Electroacoustic Transducer With Integrated Capacitive Displacement Sensing

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Solution Overview

Problem

Existing electromechanical transducers lack an effective method to measure displacement and its derivatives without affecting the mechanical dynamic performance or introducing noise, especially over a broad frequency range.

Innovation Solution

An electroacoustic transducer with an integrated capacitive sensor that includes a first electrode on the moving portion and two electrodes on the housing, varying capacitance with displacement, coupled with an impedance buffer and amplifier to produce an output voltage, allowing for non-contact displacement measurement without altering the transducer's mechanical performance.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Measurement precision

If a discrete sensor is used to measure displacement, then measurement capability is provided, but mechanical dynamic performance is affected and noise is introduced

Engineering Contradiction:

Improvedisplacement measurement capabilityVSAvoidmechanical dynamic performance

Core Design Contradiction:

Measurement precisionVSReliability

Solution Approach 1:

The sensor electrodes are integrated directly into the transducer structure, with first electrode on the moving portion and second/third electrodes on the housing, merging the sensing function with the transducer components themselves rather than using separate discrete sensors

Inventive Principle:

Principle #5Merging (Combining)

Solution Approach 2:

The moving portion serves dual functions: as the acoustic radiation element and as the carrier for the first electrode of the displacement sensor, eliminating the need for separate sensing components that would affect mechanical performance

Inventive Principle:

Principle #6Universality (Multi-functionality)

2Measurement precision

If a discrete sensor is used to measure displacement, then measurement capability is provided, but noise is introduced

Engineering Contradiction:

Improvedisplacement measurement capabilityVSAvoidnoise

Core Design Contradiction:

Measurement precisionVSObject-generated harmful factors

Solution Approach 1:

The sensor is merged with the transducer structure, placing the measurement function inside the transducer housing where it can operate in a controlled electromagnetic environment, reducing noise pickup from external sources

Inventive Principle:

Principle #5Merging (Combining)

Solution Approach 2:

The impedance buffer circuit acts as an intermediary between the capacitive sensor and the external world, isolating the sensor from noise and providing a stable interface for signal processing

Inventive Principle:

Principle #24Intermediary (Mediator)

3Measurement precision

If a discrete sensor is used, then displacement measurement is possible, but frequency range is limited

Engineering Contradiction:

Improvedisplacement measurement capabilityVSAvoidfrequency range

Core Design Contradiction:

Measurement precisionVSAdaptability or versatility

Solution Approach 1:

The mechanical displacement measurement approach is replaced with an electrical capacitive sensing system, where capacitance changes are measured and converted to displacement signals, enabling broader frequency response limited only by the electrical circuit characteristics rather than mechanical constraints

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

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

The integrated sensor enables precise displacement measurement and its derivatives, such as velocity and acceleration, with reduced noise and no significant change in mechanical dynamic performance, functioning over a broader frequency range and with lower noise compared to discrete sensors.

Implementation Method 1

A first capacitance between the first electrode and the second electrode and a second capacitance between the first electrode and the third electrode each vary similarly with a displacement of the moving portion relative to the housing

Methodology Applied

Scientific EffectCapacitance: Capacitance

Implementation Method 2

The impedance buffer may include a bias voltage source providing a fixed charge to at least one of the electrodes of the displacement sensor, and an amplifier amplifying a change in voltage between the first and second electrodes to produce an output voltage between first and second signal outputs

Methodology Applied

Scientific EffectElectrical charge and voltage amplification:

Data Source

PatentUS9049523B2Transducer with integrated sensor

Publication Date: 2015.06.02 BOSE CORP

AI summary

An electroacoustic transducer for converting electrical input signals into acoustic output signals includes a diaphragm adapted to move relative to a housing in response to the electrical input signals to produce the acoustic output signals, a displacement sensor, a bias voltage source, and an amplifier. The displacement sensor includes a first electrode adhered to the diaphragm and a second electrode on a first surface of the housing located proximate to the first electrode. A capacitance between the first electrode and the second electrode varies with a displacement of the diaphragm relative to the housing. The bias voltage source is coupled to at least one of the first electrode or the second electrode and provides a fixed charge to the electrode to which it is attached. The amplifier amplifies a change in voltage between the first and second electrodes to produce an output voltage between first and second signal outputs.