QWERTY Ltd.- manufacturer of membrane keyboards, transparent touch panels, switches, front panels, labels, magnetic switches, EL Lamps and plates. A pulser wheel consisting of such function elements as membrane switches or a magnetic field sensor, for instance a Hall effect device. Microelectromechanical systems (MEMS) technology allows the integration of magnetic field sensors with electronic components, which presents important advantages such as small size, light weight, minimum power consumption, low cost, better sensitivity and high resolution. Consequently, the magnitude of the external magnetic field is measured through the output voltage of the Wheatstone bridge. The Magnetic sensor in your smartphone is not an actual magnet, it is however capable of sensing the magnetic field of earth (using Halls effect) and determining your Direction. Thus Magnetic sensor adds details to enhance your navigation experience, but it is not a necessity. Yes you can if you have a dedicated GPS device which works only on gps signal with gps receiver inside and mostly smartphones does not have the gps receiver inside as they work on assisted GPS. Regarding the article, with special attention to the Magnetic Field Sensor, there is this little thing in Android development called the Software Orientation Sensor which uses combined input from the Accelerometer Sensor and the Magnetic Field Sensor, to basically do what a Gyro can also do if you have one (but not all Android has one) which some apps may need.
As the wheel rotates, the magnetic field sensor detects permanent magnet (2) and generates a logical electric signal. Depending on the position of the magnetic poles, permanent magnets (2) attract or repel permanent magnets (1), mounted on film switches, completing or breaking the electric circuit.
The wheel disk with mounted round permanent magnets (2) which, placed under magnetic contact (1), attract it, closing the electric circuit, can be seen under the layer of conductive paths.
We present a discussion and review of resonant magnetic field sensors based on MEMS technology. Piezoresistive sensing is simple and easy to use in resonant magnetic field sensors based on MEMS technology. Many smartphones these days including the budget devices and also the mid range devices, Don’t offer you magnetic Compass or, to be technically correct, Magnetometers.
With magnetic Compass turned on while using the navigation app, your navigation will be more precise. The company also offers other devices that supplement its range of products, including metal and plastic base plates as well as reinforcing elements for windows and membrane panel displays. In practice, these sensors exploit the Lorentz force in order to detect external magnetic fields through the displacement of resonant structures, which are measured with optical, capacitive, and piezoresistive sensing techniques. It not only reduces the device dimensions on the order of micrometers, but also integrates the mechanical and electronic components on a single chip. In the next paragraphs, three kinds of these sensors with piezoresistive sensing are presented.Beroulle et al.
In addition, this sensor has an efficient continuous offset cancellation technique, a high robustness, low cross sensitivity and competitive cost.Herrera-May et al. In this post we will cover the basics of smartphone navigation and how important is a magnetic compass in your device from navigation point of view.
From these, the optical sensing presents immunity to electromagnetic interference (EMI) and reduces the read-out electronic complexity.
This technology allows the design of portable devices such as gyroscopes, accelerometers, micromirrors, and pressure sensors [1-4]. In this case, the resonant structure will have larger amplitudes that increase the sensitivity and resolution of a resonant sensor.
In the Absence of magnetic senor you can see your position on the Map but, not your orientation. Moreover, piezoresistive sensing requires an easy fabrication process as well as a standard packaging.
A Lorentz force (FL) is obtained from the interaction between a magnetic field (Bx) and an electrical current (I) flowing through the coil, which deflects the microbeams and strains the piezoresistive gauges.
An ac excitation current (I) flows on the aluminum loop under the presence of an external magnetic field (Bx), as shown in Figure 7 (b). Magnetic sensor helps you to take that first step in the correct direction with the help of the direction pointer.
MEMS magnetic field sensors are a potential alternative for numerous applications, including the automotive industry, military, medical, telecommunications, oceanographic, spatial, and environment science.
For example, new cell phones will include several MEMS devices such as gyroscopes, accelerometers and magnetic field sensors for their Global Positioning System (GPS) and MEMS technology is expected to be a key innovation driver in the cell phone industry. Thus, the output voltage of a Wheatstone bridge shifts as a function of the magnetic field applied.
In addition, future markets will need the development of several sensors on a single chip for measuring different parameters such as the magnetic field, pressure, temperature and acceleration. The worldwide MEMS market reached $48 billion dollars in 2005, $72 billion in 2007 and is expected to reach $95 billion by 2010 [5].Magnetic field sensors have a great potential for numerous applications such as magnetic storage, automotive sensors, navigation systems, non-destructive material testing, security systems, structural stability, medical sensors, and military instruments [6].

Among the different kinds of magnetic field sensors, the Superconducting Quantum Interference Device (SQUID) is the most sensitive sensor, achieving a magnetic field resolution (minimum detectable magnetic field) on the order of several fT [7].
Piezoresistive SensingIn this section, resonant magnetic field sensors based on MEMS technology with piezoresistive sensing are discussed.Figure 4 shows a depiction of the operating principle of a MEMS magnetic field sensor that uses a resonant structure. Then the magnetic field magnitudes are translated into an electrical signal through of the Wheatstone bridge.This patent pending sensor was designed for Tenaris TAMSA Corporation for measuring residual magnetic fields in welded steel tubes. The device is used mainly in neuromagnetism (with signal levels of pT or lower), magnetic resonance and geology applications [8].
The sensor uses a piezoresistive sensing through a Wheatstone bridge with two active (placed on the microbeams) and two passive piezoresistors (deposited on the substrate).
Unfortunately, the commercial success of SQUID-based applications is still limited due to its high price that, in most cases, overrides its advantages with respect to other magnetic sensors. In addition, SQUID sensors operate at low temperatures and have high sensitivity to electromagnetic interference, requiring a sophisticated infrastructure (liquid helium supply, glass-fiber-reinforced epoxy Dewar vessels, and electromagnetic shielding) that restricts their applications.On the other hand, magnetic sensors using the Hall effect as their principle of transduction are commonly fabricated on standard Complementary Metal-Oxide Semiconductor (CMOS) technology. The interaction between a magnetic field (Bx) and an electrical current (I) originates a Lorentz force (FL) on the tip of the microbeams that changes their equivalent spring (FL acts like an additional spring force).
However, the sensor registered an offset and linearity problems at low magnetic fields range.The resonant sensors with piezoresistive sensing require simple readout circuits and present high sensitivity and low manufacture-cost.
These sensors can measure either constant or varying magnetic field: the upper frequency limit is about 1 MHz and operate well in the temperature range from ?100 to +100 °C [9]. However, magnetic sensors based on silicon may have intrinsic limits to their sensitivity and resolution, which may limit future performance gains [10]. Optical SensingIn this section, the optical sensing used in resonant magnetic field sensors based on MEMS technology is presented.A xylophone resonator used as magnetic field sensor with optical sensing was reported by Zanetti et al. In addition, they need temperature compensation circuits that can include temperature sensor and operational amplifiers (op-amps).Search coil sensors only detect time-varying magnetic fields based on Faraday's law of induction.
Commonly, they can measure magnetic fields above 20 fT [11], and use a ferromagnetic core with high permeability inside of a coil in order to increase their sensitivity. An ac drive current (I) is supplied at the resonant frequency of xylophone under an external magnetic field (Bx), producing a Lorentz force that deflects the microbar. This defection is optically sensed through a miniature laser, where it illuminates a xylophone free end and the deflection of the reflected light beam is synchronously detected with a position sensitive detector.
The miniaturization of these sensors decreases their sensitivity and they cannot detect static magnetic fields.Fluxgate sensors measure the static or low frequency magnetic field and are sensitive to both the field direction and field magnitude from 10?2 to 107 nT with a resolution of 100 pT [9]. Fluxgates are the most widely used sensors for compass navigation systems, but they are also used for detecting submarines, geophysical prospecting, airborne magnetic field mapping, and measurement of electrical current [13,14]. A background field is generated by a calibration coil to maintain a proper dynamic range and to inject fields when the xylophone resonance is lost.
However, these sensors have a complex fabrication of the magnetic core and the coils [15], as well as high mass and power consumption. The frequency response of the sensor is limited by the excitation field and the response time of the ferromagnetic material.
A magnetic field (Bx) and an ac electrical current (I) generate a Lorentz force, which bends the microbeams.
These sensors are based on the anisotropic magnetoresistive effect that occurs in ferromagnetic transition metals, in which their electrical resistance depends on the angle between the electrical current and the direction of magnetization. These deflections are measured with an optical sensing that uses two-fiber arrangement to avoid the problem of the interfering reflected light. Therefore, an external magnetic field affects the direction of the magnetization, causing a variation of the electrical resistance.
The AMR sensors have low sensitivity to mechanical stress and a power consumption of few milliwats [19].
Their applications include traffic counting, earth field sensing, electronic compasses, navigation systems, and wheel speed sensors for Anti-Block System (ABS). These sensors are saturated at small magnetic fields (about several mT) and need a complex resetting procedure; in addition, their sensitivity is degraded when the power consumption is decreased [20]. The sensor has a large dynamic range and is principally used for applications with high magnetic fields. They can be operated over an extremely wide temperature range (above +200 °C), but the standard sensor packages are limited for temperatures below +150 °C.Giant magnetoresistive (GMR) sensors have a large shift in the electrical resistance when their thin layers (a few nanometers) of ferromagnetic and non-magnetic materials are exposed to a magnetic field [21]. Generally, they detect magnetic fields from 10 to 108 nT [6] and have a die size close to 1 mm. However, this sensor needs high current magnitudes (about 50 mA) to detect small magnetic fields, which increases the temperature and deformation at the silicon microbeam. GMR sensors operate at temperatures above +225 °C, although, they have higher both offset and sensitivity temperature dependence than AMR sensors [22]. These sensors have found many applications, including magnetic read heads [23], vehicle detection and car speed monitoring [24], pneumatic cylinder position sensing, crankshaft position sensors, current detection, and noiseless locking mechanisms [25].Fiber optic sensors exploit the magnetostrictive effect for measuring magnetic fields, whereby the dimensions of the magnetostrictive material change when it is placed inside an external magnetic field.

This material is bonded over a piece of optical fiber, which is used as a leg of a Mach-Zender interferometer that measures the strain of the fiber when is exposed to a magnetic field. These sensors have a sensitivity range from 10?2 to 106 nT and are immune to electromagnetic interference (EMI) [6,26]. A problem of this sensor is the identification and incorporation of high magnetostrictive materials into a fiber by appropriate bonding or coating [27]. In addition, both temperature and pressure shifts affect the operation of this sensor.Recently, MEMS technology has been seriously considered as a candidate for the development of sensors due to the fact that they present several advantages such as small size, light weight, low-power consumption, minimum cost, high functionality, and better sensitivity and resolution. Wickenden's sensor detects the magnetic fields through the reflection of a laser diode beam (with an incident angle about 5° from vertical incidence) from one of the free ends of the xylophone microbar. Thus, new resonant magnetic field sensors based on MEMS technology have been developed by some research groups, which show important advantages on their performance.
The relation between the output response of the sensor and the applied magnetic field range has a linear behavior up to 150 ?T.
These sensors use resonant structures that exploit the Lorentz force principle for detecting magnetic fields.
Generally, they measure the displacement of resonant structures exposed to external magnetic fields through capacitive, piezoresistive and optical sensing techniques.This paper presents a review of different resonant magnetic field sensors based on MEMS technology, describing their operation principles, advantages and drawbacks, some applications, trends and challenges.
An ac current flows (I) in the microbeams to their resonant frequency under an external magnetic field (B), originating a seesaw motion of the microbeams that can be measured with an optical sensing. In addition, this section describes the principal advantages and drawbacks of several resonant magnetic fields sensors based on MEMS technology, which use piezoresistive, optical, and capacitive sensing techniques.
Section 3 discusses the potential applications of magnetic field sensors in sectors such as automotive, military, medical, oceanographic, spatial, and environment science. Section 4 presents some trends and challenges of the magnetic field sensors, and finally the paper ends with the conclusion and an outline of further work. Resonant Magnetic Field SensorsIn this section, the operation principle and detection techniques of MEMS magnetic field sensors based on resonant structures are presented.
Most resonant magnetic field sensors exploit the Lorentz force principle, in where a Lorentz force increases the displacement of a resonant structure that can be measured with optical, piezoresistive, and capacitive sensing techniques.
Thus, the sensor must operate at low pressures and needs to include an optical detection system.The resonant magnetic field sensors with optical readout system have immunity to EMI as well as a reduction in their electronic circuitry and weight. However, the optical sensing presents some problems due to the intrinsic losses of the structural imperfections of the sensors and can require complex fabrication processes. Capacitive SensingIn this section, some resonant magnetic field sensors based on MEMS technology with capacitive sensing are shown.Kadar et al. Therefore, a sensor based on a resonant structure can achieve larger output signals, increasing its sensitivity.Resonant magnetic field sensors use structures that are excited at their resonant frequencies by electrostatic forces or Lorentz forces. The sensor contains an aluminum rectangular loop on its surface that active a seesaw motion under an external magnetic field (Bx).
The application of external magnetic fields alters the deflections of the resonant structure, which can be detected through optical, capacitive, and piezoresistive sensing techniques. The excitation source can be a Lorentz force due to the interaction between an external magnetic field and an ac excitation current. This sensor requires a complex electronic circuit for the signal processing and can reach a detection limit of 1 nT when it is vacuum-packaged.Figure 13 shows a resonant magnetic field sensor reported by Emmerich and Schofthaler [51], which contains a collection of not only movable comb and fixed finger electrodes, but also a large movable conducting microbeam. When the beam is exposed to an external magnetic field (Bx) in the x-direction, then a Lorentz force (FL) is generated.
This force is generated on the conducting beam when an ac current (I) flows through it under the presence of an external magnetic field (Bx).
Furthermore, it presents an offset (approximate 60 ?T) due to parasitic couplings of the electronics, unbalanced parasitic capacitances, and a fraction of the residual magnetic field. Also, the sensor requires a complicated fabrication process and a vacuum packaging.Tucker, Wesoleck and Wickenden [52] designed a resonant magnetic field sensor based on a xylophone microbar that exploits the Lorentz force principle. The interaction between an ac sinusoidal current to the sensor resonant frequency and an external magnetic field produces a Lorentz force normal to the microbar surface.
The sensor needs a complex fabrication process, a vacuum packaging, and a differential switched capacitor modulation and demodulation technique.Figure 14 shows a resonant magnetic field sensor developed by Bahreyni et al.
The resonator is driven and kept into resonance through electrostatic actuation and sensing.
A Lorentz force (FL) normal to the crossbars is obtained with the interaction between a dc current (IXB) in the crossbars under a magnetic field (Bx) normal to the plane of the sensor.

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