Piezoelectric Sensor Strain Detection via Low-Stiffness Bonding

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Solution Overview

Problem

Conventional pressure-detecting sensors face challenges in accurately detecting pressing forces on operation surfaces, especially when attached to portable terminals with rigid materials like glass, due to the interference from protective layers and linear electrode matrices.

Innovation Solution

A pressure-detecting sensor configuration featuring a flat-membrane piezoelectric sensor with a piezoelectric film and detecting electrodes on both surfaces, attached to a plate member via a sticky agent with an elastic constant of 106 Pa or lower, and oriented at an angle to enhance strain detection and prevent cancellation of generated charge.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Strength

If a pressure-sensitive sensor is placed on a lower surface of the touch panel and covered with a protective layer, then the operation surface is protected, but the pressing force detection accuracy deteriorates

Engineering Contradiction:

Improveprotective layer protectionVSAvoidpressing force detection accuracy

Core Design Contradiction:

StrengthVSMeasurement precision

Solution Approach 1:

The invention extracts the pressure detection function from the touch panel structure by using a separate piezoelectric sensor attached to the back surface of the plate member. This separates the protective function (touch panel) from the detection function (piezoelectric sensor), allowing the protective layer to remain while enabling accurate pressing force detection through the plate member's strain transmission.

Inventive Principle:

Principle #2Taking out (Extraction)

Solution Approach 2:

The plate member serves as an intermediary that transmits the pressing force from the operation surface to the piezoelectric sensor on its back surface. The plate member's strain under pressure mediates between the external force and the sensor, enabling detection while maintaining the protective structure.

Inventive Principle:

Principle #24Intermediary (Mediator)

2Strength

If a member made of glass or the like with rigidity is attached to the operation surface, then the structural strength is improved, but the pressing force detection capability deteriorates

Engineering Contradiction:

Improvestructural strengthVSAvoidpressing force detection capability

Core Design Contradiction:

StrengthVSMeasurement precision

Solution Approach 1:

The plate member made of rigid material like glass serves as an intermediary that transmits pressing forces to the piezoelectric sensor. The rigidity provides structural strength while the plate's elastic deformation under pressure enables strain transmission to the sensor for detection.

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

Although the plate member is rigid, it functions similarly to a flexible membrane by undergoing elastic deformation under pressure. This deformation is transmitted to the piezoelectric sensor, enabling detection while maintaining structural integrity.

Inventive Principle:

Principle #30Flexible shells and thin films

3Device complexity

If matrices of linear electrodes are used to detect depression-induced charge, then the device complexity is reduced, but the pressing force detection accuracy deteriorates

Engineering Contradiction:

Improveelectrode configuration simplicityVSAvoidpressing force detection accuracy

Core Design Contradiction:

Device complexityVSMeasurement precision

Solution Approach 1:

The invention replaces the electrical field-based detection (electrode matrices detecting depression-induced charge) with a mechanical strain-based detection system. The piezoelectric sensor directly converts mechanical strain from the plate member into electrical signals, providing more accurate pressing force detection.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

Solution Approach 2:

The invention changes the detection parameter from electrical charge (depression-induced charge) to mechanical strain. By using the piezoelectric effect to convert strain directly into electrical signals, the system achieves better detection accuracy for pressing forces.

Inventive Principle:

Principle #35Parameter changes

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 configuration allows for precise detection of pressing forces by effectively straining the piezoelectric film, ensuring consistent sensor output regardless of pressure location, thus improving the accuracy of force measurement.

Implementation Method 1

the flat-membrane piezoelectric sensor includes a piezoelectric film and detecting electrodes formed on both principal surfaces, respectively, of the piezoelectric film

Methodology Applied

Scientific EffectPiezoelectric effect: Piezoelectric Effect

Data Source

PatentUS10146352B2Pressure-detecting sensor

Publication Date: 2018.12.04 MURATA MFG CO LTD

AI summary

A pressure-detecting sensor that includes a piezoelectric sensor, a rectangular plate member, and an attaching member. The piezoelectric sensor is attached to the plate member via the attaching member so that the piezoelectric sensor is located in the vicinity of an end of the plate member in the longitudinal direction of the plate member, and such that the longitudinal direction of the piezoelectric sensor is parallel to the transverse direction of the plate member. The attaching member is composed of a sticky agent having an elastic constant of 106 Pa or lower. The piezoelectric sensor has a shape having aspect ratio of 2.5 or higher.