度，不用太注意線圈之間對(duì)準(zhǔn)的問題。線圈陣列可以覆蓋很大的面積，比如ConvenientPower公司的WoW5無線充電器。

Another advantage of multi-coil systems is that they help localize the magnetic flux, reducing EM emissions, and make it possible to charge multiple receivers concurrently.

另一個(gè)多線圈的優(yōu)勢在于更好的聚集磁通量，減少電磁場泄露，使多設(shè)備同時(shí)充電成為可能。

Here are some examples of transmitters that use overlapping coils

下面是一些應(yīng)用重疊線圈的無線充電器

Coils don't need to overlap either. Solutions with non-overlapping coils can be easier easy to assemble.

當(dāng)然線圈也并不是必須重疊放置，“無重疊方案”可以更方便無線充電器的組裝。

Multi-coil transmitters can charge several receivers at the same time, simply by powering the coils underneath the receiver.

多線圈充電器只需要給里面的線圈供電就可以做到同時(shí)給多個(gè)設(shè)備充電。

Multi-coil transmitters also allow the wireless power ecosystem to scale with increasing power levels that devices demand, by powering multiple coils underneath the receiver. The first smart phones needed 3W, todays require over 7.5W and growing. We also now have tablets, ebooks readers, ultrabooks which need from 10-30W. Multi-coil systems transmit the power exactly where it is needed in a safe, efficient and controlled manner guaranteeing scalability as devices get more and more power hungry.

多線圈充電器只需要加強(qiáng)給線圈的能量就可以加大充電的功率，以適應(yīng)多種設(shè)備的功率要求。最早的智能電話需要3瓦來充電，現(xiàn)在需要超過7.5瓦而且還在增長。平板電腦，電子書，超級(jí)本會(huì)需要10到30瓦的電量。多線圈充電器可以安全有效的控制供電，并且擴(kuò)展性極強(qiáng)。

A loosely coupled system can achieve multi-device charging with a single transmitter coil, provided it is much larger than the receiver coils and the provided the receivers can tune themselves independently to the frequency of the single transmitter coil.

松耦合系統(tǒng)可以用一個(gè)發(fā)射線圈達(dá)到為多個(gè)設(shè)備充電的需求，但是要求發(fā)射線圈遠(yuǎn)遠(yuǎn)大于接收線圈，并且要求接收裝置都能夠單獨(dú)調(diào)節(jié)自身的頻率以適應(yīng)發(fā)射線圈的頻率，

The table below provides a summary of the possible transmitter configurations:

下面的表格提供了所有可能的充電形式：

As you can see, there is no optimum design. The choice of architecture will depend on the application requirements. Is efficiency important? Is EMI (electromagnetic interference) a concern? Do you need a large Z distance? Is cost the key issue? Depending on your priorities, the optimum will be different

可以看到，并沒有最完美的設(shè)計(jì)。工程師會(huì)根據(jù)不同的應(yīng)用場景選擇其結(jié)構(gòu)。是效率重要？是考慮EMI？還是需要更大的線圈間距？成本是不是重要的因素？對(duì)上述各因素的考慮優(yōu)先級(jí)不同，最優(yōu)設(shè)計(jì)的方案就不同。

Qi gives you the possibility to choose what is best for your application

Qi提供了讓你選擇最適合你的可能性。

All Qi receivers have a well-defined resonance frequency and can operate at resonance. The Qi transmitter products that are in the market today operate off-resonance, with tight coupling, because that combination provides both high power transfer and high efficiency. Most Qi transmitter products use multiple coils because they provide a better user experience.

所有Qi接收器的共振都有明確的共振頻率，并且線圈都是可以被調(diào)節(jié)在共振的狀態(tài)中。如今市場上的Qi充電器選擇緊耦合、非磁共振是因?yàn)檫@樣的結(jié)合能提供最大，最高效的能量傳輸。大多數(shù)Qi充電產(chǎn)品使用多線圈方案是因?yàn)槟芴峁└玫挠脩趔w驗(yàn)感。

At the Consumer Electronics Show in January, and at Mobile World Congress in February, you could see the first Qi transmitter products that operate at larger distance, loosely coupled, and at resonance. These resonant Qi transmitters are compatible with all Qi phones out there today. Otherwise we would not call it a Qi transmitter: If you see the Qi logo, you can be sure that the product is compatible with all other Qi products.

今年一月份的消費(fèi)者電子展上，二月的世界手機(jī)大會(huì)，我們看到第一款可以遠(yuǎn)距離供電的松耦合、共振充電設(shè)備。這些磁共振Qi充電器可以與如今所有Qi手機(jī)匹配。否則的話也不能叫做Qi充電器：如果你看到Qi的標(biāo)志，你大可放心，這個(gè)產(chǎn)品一定會(huì)與你的Qi手機(jī)匹配。

A4WP

The Alliance for Wireless Power offers only one choice: “single coil, loosely coupled, resonant”. That configuration is not optimal for all applications. The WPC believes that product developers need more options to choose from. The solution “single coil, loosely coupled, resonant” is just one of the options offered by the Wireless Power Consortium.

A4WP無線充電標(biāo)準(zhǔn)只提供了“單線圈，松耦合，共振”的選擇，但是這樣的設(shè)計(jì)并不適用于所有的應(yīng)用場景。WPC相信產(chǎn)品研發(fā)者需要更多選擇。然而，單線圈，松耦合，共振的方式只是其中一種。

The solution offered by the A4WP is not compatible with the millions of Qi phones and tablets that are already in the market. The WPC has demonstrated that it is possible to make loosely coupled resonant transmitters that are compatible with all these of Qi phones and tablets. There is no technical justification for incompatibility.

A4WP的解決方案并不適用于如今已在市場上的千千萬萬的Qi手機(jī)和手提電腦。如今，WPC已經(jīng)演示了未來這種松耦合、單線圈、磁共振的解決方案，并且會(huì)和你的Qi手機(jī)以及平板電腦匹配。