Understanding the Principles, Standards, and Benefits of Wireless Charging Technology

Content Highlights

• How do wireless chargers work?
• Wireless charger circuit schematic diagram
• Applications of wireless charging technology
• Wireless charging interface standards (Qi standard)
• Devices with wireless charging
• Wireless charging distance
• Advantages and benefits of wireless/inductive charging

Many modern gadgets are now adopting wireless charging technology. Laptop manufacturers have also embraced this innovation. The latest Apple and Samsung devices also feature wireless charging capabilities. You may wonder how wireless charging operates. Wireless charging, also known as inductive charging, uses an electromagnetic field to transfer energy between two objects via electromagnetic induction. This energy is conveyed through inductive coupling to an electronic device, which utilises the transferred energy to charge its batteries or power the device.

While it feels like a modern convenience, the fundamental technology behind wireless charging has existed for over a century. It is based on the principles of electromagnetism discovered by scientists like Michael Faraday and Nikola Tesla.

This article will break down exactly how wireless charging works, exploring the concepts of inductive coupling, magnetic resonance, and the standards that make your devices compatible.

Working of Wireless Chargers

To understand how wireless charging works, you need to understand the relationship between electricity and magnetism. They are two sides of the same coin.

• Flowing electricity can create a magnetic field.
• A changing magnetic field can create (induce) flowing electricity.

You might have heard the word ‘resonance’. Resonance is a phenomenon that occurs in nature in many different forms. In general, resonance involves energy oscillating between two modes. In a system at resonance, it is possible to have a large build-up of stored energy while having only a weak excitation to the system. The build-up occurs if the rate of energy injection into the system is greater than the rate of energy loss by the system.

The diagram below represents an electrical resonator. L = inductance, R = resistance, and C = capacitance.

The resonant frequency of the above circuit is given by: $f = 1/2π√(LC)$

Resonant frequency is the frequency at which maximum energy is stored in the system. If two resonators are placed in proximity to one another such that there is coupling between them, it becomes possible for the resonators to exchange energy.

The efficiency of the energy exchange depends on the characteristic parameters for each resonator. Maximum energy is transferred when the frequency of the two resonators is the same. By varying L and C, frequency can be varied. Let Ls be the inductance coil connected to the power source Vs, and Lr is the receiver coil. When a current is passed through Ls, it creates a magnetic field around Ls. This varying magnetic field causes current flow through Lr. Thus, energy gets transferred between coils via electromagnetic induction. At resonance, this energy transfer will touch its peak.

The Step-by-Step Process

1. Mains Power: Alternating current (AC) from the wall outlet flows into the transmitter coil inside the charging pad.
2. Magnetic Field Generation: This flowing AC electricity creates a fluctuating magnetic field around the transmitter coil. It is crucial that the current is alternating (changing direction rapidly), as only a changing magnetic field can induce a current.
3. Induction: When you place your device on the pad, the receiver coil inside the phone enters this fluctuating magnetic field.
4. Current Creation: The magnetic field pushes the electrons in the receiver coil, inducing an alternating current (AC) within your phone.
5. Conversion to DC: Your phone’s battery cannot run on AC power. Therefore, circuitry inside the phone converts this induced AC into direct current (DC), which is then used to charge the battery.

The Two Types of Wireless Charging

While the core principle is always induction, there are two common ways this is implemented based on how “tightly” the coils need to be coupled.

1. Inductive Charging (Tightly Coupled)

• This is the most common form of wireless charging used in smartphones today (like the Qi standard).
• The transmitter and receiver coils must be very close together and properly aligned. The magnetic field created by the charger is relatively small and focused.
• If the phone is slightly off-centre, or if the case is too thick, the efficiency drops dramatically, and charging stops.

Pros: High efficiency when aligned correctly; simple hardware.

Cons: Requires precise placement; very short range (usually less than 7mm).

2. Magnetic Resonant Charging (Loosely Coupled)

• In resonant wireless charging, both the transmitter and receiver coils are tuned to vibrate at the exact same electromagnetic frequency.
• Because they are “resonating” together, energy can be transferred efficiently over slightly longer distances (a few centimetres) or through thicker materials (like a tabletop).
• It also allows for “spatial freedom”, meaning you don’t have to place the device exactly in the centre of the pad, and a single pad could potentially charge multiple devices at once.

Pros: Greater spatial freedom; can charge through thicker surfaces; multi-device charging.

Cons: Generally less efficient than tight coupling; more complex hardware needed.

The Qi Standard

The Qi (pronounced ‘chee’, meaning “natural energy”) standard is the most widely adopted protocol for wireless charging in smartphones and other portable devices today. Developed by the Wireless Power Consortium, Qi enables devices from different manufacturers to be compatible with the same charging pads, promoting universal interoperability. The standard uses the principle of inductive coupling, requiring the transmitter (charging pad) and receiver (device) coils to be closely aligned for efficient energy transfer.

Qi charging typically operates at a distance of less than 7mm, which means that the device must be placed directly on or very near the charging pad. Recent advancements in the Qi standard have introduced features such as faster charging speeds, improved safety mechanisms to prevent overheating, and limited support for charging multiple devices simultaneously. As a result, Qi has become the de facto choice for convenient and reliable wireless charging in the consumer electronics industry.

Which Mobile Manufacturers Adopt Qi Standards?

Major mobile manufacturers that adopt the Qi standard for wireless charging include Apple, Samsung, Xiaomi, OnePlus, Google, Sony, LG, Huawei, and Nokia, among others. These brands incorporate Qi-enabled wireless charging in a wide range of their smartphones and accessories, ensuring broad compatibility across devices and charging pads. As a result, users can enjoy the convenience of universal wireless charging regardless of the brand of their device.

Universal Wireless Charging Adapters

If your phone doesn’t support wireless charging, need not worry, virtually any smartphone with a standard charging port (USB-C, Lightning, or Micro-USB) can be made capable of wireless charging using a simple, inexpensive accessory called a Wireless Charging Receiver (or Qi Receiver).

What is a univeral wireless charger Adapter?How it works?

The “adapter” is a paper-thin tag containing a copper coil. It plugs into your phone’s charging port and folds around to lie flat against the back of your phone. You can then put your phone case over it, hiding the adapter completely.

Compatible Devices by Port Type

Because these receivers are universal, compatibility is determined by your phone’s charging port, not the phone model itself.

How to Install It (Step-by-Step)

1. Purchase a Qi Receiver: Buy one that matches your port (e.g., “USB-C Qi Receiver”). Brands like maxfield,Nillkin and aircharge are popular for this.
2. Plug it in: Insert the receiver’s connector into your phone’s charging port.
3. Fold it back: Bend the tag so the coil rests against the back of your phone.
4. Cover it: Snap your phone case on over the receiver. The case holds the coil in place.
5. Charge: Place your phone on any standard Qi wireless charging pad.

There are two types of universal adapters available in the market: Internal adapter, which slides into the back of a case, and an external adapter, which hangs outside. Maxfield is the leading producer of internal adapters and aircharge is the front runner in the external wireless charging adapters.

Wireless Charging: Technology Benefits

• Make devices more convenient and thus more desirable to purchasers, by eliminating the need for a power cord.
• Make devices more reliable by eliminating the most failure-prone component in most electronic systems—the cords and connectors.
• Make devices safer by eliminating the sparking hazard associated with conductive interconnections.
• Reduce system cost by leveraging the ability to power multiple devices from a single source resonator.

The Drawbacks

• Efficiency Loss: Wireless charging is generally less efficient than wired charging. Some energy is lost as heat during the transfer process (roughly 15-30% loss depending on alignment).
• Slower Speeds: While getting faster, wireless charging is usually slower than the fastest wired “quick charge” technologies.
• Alignment Issues: With standard inductive chargers, finding the “sweet spot” can sometimes be finicky.

Wireless charging seems futuristic, but it relies on established laws of physics that govern how electricity and magnetism interact. By using a transmitter coil to create a magnetic field and a receiver coil to capture it, we can transfer power across a small gap without physical wires.

As technology improves, we are likely to see resonant charging become more common, eventually leading to “true” wireless charging where devices power up just by entering a room. For now, understanding how wireless charging works helps us appreciate the incredible engineering hidden inside our everyday devices.