18-02-2010, 01:19 PM
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GMR sensors
Introduction
GMR - Giant Magnetoresistance"
Discovered in the late 1980s
Very large resistance changes in materials with magnetic field
The GMR effect states significant decrease in electrical resistance in the presence of a magnetic field.
Size of magnetic field is 10-100 Oe
Features
High sensitivity for low magnetic fields
Measures field parallel to its sensitive axis
Good signal-to-noise ratio
High spatial resolution
Frequency independent sensitivity
Low cost, Less power, Small size
GMR Sensors- Technology
Stands for Giant magnetoresistance (GMR) sensors and can achieve a change of resistance of 10%“20%
In contrast with conventional magnetoresistance (MR), which exhibit a change of resistance of <3%
GMR films have two or more magnetic layers separated by a nonmagnetic layer.
Significant decrease in electrical resistance in the presence of a magnetic field.
No magnetic field: The direction of magnetization of adjacent ferromagnetic layers is anti parallel.
High-resistance, magnetic scattering.
With magnetic field: The magnetization of the adjacent ferromagnetic layers is parallel.
Lower resistance
The new GMR Technology is SDT
An insulating layer separates two magnetic layers
A resistance change of 10-40% with magnetic field
GMR Materials “Types
Unpinned sandwiches
Antiferromagnetic multilayers
Spin valves
GMR circuit technique
Due to their outstanding sensitivity, Wheatstone Bridge Circuits are very advantageous for the measurement of resistance, inductance, and capacitance.
GMR resistors can be configured as a Wheatstone bridge sensor. Two of which are active. Resistor is 2 µm wide, which makes the resistors sensitive only to the field along their long dimension.
GMR Sensors-Applications
Detection of motor vehicles
Eddy current detection
Detection of magnetic ink
Sensing of body position
Detection of motor vehicles
The Earth field acts as a biasing magnet resulting in a magnetic signature from various parts of the automobile as it passes a sensor.
The x, y, and z components of the signature can be detected by magnetic sensors buried in the road
Eddy current detection
A coil applies an ac field to the material under test.
Eddy currents generated by the applied ac field in a continuous conducting sheet below the sensor will create a mirror image of the field from the coil and will also not affect the magnetic sensor.
Detection of magnetic ink
The use of iron oxide as a pigment in black ink is utilized here
This is used for reading MICR
The magnetic sensor averages the signal over the entire height of the characters as they pass the magnetic sensor at a high rate of speed.
Sensing of body position
Plays a role in various medical evaluation
Small magnet attached to the body part to be monitored
The position of magnet is monitored
Conclusion
Available for over 25 years
Magnetic field produced either by bias magnet or electric current
Magnetic field should be above earthâ„¢s field
SDT structures are recent addition to the GMR materials
GMR sensors
Introduction
GMR - Giant Magnetoresistance"
Discovered in the late 1980s
Very large resistance changes in materials with magnetic field
The GMR effect states significant decrease in electrical resistance in the presence of a magnetic field.
Size of magnetic field is 10-100 Oe
Features
High sensitivity for low magnetic fields
Measures field parallel to its sensitive axis
Good signal-to-noise ratio
High spatial resolution
Frequency independent sensitivity
Low cost, Less power, Small size
GMR Sensors- Technology
Stands for Giant magnetoresistance (GMR) sensors and can achieve a change of resistance of 10%“20%
In contrast with conventional magnetoresistance (MR), which exhibit a change of resistance of <3%
GMR films have two or more magnetic layers separated by a nonmagnetic layer.
Significant decrease in electrical resistance in the presence of a magnetic field.
No magnetic field: The direction of magnetization of adjacent ferromagnetic layers is anti parallel.
High-resistance, magnetic scattering.
With magnetic field: The magnetization of the adjacent ferromagnetic layers is parallel.
Lower resistance
The new GMR Technology is SDT
An insulating layer separates two magnetic layers
A resistance change of 10-40% with magnetic field
GMR Materials “Types
Unpinned sandwiches
Antiferromagnetic multilayers
Spin valves
GMR circuit technique
Due to their outstanding sensitivity, Wheatstone Bridge Circuits are very advantageous for the measurement of resistance, inductance, and capacitance.
GMR resistors can be configured as a Wheatstone bridge sensor. Two of which are active. Resistor is 2 µm wide, which makes the resistors sensitive only to the field along their long dimension.
GMR Sensors-Applications
Detection of motor vehicles
Eddy current detection
Detection of magnetic ink
Sensing of body position
Detection of motor vehicles
The Earth field acts as a biasing magnet resulting in a magnetic signature from various parts of the automobile as it passes a sensor.
The x, y, and z components of the signature can be detected by magnetic sensors buried in the road
Eddy current detection
A coil applies an ac field to the material under test.
Eddy currents generated by the applied ac field in a continuous conducting sheet below the sensor will create a mirror image of the field from the coil and will also not affect the magnetic sensor.
Detection of magnetic ink
The use of iron oxide as a pigment in black ink is utilized here
This is used for reading MICR
The magnetic sensor averages the signal over the entire height of the characters as they pass the magnetic sensor at a high rate of speed.
Sensing of body position
Plays a role in various medical evaluation
Small magnet attached to the body part to be monitored
The position of magnet is monitored
Conclusion
Available for over 25 years
Magnetic field produced either by bias magnet or electric current
Magnetic field should be above earthâ„¢s field
SDT structures are recent addition to the GMR materials