Low Density Underwater Accelerometer Buoyant Housing

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Solution Overview

Problem

Conventional piezoelectric transducer accelerometers for sonar systems face challenges such as high cost, complexity, limited bandwidth, and susceptibility to delamination, especially in underwater applications where impedance mismatch between the piezoelectric material and air affects their performance.

Innovation Solution

A low-density accelerometer design featuring a buoyant outer layer and a rigid hollow housing with a disk-shaped sensing element and a solid proof mass, utilizing a shear-mode piezoelectric element that generates high voltage from shear strain, allowing for increased detection range and sensitivity while being easier and less expensive to produce.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If conventional piezoelectric transducer designs are used, then impedance matching with water is achieved, but cost and complexity increase

Engineering Contradiction:

Improveimpedance matchingVSAvoiddesign complexity

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The patent replaces the conventional mechanical piezoelectric transducer design with a low-density accelerometer design that uses a buoyant outer layer and internal proof mass. This substitution maintains the acoustic sensing function while eliminating the complexity of impedance-matched piezoelectric materials, achieving comparable reliability through a different physical approach.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

2Ease of manufacture

If flexural piezoelectric disks are used, then manufacturing is simplified, but bandwidth and sensitivity are limited

Engineering Contradiction:

Improvemanufacturing simplicityVSAvoidbandwidth and sensitivity

Core Design Contradiction:

Ease of manufactureVSManufacturing precision

Solution Approach 1:

The patent changes the fundamental operating parameters by using a low-density proof mass suspended on springs instead of flexural piezoelectric disks. This parameter change enables higher bandwidth and sensitivity while maintaining ease of manufacture through standard mechanical components and assembly processes.

Inventive Principle:

Principle #35Parameter changes

3Measurement precision

If high density proof mass is used, then acceleration sensing is improved, but mounting noise sensitivity increases

Engineering Contradiction:

Improveacceleration sensingVSAvoidmounting noise

Core Design Contradiction:

Measurement precisionVSObject-affected harmful factors

Solution Approach 1:

The patent uses a low-density proof mass that is buoyant relative to the surrounding water, creating a counterbalancing effect that reduces the impact of mounting noise. The buoyant outer layer provides upward buoyant force that counteracts the downward gravitational force on the proof mass, isolating it from vibrations and noise transmitted through the mounting structure.

Inventive Principle:

Principle #8Anti-weight (Counterweight)

4Strength

If conventional accelerometer designs are used, then structural strength is maintained, but manufacturing cost increases

Engineering Contradiction:

Improvestructural strengthVSAvoidmanufacturing cost

Core Design Contradiction:

StrengthVSEase of manufacture

Solution Approach 1:

The patent divides the accelerometer into separate modular components: a buoyant outer layer, a rigid housing, internal springs, and a proof mass. This segmentation allows each component to be manufactured independently using cost-effective processes and then assembled, reducing overall manufacturing cost while maintaining structural strength through the rigid housing design.

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

The low-density accelerometer provides enhanced sensitivity and detection range, is less affected by mounting noise, and can operate in high-pressure environments, overcoming the limitations of conventional designs.

Implementation Method 1

A piezoelectric element having longitudinal ends, a first end affixed to a base, and the second end affixed to a low density mass. When the mass is impinged upon by a sound wave, the mass moves relative to the base and exerts a force on the piezoelectric element to produce a voltage in the piezoelectric element.

Methodology Applied

Scientific EffectPiezoelectric effect: Piezoelectric Effect

Implementation Method 2

A low-density accelerometer design featuring a buoyant outer layer and a rigid hollow housing

Methodology Applied

Scientific EffectBuoyancy: Archimedes' Principle (Buoyancy)

Data Source

PatentUS10448181B2Method of manufacturing a low density underwater accelerometer

Publication Date: 2019.10.15 LOCKHEED MARTIN CORP

AI summary

A method of manufacturing a low density accelerometer comprises the steps of: providing a rigid hollow housing having an upper member and a lower member and forming a groove circumferentially along an inner surface of the rigid hollow housing about a location where the upper member is configured to meet the lower member; providing a sensor assembly including a sensing element affixed to a solid proof mass; disposing the sensor assembly in the lower member of the rigid hollow housing, such that an outer edge of the sensing element engages and is in physical contact with the groove defined in the inner surface of the rigid hollow housing; and placing the upper member of the rigid hollow housing over the lower member of the rigid hollow housing, to enclose the sensor assembly within the rigid hollow housing, wherein the sensor assembly is in physical contact with the rigid hollow housing at the groove.