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What is new as wireless
powering?
Items are powered anywhere on a wide-area desk with practical safety
and efficiency. It is not only a contactless charging.
This technology enables virtually everything on the desk to work
with electricity under the total maximum power limit[1]. |
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What are the differences from
other methods?
The power and signals are transmitted with microwaves confined in
the sheet.
-Easy to widen: The components of the wide area sheet are
only aluminum thin layers and low-loss insulators. The
electrical circuits are only at the edge of the sheet.
-Information: Wideband microwave signal transmission via the
sheet is also possible. |
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How safe?
The power absorption by direct touch
of a human body on the sheet is less than cell-phone. General
objects on the desk are not exposed to strong electromagnetic field
without any shielding. |
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Interference with other
wireless applications?
The demo system uses virtually zero
bandwidth of 2.48 GHz. The radiation is less than a highest quality
microwave oven and the bandwidth is much less than it.
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What the
methods for the safety and low
electromagnetic leakage are?
All the leakage paths, leakages from the surface and sheet edges are
blocked. Only 0.1% of the input RF power (10mW in total for one in
the three sites on the demo table) is leaking outside the sheet, in the case
there are no items on the sheet. The key technologies are summarized
as follows. |
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(1) 4mm insulator
layer as the top layer of the sheet
The aluminum mesh layer pattern is designed so that the leakage is
the minimum. A 4mm insulator layer on the surface prevents the
electromagnetic leakage into general objects touching the surface. A
special coupler with a high Q resonance can absorb the power,
otherwise, strong magnetic fields are not formed outside the sheet.
More detailed information is in the paper of Akihito Noda.
(PDF)
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(2) EBG[2]
structure around the coupler
The practical major risk from the surface is that from the coupler
edge since the special device is absorbing significant
electromagnetic power. A structure around the coupler named "EBG
structure" prevents the leakage from the coupler. The
technology was developed by NEC Corporation.
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(3) Phase control of microwave transmitters
A side-edge of the sheet has 7 microwave transmitters. The system
selects the best transmitters and control the phases for maximizing
the efficiency. This mechanism localizes the
electromagnetic density in the sheet around a target coupler and
provides perfect safety against unexpected powering to a general
object that forms high Q resonance by chance. |
| [1] On the table, there are three
independent sheet sites. One sheet site provides 10W RF power and
one item can use 4W
DC power (DC to DC efficiency is 24%) in the best case of the demo system. |
[2] Electromagnetic Band Gap (EBG)
A periodic structure for suppressing the transmission of
electromagnetic waves for specific frequencies using metamaterial
application techniques. |
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