Technology analysis weighs strengths and weaknesses of magnetic switches

CHICKASHA, Okla., 10 April 2006. Experts at Hermetic Switch Inc. in Chickasha, Okla., have completed a technology analysis that weighs the strengths and weaknesses of four magnetic switching technologies -- electromechanical reed and MEMS, and solid-state Hall and giant magnetoresistive (GMR) switches.

The analysis shows that although one technology may provide an advantage over others in a specific area, in general all of the technologies offer a variety of capabilities; design engineers should evaluate each technology based on application-specific design requirements.

Electromechanical reed switches have several strengths, according to the study. First, they do not consume power in the off mode, making them suitable for applications where conserving battery power is critical as in pacemakers, defibrillators, and hearing aids.

These switches have hermetically sealed contacts, which increases their appeal for dirty, hostile-environment applications. The reed switch family is resists the effects of electrostatic discharge (ESD), and provide switching and sensing functions in one package, which saves on overall cost and labor.

Reed switches use an established technology that dates back to 1936, and have a long and proven history of reliability. Limitations to the reed switch included relatively high cost per unit and relatively large size.

The strengths of microelectromechanical (MEMS) switches, meanwhile, include small footprint; magnetic sensitivity, high shock resistance, and relatively low cost, making them suitable for high-volume, low-cost commercial applications.

Limitations of MEMS switches, however, include ESD sensitivity, vulnerability of electrical contacts to contamination and malfunctions, and high contact resistance.

Solid-state hall effect switches, on the other hand, are relatively inexpensive and are suited for high-volume, low-cost commercial applications. Hall effect switches have long life expectancy, no contact bounce, and are resistant to shock and vibration.

Limitations of hall effect solid-state switches include their requirement for constant power, which can compromise the reliability of battery powered devices. Hall effect switches also cannot switch loads directly therefore loads must be switched using additional components, adding cost and labor. Hall effect switches are also very ESD sensitive, and should not be used in applications exposed to ESD since they could be easily damaged.

Sold-state GMR, in turn, are true solid-state devices and so have no moving parts. GMR switches have a small footprint, are very magnetically sensitive, and operates in a wide temperature range, from -40 to 150 degrees Celsius.

GMR switch limitations include the requirement for constant power, which can compromise battery life. GMR switches are susceptible to ESD damage, and are based on a relatively new technology and thereby entail some degree of risk.

For more information on the analysis, contact Hermetic Switch online at www.hermeticswitch.com.

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