Polymeric Composite Piezoelectric Speaker with Attenuation Circuit
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Solution Overview
Problem
Piezoelectric speakers using sheet-like diaphragms face challenges in achieving uniform sound pressure level-frequency characteristics due to the high mechanical quality factor of piezoelectric ceramics and the low specific gravity of polymeric materials, leading to resonance peaks and energy efficiency issues.
Innovation Solution
A speaker system utilizing a polymeric composite piezoelectric body with a viscoelastic matrix and thin film electrodes, along with a driving circuit that attenuates signal intensity at a rate of 5 dB to 7 dB per octave, to achieve uniform frequency characteristics and improved acoustic performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Weight of moving object
If piezoelectric ceramic is used as the diaphragm material, then the specific gravity is high, but the lowest resonance frequency cannot be lowered sufficiently due to the material being very hard
Solution Approach 1:
The patent uses a composite structure consisting of piezoelectric ceramic particles dispersed in a polymer matrix. This composite material combines the high specific gravity of piezoelectric ceramic with the softness and low resonance frequency characteristics of the polymer matrix, resolving the contradiction between weight and resonance frequency control.
2Strength
If polymeric piezoelectric material is used, then the material is relatively soft, but the specific gravity is low making it difficult to lower the lowest resonance frequency
Solution Approach 1:
The patent creates a composite material where piezoelectric ceramic particles (providing high specific gravity) are dispersed in a polymer matrix (providing softness). This composite structure simultaneously achieves both high specific gravity and softness, resolving the contradiction between these two properties.
3Stability of the object's composition
If the polymer material is merely soft to lower the lowest resonance frequency, then the vibration energy of the piezoelectric ceramic particles is absorbed, but energy efficiency deteriorates
Solution Approach 1:
The patent optimizes the dispersal state of piezoelectric ceramic particles within the polymer matrix and controls the polymer material properties (such as glass transition temperature and crystallinity) to achieve the right balance between softness for resonance frequency control and rigidity for energy efficiency. This parameter optimization prevents excessive energy absorption while maintaining low resonance frequency.
4Reliability
If piezoelectric ceramic with high mechanical quality factor is used, then the diaphragm exhibits sound pressure-frequency characteristics with peaks near resonance frequencies, but this is undesirable in audibility
Solution Approach 1:
The patent uses a composite structure where the polymer matrix has a lower mechanical quality factor than the piezoelectric ceramic particles. The overall system's resonance characteristics are dominated by the softer polymer matrix, which broadens the resonance peaks and reduces their prominence in the sound pressure-frequency characteristics, making them less audible and undesirable.
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 solution results in a speaker system with stable acoustic signal output, excellent flexibility, and uniform frequency characteristics, while maintaining a thin and lightweight design, effectively addressing the resonance issues and energy efficiency concerns.
Implementation Method 1
a voltage corresponding to a signal is applied to the piezoelectric ceramic to convert an expansion and contraction motion of the piezoelectric ceramic into a bending motion of the diaphragm, and thereby generating sound (a sound wave)
Implementation Method 2
a polymeric composite piezoelectric body in which piezoelectric body particles are dispersed in a viscoelastic matrix formed of a polymer material that exhibits viscoelasticity at normal temperature
Implementation Method 3
a driving circuit that attenuates signal intensity of an input signal from a signal source at a rate of 5 dB to 7 dB per octave and supplies the attenuated input signal to the electroacoustic converter film
Data Source
AI summary
The present invention provides a speaker system comprising: an electroacoustic converter film composed of a polymeric composite piezoelectric body in which piezoelectric body particles are dispersed in a viscoelastic matrix formed of a polymer material that exhibits viscoelasticity at normal temperature, and thin film electrodes formed on both surfaces of the polymeric composite piezoelectric body; and a driving circuit that attenuates signal intensity of an input signal from a signal source at a rate of 5 dB to 7 dB per octave and supplies the attenuated input signal to the electroacoustic converter film.