Ultrasonic Sensor Thermoplastic Resin Acoustic Matching
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Solution Overview
Problem
Ultrasonic sensors face low energy propagation efficiency due to the large difference in acoustic impedance between piezoelectric elements and gases, and existing solutions struggle to maintain bonding integrity and durability, especially with thermosetting resin-based acoustic matching layers.
Innovation Solution
The use of a thermoplastic resin for the first acoustic matching layer, injected from the thickness direction to reduce thermal expansion coefficients and enhance bonding, combined with a foamed resin for the second matching layer to achieve efficient impedance matching and durability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If a thermosetting resin-based acoustic matching layer is used to achieve impedance matching, then ultrasonic wave propagation efficiency is improved, but bonding integrity deteriorates due to large thermal expansion differences with the sensor housing
Solution Approach 1:
The patent changes the material parameter from thermosetting resin to thermoplastic resin, which has a coefficient of thermal expansion closer to the sensor housing. This parameter change maintains the acoustic impedance matching capability while reducing thermal expansion mismatch, thereby preventing peeling at the bonding interface and improving bonding integrity.
Solution Approach 2:
The patent uses a composite structure with two acoustic matching layers: a first acoustic matching layer made of thermoplastic resin bonded to the piezoelectric element, and a second acoustic matching layer made of foamed resin bonded to the first layer. This composite structure allows each layer to fulfill different functions - the thermoplastic layer ensures bonding integrity while the foamed resin layer provides impedance matching to the gas medium.
2Loss of energy
If the acoustic impedance of the matching layer is reduced to match the gas impedance, then ultrasonic wave propagation efficiency is improved, but the material becomes easier to deform and less suitable for the matching layer
Solution Approach 1:
The patent divides the acoustic matching function into two separate layers: the first acoustic matching layer made of thermoplastic resin that is bonded to the piezoelectric element and provides structural support, and the second acoustic matching layer made of foamed resin that is bonded to the first layer and provides impedance matching to the gas. This segmentation allows each layer to optimize for its specific function without compromise.
Solution Approach 2:
The patent employs a composite structure where the first acoustic matching layer uses thermoplastic resin with appropriate mechanical strength and the second layer uses foamed resin with low acoustic impedance. This composite material approach enables the system to simultaneously achieve both structural integrity and optimal acoustic impedance matching to the gas medium.
3Loss of energy
If two acoustic matching layers are used to achieve impedance matching, then ultrasonic wave propagation efficiency is improved, but device complexity increases
Solution Approach 1:
The patent segments the acoustic matching function into two distinct layers with different material properties and functions. The first layer (thermoplastic resin) is directly bonded to the piezoelectric element and provides mechanical support and thermal compatibility, while the second layer (foamed resin) is bonded to the first layer and provides acoustic impedance matching to the gas. This functional segmentation optimizes overall performance despite increased structural complexity.
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 improves ultrasonic sensor characteristics and durability by reducing stress from thermal changes and maintaining bonding integrity, achieving high efficiency in ultrasonic wave propagation and reliability across varying temperatures.
Implementation Method 1
the coefficient of thermal expansion in a flow direction of the resin is small, peeling due to a temperature change can be suppressed
Implementation Method 2
the ultrasonic waves most efficiently propagate from the piezoelectric element to the gas through the acoustic matching layer, when Z22=Z1×Z3 is satisfied
Implementation Method 3
piezoelectric elements used for ultrasonic sensors are generally made of ceramics
Data Source
AI summary
Ultrasonic sensor (1) includes piezoelectric element (7), first acoustic matching layer (2), and second acoustic matching layer (5) which are laminated and bonded together, piezoelectric element (7) having a rectangular bonding surface. First acoustic matching layer (2), which is adjacent to piezoelectric element (7), is bonded to piezoelectric element (7) using thermoplastic resin injected from a thickness direction of first acoustic matching layer (2) in a manner that a flow direction of the thermoplastic resin matches a longitudinal direction of piezoelectric element (7). With this configuration, ultrasonic sensor (1) that exhibits excellent temperature characteristics against such as thermal shock is provided.