Today the US Patent & Trademark Office published a patent application from Apple relating to AirPower. The invention describes adding graduating texture on the pad from a rough finish in the center through to a smooth surface at the edge in order to keep slippery iDevice from sliding around on the charging mat.

In the first patent application Apple begins by noting that inductive charge mats can experience a problem where electronic devices, such as an iPhone with a glass back could slip off the surface of the mat.  A charging mat with an uncoated silicone surface can prevent phone slippage, but silicone has poor esthetic and haptic qualities, and causes lint and dust to build up on the surface. This is the problem that Apple's invention addresses.

A common term used in Apple's patent application and in patent FIG. 4 in particular is a "Ra" measurement. A definition provided by DestinyTool states that "Most surface finish requirements are noted in Ra as opposed to an RMS value. ... Ra is calculated as the Roughness Average of a surfaces measured microscopic peaks and valleys. RMS is calculated as the Root Mean Square of a surfaces measured microscopic peaks and valleys.

Adding Texture to AirPower

In patent figures presented below in patent FIG. 4, a wireless charging mat (AirPower) has a surface area for receiving an electronic device to be charged. The surface area of AirPower includes an inner region having a rough surface texture and an outer region having s smooth surface texture, and the outer region is elevated relative to the inner region.

In some variations, the surface of the outer region has a higher coefficient of friction than the surface of the inner region.

In other variations, the surface area further includes a transition region between the inner region and the outer region, and the transition region has a surface texture gradient that continuously changes from the rough surface texture of the inner region to the smooth surface texture of the outer region. This is presented as such in patent FIG. 4 above in a color coded manner by Patently Apple.

In accordance with other embodiments of the disclosure, the surface area of the charging mat has a rough texture with friction bumps dispersed therein. The friction bumps have a smooth surface texture and form less than 20% of the surface area.

In patent FIG. 6A above we're able to see a computer generated 3-dimensional color scale of the texture along the surface of the wireless charging mat. FIG. 6B is a magnified view of region 6B in the 3-D image in FIG. 6A. FIG. 6C is a cross section view along the textured surface in FIG. 6A.

To ensure that the charging mat is sufficiently 'grippy' – a minimum number of friction bumps #602 needs to be included along the mat surface, and the friction bumps must have a substantially smooth top surface. In some embodiments, the friction bumps will account for up to 20% of the total surface area of the mat and have a height in the range of 20 .mu.m to 30 .mu.m.

In accordance with other embodiments, the surface area of the charging mat includes a first region with an asymmetrical surface texture geometry oriented so as to promote movement of an overlying electronic device toward the center of the mat.

More specifically, this is illustrated in FIG. 8A above where arrows # 804 and #806 on mat (#810) show the direction of movement that the surface texture along each of the left half and the right half of the mat surface promote.

Alternatively, as shown by arrows #824 and #826 in FIG. 8B, the surface texture of mat (#820) can be engineered so that the surface texture along the upper half of the mat promotes movement toward center line #822 of the mat while the surface texture along the lower half of the mat promotes movement toward center line of the mat. 

In still another variation shown in FIG. 8C, the surface texture of mat (#830) may be oriented in 4 different directions so that each of a right region, a left region, a top region, and a bottom region of the mat surface promotes movement toward the center of the mat, as illustrated by arrows #836, #838, #840 and #842.

Apple's patent application that was published today by the U.S. Patent Office was originally filed back in Q1 2018. Considering that this is a patent application, the timing of AirPower and these specific features to market is unknown at this time.

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