Ultrasonic Transducer Structured Coupling Layer Bandwidth
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Solution Overview
Problem
Current air-ultrasonic transducers have a narrow relative bandwidth due to poor acoustic coupling and significant secondary vibrations caused by transverse vibrations, limiting their effectiveness in non-destructive, non-contact material testing, particularly in detecting defects in composite bonds.
Innovation Solution
An ultrasonic transducer with a coupling layer featuring continuous recesses that run through its surface, designed to suppress transverse vibrations and enhance acoustic coupling, allowing for a broader frequency range and reduced secondary oscillations, thereby increasing the relative bandwidth of the ultrasonic signal.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a λ/4 coupling layer is used to improve acoustic impedance matching to air, then acoustic coupling is improved, but transverse vibrations cause unwanted secondary vibrations that lengthen the ultrasound pulse and reduce relative bandwidth
Solution Approach 1:
The coupling layer is segmented into multiple discrete elements arranged in an array, with spaces between them. This segmentation prevents the rigid connection that transmits transverse vibrations while maintaining the acoustic impedance matching function through the collective effect of multiple elements.
Solution Approach 2:
Each element in the coupling layer array has specific local properties (size, shape, positioning) optimized for acoustic coupling, while the overall distributed arrangement provides different functionality (vibration isolation) compared to a continuous layer. The local quality of each element combined with their spatial distribution resolves the contradiction.
2Reliability
If a continuous rigid coupling layer is used to bond the piezoelectric element, then acoustic coupling is enhanced, but transverse vibrations are transmitted causing secondary vibrations and reduced bandwidth
Solution Approach 1:
The coupling layer is divided into discrete elements with spaces between them, breaking the continuous rigid structure. This segmentation prevents the transmission of transverse vibrations while maintaining acoustic coupling through the distributed elements, thereby eliminating secondary vibrations without sacrificing acoustic coupling.
Solution Approach 2:
The harmful rigid connection that transmits transverse vibrations is extracted/removed from the coupling layer design. By taking out the continuous rigid structure and replacing it with discrete elements, the harmful vibration transmission is eliminated while the useful acoustic coupling function is preserved through the remaining elements.
3Ease of operation
If radial resonance mode is used for airborne ultrasound testing, then non-contact testing is achieved, but the signal is narrowband due to poor damping of radial vibrations
Solution Approach 1:
The coupling layer is segmented into discrete elements that are optimally damped, which helps control the vibration modes. This segmentation allows the system to maintain non-contact operation while improving the damping characteristics and expanding the bandwidth of the ultrasonic signal.
Solution Approach 2:
The design parameters of the coupling layer elements (size, spacing, material properties) are optimized to change the vibration damping characteristics. By adjusting these parameters, the system achieves better bandwidth while maintaining the non-contact testing capability through controlled vibration modes.
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 significantly reduces secondary vibrations, shortening the ultrasonic pulse duration and increasing the relative bandwidth from 10% to 40%, enabling more effective detection of defects in composite materials without the need for contact or immersion techniques.
Implementation Method 1
an ultrasonic transducer (10) comprising a piezoelectric element (11) and a coupling layer (13)
Implementation Method 2
the coupling layer (13) has a structure formed by recesses (14). The recesses (14) are designed such that the front face of the coupling layer (13) runs parallel to the surface of the piezoelectric element (11)
Implementation Method 3
One challenge in airborne ultrasound testing is the use of air as the coupling medium, as ultrasound radiation in air is characterized by poor acoustic coupling. Acoustic matching describes the different impedance between the fixed transducer medium and the propagation medium, air.
Data Source
Figure 1a~1f
Figure 2a~2d
Figure 3
AI summary
The invention relates to an ultrasonic transducer comprising a piezoelectric element and a coupling layer. The coupling layer is applied to the sound-emitting side of the piezoelectric element and has a structure formed by recesses. The invention further relates to a method for reducing unwanted vibrations of the ultrasonic signal from the ultrasonic transducer according to the invention, as well as the use of the method according to the invention in non-destructive, in particular non-contact, material testing.