Piezoelectric Sensor Layout for Separating Pressure and Bending Signals
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Solution Overview
Problem
Existing flexible organic piezoelectric sensors face challenges in separating signals from muscle expansion/contraction and bending/contraction, leading to increased signal noise and decreased reproducibility due to design constraints and difficulty in controlling sensor thickness and neutral axis alignment.
Innovation Solution
A measuring device comprising first and second piezoelectric elements with a common piezoelectric layer, each with a partial piezoelectric layer and electrodes, and an expansion/contraction suppression layer with higher elasticity, allowing for precise detection of in-plane and film thickness direction expansions/contractions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a flexible organic piezoelectric sensor is used to measure body surface displacement, then the sensor can be attached to various body sites and measure muscle activity, but the signal from contact pressure changes cannot be separated from the signal from sensor bending, leading to increased signal noise and decreased reproducibility
Solution Approach 1:
The sensor is divided into two distinct piezoelectric elements with different structural configurations. The first piezoelectric element is configured with its neutral axis coinciding with the center line in the thickness direction to detect contact pressure, while the second piezoelectric element is configured with its neutral axis offset from the center line to detect bending. This segmentation allows separate detection and subsequent separation of pressure and bending signals, resolving the signal mixing problem that degrades measurement precision and reproducibility.
Solution Approach 2:
Different regions of the sensor structure are assigned different functional properties. The first piezoelectric element is specifically designed with uniform thickness above and below the piezoelectric layer to create a neutral axis at the center line, making it insensitive to bending. The second piezoelectric element is designed with non-uniform thickness to create an offset neutral axis, making it sensitive to bending. This local differentiation of structural quality enables selective detection of different physical quantities.
2Adaptability or versatility
If one piezoelectric element is configured to coincide with the neutral axis to make it insensitive to bending, then it can function as a pressure sensor, but it requires uniform thickness of electrode, base material, and protective film which imposes large design constraints and makes control difficult
Solution Approach 1:
The problem of achieving neutral axis alignment is extracted and solved independently for each piezoelectric element. Rather than attempting to make a single complex sensor do both jobs, the function of pressure detection is extracted into the first piezoelectric element with simplified uniform thickness design, while the bending detection function is extracted into the second piezoelectric element with offset neutral axis design. This separation reduces the design constraints on each individual element.
Solution Approach 2:
The thickness parameter of the piezoelectric layer and surrounding materials is deliberately changed between the two elements. The first element maintains uniform thickness parameters to achieve center-line neutral axis alignment for pressure detection. The second element uses varied thickness parameters to achieve offset neutral axis alignment for bending detection. This parameter differentiation simplifies the design process for each element while achieving the desired functional properties.
3Ease of operation
If the sensor is made thinner to improve flexibility, then it can be more easily attached to the body, but control of the sensor becomes more difficult
Solution Approach 1:
The sensor structure is designed to be dynamically responsive to different types of deformation. The first piezoelectric element is configured to dynamically respond to compressive forces (pressure) while the second element dynamically responds to bending forces. This dynamic differentiation allows the thin flexible sensor to maintain ease of operation while the distinct response characteristics of each element simplify control by allowing separate signal processing for pressure and bending components.
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 accurate differentiation between in-plane and film thickness direction expansions/contractions, improving signal separation and measurement precision by using a flexible organic piezoelectric material with an expansion/contraction suppression layer.
Implementation Method 1
a piezoelectric layer provided in common for the first piezoelectric element and the second piezoelectric element
Data Source
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AI summary
This measuring device includes: a first piezoelectric element (20) and a second piezoelectric element (21); and a piezoelectric layer 40 which is provided in common for the first piezoelectric element (20) and the second piezoelectric element (21), and which includes a first partial piezoelectric layer (40A) and a second partial piezoelectric layer (40B). The first piezoelectric element (20) includes a first lower electrode (31), the first partial piezoelectric layer (40A) provided on the first lower electrode (31), a first upper electrode (33) provided on the first partial piezoelectric layer (40A), and an expansion/contraction suppression layer (34) provided on the first partial piezoelectric layer (40A) so as to cover the first upper electrode (33). The second piezoelectric element (21) includes a second lower electrode (35), the second partial piezoelectric layer (40B) provided on the lower electrode (35), and a second upper electrode (37) provided on the second partial piezoelectric layer (40B). The modulus of elasticity of the expansion/contraction suppression layer (34) is higher than that of the piezoelectric layer (40).