Ultrasonic Microphone Self-Test via Structure-Borne Noise
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Solution Overview
Problem
Existing ultrasonic microphones for stationary leak monitoring of compressed gas systems are limited in their ability to comprehensively check for various error types during self-tests, such as defects in the bond, membrane destruction, stress due to dirt, and electronics drift, due to susceptibility to ambient noise and interference between multiple sensors.
Innovation Solution
An ultrasonic microphone design with a self-test device integrated within the housing, utilizing a piezo composite sound transducer element and a separate test signal generator to produce structure-borne noise, which minimizes ambient noise interference and allows for a comprehensive check of error types by propagating vibrations through the microphone components and their connections.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a loudspeaker is used to generate test signals during self-test, then the test signal can be generated externally, but ambient noise interferes with the test results and multiple sensors influence each other
Solution Approach 1:
The test signal generation function is extracted from the external environment (loudspeaker) and moved inside the microphone housing to an internal piezoelectric element. This isolation removes the test signal generation from ambient noise sources, eliminating the interference problem while maintaining the ability to generate comprehensive test signals for self-diagnosis
Solution Approach 2:
Structure-borne noise through the housing wall serves as an intermediary transmission path for the test signal. The piezoelectric element generates vibrations that propagate through the housing structure to the membrane, providing a controlled transmission path that is immune to ambient acoustic noise while still enabling comprehensive component testing
2Device complexity
If the generator is switched off to observe natural vibrations, then the structure is simple, but ambient sound superimposes on membrane vibration and falsifies test results
Solution Approach 1:
Instead of observing natural decay vibrations once the generator is off, the system uses periodic excitation by switching between the piezoelectric test signal generator and the microphone element. This active periodic testing allows controlled measurement of membrane response at specific frequencies without being affected by ambient noise or requiring the generator to be completely off
Solution Approach 2:
The microphone housing and membrane structure serve dual purposes: they are both the object being tested and the transmission path for the test signal. The housing acts as both the protective enclosure and the acoustic waveguide, eliminating the need for separate test equipment and reducing overall system complexity while maintaining measurement accuracy
3Measurement precision
If high sound intensity is selected for self-test, then the test signal can be detected in ambient noise, but multiple sensors in close proximity influence each other
Solution Approach 1:
The test signal transmission is moved from the acoustic dimension (airborne sound) to the structural dimension (solid-borne vibrations through the housing). This dimensional change allows high-intensity testing without acoustic interference between nearby sensors, as structure-borne vibrations are contained within each housing and do not propagate through the air to affect other sensors
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 design enables robust and comprehensive self-testing, reducing the influence of ambient noise and allowing detection of multiple error types, enhancing the reliability and accuracy of leak monitoring while maintaining sensitivity and compactness.
Implementation Method 1
The sound transducer elements of the ultrasonic microphone and the self-test device are preferably components of piezo composites
Implementation Method 2
utilizing a piezo composite sound transducer element and a separate test signal generator to produce structure-borne noise, which minimizes ambient noise interference and allows for a comprehensive check of error types by propagating vibrations through the microphone components and their connections
Data Source
Figure 1~3
Figure 4~5
AI summary
The invention relates to an ultrasonic microphone (10), wherein the ultrasonic microphone (10) comprises a diaphragm (11), a first transducer element (17), and a device for performing a self-test, characterized in that the first transducer element (17) and the device for performing the self-test are together contained in the housing (13) of the ultrasonic microphone (10). The invention further relates to a method for performing a self-test of an ultrasonic microphone (10) according to one of the preceding claims, wherein the method comprises the steps of: • Electrical excitation of vibrations of the microphone diaphragm (11); • Plausibility check of the recorded signals, characterized in that a second transducer (16) serves to generate the vibrations.With the ultrasound microphone according to the invention, it is possible within the scope of the self-test to simultaneously detect various faults that can lead to a change in the vibration characteristics of the sensor (receiver transducer), such as defects in the adhesive bond between the transducer and the membrane, destruction of the membrane, stress on the membrane due to contamination, defect of the piezo composite and defects or drift of the electronics.