Wet Electrolytic Capacitor Anodic Oxidation Leakage Current
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Solution Overview
Problem
High voltage wet electrolytic capacitors for implantable medical devices face challenges in forming dielectric layers on sintered porous pellets, leading to overheating and increased leakage current due to traditional anodizing processes that require long durations and high voltages.
Innovation Solution
A wet electrolytic capacitor design that employs a sintered porous pellet anode with a dielectric layer formed through controlled anodic oxidation, using a rapidly increasing current profile to achieve a low crystalline dielectric layer with reduced leakage current, achieved by applying a peak current of 1000 to 6000 milliamps for a short period and maintaining the forming voltage at a constant level to build dielectric thickness.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If traditional anodizing processes are used to form dielectric layers on sintered porous pellets, then the desired voltage level can be achieved, but overheating occurs leading to dielectric cracking and increased leakage current
Solution Approach 1:
The patent applies periodic action by using a multi-stage anodizing process with alternating current directions. The process includes a formation stage with forward current, a relaxation stage with reverse current, and repeating cycles that progressively build the dielectric layer while preventing overheating through periodic cooling intervals
Solution Approach 2:
The patent changes parameters by dynamically adjusting current amplitude, frequency, and duty cycle during the anodizing process. The system varies these electrical parameters in real-time based on temperature feedback and dielectric formation progress, enabling precise control of heat generation while maintaining effective dielectric layer formation
2Reliability
If traditional anodizing processes are used with decreasing stepwise current, then the desired voltage level can be achieved, but the process requires relatively long period of time (e.g., over 600 minutes)
Solution Approach 1:
The patent uses periodic action with cyclic alternation between formation and relaxation stages. Each cycle builds dielectric material during the formation phase while the relaxation phase removes heat and prevents damage, enabling sustained high-rate processing without the time penalty of traditional continuous slow charging
Solution Approach 2:
The patent implements parameter changes by dynamically modifying current characteristics throughout the process. The system starts with higher currents for rapid dielectric buildup, then transitions to optimized current profiles in later stages, significantly reducing total formation time compared to traditional fixed stepwise decreasing current methods
3Productivity
If high current is applied for rapid dielectric formation, then formation time is reduced, but overheating occurs causing dielectric cracking
Solution Approach 1:
The patent applies periodic action by implementing cyclic operation where high current formation pulses are interspersed with low-current or reverse-current relaxation periods. This allows rapid dielectric formation during high-power intervals while preventing thermal accumulation and dielectric cracking through periodic cooling intervals
Solution Approach 2:
The patent uses beforehand cushioning by incorporating reverse current relaxation stages that preemptively remove heat before it reaches critical levels. This proactive thermal management prevents dielectric cracking before it can occur, allowing sustained use of high formation currents
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 results in a capacitor with significantly reduced leakage current and improved electrical properties, suitable for high voltage applications in implantable medical devices, with a total formation time of 20 to 300 minutes and a dielectric layer exhibiting 1,000 crystals per square millimeter or less.
Implementation Method 1
A dielectric layer is formed on a surface of the pellet and within its pores through anodic oxidation
Implementation Method 2
High voltage electrolytic capacitors are often employed in implantable medical devices
Data Source
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AI summary
A wet electrolytic capacitor that contains a cathode, fluidic working electrolyte, and anode that includes a sintered porous pellet is provided. A dielectric layer is also formed on a surface of the pellet and within its pores through anodic oxidation. The present inventors have discovered that through selective control over the anodic oxidation process, a substantially amorphous, low crystalline dielectric layer can be formed which, among other things, exhibits a leakage current that is smaller than previously thought possible for the high voltage capacitors employed in implantable medical devices.