Ossia’s Wireless Charging Tech Could Be Available By Next Year

The Cota wireless power system delivers 1 watt up to 1 meter away

3 min read
Photo-illustration of Ossia's Cota wireless power system charging multiple devices.
Photo-illustration: Ossia

Wireless power company Ossia has received authorization from the U.S. Federal Communications Commission (FCC) for its Cota wireless power system. The FCC authorization is a crucial step toward Ossia’s goal of seeing devices that incorporate Cota on the market in 2020.

While supplying power wirelessly seems like a promising idea in theory, the technology has been explored for years and its reality has never quite lived up to the hype. In all likelihood, the most sophisticated example you’ve seen of wireless charging is something like the wireless charging pads on coffee shop tables. Such pads require you to leave your device on them, making it difficult or impossible to use your gadget at the same time. That’s a far cry from being able to set down your device anywhere in the room and have it charge, or charge while you’re using it.

The physics of making such a thing possible are, it turns out, tricky. There’s been no shortage of ideas for wireless charging methods; startup uBeam, for example, has promised ultrasonic power transmitters but struggled to deliver for years. Energous, another startup, sells a charger that uses beamforming to create pockets of 900 MHz radio waves to provide power to nearby devices.

Ossia’s approach with Cota is similar to Energous in the sense that Cota uses radio waves to provide power (though in Cota’s case, it’s via 2.4 GHz radio waves). But Cota goes a step further, by homing in on devices and directing radio waves at them. Ossia’s approach is more precise than Energous’ approach, and allows users to handle and move devices without worrying about accidentally removing the device from the pocket of RF energy. Devices ping Cota up to 100 times per second with their locations, and Cota then beams power right back along the path it received the signal from. 

Those of you who are savvy about spectrum will notice that the spectrum Cota uses (2.4 GHz) is close to bands allocated for Wi-Fi and 5G (2.5 GHz). Ossia says that the FCC imposed strict limits on emissions outside of the 2.4 GHz band, and so Cota will not interfere with its neighbors on the spectrum. Ossia has plans to eventually deliver power using 5.8 GHz spectrum as well, close to Wi-Fi’s other main band (5 GHz), and will have to meet the same requirement there.

Cota must also comply with the FCC’s Specific Absorption Rate (SAR) requirements. SAR is a measurement of the rate at which RF energy is absorbed by the body. For cell phones, for example, the FCC has set a SAR of 1.6 watts per kilogram. Any cell phone that delivers less than 1.6 W/kg into the human body is therefore considered safe by the agency. For authorization, Ossia had to show that Cota did not exceed the 1.6 W/kg SAR either.

Ossia doesn’t plan to manufacture Cota-enabled devices itself. Instead, it wants to license the tech to commercial partners that Ossia hopes will have devices featuring Cota on shelves by next year.

The FCC authorization grants permission for Cota power sources to transmit power up to 1 meter. Though the company has talked about delivering power wirelessly to devices up to 10 meters away, 1 meter is a solid first step. According to the company, Cota power sources can deliver up to 1 watt of power at that distance.

Ossia says that the company is preparing more submissions to the FCC for consumer use cases. Ultimately, the company sees two potential uses for its technology. The first option is to use Ossia’s Forever Batteries, announced at CES 2018, to replace traditional AA batteries in devices. Forever Batteries include antennas to send location signals and receive power from a Cota device to allow wireless charging (Ossia says there’s no reason the Forever Battery couldn’t be developed for other battery types).

The more radical option is to remove a device’s battery altogether, and use antennas to power battery-less devices. While this may not be fully suitable for the home (your battery-less smartphone would be dead as soon as you left the house), it could be ideal for IoT networks, where replacing dead batteries could be prohibitively expensive or time-consuming.

This post was updated on 28 June 2019.

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The Inner Beauty of Basic Electronics

Open Circuits showcases the surprising complexity of passive components

5 min read
A photo of a high-stability film resistor with the letters "MIS" in yellow.
All photos by Eric Schlaepfer & Windell H. Oskay

Eric Schlaepfer was trying to fix a broken piece of test equipment when he came across the cause of the problem—a troubled tantalum capacitor. The component had somehow shorted out, and he wanted to know why. So he polished it down for a look inside. He never found the source of the short, but he and his collaborator, Windell H. Oskay, discovered something even better: a breathtaking hidden world inside electronics. What followed were hours and hours of polishing, cleaning, and photography that resulted in Open Circuits: The Inner Beauty of Electronic Components (No Starch Press, 2022), an excerpt of which follows. As the authors write, everything about these components is deliberately designed to meet specific technical needs, but that design leads to “accidental beauty: the emergent aesthetics of things you were never expected to see.”

From a book that spans the wide world of electronics, what we at IEEE Spectrum found surprisingly compelling were the insides of things we don’t spend much time thinking about, passive components. Transistors, LEDs, and other semiconductors may be where the action is, but the simple physics of resistors, capacitors, and inductors have their own sort of splendor.

High-Stability Film Resistor

A photo of a high-stability film resistor with the letters "MIS" in yellow.

All photos by Eric Schlaepfer & Windell H. Oskay

This high-stability film resistor, about 4 millimeters in diameter, is made in much the same way as its inexpensive carbon-film cousin, but with exacting precision. A ceramic rod is coated with a fine layer of resistive film (thin metal, metal oxide, or carbon) and then a perfectly uniform helical groove is machined into the film.

Instead of coating the resistor with an epoxy, it’s hermetically sealed in a lustrous little glass envelope. This makes the resistor more robust, ideal for specialized cases such as precision reference instrumentation, where long-term stability of the resistor is critical. The glass envelope provides better isolation against moisture and other environmental changes than standard coatings like epoxy.

15-Turn Trimmer Potentiometer

A photo of a blue chip
A photo of a blue chip on a circuit board.

It takes 15 rotations of an adjustment screw to move a 15-turn trimmer potentiometer from one end of its resistive range to the other. Circuits that need to be adjusted with fine resolution control use this type of trimmer pot instead of the single-turn variety.

The resistive element in this trimmer is a strip of cermet—a composite of ceramic and metal—silk-screened on a white ceramic substrate. Screen-printed metal links each end of the strip to the connecting wires. It’s a flattened, linear version of the horseshoe-shaped resistive element in single-turn trimmers.

Turning the adjustment screw moves a plastic slider along a track. The wiper is a spring finger, a spring-loaded metal contact, attached to the slider. It makes contact between a metal strip and the selected point on the strip of resistive film.

Ceramic Disc Capacitor

A cutaway of a Ceramic Disc Capacitor
A photo of a Ceramic Disc Capacitor

Capacitors are fundamental electronic components that store energy in the form of static electricity. They’re used in countless ways, including for bulk energy storage, to smooth out electronic signals, and as computer memory cells. The simplest capacitor consists of two parallel metal plates with a gap between them, but capacitors can take many forms so long as there are two conductive surfaces, called electrodes, separated by an insulator.

A ceramic disc capacitor is a low-cost capacitor that is frequently found in appliances and toys. Its insulator is a ceramic disc, and its two parallel plates are extremely thin metal coatings that are evaporated or sputtered onto the disc’s outer surfaces. Connecting wires are attached using solder, and the whole assembly is dipped into a porous coating material that dries hard and protects the capacitor from damage.

Film Capacitor

An image of a cut away of a capacitor
A photo of a green capacitor.

Film capacitors are frequently found in high-quality audio equipment, such as headphone amplifiers, record players, graphic equalizers, and radio tuners. Their key feature is that the dielectric material is a plastic film, such as polyester or polypropylene.

The metal electrodes of this film capacitor are vacuum-deposited on the surfaces of long strips of plastic film. After the leads are attached, the films are rolled up and dipped into an epoxy that binds the assembly together. Then the completed assembly is dipped in a tough outer coating and marked with its value.

Other types of film capacitors are made by stacking flat layers of metallized plastic film, rather than rolling up layers of film.

Dipped Tantalum Capacitor

A photo of a cutaway of a Dipped Tantalum Capacitor

At the core of this capacitor is a porous pellet of tantalum metal. The pellet is made from tantalum powder and sintered, or compressed at a high temperature, into a dense, spongelike solid.

Just like a kitchen sponge, the resulting pellet has a high surface area per unit volume. The pellet is then anodized, creating an insulating oxide layer with an equally high surface area. This process packs a lot of capacitance into a compact device, using spongelike geometry rather than the stacked or rolled layers that most other capacitors use.

The device’s positive terminal, or anode, is connected directly to the tantalum metal. The negative terminal, or cathode, is formed by a thin layer of conductive manganese dioxide coating the pellet.

Axial Inductor

An image of a cutaway of a Axial Inductor
A photo of a collection of cut wires

Inductors are fundamental electronic components that store energy in the form of a magnetic field. They’re used, for example, in some types of power supplies to convert between voltages by alternately storing and releasing energy. This energy-efficient design helps maximize the battery life of cellphones and other portable electronics.

Inductors typically consist of a coil of insulated wire wrapped around a core of magnetic material like iron or ferrite, a ceramic filled with iron oxide. Current flowing around the core produces a magnetic field that acts as a sort of flywheel for current, smoothing out changes in the current as it flows through the inductor.

This axial inductor has a number of turns of varnished copper wire wrapped around a ferrite form and soldered to copper leads on its two ends. It has several layers of protection: a clear varnish over the windings, a light-green coating around the solder joints, and a striking green outer coating to protect the whole component and provide a surface for the colorful stripes that indicate its inductance value.

Power Supply Transformer

A photo of a collection of cut wires
A photo of a yellow element on a circuit board.

This transformer has multiple sets of windings and is used in a power supply to create multiple output AC voltages from a single AC input such as a wall outlet.

The small wires nearer the center are “high impedance” turns of magnet wire. These windings carry a higher voltage but a lower current. They’re protected by several layers of tape, a copper-foil electrostatic shield, and more tape.

The outer “low impedance” windings are made with thicker insulated wire and fewer turns. They handle a lower voltage but a higher current.

All of the windings are wrapped around a black plastic bobbin. Two pieces of ferrite ceramic are bonded together to form the magnetic core at the heart of the transformer.

This article appears in the February 2023 print issue.