Parallel MEMS Switches for Arc Suppression
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Solution Overview
Problem
Microelectromechanical systems (MEMS) electrical switches face failure due to arcing and damage from high voltage and current, as soft, compliant contact materials used for low resistance switches are vulnerable to heat generated by arcing, leading to irreversible damage.
Innovation Solution
A multiple switch MEMS device is designed with a higher resistance, durable sacrificial switch that closes first, followed by a lower resistance, less durable switch, to protect the latter from initial high voltage and current, and opens before the former to manage voltage transients, using independent or sequentially actuated cantilevered beams or contact points.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If soft, compliant contact material is used to reduce contact resistance, then the contact resistance is reduced, but the switch becomes vulnerable to arcing damage and heat damage
Solution Approach 1:
The patent divides the single switch function into two separate switches: a durable high-resistance switch and a less durable low-resistance switch. This segmentation allows each switch to be optimized for its specific function - one for durability and arc suppression, the other for low contact resistance - thereby resolving the contradiction between low resistance and arc vulnerability
Solution Approach 2:
The durable high-resistance switch acts as an intermediary protective element that absorbs the harmful effects of arcing and high voltage transients during switch closure. This intermediary protects the low-resistance switch from damage while allowing it to maintain its low resistance property for optimal current conduction
2Reliability
If a single low resistance switch is used, then the contact resistance is minimized, but the switch lifetime is reduced due to arcing and high voltage damage
Solution Approach 1:
The switch system is segmented into two functional components with different durability characteristics. The durable switch handles the stressful closure event, while the less durable switch handles normal operation, thereby extending the overall system lifetime while maintaining low resistance
Solution Approach 2:
The patent employs a sacrificial durable switch that can withstand arcing and high voltage stress, effectively serving as a protective element that may degrade faster than the low-resistance switch but whose failure mode protects the more critical low-resistance component, thereby extending operational lifetime
3Reliability
If the lower resistance switch closes first, then the on-state resistance is minimized, but the switch suffers from high voltage and current damage
Solution Approach 1:
The durable high-resistance switch closes first as a preliminary protective action, establishing a current path that limits inrush current and absorbs voltage transients. This preliminary closure protects the low-resistance switch from damage before it closes and assumes the bulk of the current load
4Device complexity
If a single switch structure is used, then the device complexity is low, but the ability to manage both low resistance and arc suppression is insufficient
Solution Approach 1:
The single switch is segmented into two coordinated switches with distinct functional roles. This segmentation increases complexity slightly but provides the necessary capability to simultaneously achieve low on-state resistance and effective arc suppression, resolving the contradiction between simplicity and performance
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 reduces the risk of arcing damage to the lower resistance switch by handling initial high currents and voltages with the higher resistance switch, extending the switch's lifetime and maintaining low resistance in the 'on' state while managing transients during opening and closing.
Implementation Method 1
the contact between the shunt bar 6 conductors and the contacts 5 needs to be as intimate as possible. In order to make lower resistance contacts, the contact material tends to be relatively soft and compliant, in order to form a junction in which the metals are in intimate contact. Because the material is soft, it is relatively vulnerable to arcing, wherein high voltage, high current discharges occur across the contacts.
Implementation Method 2
The multiple switches are opened with the lower resistance, less durable switch opening before the higher resistance, higher durability switch, in order to protect the lower resistance, less durable switch from transients which may occur as the switch is opened.
Data Source
AI summary
A multiple switch MEMS structure has a higher resistance, higher durability switch arranged in parallel with a lower resistance, less durable switch. By closing the higher resistance, high durability switch before the lower resistance, less durable switch, the lower resistance, less durable switch is protected from voltage transients and arcing which may otherwise damage the lower resistance, less durable switch. By appropriate selection of dimensions and materials, the high resistance, high durability switch may be assured to close first, as well as open first, thereby also protecting the lower resistance, less durable switch from voltage transients upon opening as well as upon closing.