Power button Touch ID on the iPad Air 4 was an 'incredible feat'

The power button on the iPad Air 4 now houses the Touch ID sensor.

Apple revealed its iPad Air 4 on September 15, complete with an updated A14 Bionic chip, a design inspired by the iPad Pro line, and a larger 10.9-inch display. Arguably the biggest departure for the iPad Air is its biometric alterations, with Touch ID moved from the now-gone Home button to the power button on the top.

Speaking on the iJustine and Jenna Ezarik podcast Same Brain published on Saturday, Apple VP of hardware engineering John Ternus and Apple VP of product marketing Bob Borchers talked about the changes that the iPad lineup underwent during the September event.

On the subject of Touch ID on the tablet, Borchers described the change as "an incredible feat of engineering to get that fingerprint sensor with all of the capability and all of the security into that form factor."

When asked if the power button Touch ID was using the same technology as the original but in a smaller form factor, Ternus suggested it was more an "evolution of the technology" employed by the system. "We wanted to get to the full-screen design and so we wanted to get rid of the Home button on the chin, and so we had to come up with another place for the Touch ID sensor."

"What made it so challenging is this really narrow aspect ratio that it has," Ternus offered, due to being on the top of a slimline button. "If you think about it, it's only ever seeing a smaller slice of your fingerprint than what a traditional, you know, what our older sensor could do."

Ternus continued "it has to be incredibly sensitive and it also has to capture as you go through the enrollment process and then as it continues to adapt over time, a broader view of the fingerprints. So no matter how you touch it with your finger, it's got that particular portion captured and so it can do the match."

A "lot of algorithm work, a lot of hardcore silicon" was put into practice to create "such a capable sensor in such a tiny little space," but one that Borchers pointed out was "a really sophisticated space" due to the other items in the region that have to be managed while introducing a new sensor.

"On the cellular iPads, the top portion of the enclosure is the antenna," Ternus explained, which meant they had to place "this incredibly sensitive Touch ID sensor right inside an incredibly sensitive antenna, and had to figure out how to make them work with each other and not be talking over each other and causing interference."

"As these products become more feature rich, and obviously more compact and condensed, it's becoming more and more critical that our teams are collaborating really, really tightly together," he continued, "because the Touch ID team and the antenna team had to be in lockstep through the entire engineering process."

Apple's design for a power button Touch ID sensor may find its way into more products in the future. One day before the iPad Air 4's launch, analyst Ming-Chi Kuo forecasted that more iPad models that lack Face ID will adopt the change in 2021.