Piezoelectric Buzzer Harmonic Resonance for Low-Frequency Sound Pressure
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Solution Overview
Problem
Existing acoustic devices using piezoelectric buzzers struggle to maintain high sound pressure levels when outputting warning sounds at frequencies lower than the frequency at which the sound pressure is maximum, making it difficult to increase sound pressure levels without increasing buzzer size or power consumption.
Innovation Solution
An acoustic device with a resonance circuit and switching circuit that generates a composite drive voltage by oscillating at an oscillation frequency within a specific range relative to the fundamental frequency, emphasizing harmonics to enhance sound pressure levels, particularly by adjusting the oscillation frequency to satisfy the condition fn-1/2f0 ≤ f1 ≤ fn+1/2f0, where fn is the harmonic frequency and f0 is the fundamental frequency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If a piezoelectric buzzer operates at a frequency lower than its peak sound pressure frequency, then the warning sound frequency can be reduced, but the sound pressure level decreases
Solution Approach 1:
The patent applies periodic action by using pulse width modulation (PWM) to periodically switch the piezoelectric buzzer on and off at a frequency lower than the peak frequency. This periodic switching generates harmonics that include the peak frequency component, allowing the buzzer to operate at a lower fundamental frequency while still producing strong sound pressure at the peak frequency through harmonic content. The periodic nature of the PWM signal creates multiple frequency components (fundamental frequency and its harmonics), resolving the contradiction between low operating frequency and high sound pressure level.
2Stress or pressure
If the piezoelectric buzzer size is increased to improve sound pressure level at low frequencies, then sound pressure increases, but device size increases
Solution Approach 1:
The patent changes the electrical parameters of the drive signal rather than the physical parameters of the buzzer. By modifying the drive frequency and duty cycle parameters through PWM control, the system achieves high sound pressure levels without changing the buzzer's physical size. This parameter change approach allows the same compact buzzer to operate effectively at low frequencies by exploiting harmonic generation, thus resolving the contradiction between sound pressure level and device size.
3Stress or pressure
If power consumption is increased to raise sound pressure level at low frequencies, then sound pressure improves, but energy consumption increases
Solution Approach 1:
The patent uses periodic action through PWM to achieve high sound pressure levels with reduced power consumption. By switching the buzzer on and off periodically rather than applying continuous voltage, the system generates harmonics that produce strong sound pressure at the peak frequency while consuming less average power. The periodic switching allows the buzzer to operate at a lower duty cycle while still achieving high sound pressure through harmonic content, resolving the contradiction between sound pressure level and power consumption.
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 effectively increases the sound pressure level of warning sounds, even at frequencies lower than the peak sound pressure frequency, without increasing the size or power consumption of the piezoelectric buzzer, thereby enhancing the acoustic device's performance.
Implementation Method 1
a piezoelectric element and a thin metal plate which are bonded together to form a piezoelectric buzzer
Implementation Method 2
a resonance circuit configured to receive a first voltage from the switching circuit, generate a second voltage which oscillates at an oscillation frequency f1 during an OFF time period, and output a composite voltage of the first voltage and the second voltage to the piezoelectric buzzer
Data Source
Figure 1~2
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AI summary
An acoustic device for warning sound and an acoustic system are provided which are configured to increase, also when a warning sound at a relatively low frequency is output, a sound pressure level of the warning sound. An acoustic device for warning sound includes a switching circuit and a resonance circuit. A relationship among a frequency fn of an Nth harmonic, a fundamental frequency f0 of a drive voltage V2, and an oscillation frequency f1 is fn-1/2f0 ≤ f1 ≤ fn+1/2f0, where the Nth harmonic is one harmonic of a plurality of harmonics of the drive voltage V2, a sound pressure level of an output sound from the piezoelectric buzzer at the Nth harmonic being higher than a sound pressure level of the output sound from the piezoelectric buzzer at the fundamental frequency f0.