Wireless

July 19, 2022

I think it is only fitting after my rant on distracted driving on Saturday that I was unable to access my cell phone when I got into the car this morning.  I had been playing my crossword app until late last night and had run the battery well below the 20% minimum charge level.  I plugged it into the charger last night, but it was too low to accept a charge.  When I plugged it into the car charger it was still too low, and it refused to take a charge.  I took the phone inside to my local electronic guru (Melissa) and when she put the phone on her wireless charger the battery immediately began to accept the charge.  I grabbed my own wireless charger and brought it to work so I could use my phone there.  Of course, the wireless charger did not have the proper interface and would not work in the car.  However, since the recharge had begun with the wireless charger the car charger now worked and the battery began to take the charge.

When I looked online, I found wireless power transfer (WPT), wireless energy transmission (WET), or electromagnetic power transfer, is the transmission of electrical energy without wires as a physical link.  In a WPT system, a transmitter device driven by electric power from a power source generates a time-varying electromagnetic field which transmits power across space to a receiver device.  The receiver then gets power from the field and supplies it to an electrical load.  WPT technology can eliminate the use of the wires and batteries to increase the mobility, convenience, and safety of an electronic device for users.  WPT fall into two categories, near field and far-field.  In near field or non-radiative techniques, power is transferred over short distances by magnetic fields using inductive coupling between coils of wire, or by electric fields using capacitive coupling between metal electrodes.  Inductive coupling is the most widely used wireless technology and its applications include charging handheld devices like phones or implanted medical devices.

Inductive coupling is the oldest and most widely used wireless power technology and is virtually the only one used in commercial products.  Inductive charging stands are used for cordless devices in wet settings (toothbrushes and shavers) to reduce the risk of electric shock.  “Transcutaneous” recharging is also used in biomedical prosthetic devices implanted in the human body (pacemakers and insulin pumps) to avoid wires passing through the skin.  Inductive coupling is also used to charge electric vehicles and to charge or power transit vehicles (buses and trains).  The fastest growing use is wireless charging pads to recharge mobile and handheld wireless devices such as laptop and tablet computers, computer mouse, cellphones, digital media players, and video game controllers.  In the US, the Federal Communications Commission (FCC) provided its first certification for a wireless transmission charging system in December 2017.  Ordinary inductive coupling can only achieve high efficiency when the coils are very close together and usually adjacent.  With our wireless phone chargers, the electromagnets lock together when adjacent.

Thoughts:  An important issue associated with wireless power systems is limiting the exposure of people and other living things to potentially injurious electromagnetic fields.  Cell phones emit electromagnetic radiation fields like any other wireless power system and are regulated and are required to meet federal standards.  Cell phones are often cited as dangerous because of how close they are to the body when used (i.e., next to your ear or head).  Each country determines which local regulatory body governs safety of non-ionizing electromagnetic radiation, often referred to as radio frequency (RF), and allowable radiation levels for exposure vary.  I use my wireless phone without giving much thought to the consequences.  Others chose not to use these devices.  Act for all.  Change is coming and it starts with you.