What is a magnetic sensor
A magnetic sensor is a device which is capable of sensing the magnetic field and extracting information from it and the information is related to the magnetic induction along an axis which is transduced by the sensor into an electric signal so a magnetic sensor is a transducer which will convert a magnetic field into a corresponding electrical signal. Mostly magnetic sensors are small and it is compatible with micro-electronics in terms of materials, technologies and operating conditions. Mostly magnetic sensors are not used to measure the magnetic field, there are other parameters which is measured by this they are wheel speed, presence of magnetic ink, vehicle detection or heading determination. These parameters cannot be measured directly but it can be determined by the changes or disturbances in the magnetic field. Magnetic sensors can detect rotation, angle, or electric current indirectly.
What is a magnetic sensor microsystem
A magnetic sensor is rarely used alone, mostly it is combined with other small size devices into a so-called magnetic sensor microsystem. A magnetic sensor microsystem is a complex device that transforms a magnetic signal into an electric signal. Process this signal and transmits the result to other electronic systems. The essential components for this micro-systems are a magnetic sensor, biasing, signal processing and interface circuits and in certain cases, it will also use some components like magnetic concentrators, permanent magnets, and coil. All of these components are arranged in a suitable manner of small dimension, in the millimeter or the centimeter range. The magnetic signal to be detected by a magnetic sensor microsystem may be associated with an external magnetic field.
What is a low field sensor
Low field sensors are used for medical applications and military surveillance they are bulky and costly when compared to other magnetic field sensors. It must be taken care properly because the earth’s field since daily variation’s in the earth’s field could exceed the measurement range of a low field sensor.
Types of Magnetic sensors
Superconducting quantum interference device is the most sensitive low field sensor and its work is based on the point-contact junction to measure extremely low current squid magnetometer has the capability to sense in the range of several fempto tesla to 9 tesla this can be used for medical field because the neuromagnetic field of the human brain is only a few tenths of a fempto tesla.
The search coil is another low field magnetic sensor and it is based on faradays law of induction which states that a voltage induced in a coil is proportional to the changing magnetic field in the coil, this induced voltage will create a current which is proportional to the rate of change of field. The sensitivity of the search coil is dependent on the permeability of the core and the area and the number of turns of the coil. Search coil will only work if the coil is either be in a varying magnetic field or moving through a magnetic field. This will restrict the search coil from detecting static or slowly changing fields. These sensors are used in traffic control signals.
Fluxgate magnetometers are the most commonly used sensor for compass navigation systems. It is also used for geophysical prospecting and airborne magnetic field mapping. The most used magnetometer is the second harmonic device and this device has two coils a primary and a secondary wrapped around a high permeability ferromagnetic core and in the presence of an external magnetic field magnetic induction of this core changes. A drive signal is applied to the primary winding at a frequency that causes the core to oscillate between saturation points, the secondary winding outputs a signal that is coupled through the core from the primary winding, this signal is affected by the change in the core permeability and appears as an amplitude variation in the sense coil output. Sense signal can be demodulated and low pass filtered by using a phase-sensitive detector to get the magnetic field value
Magnetoinductive magnetometers are sensors with simply a single winding coil on a ferromagnetic core that changes permeability within the earth’s field and the sense coil is the inductance element in a relaxation oscillator. The frequency of the oscillator is proportional to the field being measured. Static DC current is used to bias the coil in a linear region of operation, microprocessor capture/compare port can be used to monitor the oscillator frequency to determine the field values. They have limited temperature range and they are used in compass applications
Hall devices are the widely used magnetic sensor, it is an electronic device with four terminals. If a perpendicular magnetic field is applied to the device then a voltage will appear between the sense contacts. The magnitude of the magnetic field can be measured by the hall-effect sensor