Capacitive Ultrasonic Transducer High-Temperature Membrane
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Solution Overview
Problem
Conventional ultrasonic sensors, including both piezoceramic and capacitive types, are limited by their temperature resistance, failing to operate effectively in extreme temperature environments such as those found in internal combustion engines, where temperatures can range from -40°C to 1000°C, due to material fatigue, oxidation, and electrical breakdowns.
Innovation Solution
The ultrasonic transducer features a membrane made of high-temperature resistant materials like Ni-Cr alloys or austenitic steels, with an amorphous insulating layer and a multi-layer diffusion barrier back electrode, and is designed with a clamping ring to apply tensile stress, allowing for temperature resistance up to several hundred degrees Celsius, even in oxidizing and reducing media.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If conventional capacitive ultrasonic transducers use metal-coated membranes stretched over electrically conductive substrates, then the transducer can function as an ultrasonic sensor, but the membrane cannot withstand temperatures above 300°C due to oxidation and rapid destruction
Solution Approach 1:
The patent employs a composite membrane structure consisting of a metal base layer (Ni-Cr alloy or austenitic steel) providing mechanical strength and high-temperature stability, combined with a ceramic coating layer (alumina or aluminum oxide) providing oxidation resistance. This composite structure enables the membrane to withstand temperatures up to 1000°C while maintaining structural integrity and preventing oxidation-induced failure.
Solution Approach 2:
The patent changes the material parameters of the membrane by selecting specific alloy compositions with chromium content of at least 16% and aluminum content of at least 1%, and applying ceramic coatings with specific thickness ranges (0.5-5 μm). These parameter changes transform the membrane from a conventional metal-coated structure vulnerable to oxidation into a high-temperature resistant composite structure capable of operating in extreme environments.
2Temperature
If conventional insulation layers and electrodes are used in ultrasonic transducers, then the device can be manufactured with standard materials, but electrical breakdowns occur at high temperatures due to insulation layer restructuring and metal diffusion into silicon
Solution Approach 1:
The patent introduces a diffusion barrier layer as an intermediary between the metal rear electrode and the silicon substrate. This intermediate layer (such as tungsten, molybdenum, or titanium) prevents direct contact and diffusion between the metal electrode and silicon crystal, even at high temperatures up to 1000°C, thereby eliminating the harmful effect of metal diffusion that would cause electrode disappearance and electrical breakdown.
Solution Approach 2:
The patent employs composite electrode structures with multiple functional layers: a reflective metal layer (silver, aluminum, or platinum) for electrical conductivity and acoustic reflection, and a diffusion barrier layer (tungsten, molybdenum, or titanium) for thermal and chemical stability. This composite electrode structure resists electrical breakdown by preventing insulation layer degradation and metal-silicon diffusion at high temperatures.
3Temperature
If piezoceramic ultrasonic sensors are used, then the sensors can operate at moderate temperatures, but they suffer from material fatigue and permanent destruction when exposed to temperatures above 350°C due to Curie temperature limitations
Solution Approach 1:
The patent replaces the piezoceramic mechanical system with a capacitive electrostatic system. Instead of relying on piezoelectric crystals that lose their properties above 350°C, the invention uses a capacitive transducer with a charged membrane and electrode structure that generates ultrasonic waves through electrostatic forces. This substitution eliminates the Curie temperature limitation and enables operation at temperatures up to 1000°C while maintaining reliability.
4Temperature
If aluminum membranes are used in conventional capacitive transducers, then the membranes can be manufactured with thin material layers, but oxidation occurs at temperatures above 300°C leading to rapid destruction
Solution Approach 1:
The patent applies a ceramic coating layer (alumina or aluminum oxide) as an intermediary protective layer on the metal membrane surface. This coating acts as a barrier between the metal membrane and the oxidizing environment, preventing oxidation even at temperatures up to 1000°C. The coating layer is applied with controlled thickness (0.5-5 μm) to provide effective protection while maintaining the membrane's acoustic and mechanical properties.
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 the ultrasonic transducer to maintain operability in extreme temperatures, preventing material degradation and electrical breakdowns, thus extending its usage in harsh environments like internal combustion engines, chemical, and food industries.
Implementation Method 1
the membrane being subjected to tensile stress in the surface direction
Implementation Method 2
the insulating layer consists of a material with an amorphous structure
Implementation Method 3
the back electrode has a multi-layer structure, at least one layer forming a diffusion barrier to the base material of the back plate
Implementation Method 4
the material of the membrane is selected from the group of Ni-Cr alloys, austenitic steels, ferritic steels or 'superalloys'
Data Source
Figure 1~2
AI summary
The invention relates to a capacitive ultrasonic transducer, comprising a sensor head having a back plate, the structured front side of which is provided with an insulating layer and the back side of which is provided with an electrode. In order to achieve an improved design by means of which increased temperature resistance up to a few hundred degrees Celsius can be achieved even in strongly oxidative and reductive media, a tensile stress in the planar direction is applied to the membrane provided as a sound generator.