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Sorry I missed yesterday. I had a paper to finish revisions on and email in, and my section of another paper to complete and email to my group leader. I completed both, however, and I finished a final exam this morning as well.
To make up for the delay, I shallbore you out of your skull with blathering tell you about microelectromechanical sensor devices.
One of the largest fields of MEMS is sensors. A major factor in this is the automotive industry, which exploits the small size and low cost of MEMS devices for several purposes, most famously airbag systems. Microsensors can be broken down into four major categories, although several more are common: mechanical sensors, chemical and biological sensors, radiation sensors, and thermal sensors.
The most common type of piezoelectric device employed is the piezoresistor – a substance whose resistance changes with strain in a useful manner. These are especially convenient for micromanufacture, as they can be created by simply 'doping' (introducing controlled amounts of impurity into) silicon, which is already the chief material for MEMS devices (Banks). These piezoresistors are used for pressure sensors and for accelerometers, as well as for simply detecting strain in materials.
Capacitive sensors work through detecting changes in capacitance due to distortion. One common purpose these are set to is pressure detection. One way to achieve this is with two thin sheets of silicon separated by a piece of glass, with a vacuum between them; any change in pressure will cause the silicon plates to move closer or further apart, and change the capacitance. They also can be used in accelerometers. However, capacitive sensors have the disadvantage relative to piezoresistive sensors that small changes in capacitance are harder to detect.
As mentioned before, this category of sensors appears in a broad set of applications. For example, since mass-produced MEMS accelerometers are smaller and cheaper than classical accelerometers, they have become common for detecting impacts in order to deploy airbags. Furthermore, they are slowly beginning to enter use as components of smart suspension systems, allowing for smoother rides and/or better traction through variable stiffness springs and dampers (Bryzek et al.).
Now that my diaristic obligations have been fulfilled, I shall nap. Or try to nap. Or just lie in bed for half an hour. Yeah.
To make up for the delay, I shall
One of the largest fields of MEMS is sensors. A major factor in this is the automotive industry, which exploits the small size and low cost of MEMS devices for several purposes, most famously airbag systems. Microsensors can be broken down into four major categories, although several more are common: mechanical sensors, chemical and biological sensors, radiation sensors, and thermal sensors.
Mechanical Sensors:
This is probably the broadest category of sensors, and probably the most prevalent. Mechanical sensors are all those devices which detect mechanical properties: stresses, pressures, deformations, and accelerations. These categories are further divided by the multiple methods for detecting each of these properties. Mechanical sensors can be based on any of a number of physical phenomena, but the most widespread of these are piezoelectric effects and capacitance.The most common type of piezoelectric device employed is the piezoresistor – a substance whose resistance changes with strain in a useful manner. These are especially convenient for micromanufacture, as they can be created by simply 'doping' (introducing controlled amounts of impurity into) silicon, which is already the chief material for MEMS devices (Banks). These piezoresistors are used for pressure sensors and for accelerometers, as well as for simply detecting strain in materials.
Capacitive sensors work through detecting changes in capacitance due to distortion. One common purpose these are set to is pressure detection. One way to achieve this is with two thin sheets of silicon separated by a piece of glass, with a vacuum between them; any change in pressure will cause the silicon plates to move closer or further apart, and change the capacitance. They also can be used in accelerometers. However, capacitive sensors have the disadvantage relative to piezoresistive sensors that small changes in capacitance are harder to detect.
As mentioned before, this category of sensors appears in a broad set of applications. For example, since mass-produced MEMS accelerometers are smaller and cheaper than classical accelerometers, they have become common for detecting impacts in order to deploy airbags. Furthermore, they are slowly beginning to enter use as components of smart suspension systems, allowing for smoother rides and/or better traction through variable stiffness springs and dampers (Bryzek et al.).
Chemical and Biological Sensors:
Chemical and biological sensors detect those things: chemical and biological substances. In recent years, this category has been growing quickly in reaction to fears about terrorism, but it has been of interest in medicine for some time before that. One common form of chemical/biological sensor is based off of the MOSFET transistor design; by replacing the gate with a biological component, specific kinds of ions can be detected (Banks).Radiation Sensors:
Radiation sensors is a broader category than it may sound: 'radiation' in this context often refers to light, a definition which accounts for a large fraction of the radiation sensors market. The main forms of light sensors, however, are the standard photodiodes, phototransistors, and other solid-state devices, but there are also many active components, such as optical switches, to consider. One of the most high-tech fields to which this applies is optical communications, naturally.Thermal Sensors:
Thermal sensors, devices which monitor absolute values of or differences in temperatures, have been around for some time, but the growth of the MEMS industry has brought some valuable improvements to such devices. For example, by fabricating 'bridges' separating the thermocouple or other thermal detector from the main body of the circuit, higher efficiencies can be obtained due to the greater degree of insulation (Banks).Sources on MEMS sensors:
- Banks, Danny. Introduction to Microengineering. <http://www.dbanks.demon.co.uk/ueng/>
- J Bryzek, K Petersen, W McCulley. Micromachines on the March, IEEE Spectrum, 31 (5), May 1994, pp 20-31. <http://ieeexplore.ieee.org/xpl/tocresult.jsp?isYear=1994&isnumber=6909&Submit32=Go+To+Issue>
Now that my diaristic obligations have been fulfilled, I shall nap. Or try to nap. Or just lie in bed for half an hour. Yeah.
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