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`SETTING THE INTERNATIONAL STANDARD FOR INTEROPERABLE WIRELESS CHARGING
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`Efficiency
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`Figure of merit
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`Quality factor
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`Coupling factor
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`Reflected impedance
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`Resonant coupling
`
`Inductive Power Transmission
`
`Dries van Wageningen and Eberhard Waffenschmidt, Philips Research
`The basic principle of an inductively coupled power transfer system is shown in Figure 1. It consist of a
`transmitter coil L1 and a receiver coil L2. Both coils form a system of magnetically coupled inductors. An
`alternating current in the transmitter coil generates a magnetic field which induces a voltage in the
`receiver coil. This voltage can be used to power a mobile device or charge a battery.
`
`The efficiency of the power transfer depends on the coupling (k) between the inductors and their quality
`(Q). (See also Figure of merit)
`The coupling is determined by the distance between the inductors (z) and the relative size (D2 /D). The
`coupling is further determined by the shape of the coils and the angle between them (not shown).
`
`EMF limits - basic restrictions
`
`Maximum power transfer into space
`
`
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`Shielding effectiveness
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`Further Reading
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`Comparison of power savings
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`Making wireless truly wireless
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`Blog
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`08/11/2011 Waterproof Qi phone
`07/28/2011 Qi certification service in
`Taiwan
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`https://web.archive.org/...b/20110821051544/http://www.wirelesspowerconsortium.com/technology/basic-principle-of-inductive-power-transmission.html[1/26/2021 8:14:51 AM]
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`1
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`APPLE 1032
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`Transfer efficiency - Wireless Power Consortium
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`SETTING THE INTERNATIONAL STANDARD FOR INTEROPERABLE WIRELESS CHARGING
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`Transfer efficiency
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`Dries van Wageningen and Eberhard Waffenschmidt, Philips Research
`Figure 2 shows the calculated optimal achievable efficiency of a system according to Figure 1 with the
`assumption of a quality factor of 100. All dimensions are scaled to the diameter of the larger coil D,
`which ever it is (transmitter or receiver coil).
`The values are shown as a function of the axial distance of the coils (z/D). The parameter is the diameter
`of the smaller coil D2.
`The figure shows that
`
`The efficiency drops dramatically at larger distance (z/D > 1) or at a large size difference of the coil
`(D2/D < 0.3)
`A high efficiency (>90%) can be achieved at close distance (z/D < 0.1) and for coils of similar size
`(D2/D = 0.5..1)
`
`This shows that inductive power transmission over a large distance, e.g. into a space, is very inefficient.
`Today, we cannot afford to waste energy for general power applications by using such a system.
`On the other hand, the figure shows that inductive power transmission in the proximity of the devices,
`e.g. at a surface, can be really efficient and competitive to wired solutions. Wireless proximity power
`transmission combines comfort and ease of use with today’s requirements for energy saving.
`
`How it works
`
`Total energy consumption
`
`Basic principle
`
`Efficiency
`
`Figure of merit
`
`Quality factor
`
`Coupling factor
`
`Reflected impedance
`
`Resonant coupling
`
`EMF limits - basic restrictions
`
`Maximum power transfer into space
`
`Shielding effectiveness
`
`Further Reading
`
`Comparison of power savings
`
`Making wireless truly wireless
`
`Blog
`
`08/25/2011 Ultrasound power
`08/23/2011 New transmitter technology
`
`Sitemap - Privacy policy - Terms of use
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`<< Previous
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`Next >>
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`
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`https://web.archive.org/web/20110828201958/http://www.wirelesspowerconsortium.com/technology/transfer-efficiency.html[1/26/2021 8:15:26 AM]
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