GLOBAL POSITIONING SYSTEM - Overview

EE352N

ELECTRICAL AND ELECTRONIC

INSTRUMENTATION – CHAPTER V

1

GLOBAL POSITIONING SYSTEM - Overview

• Official name of GPS is NAVigational Satellite Timing And Ranging Global Positioning System (NAVSTAR GPS)

• Global Positioning Systems (GPS) is a form of Global Navigation Satellite System (GNSS)

– Only completely functional one of its kind at this time

• First developed by the United States Department of Defense.

• Consists of two dozen GPS satellites in medium Earth

orbit (The region of space between 2000km and 35,786

km)

Overview (continued)

• Made up of two dozen satellites working in unison are known as a satellite constellation.

• This constellation is currently controlled by the United States Air Force 50th Space Wing.

• Mainly used for navigation, map-making and

surveying.

Operation Overview

 A GPS receiver can tell its own position by using the position data of itself, and compares that data with 3 or more GPS satellites.

 To get the distance to each satellite, the GPS transmits a signal to each satellite.

 The signal travels at a known speed.

 The system measures the time delay between the signal transmission and signal reception of the GPS signal.

 The signals carry information about the satellite’s location.

 Determines the position of, and distance to, at least three satellites, to reduce error.

 The receiver computes position using trilateration.

Trilateration

GPS Functionality

• GPS systems are made up of 3 segments

– Space Segment (SS)

– Control Segment (CS)

– User Segment (US)

Control Segment Space Segment

User Segment

Three Segments of the GPS

Monitor Stations

Ground Antennas Master Station

Space Segment

• GPS satellites fly in circular orbits at an altitude of 20,200 km and with a period of 12 hours.

•

• Powered by solar cells, the satellites continuously orient themselves to point their solar panels toward the sun and their antenna toward the earth.

• Orbital planes are centered on the Earth.

• Each planes has about 55° tilt relative to Earth's

equator in order to cover the polar regions.

Space Segment (Continued)

• Each satellite makes two complete orbits each sidereal day.

– Sidereal - Time it takes for the Earth to turn 360 degrees in its rotation

• It passes over the same location on Earth once each day.

• Orbits are designed so that at the very least,

six satellites are always within line of sight

from any location on the planet.

Space Segment (Continued)

• There are currently 30 actively broadcasting satellites in the GPS constellation.

• Redundancy is used by the additional satellites to improve the precision of GPS receiver calculations.

• A non-uniform arrangement improves the

reliability and availability of the system over

that of a uniform system, when multiple

satellites fail

Control Segment

• The CS consists of 3 entities:

– Master Control System – Monitor Stations

– Ground Antennas

Kwajalein Atoll US Space Command

Control Segment

Hawaii

Ascension Is. Diego Garcia Cape Canaveral

Ground Antenna Master Control Station Monitor Station

Master Control Station

• The master control station, located at Falcon Air Force Base in Colorado Springs, Colorado, is responsible for overall management of the remote monitoring and transmission sites.

• GPS ephemeris is the tabulation of computed

positions, velocities and derived right ascension

and declination of GPS satellites at specific times

for eventual upload to GPS satellites.

Monitor Stations

• Six monitor stations are located at Falcon Air Force Base in Colorado, Cape Canaveral, Florida, Hawaii, Ascension Island in the Atlantic Ocean, Diego Garcia Atoll in the Indian Ocean, and Kwajalein Island in the South Pacific Ocean.

• Each of the monitor stations checks the exact

altitude, position, speed, and overall health of

the orbiting satellites.

Monitor Stations (continued)

• The control segment uses measurements collected by the monitor stations to predict the behavior of each satellite's orbit and clock.

• The prediction data is transmitted, to the satellites for transmission back to the users.

• The control segment also ensures that the GPS satellite

orbits and clocks remain within acceptable limits. A

station can track up to 11 satellites at a time.

Monitor Stations (continued)

• This "check-up" is performed twice a day, by each station, as the satellites complete their journeys around the earth.

• Variations such as those caused by the gravity

of the moon, sun and the pressure of solar

radiation, are passed along to the master

control station.

Ground Antennas

• Ground antennas monitor and track the satellites from horizon to horizon.

• They also transmit correction information to

individual satellites.

User Segment

• The user's GPS receiver is the US of the GPS system.

• GPS receivers are generally composed of an antenna, tuned to the frequencies transmitted by the satellites, receiver-processors, and a highly-stable clock, commonly a crystal oscillator).

• They can also include a display for showing location and speed information to the user.

• A receiver is often described by its number of channels

this signifies how many satellites it can monitor

simultaneously. As of recent, receivers usually have

between twelve and twenty channels.

Navigational Systems

• GPS satellites broadcast three different types of data in the primary navigation signal.

– Almanac – sends time and status information about the satellites.

– Ephemeris – has orbital information that allows the receiver to calculate the position of the satellite.

• This data is included in the 37,500 bit Navigation Message, which takes 12.5 minutes to send at 50 bps.

Navigational Systems (cont’d)

• Satellites broadcast two forms of clock information

– Coarse / Acquisition code (C/A) - freely available to the civilians.

– The C/A code is a 1,023 bit long pseudo-random code broadcast at 1.023 MHz, repeating every millisecond.

– Restricted Precise code (P-code) - reserved for military usage. The P-code is a similar code broadcast at 10.23 MHz, but it repeats only once a week.

– Information is encrypted and needs key to access.

Position Calculation

• The satellites are equipped with atomic clocks

• Receiver uses an internal crystal oscillator-based clock that is continually updated using the signals from the satellites.

• Receiver identifies each satellite's signal by its

distinct C/A code pattern, then measures the

time delay for each satellite.

Position is Based on Time

t2

Distance between satellite and

receiver = “(t2-t1) times the speed of light”

t1

Signal leaves satellite at time “t1”

Signal is picked up by the

receiver after time “t2-t1”

Pseudo Random Noise Code

Receiver pulse

Identical to satellite pulse

Satellite pulse received at the reciever.

Time

Difference

Coded pulses are received by receiver by Almanac and contains the identity of the satellite.

Position Calculation (cont’d)

• The receiver emits an identical C/A sequence using the same code the satellite used.

• By aligning the two sequences, the receiver can measure the delay and calculate the distance to the satellite, called the pseudorange.

• Orbital position data from the Navigation

Message is used to calculate the satellite's

precise position.

Signal From One Satellite

The receiver is

somewhere on this sphere.

Knowing the position and the distance of a satellite indicates that the receiver is located somewhere on the surface of an imaginary sphere centered on that satellite and whose radius is the distance to it as shown above.

Signals From Two Satellites

Knowing the position and the distance from second satellite also indicates that the receiver is located somewhere on the circle formed by the two surfaces of imaginary spheres centered on the two satellites and whose radius is the distance to it.

The receiver is somewhere on this circle .

Signals From Two Satellites

The receiver is at one of the two points shown by yellow points

Thus for finding out 2D position of reciever, 3 satellites are must. Known as Trilateration

Three Dimensional (3D) Positioning

Forfinding out 3D position of reciever, 4 satellites are must.

Triangulating Correct Position

Position Calculation (cont’d)

• Orbital position data from the Navigation

Message is used to calculate the satellite's

precise position.

Position Calculation (cont’d)

• When four satellites are measured at the same time, the point where the four imaginary spheres meet is recorded as the location of the receiver.

• Earth-based users can substitute the sphere of the planet for one satellite by using their altitude.

Often, these spheres will overlap slightly instead

of meeting at one point, so the receiver will yield

a mathematically most-probable position.

Issues That Affect Accuracy

• Changing atmospheric conditions change the speed of the GPS signals as they pass through the Earth's atmosphere and ionosphere.

– Effect is minimized when the satellite is directly overhead

– Becomes greater for satellites nearer the horizon, since the signal is affected for a longer time.

– Once the receiver's approximate location is

known, a mathematical model can be used to

estimate and compensate for these errors.

Issues That Affect Accuracy (cont’d)

• Clock Errors can occur when, for example, a GPS satellite is boosted back into a proper orbit.

– The receiver's calculation of the satellite's position will be incorrect until it receives another

ephemeris update.

– Onboard clocks are accurate, but they suffer from

partial clock drift.

Issues That Affect Accuracy (cont’d)

• GPS signals can also be affected by multipath issues

– Radio signals reflect off surrounding objects at a location. These delayed signals can cause

inaccuracy.

– Less severe in moving vehicles. When the GPS antenna is moving, the false solutions using

reflected signals quickly fail to converge and only

the direct signals result in stable solutions.

Sources of Signal Interference

Earth’s Atmosphere

Solid Structures

Metal Electro-magnetic Fields

Receiver Errors are Cumulative!

User error = +- 1 km

System and other flaws = < 9 meters

GPS Satellite Geometry

 Satellite geometry can affect the quality of GPS signals and accuracy of receiver trilateration.

 Dilution of Precision (DOP) reflects each satellite’s position relative to the other satellites being accessed by a receiver.

 There are five distinct kinds of DOP.

 Position Dilution of Precision (PDOP) is the DOP value used most commonly in GPS to determine the quality of a receiver’s position.

 It’s usually up to the GPS receiver to pick satellites which provide the best position triangulation.

 Some GPS receivers allow DOP to be manipulated by the user.

Ideal Satellite Geometry

N

S

W E

Position Dilution of Precision (PDOP)

Good Satellite Geometry

Good Satellite Geometry

Poor Satellite Geometry

N

S

W E

Poor Satellite Geometry

Poor Satellite Geometry

DGPS Site x+30, y+60

x+5, y-3

True coordinates = x+0, y+0

Correction = x-5, y+3 DGPS correction = x+(30-5) and

y+(60+3)

True coordinates = x+25, y+63

x-5, y+3

Differential GPS

DGPS Receiver Receiver

Methods of Improving Accuracy (cont’d)

• Augmentation

– Relies on external information being integrated into the calculation process.

– Some augmentation systems transmit additional information about sources of error.

– Some provide direct measurements of how much the signal was off in the past

– Another group could provide additional

navigational or vehicle information to be

integrated in the calculation process.

GLOBAL POSITIONING SYSTEM - WAYPOINTS

• A waypoint is based on coordinates entered into a GPS receiver’s memory.

• It can be either a saved position fix, or user entered coordinates.

• It can be created for any remote point on earth.

• It must have a receiver designated code or number, or a user supplied name.

• Once entered and saved, a waypoint remains unchanged in the receiver’s memory until edited or deleted.

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Start = Waypoint

PLANNING A NAVIGATIONAL ROUTE

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HOW A RECIEVER SEES YOUR ROUTE

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GPS NAVIGATION TERMINOLOGY

N(000⁰)

(0⁰)

N Desired Track

(DTK) (xº⁾

Present Location

Tracking (TRK) (xº⁾

Active GOTO Waypoint

Course Made Good (CMG) (CMG) (xº)

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GPS NAVIGATION-ON THE GROUND

Active GOTO Waypoint

Bearing =

Course Over Ground (COG) = Cross Track Error (XTE) =

Location Where GOTO Was Executed

Bearing = 65⁰ COG = 5⁰ XTE = 1/2 mi.

Bearing = 78⁰ COG = 350⁰ XTE

= 1/3 mi.

Bearing = 40⁰ COG = 104⁰ XTE

= 1/4 mi.

N

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ELECTROMECHANICAL METER

• Has a spinning disc and a mechanical counter display.

• Operates by counting the revolutions of a metal disc.

• Speed is proportional to the power drawn i.e. ω=K v i

• Nearby coils spin the disc by inducing eddy currents and a force proportional to the instantaneous current and voltage.

• A Permanent magnet exerts a damping force on the disc.

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SOLID-STATE ELECTRONIC METERS

•

These devices digitize the instantaneous voltage and current via a high-resolution ADC.

•

A microprocessor multiplies voltage and current to give the instantaneous power in watts.

•

Integration over time gives energy used in kilowatt hours (kWh).

•

The energy data is displayed on a liquid-crystal display (LCD).

•

It also measures other parameters such as power factor and reactive power.

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COMMUNICATION

•

Modes of meter reading:

1) Walk by 2) Drive by 3) Network Connection

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•

A smart meter records the energy consumption for the specified interval (half or one hour) of time for which it is programmed.

•

This meter has a facility to store the data recorded in the interval and reproduce it whenever required.

•

These meters enable a two-way communication between the meter and the central system.

•

These meters are embodied with the feature of monitoring the quality of the power.

SMART METERS

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SMART METERS

POWER CONSUMPTION (MW)

PEAK HOURS

HOURS

0500 0700 0900 1100 1300 1500

0300

0100

2300

21001900

1700

OFF-PEAK

HOURS ELECTRIC UTILITY IS UNDER UTILIZED ADDITIONAL PLANTS

OPERATED

•

Better utilization of utilities.

PLANT CAPACITY

1500

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SMART METERS

•

Higher rates during peak hours and lower during non-peak hours.

•

This allows savvy consumers to save money by running major appliances, such as washers and dryers, during lower-cost, off-peak periods. This can also be controlled by the utility.

•

Better Demand Side Management.

•

Economical and flexible operation.

•

Prevention of frauds and power-thefts.

•

Quick fault detection and fault clearing.

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SMART METERS

BASIC BLOCK DIAGRAM OF A SMART METER ₅₈

SMART METERS

•

Interconnection to premise-based networks and devices (e.g., distributed generation).

•

Ability to read other, on-premise or nearby commodity meters (e.g., gas, water).

•

Can better manage number of Hybrid Electric Vehicles on road.

•

A technology known as Power line Carrier Systems (PCS) is used to send coded signals along a home's existing electric wiring to programmable switches.

•

PCS transmitter send this signal into power line which can be tapped from any power outlet at home.

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SMART METERS-COMMUNICATION WITH UTILITY

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SMART METERS

•

Smart Meter Plays an important role in a Smart Grid.

DSM

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WIDE AREA MEASUREMENT SYSTEMS

•

Wide Area Measurement monitor network stability of the power system network.

•

It includes States (V and δ) determination and grid imbalance (voltage stability, phase Imbalance).

•

Observability – If all the states (V & δ) can be measured or calculated using the existing measurement data then the system is said to be observable.

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WIDE AREA MEASUREMENT SYSTEMS- OBSERVABILITY

(V,δ,I₁,I₂) Meter

I₁ 1

2

3

I₂

4

(V,δ,I₁,I_3, I₄)

I₁ 1

2

3

I₃

4 Meter

I₄

Unobservable System Observable System

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WIDE AREA MEASUREMENT SYSTEMS

• Disturbance recording.

• Network safety.

• Generation control.

• Improved planning will also result from the data gathered from WAMS.

• Supervisory Control and Data Acquisition SCADA / PMU.

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WIDE AREA MEASUREMENT SYSTEMS

•

In short, SCADA has following functions:

1. Data acquisition

2. Supervisory control

3. Alarm display and control

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WAMS-STATE ESTIMATION

Z=h(X)+ϵ

Z – Measurement vector.

X – states of system (V,δ)

h- function relating X with Z (A theoretical relation between measured quantity and states).

ϵ- Noise in measurement or error.

Real and Reactive Power Flows P_ij = F1(Vi,Vj, δi, δj)

Q_ij = F2(Vi,Vj, δi, δj)

Real and Reactive Power Injections Pi = F(Vi,Vj, δi, δj)

Qi = F(Vi,Vj, δi, δj)

where j belongs to all the buses connected to bus i.

These are the functions h(X) relating Power injections and Power flows to States of the system

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WAMS-STATE ESTIMATION

•

To estimate correct values of states from the measured data, state estimation is done.

•

Estimation is done such that mean error ϵ or mean square error ϵ^Tϵ is minimized. i.e. (Z-h(X))^T (Z-h(X))

STEPS

1. Assume initial values of states (V_o, δ_o).

2. Calculate values of measured quantities by theoretical relation h(X).

3. There will be error in measured value Z and calculated value h(X).

4. Calculate error ϵ=Z-h(X) or mean square error ϵ^Tϵ.

5. Based on this error update (modify) state vector X.

6. If this updated state vector X(V₁, δ₁) is very near to old state vector X₀(V_o, δ_o), stop estimation. X(V₁, δ₁) is estimated value.

7. If this updated state vector X(V₁, δ₁) is not close to old state vector X₀(V_o, δ_o), Goto step 2.

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WAMS-STATE ESTIMATION

•

SCADA data is very slow. In appropriate for dynamic studies.

•

Voltage angles cannot be measured, but rather estimated using the data of WAMS.

•

The estimated value of voltage angles has low accuracy.

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At different locations

SUBSTATION A SUBSTATION B

t = t₁ t = t₁

Measurement at Substation A Measurement at Substation B

V Phasors of station A and station B

Figure 2: Synchrophasor Measurements

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SYNCHROPHASOR MEASUREMENTS

δ

• Synchrophasor measurements are synchronized with common time reference.

• Along with the measurements, the exact time of the measurement is also included.

• Angle difference between two phasors can be compared.

• Phasor Measurement Units are such devices.

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SYNCHROPHASOR MEASUREMENT

• PMUs measure Voltage of the bus on which it is placed, Voltage angle  and Currents & Current angles of the branches connected to the bus.

• It is synchronized with Satellite atomic clock via some communication channel.

• High-speed synchronized sampling with 1 microsecond accuracy.

• Voltage and Voltage angles of the neighboring buses can be estimated.

• A PMU converts a non-linear estimator into a linear estimator.

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PHASOR MEASUREMENT UNITS

PHASOR MEASUREMENT UNITS

ANTI-ALIASING FILTERS

16-BIT A/D CONVERTER PHASE-LOCKED

OSCILLATOR GPS RECEIVER

PHASOR

MICROPROCESSOR

MODEM Analog Inputs

(From CT, PT etc)

Phasor Measurement Unit Block Diagram

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WAMPS-ONLY PMUs

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PMU PMU PMU PMU PMU PMU

DATA STORAGE PMUs/Meters located in Sub-Stations

SUPER DATA CONCENTRATOR

DATA CONCENTRATOR

DATA CONCENTRATOR

Wide Area Measurement System

• Present cost of a Phasor Measurement Unit is very high.

• Hence, Placed at selective (optimal) locations.

• Therefore in actual practice, WAMS of present day power system network includes conventional measurements with PMUs placed at optimal locations.

• PMU cost is expected to go down in recent years.

• Real potential of Synchrophasor Measurements is yet to be explored.

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SMART SENSORS

• At a minimum, A Smart Sensor is the combination of a sensing element with processing capabilities provided by a microprocessor.

• Smart Sensors are basic sensing elements with embedded intelligence.

• The sensor signal is fed to the microprocessor, which processes the data and provides an informative output to an external user.

• It is a complete self-contained sensor system that includes the capabilities for logging, processing with a model of sensor response and other data, self-contained power, and an ability to transmit or display informative data to an outside user.

• . 75

SMART SENSORS

Integration of silicon microprocessors with sensor technology can not only provide interpretive power and customized outputs, but also significantly improve sensor system performance and capabilities.

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APPLICATIONS - SMART SENSORS

• Awareness of our surroundings

• Provide safety.

• Security, and Surveillance.

• Enable monitoring of our health

• Enable monitoring of our Environment.

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SMART SENSORS

The smart sensor possesses several functional layers

• Signal detection from discrete sensing elements

• Signal processing, data validation and interpretation

• Signal transmission and display.

SENSORS

Analog-Digital-Analog Signal Processing

Communications Electrical/Optical

Physical/Chemical Stimulus

SMART SENSOR SYSTEM

Processed

Sensor Information to User

User Commands for sensor

Operations

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POWER

SMART SENSORS

• Multiple sensors can be included in a single smart sensor system whose operating properties, such as bias voltage or temperature, can be set by the microprocessor.

• The sensor elements interface to signal control and conditioning stages that will provide both excitation and signal data logging and conditioning.

• The data acquisition layer will convert the signal from analog to digital and acquire additional parameters of interest to provide compensation when needed.

• Compensation is provided for thermal drift, long term drift, etc.

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SMART SENSORS

• The processed data becomes information and can then be transmitted to external users.

• The user can choose the complexity of the data transmitted:

from a single reading to a complete download of the sensor system’s parameters.

• Intelligent features can be included at the sensor level like: self- calibration, self-health assessment, self-healing, and compensated measurements (auto zero, calibration, temperature, pressure, relative humidity correction).

• A Smart Sensor is thus self-aware and can assess its own health or status and assess even the validity of the processed data. ₈₀

SMART SENSORS

• The smart sensor system can optimize the performance of the individual sensors for better understanding the measurement, and the environment in which the measurement is made.

• It is adaptable to a changing environment.

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SMART SENSORS-NETWORKS

• New generation of smart sensors can be networked through the communication Interface.

• They have the capability of individual network self-identification and communication allowing reprogramming of the smart sensor system as necessary.

• The output from a number of sensors within a given region can be correlated not only to verify the data from individual sensors, but also to provide a better situational awareness.

• Such communication can be between a single smart sensor and communication hub or between individual smart sensors

themselves. ₈₂

SMART SENSORS-ADVANCEMENTS

• There are many examples of technology advancements in sensors, power, and communications that can enable future smart sensor systems.

GOALS

• Cost-effective, reliable, self-monitoring, reconfigurable, and can operate indefinitely.

ACHIEVED THROUGH

• Advanced Microprocessor technology, MEMS, sensor elements, micro-fabrication and nanotechnology.

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LOW POWERED SENSOR ELEMENTS

• Example – Sensor based on a microhotplate.

• Microfabricated hotplates offer a lower power platform for high temperature metal oxide conductometric sensors.

• Heating rates up to 106 ^oC/s and minimal power consumption due to the small thermal mass of the microhotplates.

• This sensor responds to ambient gas changes in nanoseconds having a measured transient response time-constant of 12 μs in helium.

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LOW POWERED SENSOR ELEMENTS

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LOW POWERED SENSOR ELEMENTS

• Temperature of the bridge, and hence electrical resistance, is a function of the thermal conductivity of the surrounding gas ambient.

• Sensitivity - 2.05 mohms/ppm for helium and 0.71ohms/ppm for methane at 3.6

• The microfabricated sensor elements shown have extremely low power consumption.

• 4 mW continuous and, <4 μW when operated on a duty cycle of millisecond.

• Can run for years on a small battery.

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POWER: BATTERY OR ENERGY HARVESTING

• Small scale energy systems for the smart sensor applications will generally consider batteries and energy harvesting options.

• Li-ion, Li-polymer, and metal-air rechargeable batteries.

Open circuit voltage – 3.6 Volts.

Energy Density - 160 and 130-200 Wh/kg.

• Energy harvesting –

Piezoelectric crystals or fibers, thermoelectric generators, solar cells, electrostatic, and magnetic energy capture devices.

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POWER: BATTERY OR ENERGY HARVESTING

EXAMPLE – PIEZOELECTRIC ENERGY SYSTEM.

• A piezoelectric energy system will produce a small voltage when it is physically deformed.

• Deformation can be caused by mechanical vibration that may be generated by the proper mounting of sensor in a mechanically vibrating environment.

EXAMPLE – THERMOELECTRIC GENERATORS.

• Sensitivity: 100-200 uV/°C per junction.

These two energy systems Smart Sensors can derive sufficient energy from its surroundings to provide either total or backup power for a smart sensor application.

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SMART SENSORS - WIRELESS COMMUNICATION

• The smart sensor system will require an electrical interface that will transmit the sensor outputs to an external data collection, recording or acquisition system.

• Ideally, this interface does not require wiring and can be accomplished by wireless telemetric methods.

• MEMS technology, provides a technical approach for wireless communication system development.

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EXAMPLES – POCKET SMART SENSORS

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EXAMPLES – LICK AND STICK LEAK SENSORS

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MICRO ELECTRO-MECHANICAL SYSTEMS

(MEMS)

Micro-Electro-mechanical Systems (MEMS)

• Micro-fabrication makes the MEMS.

• Unlike Micro Electronic Circuits. MEMS have holes, cavity, channels, cantilevers, membranes, etc, and, in some way, imitate `mechanical' parts.

• This has a direct impact on their manufacturing process.

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Micro-Electro-mechanical Systems (MEMS)

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ENERGY DOMAINS

• Thermal (temperature, heat and heat flow)

• Mechanical(force, pressure, velocity, acceleration, position)

• Chemical(concentration, pH, reaction rate)

• Magnetic(field intensity, flux density, magnetization)

• Radiant (intensity, wavelength, polarization, phase)

• Electrical (voltage, charge, current)

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SCALING

• Let the dimensions be scaled by factor S:

L

^new

= L

^{old *}

S , B

^new

= B

^{old *}

S , H

^new

= H

^{old *}

S

VOLUME: V

^new

= V

^{old *}

S

³

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SCALING

97

SCALING

98

•

The force due to surface tension scales as S¹.

•

The force due to electrostatics with constant field scales as S².

•

The force due to certain magnetic forces scales as S³.

•

Gravitational forces scale as S⁴.

WATER BUG

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•

The weight of the water bug scales as the volume, or S³,

•

While the force used to support the bug scales as the surface tension (S¹) times the distance around the bug’s foot (S¹), and the force on the bug’s foot scales as S¹ × S¹ = S^2.

•

When the scale size, S, decreases, the weight decreases more rapidly than the surface tension forces.

•

Changing from a 2-m-sized man to a 2-mm-sized bug decreases the weight by a factor of a billion, while the surface tension force decreases by only a factor of a million.

•

Hence, the bug can walk on water.

WATER BUG

100

GRAVITATIONAL FORCE- SCALING

101

GRAVITATIONAL FORCE- SCALING

102

• Gravitational potential energy scales as S⁴.

• If the dimensions of a system are scaled from meters (human size) to 0.1 mm (ant size), the gravitational potential energy scales as: (1/10000)4 = 1/10,000,000,000,000,000.

• The potential energy decreases by a factor of ten trillion.

• This is why an ant can walk away from a fall that is 10 times it’s height, and we do not!

ADVANTAGES-MEMS

103

•

Minimize energy and materials use in manufacturing, low cost.

•

Redundancy and arrays.

•

Integration with electronics.

•

Reduction of power budget.

•

Faster devices, Increased selectivity and sensitivity.

•

Exploitation of new effects through the breakdown of continuum theory in the micro-domain.

•

Improved reproducibility (batch fabrication).

•

Improved accuracy and reliability.

•

Minimally invasive (e.g. pill camera).

MEMS - SOME APPLICATIONS

104

MEMS - SOME APPLICATIONS

105

MEMS - SOME APPLICATIONS

106

MEMS - SOME APPLICATIONS

107

• Crash Sensing for Airbag Control

• Vehicle Dynamic Control

• Rollover Detection

• Antitheft Systems

• Electronic Parking

• Brake Systems

• Vehicle Navigation Systems

MEMS - SOME APPLICATIONS

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Automotive Airbag Accelerometer

The accelerometer structure is a bulk micromachined suspended silicon mass over a fixed metal electrode that provides a capacitive output as a function of acceleration.

• The sensor is created by anodically bonding a micromachined silicon wafer to a glass wafer and etching away the bulk of the silicon, leaving only the suspended silicon mass.

Sensor Electronic Circuit

MEMS - SOME APPLICATIONS

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MEMS - SOME APPLICATIONS

110

• Electronics occupy the majority of the 3 mm² chip area.

• 2-axis device

MEMS - SOME APPLICATIONS

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Virtual Reality (VR) Systems

• A VR systems’ utility is intimately connected to how convincingly it can recreate life.

• Accelerometers and angular rate sensors) are required to achieve credibility.

• Accelerometer data are converted into positional information via double integration.

• Angular rate sensors determine rotational position by integrating the angular rate.

MEMS - SOME APPLICATIONS

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MEMS - SOME APPLICATIONS

BIONIC EYE

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MEMS – PILL CAMERA

MEMS - SOME APPLICATIONS

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MEMS - SOME APPLICATIONS

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MEMS - SOME APPLICATIONS

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MEMORY MEMS - MILLIPEDES

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Array of AFM tips write and read bits – Potential for low and adaptive power MILLIPEDES

Highly Parallel, very dense AFM data Storage system – 500 Gb / Sq. inch

NANO-INSTRUMENTATION

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• Nanotechnology emerges from a broad range of scientific fields that converge due to the continuous miniaturization.

• In 1960’s critical dimensions reached the level of 100 μm.

• 20 years later “micromechanics” reached 1 μm. During this evolution fabrication tools were changed significantly, and models of our understanding developed into finer and finer details.

• But the basic understanding was based on continuum mechanics, where the atomic structure of matter is mostly neglected.

NANO-INSTRUMENTATION

120

• When critical dimensions reached the 100 nm level around year 2000, traditional machining became technically problematic.

• The concept of continuum mechanics broke down as the atomic structure of materials becomes directly relevant for the mechanical properties of materials.

• This is the scientific challenge of nanotechnology: the traditional concepts break down, and so do the terminology and parameters that we use to describe the phenomena.

• New concepts and terminology have to be developed, and these are likely to be significantly more complex than we have been used to.

NANO-INSTRUMENTATION

121

• Nanotechnology includes the investigation and manufacture of any mechanical, electronic, chemical, and biological system by molecular assembly, the so-called bottom-up approach, as well as the so-called top-down approach by miniaturization of processes and products.

NANO-INSTRUMENTATION

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Examples of critical dimensions are:

• Roughness of a sheet metal for car body production where paintability is the required function.

• The edge in an optical filter for telecommunication, where the edge itself may be several μm.

• Porosity of polymer molecular membranes for advanced drug delivery.

• Distances in molecules, where the function is associated with a particular configuration.

NANO METROLOGY

• INTRFEROMETRY

• SCANNING ELECTRON MICROSCOPE

• ATOMIC FORCE MICROSCOPY

• XRAY ABSORPTION SPECTROMETRY

• ELECTRON SPECTROSCOPY FOR CHEMICAL ANALYSIS

• AUGER

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NANO METROLOGY

Displacement Interferometry

• Displacement Interferometry is based on the light-dark transitions corresponding to constructive and destructive interferences in a classical Michelson interferometer setup.

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DISPLACEMENT

MOVING OPTICAL ELEMENT MEASUREMENT BEAM

MEASUREMENT OPTIC FROM LASER

(1 OR 2 WAVELENGTHS)

RECOMBINED BEAM

FIXED REFERENCE OPTICAL ELEMENT

Displacement d = λ/2(N+∆  /2  )

Resolution – 10nm – 0.1 nm

NANO METROLOGY SCANNING

ELECTRON MICROSCOPE

NANO METROLOGY SCANNING ELECTRON MICROSCOPE

• The SEM uses electrons instead of light to form an image.

• A beam of electrons is produced at the top of the microscope by heating of a metallic filament.

• The electron beam follows a vertical path through the column of the microscope. It makes its way through electromagnetic lenses which focus and direct the beam down towards the sample.

• Once it hits the sample, other electrons

• ( backscattered or secondary ) are ejected from the sample. Detectors collect the secondary or backscattered electrons, and convert them to a signal that is sent to a viewing screen similar to the one in an ordinary television, producing an image.

How do we get an image?

156 electrons!

Image Detector

Electron gun

288 electrons!

Electron beam-sample interactions

 The incident electron beam is scattered in the sample, both elastically and inelastically

 This gives rise to various signals that we can detect (more on that on next slide)

 Interaction volume increases with increasing acceleration voltage and decreases with increasing atomic number

Signals from the sample

Incoming electrons Secondary electrons

Backscattered electrons

Auger electrons

X-rays

Cathodo-

luminescence (light)

Sample

Where does the signals come from?

• Diameter of the interaction

volume is larger than the electron spot

 resolution is poorer than the size of the electron spot

Secondary electrons (SE)



Generated from the collision between the incoming electrons and the loosely bonded outer electrons



Low energy electrons (~10-50 eV)



Only SE generated close to surface escape (topographic information is obtained)



Number of SE is greater than the number of incoming electrons



We differentiate between SE1 and

SE2

 The secondary electrons that are generated by the incoming electron beam as they enter the surface

 High resolution signal with a resolution which is only limited by the electron beam diameter

SE1

Backscattered electrons (BSE)

 A fraction of the incident electrons is retarded by the electro-magnetic field of the nucleus and if the scattering angle is greater than 180° the electron can escape from the surface

 High energy electrons (elastic scattering)

 Fewer BSE than SE

SE2

 The secondary electrons that are generated by the backscattered electrons that have returned to the surface after several inelastic

scattering events

 SE2 come from a surface area that is bigger than the spot from the

incoming electrons  resolution is poorer than for SE1 exclusively

Sample surface

Incoming electrons SE2

ATOMIC FORCE MICROSCOPY

135

Photodiode

Laser

Scanner

Cantilever + Sharp probe Photodiode

Laser

Scanner

Cantilever + Sharp probe Photodiode

Laser

Scanner

Cantilever + Sharp probe Photodiode

Laser

Scanner Photodiode

Laser

Scanner Photodiode

Laser

Scanner

Cantilever + Sharp probe Photodiode

Laser

Scanner

Cantilever + Sharp probe Photodiode

Laser

Scanner

Cantilever + Sharp probe Photodiode

Laser

Scanner

Cantilever + Sharp probe Photodiode

Laser

Scanner

Cantilever + Sharp probe Photodiode

Laser

Scanner

Cantilever + Sharp probe Photodiode

Laser

Scanner

Cantilever + Sharp probe

During scanning, the sample surface may

lift the cantilever up, resulting in corresponding move up of the optical reflection spot on the photodiode. However, this single photodiode couldn’t detect small position change of the spot.

(Click for the next)

Let’s split the photodiode into two – the “top” and the “bottom”.

Assume that the optical reflection spot originally locates in the exactly middle of this split photodiode, resulting in the exactly same voltage output from the two photodiodes. So, the difference between the “top” (T) and the “bottom” (B) is zero.

(Click for the next)

Optical level detection

Photodiode

Laser

Scanner

Cantilever + Sharp probe

Voltage Difference Between Top & Bottom Photodiodes

Photodiode

Laser

Scanner

Cantilever + Sharp probe

Top-Bottom Signal (V) or Deflection (nm) or Force (nN)

Quad photodiode to detect Both vertical and horizontal Movements of the light spot.

With this “split photodiode”, any slight vertical movement of the reflection spot position is detected by checking the

difference between the “top” and the “bottom” photodiode dutputs (the “T-B signal”).

• Direct mechanical contact between the probe and the sampler surface

– Essential difference from traditional microscopy

• How AFM “feels” the surface topography?

– Optical level detection

• Constant-height scan versus Constant-force scan

How AFM works

Constant-height scan

Constant-force scan

Optical level detection in constant-force mode

Photodiode

Laser

Z scanner

Cantilever + Sharp probe Photodiode

Laser

Z scanner

Cantilever + Sharp probe Photodiode

Laser

Z scanner

Cantilever + Sharp probe

In constant-force mode, whenever the sample surface topography would result in the cantilever deflection change, the other end of cantilever would be accordingly

adjusted so that the cantilever deflection angle, and hence the contact force, would keep

constant.

Horizontal

Feedback control in constant-force mode

P.I.D. Control

In constant-force mode, the cantilever’s vertical position is adjusted by an

electronic feedback loop, with the T-B signal as the input and the vertical scanner voltage as the output.

Vertical

Constant-force scan vs.

constant-height scan

Constant-force mode Constant-height mode

Constant-force scan vs.

constant-height scan

Constant-force

• Advantages:

– Large vertical range – Constant force (can be

optimized to the minimum)

• Disadvantages:

– Requires feedback control

– Slow response

Constant-height

• Advantages:

– Simple structure (no feedback control) – Fast response

• Disadvantages:

– Limited vertical range (cantilever bending and detector dynamic range) – Varied force

How AFM works

• Direct mechanical contact between the probe and the sampler surface

– Essential difference from traditional microscopy

• How AFM “feels” the surface topography?

– Optical level detection

• Constant-height scan and constant-force scan

• Feedback control in constant-force scan

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