Piezoelectric Cantilever Force Sensor via Variable Capacitance
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Solution Overview
Problem
Existing technologies face challenges in accurately and simply measuring external forces such as acceleration, pressure, and magnetic forces using piezoelectric devices, requiring high accuracy and complex structures.
Innovation Solution
A piezoelectric device with a cantilever-supported crystal piece, featuring excitation electrodes, a movable electrode forming a variable capacitor, and a frequency information detecting unit, which changes capacitance and oscillation frequency in response to external forces, allowing for precise force measurement.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a piezoelectric device is used to detect external force, then measurement precision is improved, but device complexity increases
Solution Approach 1:
The patent combines the piezoelectric element, excitation electrodes, movable electrode, and fixed electrode into an integrated sensor structure. The piezoelectric piece serves dual functions: it acts as both the sensing element that detects external force and as part of the oscillating system that generates the measurement signal, eliminating the need for separate detection and actuation components.
Solution Approach 2:
The piezoelectric piece performs multiple functions simultaneously: it serves as the structural cantilever element, the sensing element that generates charge in response to external force, and part of the oscillating system. This multi-functionality reduces the number of separate components needed, thereby simplifying the overall device structure while maintaining high measurement precision.
2Device complexity
If a simple device structure is used, then device complexity is reduced, but measurement precision deteriorates
Solution Approach 1:
The patent utilizes mechanical vibration of the cantilever-supported piezoelectric piece as the core measurement mechanism. By exciting the piezoelectric element to vibrate and measuring changes in its oscillation characteristics in response to external force, the system achieves high measurement precision through a relatively simple structure that leverages natural mechanical phenomena rather than complex electronic sensing systems.
Solution Approach 2:
The measurement is based on detecting changes in oscillation parameters (frequency, amplitude, or phase) of the piezoelectric piece when external force is applied. This parameter-based detection approach allows for high precision measurement using simple hardware, as it converts the physical quantity measurement into a signal processing task that can be achieved with minimal additional components.
3Measurement precision
If piezoelectric piece bending is used to change capacitance, then measurement sensitivity is improved, but device complexity increases
Solution Approach 1:
The patent employs a dynamic capacitance measurement approach where the movable electrode is positioned to form a variable capacitor with the fixed electrode. As the piezoelectric piece bends in response to external force, the distance between these electrodes changes dynamically, causing the capacitance to vary. This dynamic capacitance change provides a sensitive measurement signal that directly reflects the magnitude of the applied force.
Solution Approach 2:
The capacitance formed between the movable and fixed electrodes serves as an intermediary mechanism that translates the mechanical bending of the piezoelectric piece into an electrical signal. This capacitance variation acts as a mediator that amplifies the small mechanical displacements into measurable electrical changes, thereby improving detection sensitivity without requiring complex transduction mechanisms.
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 high-accuracy detection of external forces with a simple device structure, capable of measuring slight deformations and various types of forces, including acceleration and magnetic forces, through changes in oscillation frequency.
Implementation Method 1
a piezoelectric piece supported at one end on a base; one excitation electrode and another excitation electrode provided on one face side and another face side, respectively, of the piezoelectric piece; capacitance between the fixed electrode and the movable electrode is changed by bending of the piezoelectric piece
Data Source
AI summary
A device is provided for a detecting external force applied to piezoelectric piece. A crystal piece is cantilever-supported in a container. Excitation electrodes are formed on an upper face and lower face, respectively. A movable electrode, connected via a lead-out electrode to the excitation electrode, is formed on the lower face side at a front end of the crystal piece. A fixed electrode is provided on a bottom portion of the container to face this movable electrode. The excitation electrode on the upper face side and the fixed electrode are connected to an oscillation circuit. When the crystal piece bends in response to an applied external force, capacitance between the movable electrode and fixed electrode, changes. This capacitance change results in a corresponding change in oscillation frequency of the crystal piece.