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MEMS


Sensor Basics: Potentiometer

The resistance of a given sample will increase with the length, but decrease with greater cross-sectional area.

http://en.wikipedia.org/wiki/Resistivity


Sensor Basics: Potentiometer

http://en.wikipedia.org/wiki/Potentiometer

If RL is large compared to the other resistances (like the input to an operational amplifier), the output voltage can be approximated by the simpler equation:


Sensor Basics: Strain Gauge

Strain is the amount of deformation of a body due to an applied force. More specifically, strain (e) is defined as the fractional change in length, as shown in Figure 1.

Figure 1. Definition of Strain

http://zone.ni.com/devzone/cda/tut/p/id/3642

The gauge is attached to the object by a suitable adhesive, such as cyanoacrylate. As the object is deformed, the foil is deformed, causing its electrical resistance to change. This resistance change, usually measured using a Wheatstone bridge, is related to the strain by the quantity known as the gauge factor.



A typical strain gauge arranges a long, thin conductive strip in a zig-zag pattern of parallel lines such that a small amount of stress in the direction of the orientation of the parallel lines results in a multiplicatively larger strain over the effective length of the conductorand hence a multiplicatively larger change in resistancethan would be observed with a single straight-line conductive wire.

http://en.wikipedia.org/wiki/Strain_gage

Typical foil strain gauge. The gauge is far more sensitive to strain in the vertical direction than in the horizontal direction.



http://en.wikipedia.org/wiki/Strain_gage

Visualization of the working concept behind the strain gauge on a beam under exaggerated bending.


Sensor Basics: Wheatstone Bridge

http://en.wikipedia.org/wiki/Wheatstone_bridge

It is used to measure an unknown electrical resistance by balancing two legs of a bridge circuit, one leg of which includes the unknown component.

+-



In the figure, Rx is the unknown resistance to be measured; R1, R2 and R3 are resistors of known resistance and the resistance of R2 is adjustable.

If the ratio of the two resistances in the known leg (R2 / R1) is equal to the ratio of the two in the unknown leg (Rx / R3), then the voltage between the two midpoints (B and D) will be zero and no current will flow through the galvanometer Vg.

R2 / R1 = Rx / R3



If R1, R2, and R3 are known, but R2 is not adjustable, the voltage difference across or current flow through the meter can be used to calculate the value of Rx,


Sensor Basics: Piezoresistive effect

The piezoresistive effect describes the changing resistivity of a semiconductor due to applied mechanical stress.

In semiconductors, changes in inter-atomic spacing resulting from strain affects the bandgaps making it easier (or harder depending on the material and strain) for electrons to be raised into the conduction band. This results in a change in resistivity of the semiconductor.

http://en.wikipedia.org/wiki/Piezoresistive_effect


Sensor Basics: Piezoresistive effect

Piezoresistivity is defined by

Piezoresistivity has a much greater effect on resistance than a simple change in geometry and so a semiconductor can be used to create a much more sensitive strain gauge, though they are generally also more sensitive to environmental conditions (esp. temperature).


Sensor Basics: Capacitive Sensors

Capacitive sensors use the electrical property of "capacitance" to make measurements. Capacitance is a property that exists between any two conductive surfaces within some reasonable proximity.



Spacing variation[5]

Spacing variation of parallel plates is often used for motion detection if the spacing change is less than the electrode size. The parallel plate capacitance formula shows that capacitance is inversely related to spacing. This gives a conveniently large value of capacitance at small spacing, but it does often require signal conditioning which can compensate for the parabolic capacitance-motion relationship. This is easily done by measuring impedance rather than capacitance.



Area variation[5]

As these plates slide transversely, capacitance changes linearly with motion. Quite long excursions are possible with good linearity, but the gap needs to be small and well-controlled.

d



, Signal Conditioning[5]

An R-C relaxation oscillator such as the venerable 555 or its CMOS update, the 7555, converts capacitance change into a change of frequency or pulse width.The RC oscillator used with a spacing-variation capacitor will produce a frequency output which is linear with spacing, while an area-variation capacitor is linearized by measuring pulse width.


Sensor Basics: LVDT

LVDT (Linear Variable Differential Transformer)

A type of electrical transformer used for measuring linear displacement.

An LVDT Displacement Transducer comprises 3 coils; a primary and two secondaries.

http://www.rdpe.com/ex/hiw-lvdt.htm


Sensor Basics: Hall Effect

For a simple metal where there is only one type of charge carrier (electrons) the Hall voltage VH is given by

where I is the current across the plate length, B is the magnetic flux density, d is the depth of the plate, e is the electron charge, and n is the charge carrier density of the carrier electrons.

Hall probes are often used as magnetometers, i.e. to measure magnetic fields.

http://en.wikipedia.org/wiki/Hall_effect



Physics Animation Model The Hall-Effecthttp://www.youtube.com/watch?v=_ATDraCQtpQ



http://en.wikipedia.org/wiki/Hall_effect_sensor

A Hall effect sensor is a transducer that varies its output voltage in response to changes in magnetic field. Hall sensors are used for proximity switching, positioning, speed detection, and current sensing applications.


Sensor Basics: Piezoelectric Effect

Piezoelectricity is the charge which accumulates in certain solid materials (notably crystals, certain ceramics, and biological matter such as bone, DNA and various proteins) in response to applied mechanical strain.

http://en.wikipedia.org/wiki/Piezoelectric_sensor

A piezoelectric disk generates a voltage when deformed (change in shape is greatly exaggerated)


Sensor Basics: Piezoelectric Effect

Even though piezoelectric sensors are electromechanical systems that react to compression, the sensing elements show almost zero deflection.

Additionally, piezoelectric technology is insensitive to electromagnetic fields and radiation, enabling measurements under harsh conditions.

One disadvantage of piezoelectric sensors is that they cannot be used for truly static measurements.

http://en.wikipedia.org/wiki/Piezoelectric_sensor


Sensor Basics: Thermoelectric Effect

The thermoelectric effect is the direct conversion of temperature differences to electric voltage and vice versa. A thermoelectric device creates a voltage when there is a different temperature on each side.

At atomic scale (specifically, charge carriers), an applied temperature gradient causes charged carriers in the material, whether they are electrons or electron holes, to diffuse from the hot side to the cold side, similar to a classical gas that expands when heated; hence, the thermally induced current.

http://en.wikipedia.org/wiki/Seebeck_effect#Seebeck_effect


Sensor Basics: Thermoelectric Effect

The Seebeck effect is the conversion of temperature differences directly into electricity.

The effect is that a voltage, the thermoelectric EMF, is created in the presence of a temperature difference between two different metals or semiconductors. This causes a continuous current in the conductors if they form a complete loop. The voltage created is of the order of several microvolts per kelvin difference. One such combination, copper-constantan, has a Seebeck coefficient of 41 microvolts per kelvin at room temperature.

http://en.wikipedia.org/wiki/Seebeck_effect#Seebeck_effect

SA and SB are the Seebeck coefficients (also called thermoelectric power or thermopower) of the metals A and B as a function of temperature, and T1 and T2 are the temperatures of the two junctions.

The Seebeck effect is commonly used in a device called a thermocouple.


In physics, the Coriolis effect is an apparent deflection of moving objects when they are viewed from a rotating reference frame. In a reference frame with clockwise rotation, the deflection is to the left of the motion of the object; in one with anti-clockwise rotation, the deflection is to the right.

The vector formula for the magnitude and direction of the Coriolis acceleration is

where (here and below) ac is the acceleration of the particle in the rotating system, v is the velocity of the particle in the rotating system, and is the angular velocity vector which has magnitude equal to the rotation rate and is directed along the axis of rotation of the rotating reference frame, and the symbol represents the cross product operator.

Sensor Basics: Coriolis Effect

http://en.wikipedia.org/wiki/Coriolis_effect


Sensor Basics: Coriolis Effect

coriolis effect (2-11)

http://www.youtube.com/watch?v=mcPs_OdQOYU

Foucault's pendulum - 2http://www.youtube.com/watc

h?v=wlhHWYKswik


[6]

High Reliability Rugged, well-proven technology

Low manufacturing costs Efficient mass production

Severe operating condition Highly resistant packaging

Low volume Miniaturisation techniques

High accuracy Local fault compensation


:

[1]


MEMS (Micro Electro Mechanical System)

: 25mm MEMS: 2~3mm, package 8~9mm [3]


MEMS: Capacitive Sensor

Parallel Plate Capacitor

http://www.eecs.berkeley.edu/~boser/pdf/



Transverse Comb

Parallel multiplates can to increase the sensor capacitance in a small volume.

http://www.capsense.com/capsense-wp.pdf



Transverse Comb



MEMS

Signal Conditioning


ADXL 50 Layout


MEMS

http://www.eecs.berkeley.edu/~boser/pdf/overview.pdf


MEMS [3]


MEMS [3]

(diaphragm)


MEMS [3]

1)

(capacitive)

,

,

2)

(piezo-resistive)

,

,


MEMS [3]


MEMS [3]

1)

2)

,


MEMS [3]


MEMS [3]

(Yaw-rate Sensor)

(Coriolis effect)


MEMS

The ADXRS gyros take advantage of this effect by using a resonating mass analogous to the person moving out and in on a rotating platform. The mass is micromachined from polysilicon and is tethered to a polysilicon frame so that it can resonate only along one direction.

http://www.analog.com/library/analogdialogue/archives/37-03/gyro.html

Figure 3 shows that when the resonating mass moves toward the outer edge of the rotation, it is accelerated to the right and exerts on the frame a reaction force to the left. When it moves toward the center of the rotation, it exerts a force to the right, as indicated by the orange arrows.


MEMS

To measure the Coriolis acceleration, the frame containing the resonating mass is tethered to the substrate by springs at 90 relative to the resonating motion, as shown in Figure 4. This figure also shows the Coriolis sense fingers that are used to capacitively sense displacement of the frame in response to the force exerted by the mass, as described further on.


Figure 4. Schematic of the gyros mechanical structure.


MEMS


Figure 5. The frame and resonating mass are displaced laterally in response to the Coriolis effect. The displacement is determined from the change in capacitance between the Coriolis sense fingers on the frame and those attached to the substrate.


MEMS


Figure 6. Photograph of mechanical sensor. The ADXRS gyros include two structures to enable differential sensing in order to reject environmental shock and vibration.

Figure 7. Photograph of ADXRS gyro die, highlighting the integration of the mechanical rate sensor and the signal conditioning electronics.


[4]

USN (Ubiquitous Sensor Network): (field)

(gateway)


[4]

, ,


[4]


: Catalytic Converter ( )

A three-way catalytic converter has three simultaneous tasks:

http://en.wikipedia.org/wiki/Catalytic_Converter

Metal-core converter

Ceramic-core converter http://www.bladeyourride.com/how-to-take-care-of-your-catalytic-converter/


(Optimum air fuel ratio)

14.7:1

http://www.originlab.com/index.aspx?go=Solutions/CaseStudies&pid=227


http://ecohho.wordpress.com/what-is-hho/hydrogen-fuel-on-demand/unleash-the-true-power-of-water/understanding-an-efie/understanding-an-o2-oxygen-sensor/


NOX, HC, CO

N, H2O, CO2

.

NOX (N) (O2) , HC CO

CO2 ,

NOX ,

HC CO

14.7:1 .

, ,


Zirconia sensor

Titania sensor

http://en.wikipedia.org/wiki/Oxygen_sensor


Zirconia sensor

The zirconium dioxide, or zirconia, lambda sensor is based on a solid-state electrochemical fuel cell called the Nernst cell. Its two electrodes provide an output voltage corresponding to the quantity of oxygen in the exhaust relative to that in the atmosphere.

http://www.vcoa.org/700-900-faq/EngineSensors.html


Titania sensor

A less common type of narrow-band lambda sensor has a ceramic element made of titanium dioxide (titania). This type does not generate its own voltage, but changes its electrical resistance in response to the oxygen concentration.

http://blog.naver.com/PostView.nhn?blogId=autokyw&logNo=70044118012


(Airflow Sensor)

http://en.wikipedia.org/wiki/Mass_flow_sensor

Vane meter sensor (VAF sensor)

Hot wire sensor (MAF)

Coldwire" sensor

Krmn vortex sensor


(Airflow Sensor)

http://www.aa1car.com/library/vaf_sensors.htm

Vane meter sensor (VAF sensor)


(Airflow Sensor)

Hot wire sensor (MAF)

The theory of operation of the hot wire mass airflow sensor is similar to that of the hot wire anemometer (which determines air velocity).

This is achieved by heating a wire with an electric current that is suspended in the engines air stream, like a toaster wire.

The wire's electrical resistance increases as the wires temperature increases, which limits electrical current flowing through the circuit. When air flows past the wire, the wire cools, decreasing its resistance, which in turn allows more current to flow through the circuit. As more current flows, the wires temperature increases until the resistance reaches equilibrium again.

The amount of current required to maintain the wires temperature is directly proportional to the mass of air flowing past the wire.The integrated electronic circuit converts the measurement of current into a voltage signal which is sent to the ECU.


(Airflow Sensor)

Krmn vortex sensor

A Krmn vortex sensor works by setting up a laminar air stream. The air stream is disrupted by a vertical bow in the sensor. This causes a wake in the air stream and subsequently the wake will collapse repeatedly and cause Krmn vortexes. The frequency of the resulting air pressure oscillation is proportional to the air velocity.

These vortexes can either be read directly as a pressure pulse against a sensor, or they can be made to collide with a mirror which will then interrupt or transmit a reflected light beam to generate the pulses in response to the vortexes. The first type can only be used in pull thru air (prior to a turbo- or supercharger), while the second type could theoretically be used push or pull thru air (before or after a forced induction application like the previously mentioned super- or turbocharger). Instead of outputting a constant voltage modified by a resistance factor, this type of MAF outputs a frequency which must then be interpreted by the ECU.


NDIR [1]

4.26um

http://v2010.raesystems.com/~raedocs/App_Tech_Notes/Tech_Notes/TN-169_NDIR_CO2_Theory.pdf


NDIR [1]

NDIR (Non-Dispersive Infrared)


1. , , Auto Journal 2008.06, pp. 36-42.

2. , , , Auto Journal 2008.06, pp. 22-28.

3. , , , , , MEMS , 1284 2007.2.21, pp. 21-36.

4. , , Machinery Industry, 2008.3, pp. 66-73, http://www.koami.or.kr/webzin/2k803/8.pdf.

5. L. K. Baxter, Capacitive Sensors, http://www.capsense.com/capsense-wp.pdf

6. , Automotive Sensors and Measurements, , 2010 , , 2010.

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