Experimental wireless lamps at 130 kHz
These oldest leds are powered by a strong magnetic field in the LW-band.
In the air-cored coils of 20 mm a power of 100 mW is available within a short distance of 100 mm. With the high-Q ferrite rods (5*50 mm) this power can be drawn from a larger distance. Some of the air-coils are indirectly powered by the ferrite-coils.
The 15 cm litz-wire transmit-coil below is tuned at the working frequency and driven by
a high efficiency RF-generator which consumes only 3 W from 12 V.
Wireless lamps at 13.56 MHz
At 13,56 MHz a much higher sensitivity and Q-factor is attainable in the receive-coils, so less copper and a lower field-strengths are needed, compared to 130 kHz.
These lamps below demonstrate the power absorption with single wire ring- loops and with small 8-turm 20mm loops .
The magnetic field is generated with only 0,5 Amps in an 8-loop of single thin wire
below the table. The transmitter feeds the 0,5 mm wire with only 1 Watt RF-power,
resulting is a local magnetic field-strength of 600mA/m, and <0,02 mA/m at 10 meters,
far below the limits (EN300330: 0,125 mA/m at 10 meters).
The higher frequency of 13,56 MHz makes this system more energy-efficient than the ferrite-coils
at 130 kHz. At the table-surface a power of 100 mW is available, at a height of 50 cm this drops to 10 mW.
Latest wireless lamps at 6.78 MHz
At 6.78 MHz more field-strength x frequency -product is allowed than on 13.56 MHz.
More efficient O-loops are used than the low-radiation, but less efficient 8-loop for 13,56 MHz. These flat lamps are tuned at 6.78 MHz.
Receive-coil is a 8 turn spiral of 50 mm on PCB.
Transmitter is a small 500mW- 6.78 MHz generator on a 3×4 cm PCB, consuming only
700mW from 5V, driving a 40cm circular or square loop of 3mm-wire as antenna.