How It Works: Linear Resonant Actuators

It heavily uses sentences of the form "Subordinate clause, independent clause", starting many sentences with one of the words although, since, unlike, or rather. This makes it hard to read after a while.

“When the voice coil is driven at the resonant frequency of the spring, the entire actuator vibrates with a perceptible force. Although the frequency and amplitude of a linear resonant actuator may be adjusted by changing the AC input, the actuator must be driven at its resonant frequency to generate a meaningful amount of force for a large current.”

Ok, got the basic principle and the key constraint (resonance) in the first paragraph.

“The voice coil remains stationary inside of the device while it produces a vibration and presses against a moving mass. By driving the magnetic mass up and down against the spring, the LRA as a whole will be displaced and produce a vibration.”

The first sentence feels like a repetition of the basic principle, but I get that (together with the second sentence) there is a subtle point being made: the whole assembly vibrates. I'd cut the first sentence or make the comparison more clear: “Although the voice coil is stationary within the LRA, … the LRA as a whole moves.”

The speaker comparison is good for illustrating the resonance constraint, but the conclusion simply repeats rather than expound on the principle. Leading the reader can make the implicit connection more obvious and avoid repetition: “While speakers can be driven at arbitrary frequencies, the physical spring within an LRA imposes a …”

“Rather than directly transferring the force produced by the voice coil to the skin, the device optimizes for power consumption by taking advantage of the resonant frequency of the spring. If the voice coil pushes the magnetic mass against the spring at the spring’s resonant frequency, the device can produce a vibration of higher amplitude more efficiently.”

This paragraph reintroduces resonance, but as an efficiency improvement. It feels repetitive, but there is an important point here that is left as a connection for the reader to draw: Offset rotating masses don't use resonance and draw much more power. I would actually use this in the leader. Instead of introducing resonance as a just a component of the system, make it the key. Instead of “that is DC and this is AC” (the impression I got from the first paragraph, lead with “that uses brute force and this uses a cool property of spring systems: resonance.” The latter is much more interesting, and can help reduce the repetition.

“Although the frequency can be changed, the LRA will typically be operated within a narrow frequency range to optimize its power consumption—if the device is driven at the resonant frequency of the spring, it will consume less power to produce a vibration of equal magnitude”

Repeating the basic principle again. Get rid of this and get right to the next sentence about how you can use a fixed frequency/varying frequency.

Hope this helps!