Piezoelectric Heart Rate Sensing for Low-Power Wearables

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Solution Overview

Problem

Optical sensing techniques like photoplethysmography (PPG) are not suitable for continuous long-term heart rate monitoring in wearable devices due to high energy consumption and bulkiness, which compromises usability and user experience.

Innovation Solution

The use of passive piezoelectric or pressure-sensitive sensors strategically placed on wearable devices, such as eyewear, to detect minute pulsatile vibrations in arteries, eliminating the need for excitation energy and significantly reducing power consumption, combined with dual sensors to enhance signal quality and reliability.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Measurement precision

If optical PPG sensing techniques are used to measure heart rate, then heart rate monitoring capability is achieved, but energy consumption increases significantly and device size increases

Engineering Contradiction:
Improveheart rate measurementVSAvoidenergy consumption
Core Design Contradiction:
Measurement precisionVSUse of energy by moving object

Solution Approach 1:

The patent replaces the optical PPG sensing system with a mechanical piezoelectric sensing system. Instead of using LEDs and photodiodes to detect blood volume changes optically, the invention uses piezoelectric sensors to detect mechanical vibrations from arterial pulsations directly through the skin. This mechanical substitution eliminates the need for high-current LED driving circuits and complex optical processing, reducing energy consumption by 100-1000 times while maintaining heart rate measurement capability.

Inventive Principle:
Principle #28Mechanics substitution (Replace mechanical system)

Solution Approach 2:

The patent changes the sensing parameter from optical absorption (PPG) to mechanical vibration frequency (piezoelectric). By measuring the frequency of arterial wall vibrations caused by blood pulsation rather than optical property changes, the system achieves equivalent heart rate information with dramatically lower power requirements and simpler circuitry.

Inventive Principle:
Principle #35Parameter changes

2Measurement precision

If optical PPG sensing techniques are used to measure heart rate, then heart rate monitoring capability is achieved, but device weight and size increase compromising usability

Engineering Contradiction:
Improveheart rate measurementVSAvoiddevice weight
Core Design Contradiction:
Measurement precisionVSWeight of moving object

Solution Approach 1:

The patent replaces the optical PPG sensing system with a mechanical piezoelectric sensing system. Instead of using LEDs and photodiodes to detect blood volume changes optically, the invention uses piezoelectric sensors to detect mechanical vibrations from arterial pulsations directly through the skin. This mechanical substitution eliminates the need for high-current LED driving circuits and complex optical processing, reducing energy consumption by 100-1000 times while maintaining heart rate measurement capability.

Inventive Principle:
Principle #28Mechanics substitution (Replace mechanical system)

3Reliability

If dual piezoelectric sensors are used to detect pulsatile vibrations, then signal quality and reliability improve, but device complexity increases

Engineering Contradiction:
Improvesignal qualityVSAvoidsensor configuration
Core Design Contradiction:
ReliabilityVSDevice complexity

Solution Approach 1:

The patent combines the outputs of two piezoelectric sensors through differential amplification to reject common-mode noise and enhance the pulsatile signal. By placing sensors on opposite sides of an artery and subtracting their outputs, the system eliminates motion artifacts and environmental interference that affect both sensors equally, thereby improving signal quality and reliability while using simple analog circuitry.

Inventive Principle:
Principle #5Merging (Combining)

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

Enables continuous, long-term heart rate monitoring with reduced battery size and weight, improved aesthetics, and increased usability by consuming 100-1000 times less power than optical PPG techniques, while providing resilient pulse signals against motion-induced noise.

Implementation Method 1

a first piezoelectric sensor configured to be in communication with skin of the subject, the first piezoelectric sensor configured to generate a first voltage signal in response to a periodic vibration in at least one artery of the subject

Methodology Applied
Scientific EffectPiezoelectric effect: Piezoelectric Effect

Data Source

PatentUS12042259B2Noise resilient, low-power heart rate sensing techniques
Publication Date: 2024.07.23 INTEL CORP
  • US12042259B2 patent drawing
  • US12042259B2 patent drawing
  • US12042259B2 patent drawing

AI summary

An apparatus for sensing a heart rate of a subject, including an eyewear frame and a heart rate sensing circuit. The sensing circuit includes first and second piezoelectric sensors configured to be in communication with the subject's skin and to generate first and second voltage signals in response to a periodic vibration in at least one artery of the subject, a first voltage amplifier configured to receive the first voltage signal and output a first amplified voltage signal related to the heart rate of the subject, a second voltage amplifier configured to receive the second voltage signal and output a second amplified voltage signal related to the heart rate of the subject, and a device configured to output a differential signal that is a representation of a difference between the first amplified voltage signal and the second amplified voltage signal that relates to the heart rate.