Wirelessly charging your smarphones

Your phone starts charging right away when you place your smartphone on the station. It’s called wireless charging. Without the need of plugging in, charging your phone becomes easy and convenient. But, do you know how wireless charging really works and where you can use it?

Wireless data transmission is now working nearly everywhere all over the world. It happens when you watch a movie, read a message and communicate with your friends on your mobile phone. However, the wireless entertainment will have to end a few hours later when your phone battery is dead.

While older smartphones may not be equipped with the wireless charging function, most of the newer smartphones support wireless charging. Just like charging your electric toothbrush, all you need to do is put the smartphone on a charging station. The difference is that charging smartphones requires more power. Let’s explore how wireless charging really works and the requirements for it.

The way wireless charging works

Despite its name- wireless charging, it doesn’t work entirely without cables. Charging stations are constantly powered by the power cable connected to the outlet. And the smartphones are charged wirelessly while placed on the charging station. With a coil inside the charging station, the electricity creates a magnetic field. The smartphone gets charged when it’s within the magnetic field. There’re two types of charging-inductive and resonant, which you will learn more about below.

Inductive charging VS resonant charging

Inductive charging (also known as wireless charging or cordless charging) is a type of wireless power transfer. It uses electromagnetic induction to provide electricity to portable devices. The most common application is the Qi wireless charging standard for smartphones, smartwatches and tablets. Inductive charging is also used in vehicles, power tools, electric toothbrushes, and medical devices. The portable equipment can be placed near a charging station or inductive pad without needing to be precisely aligned or make electrical contact with a dock or plug.

Energy is transferred through inductive coupling. An alternating current is run through an induction coil in the charging station or pad (the primary or transmission coil.) Any moving electric charge creates a magnetic field, as stated by Oersted’s law. The magnetic field fluctuates in strength as the AC current is continually changing amplitude. A changing magnetic field generates an electromotive force otherwise known as Faraday’s law of induction. This makes an alternating electric current in a second induction coil (the receiving, or secondary coil) in the portable device. It is then converted to direct current with a rectifier and used to charge a battery or provide operating power.

Greater distances between sender and receiver coils can be achieved when the inductive charging system uses resonant inductive coupling, where a capacitor is added to each induction coil to create two LC circuits with a specific resonance frequency. The frequency of the alternating current is matched with the resonance frequency, and the frequency chosen depending on the distance desired for peak efficiency. Recent improvements to this resonant system include using a movable transmission coil (i.e., mounted on an elevating platform or arm) and the use of other materials for the receiver coil such as silver-plated copper or sometimes aluminum to minimize weight and decrease resistance due to the skin effect.

Advantages of resonant charging over inductive charging

  • Resonant charging can charge multiple devices at one time
  • Resonant charging makes it possible to put the device with some misalignment
  • Resonant charging allows longer distance between the charging station and the device
  • Resonant charging has greater efficiency with more energy reaching the battery

Resonant charging is technically more complicated than inductive charging. More components are needed and it is more expensive to make.

Applications for wireless charging

Not only smartphones can be charged wirelessly, but also an increasing number of other devices are being charged wirelessly. Like:

  • smartwatches
  • Bluetooth headphones
  • notebooks
  • tablets
  • cordless screwdrivers
  • vacuum cleaners
  • lawnmowers
  • electronic drones
  • Medical devices
  • Smart home and IoT devices
  • In-car charging

The list goes on and on.

Advantages of wireless charging on these applications

  • easy and convenient
  • removes the hassle of refueling your device
  • charging on-the-go. Charging stations at public places, like restaurants and coffee chains, allow you to charge your smartphone immediate while you’re out and about
  • there will be less wear and tear on the charging socket as it is used less often
  • suppose there will be no charging sockets on the phone, the risks of moisture and dirt getting inside the phone will disappear
  • with medical devices, wireless charging has its benefit for being hygiene. It is much easier to disinfect the devices which don’t come with a socket for the charging cable.
  • electric vehicles could also be charged wirelessly with more energy to be transferred.

What is Qi standard?

Qi (pronounced /tʃiː/ CHEE; from the Chinese word qi) is an open interface standard that defines wireless power transfer using inductive charging over distances of up to 4 cm (1.6 inches), developed by the Wireless Power Consortium. The system uses a charging pad and a compatible device, which is placed on top of the pad, charging via resonant inductive coupling.

Mobile device manufacturers that are working with the standard include Apple, Asus, Google, HTC, Huawei, LG Electronics, Motorola Mobility, Nokia, Samsung, BlackBerry, Xiaomi, and Sony.

First released in 2008, the Qi standard had by 2019 been incorporated into more than 160 smartphones, tablets and other devices.

Qi charging stations in automobiles and furniture

We have seen an increase of charging stations integrated in vehicles and furniture. Charging stations can be connected to the cigarette lighter in cars but now they’re integrating charging stations in the vehicles.  And Ikea has lamps with integrated inductive charging stations. More companies around the world are involved in the embedded wireless charging market to make charging easier.

How do you use an inductive charging station

You place the smartphone on the charging station, but you must make sure that you position the device quite precisely. The charging process works only if the coil in the smartphone is above the coil in the charger. If the two coils are too far apart, the charging process is interrupted.

To prevent this and stop the phone sliding around, the contact surface of most charging stations is made from an anti-slip material. Some charging stations even have magnets to hold the smartphone in the correct position.

However, the correct position is usually not enough. Ideally, the smartphone should touch the charging station without a cover – but for the charging process, most stations can handle covers that are just a few millimeters thick.

Some charging stations use several coils. These provide more flexibility with regard to positioning the smartphone on the charger. Depending on the charging station, several devices, such as a smartphones and smartwatches can be charged at the same time. However, these charging stations are much more expensive that those with one coil and are currently used mainly in automobiles.

To date, wireless charging is somewhat slower than charging with a cable. Most charging stations provide 5 watts of power, while chargers with cable have 10 watts and more. The situation is somewhat different with the Qi standard. This now supports fast charging with up to 15 watts. The first smartphones that support this are already available.

Depending on the station, smartphones may only be moved to a certain extent during charging. This limits the functions during charging. But charging stations on which cell phones are positioned at a certain angle are also available. This allows you to watch movies while the phone is charging.

If you want to check the charging status of the battery and remove the smartphone from the station to do this, the charging process is interrupted. Because of this, many charging stations show the charge status with LEDs – and users can see this easily without having to move or remove the device.


Is wireless charging dangerous?

The charging stations are shielded so that the range of the magnetic field is very limited or is aimed in a specific direction. Besides, with smartphones the magnetic field is weak and exists only when a device is being charged.

There is a risk with foreign metal objects: as with induction stoves, they can become extremely hot when they get into the magnetic field of the charging coil. But “smart” charging stations are already available. They detect when a foreign object is between the smartphone and the contact surface and stop the charging process.


The future of wireless charging

The number of devices that can be charged wirelessly is increasing continuously. According to IHS Markit, the market for wireless electricity supply continued to gather momentum in 2018. In 2018, worldwide sales of wireless power receivers and transmitters across all applications and product segments rose to 600 million units – a 37 percent increase compared to the previous year. IHS Markit forecasts that approximately 2.1 billion units will be shipped worldwide by 2023.

With the increase in fast charging options, acceptance among users will also continue to grow. Beginning with smartphones, wireless charging will also be possible for many other devices. Headphones, smartwatches, and fitness trackers, but also medical devices with low power consumption, such as pacemakers, will benefit from this. Depending on the stage of development in technology, higher charging power may also be possible in the future.