Ultrasonic touch sensing parasitic wave rejection

Abstract

Improving the accuracy of ultrasonic touch sensing via the reduction, elimination and/or rejection of parasitic ultrasonic reflections caused by unintended touches is disclosed. The adverse effects of these parasitic reflections can be mitigated by disrupting the symmetry of the true reflections (from the intended touch) and the parasitic reflections (from unintended touches) so that the true touch can be disambiguated from unintended touches. Identification of the true touch can then enable accurate touch localization.

Description

FIELD OF THE DISCLOSURE[0001]This relates generally to ultrasonic touch sensing systems, and more particularly, to the rejection of parasitic waves caused by objects making inadvertent contact with a touch surface of an ultrasonic touch sensing system.BACKGROUND OF THE DISCLOSURE[0002]Many types of electronic devices are presently available that are capable of receiving touch input to initiate operations. Examples of such devices include desktop, laptop and tablet computing devices, smartphones, media players, wearables such as watches and health monitoring devices, smart home control and entertainment devices, headphones and earbuds, and devices for computer-generated environments such as augmented reality, mixed reality, or virtual reality environments. Many of these devices can receive input through the physical touching of buttons or keys, mice, trackballs, joysticks, touch panels, touch screens and the like. Capacitive touch sensing, in particular, has become popular. With capa...

AI Technical Summary

Benefits of technology

[0005]Accordingly, some examples of the disclosure are directed to improving the accuracy of ultrasonic touch sensing via the reduction, elimination and / or rejection of parasitic ultrasonic reflections. Fundamentally, the adverse effects of these parasitic reflections can be mitigated by disrupting the symmetry of the true reflections (from the intended touch) and the parasitic reflections (from the unintended touch). In one example, an absorbent material can be placed in a location where unintended object touches (e.g., from an ear or cheek) are expected, so that ultrasonic waves propagated in the direction of the unintended touching object are absorbed by the absorbent material, resulting in significant attenuation of the amplitude of the parasitic reflection as compared to the true reflection from an intended touch (e.g., from a finger). This attenuation of the parasitic wave can disrupt the symmetry of the amplitude of the parasitic and true reflections, which can allow for rejection of the parasitic reflection and processing of the true reflection. In another example, the ultrasonic transducer can be placed in an area where unintended object touches are expected, so that parasitic reflections can be received at the transducer much earlier than true reflections from an intended touch. This time separation of the parasitic wave from the true wave can disrupt the symmetry of the parasitic and true reflections, which can allow for rejection of the parasitic reflection and processing of the true reflection. In yet another example, a multi-element phased array of ultrasonic transducers can be employed to selectively direct ultrasonic waves in different directions at different times. For example, the phased array can first direct ultrasonic waves towards an area where unintended object touches are expected, and then direct ultrasonic waves towards an area where intended touches are expected. The time separation of the directional ultrasonic waves can cause true reflections from an intended touch, and parasitic reflections from an unintended touch, to be received back at the transducer at different times. This time separation of the parasitic wave from the true wave disrupts the symmetry of the parasitic and true reflections, which can allow for rejection of the parasitic reflection and processing of the true reflection.

Problems solved by technology

However, the conductive electrodes of capacitive touch sensing systems can interfere with the performance of nearby electronics such as antennas or other systems that are adversely affected by the presence of conductive material.

In addition, capacitive touch sensing systems can experience sensing errors or reduced performance when conductive, electrically-floating liquids (e.g., water droplets) or insulated objects (e.g., gloved fingers) come into contact with its touch-sensitive surface.

This can be particularly problematic for devices that are intended for outdoor use, exercise, and other situations where bodies of water, rain, or perspiration may be present, or for devices that are intended for use in cold weather, where gloved fingers are to be expected.

Ultrasonic touch sensing systems, like other touch sensing systems, can be adversely affected when an object unintentionally makes contact with the touch-sensitive surface, either alone or at the same time as an intended touch.

When an unintended touch occurs at the same time as an intended touch, the ultrasonic transducers may be unable to distinguish the parasitic reflections from “true” reflections caused by an intended touch (due to the rough “symmetry” of the true and parasitic reflections), and the parasitic reflections can corrupt the proper detection of the valid touch.

In one example, an absorbent material can be placed in a location where unintended object touches (e.g., from an ear or cheek) are expected, so that ultrasonic waves propagated in the direction of the unintended touching object are absorbed by the absorbent material, resulting in significant attenuation of the amplitude of the parasitic reflection as compared to the true reflection from an intended touch (e.g., from a finger).

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