MEMS Sound Producing Device Resonance Frequency Design

Solution Overview

Problem

Micro Electro Mechanical System (MEMS) sound producing devices suffer from severe membrane excursion and extended ringing due to high resonance quality factor, leading to increased Total Harmonic Distortion (THD) and Inter-modulation (IM), causing 'colored' and 'muddied' sound quality, as they inherit design methodologies from Magnet and Moving Coil (MMC) devices without considering their distinct characteristics.

Innovation Solution

Designing a MEMS sound producing device with a resonance frequency significantly higher than the maximum audio frequency, coupled with a high quality factor, to avoid resonance within the audio band, thereby minimizing membrane excursion and ringing, and incorporating a compensating circuit to ensure linearity between the input audio signal and membrane displacement.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Power

If the resonance frequency is set within the audio band to increase membrane displacement and SPL, then sound pressure level is improved, but resonance causes membrane excursion and ringing leading to increased THD and IM

Engineering Contradiction:

Core Design Contradiction:

PowerVSObject-generated harmful factors

Solution Approach 1:

The patent converts the harmful resonance effect into a beneficial one by carefully positioning the resonance frequency at the upper boundary of the audio band. The resonance is used to enhance SPL in the upper frequency range while its harmful effects (membrane excursion and ringing) are minimized by ensuring the resonance frequency does not overlap with the main audio content frequencies.

Inventive Principle:

Principle #22Blessing in disguise (Convert harm into benefit)

Solution Approach 2:

The patent changes the resonance frequency parameter from a conventional position within the audio band to a specific position at the upper boundary (20kHz or higher). This parameter change allows the system to maintain high SPL through resonance while avoiding the harmful membrane excursion and ringing that occur when resonance frequencies fall within the main audio band.

Inventive Principle:

Principle #35Parameter changes

2Power

If the resonance quality factor is increased to enhance resonance effect, then sound pressure level is improved, but membrane excursion and extended ringing are exacerbated

Engineering Contradiction:

Core Design Contradiction:

PowerVSDuration of action of moving object

Solution Approach 1:

The patent converts the potentially harmful high Q-factor resonance into a beneficial feature by positioning it at the upper audio band boundary. The high Q-factor provides strong SPL enhancement where needed, while the harmful extended ringing is minimized because the resonance frequency is positioned above the main audio content, causing the ringing to occur in a frequency range less perceptible to human hearing.

Inventive Principle:

Principle #22Blessing in disguise (Convert harm into benefit)

3Ease of manufacture

If MEMS design methodology from MMC is applied, then manufacturing is simplified, but severe membrane excursion and extended ringing occur due to high resonance quality factor

Engineering Contradiction:

Core Design Contradiction:

Ease of manufactureVSObject-generated harmful factors

Solution Approach 1:

The patent maintains the simple MEMS manufacturing approach but introduces a critical parameter change: positioning the resonance frequency at the upper boundary of the audio band (20kHz or higher) rather than within the conventional audio range. This parameter modification allows the system to retain manufacturing simplicity while eliminating the harmful membrane excursion and ringing effects.

Inventive Principle:

Principle #35Parameter changes

4Object-generated harmful factors

If resonance frequency is positioned above the audio band, then membrane excursion and ringing are reduced, but sound pressure level in the upper frequency range may be compromised

Engineering Contradiction:

Core Design Contradiction:

Object-generated harmful factorsVSPower

Solution Approach 1:

The patent converts what could be seen as a compromise (positioning resonance above the audio band) into a benefit by utilizing the resonance to enhance SPL precisely in the upper frequency range where it occurs. The resonance provides SPL boost without causing harmful membrane excursion or audible ringing, as the resonance frequency is positioned at or above 20kHz where human hearing sensitivity decreases.

Inventive Principle:

Principle #22Blessing in disguise (Convert harm into benefit)

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 enhances sound quality by eliminating resonance within the audio band, reducing THD and IM, and allowing precise control over membrane position, resulting in improved sound fidelity and reduced distortion.

Implementation Method 1

MEMS (Micro Electro Mechanical System) microspeakers become another breed of sound producing devices (SPD) which make use of thin film piezoelectric material as actuator

Methodology Applied

Scientific EffectPiezoelectric effect: Piezoelectric Effect

Implementation Method 2

the resonance frequency is higher than the maximum frequency plus a half of the resonance bandwidth

Methodology Applied

Scientific EffectResonance: Resonance

Data Source

PatentUS10805751B1Sound producing device

Publication Date: 2020.10.13

AI summary

A sound producing device (SPD) is provided. The SPD comprises a membrane, having a resonance frequency and a resonance bandwidth; and an actuator, disposed on the membrane, receiving a driving signal corresponding to an input audio signal; wherein the input audio signal has an input audio band which is upper bounded by a maximum frequency; wherein the resonance frequency is higher than the maximum frequency plus a half of the resonance bandwidth.