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Micro-electromechanicalsystems (MEMS)
Introduction
solid-state switches like pin diodes have a large insertion loss (typically 1 dB) in the on state and poor electrical isolation in the off state.
The term MEMS refers to collection of micro sensors and actuators which can sense its environment and have the ability to react to changes in the environment with the use of microcircuit control.
MEMS switches are devices that use mechanical movement to achieve a short circuit or an open circuit in the RF transmission line.
The forces required for the mechanical movement can be obtained using electrostatic, magnetostatic,piezoelectric, or thermal designs.
The beauty of MEMS switches is their near-ideal behavior and
the relative ease of their circuit designs.
Developments in mems have facilitated exciting advancements
in the field of sensors and control components.
MEMS are quietly changing the way you live, in ways that you might never imagine. Most new cars have over a dozen MEMS devices, making your car safer, more energy efficient, and more environmentally friendly. MEMS are finding their way into a variety of medical devices, and everyday consumer products.
2.Surface micromachining :-
Repetitive sequence of depositing thin films on a wafer, photo patterning the films, and then etching the patterns into the films. In order to create moving, functioning machines.
Requires more fabraction steps than bulk micromachining and is more expensive.
3.LIGA:-
Creates small,high aspect ratio devices using x-ray lithography.
Inexpensive fabraction technolgy.
4.Integrated MEMS Technologies:-
It is possible to fabricate micromachines and microelectronics on the same piece f silicon since MEMS devices are created with same tools used to create integrated circuits.
MEMS DEVICES
MEMS ACCELEROMETERS:-
Accelerometer is an electromechanical device that measures acceleration forces.These forces may be static or dynamic.They are being incorporated into more and more personal devices such as media players and in smart phones for user interface control.
Some companies like IBM &APPLE have started using accelerometers in their laptops to protect hard drives from damage.
Shoe-Based Sensors: How They Work
They work on chip-scale inertial sensors that meet the power and size requirements for portable applications. However, they suffer from a rapid growth in position error due to inherent bias drift and noise in the sensors.
To limit this error growth, a RF velocity sensor that detects when a shoe touches the ground.
As seen in the pictures on the following page, three kinds of shoe sensors are implanted in a shoe.
The RF terrain-relative velocity (TRV ) sensor mounted on the heel and toe is used for ZUPting the position computed from the accelerometers in the MEMS-based inertial measurement unit (IMU ).
The magnetometers in the IMU are used for ZUPting the heading computed from the gyroscope on the IMU.
Shoe relative sensors (SRS ) on one shoe form a constellation which can then be used to find the location of a moving shoe with respect to a stationary shoe.
Advantages
Low cost (can even be made “disposable”)
They are useful in the field of defense of a nation
Will work for many machine health applications
Onboard signal conditioning. No charge amplifiers required.
Disadvantages
Performance still below that of more expensive sensors
May not be available in industrial hardened packages
MEMS Features
Low interference with environment
Accurate, Compact, Shock resistant
Inexpensive - based on IC batch fabrication
Use in previously unfeasible domains
Redundancy
Large sampling size, greater data certainty
CONCLUSION
MEMS-based sensors are a crucial component in automotive electronics, medical equipment, smart portable electronics such as cell phones and hard disk drives, computer peripherals, and wireless devices.
These sensors began in the automotive industry especially for crash detection in airbag systems. Throughout the 1990s to today, the airbag sensor market has proved to be a huge success using MEMS technology.
MEMS-based sensors are now becoming pervasive in everything from inkjet cartridges to cell phones. Every major market has now embraced the technology.