Wireless charging is any of several methods of charging batteries without the use of cables or device-specific AC adaptors. Wireless charging can be used for a wide variety of devices including cell phones, laptop computers and MP3 players as well as larger objects, such as robots and electric cars. Radio charging is used for charging items with small batteries and low power requirements, such as watches, hearing aids, medical implants, cell phones, MP3 players and wireless keyboard and mice. Radio waves are already in use to transmit and receive cellular telephone, television, radio and Wi-Fi signals. Wireless radio charging works similarly. A transmitter, plugged into a socket, generates radio waves. When the receiver attached to the device is set to the same frequency as the transmitter, it will charge the device's battery. A universal wireless battery charger for portable and mobile devices can use ambient Radio Frequency (RF) or electromagnetic signals as a renewable energy resource, emitted by different sources for communications. In this paper, we designed a RF circuit that enables to charging mobile devices. This will result in continuous charging of device especially in urban areas where the density of RF sources is high
There are three methods of wireless charging:
1. Radio charging
2. Inductive charging
3. Resonance charging
Electromagnetic (EM) radiation is a self-propagating wave in space with electric and magnetic components. One important type of electromagnetic radiation on basis of frequency is “Radio Waves” with frequency range of 30Hz to 300GHz . A circuit can be used with a cellular phone or a mobile device to capture the unwanted electromagnetic signals in the atmosphere and use the power of these signals to power some essential functions of the device or recharge the battery. RFID devices use the principle to transmit power (1-100μW) to RFID transponders . The advantage of the designed circuit will be to use the electromagnetic signals present in atmosphere as a renewable energy source and transform the electromagnetic waves present in atmosphere in to the electric power, making a universal charger.
Fig. 1 show the block diagram of the system, where RF signals generated by multiple RF sources are captured by antenna. Using matching circuit for antenna along with rectifier, generated DC power is used by charging controller to run the mobile device terminal functions or recharge its battery. Extracting the electromagnetic energy from environment and converting it to useful electrical energy is called Energy harvesting. Studies have shown that <1μW/cm2 is available for RF sources unless it is near the RF source . Due to this low power generation most work
from energy harvesting from RF is in microwave range.
Figure 1: Wireless Charging System Architecture
II. OVERVIEW OF WIRELESS CHARGING
Wireless charging technique already exists in active RFID reader where power is transmitted to Transponder Wirelessly. Commercial products are available in market which transfers electrical power wirelessly to a short distance and works in RF and Microwave range. These devices have RF transmission source which generates the RF energy. The Electromagnetic sources are already existing around us in the form of Mobile phone, base station, wireless internet connections, DMB...