Phased Array Ultrasound Transducers for Eye Tracking

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Solution Overview

Problem

Conventional eye tracking methods in virtual reality headsets rely on expensive, power-hungry cameras that impose constraints on device size and proximity to the user's eye, limiting their suitability for augmented reality applications.

Innovation Solution

A depth sensing system utilizing a phased array of ultrasound transducers to scan facial features, including eyes, ears, and forehead, estimating gaze direction by transmitting and receiving ultrasonic signals and adjusting beam focus based on distance measurements.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Measurement precision

If conventional cameras are used for eye tracking, then gaze direction can be detected, but the device becomes expensive, large, and power-consuming

Engineering Contradiction:

Improvegaze direction detection accuracyVSAvoidpower consumption

Core Design Contradiction:

Measurement precisionVSUse of energy by moving object

Solution Approach 1:

The patent replaces the optical camera-based eye tracking system with an acoustic ultrasound-based system. The ultrasound transducer emits acoustic waves that reflect off the eye surface, and the reflected signals are processed to determine gaze direction. This substitution of mechanical/optical detection with acoustic detection achieves the technical effect of reducing power consumption while maintaining eye tracking functionality, as acoustic systems generally consume less power than high-resolution camera systems.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

2Measurement precision

If conventional cameras are used for eye tracking, then gaze direction can be detected, but the device size increases

Engineering Contradiction:

Improvegaze direction detection accuracyVSAvoiddevice size

Core Design Contradiction:

Measurement precisionVSVolume of moving object

Solution Approach 1:

The patent replaces the bulky camera system with a compact ultrasound transducer array. The transducer chip integrates multiple piezoelectric elements that can be manufactured in small form factors, enabling the device to maintain accurate eye tracking functionality while significantly reducing the overall device volume and allowing closer placement to the user's eye.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

3Volume of moving object

If a detection element is placed close to the user's eye, then device size is reduced, but conventional cameras cannot achieve accurate detection at such proximity

Engineering Contradiction:

Improvedevice sizeVSAvoideye orientation detection accuracy

Core Design Contradiction:

Volume of moving objectVSMeasurement precision

Solution Approach 1:

The patent employs an ultrasound transducer array specifically designed for close-proximity operation. The phased array configuration enables beamforming and focusing at very short distances from the eye surface, achieving accurate gaze detection even when the device is placed immediately adjacent to the user's eye. The acoustic waves can penetrate and reflect off the eye surface effectively at these close ranges, where optical systems struggle with working distance constraints.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

Solution Approach 2:

The patent divides the detection function into multiple piezoelectric elements arranged in a phased array on the transducer chip. Each element can independently transmit and receive acoustic signals, and by controlling the phase and amplitude of each element, the system can focus acoustic energy and detect reflections from specific regions of the eye. This segmentation enables precise spatial resolution and accurate gaze detection at close proximity.

Inventive Principle:

Principle #1Segmentation

Applied Scientific Principles

This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.

Function Achieved in This Case

This approach reduces power consumption, allows for a smaller, more compact design, and enables accurate eye tracking even when the eye is closed, providing efficient and precise gaze direction estimation for augmented reality applications.

Implementation Method 1

A depth sensing system utilizes a phased array of ultrasound transducers to scan facial features, including eyes

Methodology Applied

Scientific EffectUltrasound: Ultrasound

Implementation Method 2

transmitting and receiving ultrasonic signals and adjusting beam focus based on distance measurements

Methodology Applied

Scientific EffectReflection: Reflection

Implementation Method 3

Each of the ultrasound transducers comprises a Piezoelectric Micromachined Ultrasonic Transducer (PMUT)

Methodology Applied

Scientific EffectPiezoelectric effect: Piezoelectric Effect

Data Source

PatentUS11526018B2Phased array of ultrasound transducers for depth sensing

Publication Date: 2022.12.13 META PLATFORMS TECHNOLOGIES LLC

AI summary

A depth sensing system is configured to track one or both eyes of a user. The depth sensing system includes a transducer chip comprising a phased array of ultrasound transducers that transmit a signal at an eye of the user and detect a reflected signal from the eye. A controller estimates an orientation of the eye based on the reflected signals received by the phased array. The depth sensing system may be part of a headset that includes a display element configured to display content to a user wearing the headset.