Acoustic Interface Off-Resonance Driving for Alarm Data Rate
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Piezoelectric sounders in alarm devices take a significant time to build up to maximum resonance, leading to a long 'ring-down' time that limits data rate and causes decoding errors, typically allowing less than 25 bits per second due to the difficulty in distinguishing between consecutive data bits.
Innovation Solution
An acoustic interface using a microcontroller to generate control signals with pulse widths significantly shorter than the piezoelectric disc's natural frequency, driving the disc off-resonance to reduce ring-down time and increase data rate, employing Frequency Shift Keying (FSK) for efficient data transmission.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If the piezoelectric disc is driven at resonance to maximize sound output, then the sound intensity is improved, but the ring-down time increases which limits the data rate
Solution Approach 1:
The patent applies periodic pulsed driving instead of continuous resonance driving. The piezoelectric disc is driven with periodic pulses that excite resonance temporarily, then allowed to ring down naturally. This periodic on-off cycling enables discrete data bit transmission while utilizing resonance for maximum sound output during the active phase, resolving the contradiction between sound intensity and data rate.
Solution Approach 2:
The system dynamically adjusts the driving state of the piezoelectric disc between resonance and non-resonance phases. By controlling the timing and duration of resonance excitation pulses, the system optimizes the balance between achieving maximum sound output for reliable detection and allowing sufficient ring-down time for clear bit discrimination, thereby improving both sound intensity utilization and data rate.
2Productivity
If the data rate is increased to improve productivity, then the transmission speed is improved, but decoding errors increase due to difficulty in discriminating consecutive bits
Solution Approach 1:
The system incorporates feedback mechanisms where the acoustic output is monitored and the timing of subsequent pulses is adjusted based on the observed ring-down characteristics. This feedback allows the system to optimize the balance between data rate and bit discrimination clarity, maintaining high productivity while ensuring reliable decoding by adapting to actual acoustic conditions.
Solution Approach 2:
By using periodic pulsing with carefully controlled duty cycles and intervals, the system creates distinct temporal patterns for data bits. The periodic nature ensures sufficient time separation between bits even at high data rates, allowing reliable discrimination while maintaining high transmission speed through optimized pulse timing.
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
Achieves a data rate 5-10 times faster than prior methods while maintaining lower audio output levels, allowing for clear discrimination between data bits and reducing decoding errors.
Implementation Method 1
In a piezoelectric sounder or horn disc oscillation takes a certain time to build up to maximum resonance
Implementation Method 2
For a disc having a natural frequency of 3kHz, the period is 330μs, and so it may take more than 3ms before the output sound reaches a maximum. If driving the disc at resonance the disc will continue to ring even after the circuit has de-energized.
Data Source
Figure 1(a)~1(b)
Figure 2~3
Figure 4~5
AI summary
An acoustic interface (1) is for a device such as an alarm device. It has a vibratory element piezoelectric horn (2) and a drive circuit (8, 5) with a processor (8) for delivering drive electrical signals (7) to the horn to cause it to vibrate and generate a sound signal with encoded binary data. The piezo horn (2) has a natural frequency, and the control signals are frequency encoded with pulses having pulse widths (tp) which are significantly shorter than the vibrating member natural frequency period (1/fN). The encoding processor (8) provides the control signals via a feedback transistor (5) and a voltage oscillator (6), the vibratory element (2) having at least three electrical contacts of which two are for power and a third is for feedback to the feedback transistor (5), in which mechanical oscillation of the vibratory element generates an electrical feedback signal used to amplify this control signal (7).