What are Wireless Charging Coils?

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Editorial Team - everything PE

Sep 12, 2021


Wireless charging coils are used to generate power wirelessly. These coils operate by transferring wireless power (electrical energy) from the transmitter to the receiver coil by the process of electromagnetic induction. Electromagnetic induction is a phenomenon in which a change in current through the transmitter coil induces a voltage across the ends of the receiver coil. This process is also referred to as inductance coupling or magnetic coupling.

Wireless charging is also called cordless charging as the transmission of electrical energy is without using wires between the transmitter and receiver. The coils are normally made of copper which offers good conductivity. The transmitter coil is connected to the charging pad/charging station/power plug, and a receiver coil is connected to the device that needs to be charged. Some coils can perform both transmit and receive functions.

The wireless charging coils are ideal for use in inductive charging applications to charge devices such as cell phones, handheld devices, tablets, gaming controllers, wearable devices, smartwatches, digital cameras, small consumer electronic devices, charging electric vehicles, robotic cleaners, and drones applications.

Key Specifications of Wireless Charging Coils:

Configuration: It represents the configuration of the wireless charging coils. This coil is available in three different configurations - transmitter coil, receiver coil, and transmitter+receiver coil.

Charging standard: It represents the charging standard with which the wireless charging coil complies. WPC Qi, Airfuel, and NFC are some of the most common wireless charging standards.

WPC standard: It defines the type of coil configuration and the communication protocol so that any device operating under this standard will be able to pair with any other WPC-compliant devices. Key WPC standards are WPC MP-A11, WPC MP-A13, WPC MP-A1, WPC MP-A15, and WPC MP-A9.

Output Power: It represents the output power of the wireless charging coil and is expressed in Watts (W).

Output Voltage: It represents the magnitude of the output voltage of the wireless charging coil and is expressed in volts (V).

Output Current: It represents the magnitude of the output current of the wireless charging coil and is expressed in Ampere (A).

Number of Coils: It represents the number of coils present in a wireless charging coil. Multiple coils are often used to allow wireless charging from different angles.

Quality factor: The Q factor/quality factor is defined as the ratio of apparent power to the power losses in a wireless charging coil. Apparent power is defined as the product of angular frequency and inductance.

where ω = 2πf. Q is mainly dependent on the shape, size, and material of the coil.

Inductance: It represents the inductance value of the wireless charging coils and is expressed in µH.

Self-resonant frequency (SRF): It is defined as the frequency at which resonance occurs between the inductance and the parasitic capacitance of an inductor and is expressed in MHz.

Dynamic contact resistance (DCR): It is defined as the resistance of the contact between the charging coil and its connection with the source/load.