Lesson 3

Sensors and Sensor Networks

What are sensors and what are they for?

Various sensors and their features

What are sensor networks & their interconnections?

Sensor network technologies & applications

Sensor and Actuator A sensor is a device that measures a physical quantity and

converts it into a signal which can be read by an observer

or by an instrument. (Wikipedia)

An actuator is a device for moving/controlling a mechanism/system,

or generate some output, e.g., motor, LED, buzzer, speaker, etc.

Sensors and actuators are bridges between real and digital worlds

Sensor

Input Signal Output Signal

Various Sensors

Phidgetsセンサー

Moteセンサー

Force sensor Touch sensor

Vib. sensorMotion sensor

Solar Cell

Digital Infrared Ranging

Compass

Touch Switch

Pressure Switch

Limit Switch

Magnetic Reed Switch

Magnetic Sensor

Miniature Polaroid Sensor

Polaroid Sensor Board

Piezo Ultrasonic Transducers

Pyroelectric Detector

Thyristor

Gas Sensor

Gieger-MullerRadiation Sensor

Piezo Bend Sensor

Resistive Bend Sensors

Mechanical Tilt Sensors

Pendulum Resistive Tilt Sensors

CDS Cell Resistive Light Sensor

Hall EffectMagnetic Field

Sensors

Compass

IRDA Transceiver

IR Amplifier Sensor

IR ModulatorReceiverLite-On IR

Remote Receiver

Radio ShackRemote Receiver

IR Sensor w/lens

GyroAccelerometer

IR ReflectionSensor

IR Pin Diode

UV Detector

Metal Detector

General Ubiquitous System Model

Sensors

Actuators

人人体物体器具空間環境

ユビキタス

情報自動な取得、保存、処理、管理、分析、判断、使用、など

Multimedia Information

Comfortable Services

Contexts

Context-Aware

A ubiquitous/pervasive/AmI/CPS system can be regarded as a special

kind of information systems which use sensors to acquire various

information (of called context), process the contextual information,

and then take some responses through actuators.

IntelligentProcessing

Sensing & Action(Sensor Network)

Real/Physical World

Types of Sensors Acoustic, sound, vibration

-- Microphone, geophone, seismometer, accelerometer, …

Automotive, transportation

-- Speedometer, map sensor, water sensor, parking sensor, …

Chemical

-- Sensing carbon, gas, hydrogen, oxygen, smoke, etc.

Electric, magnetic, radio

-- Hall effect, magnetometer, metal detector, telescope, …

Environment, weather, moisture, humidity

-- Leaf sensor, rain/snow gauge, pyranometer, …

Flow, fluid velocity

-- Air flow meter, flow sensor, water meter, …

Ionising radiation, subatomic particles

-- Cloud chamber, neutron detection, particle detector, …

Types of Sensors (Cont.)

Navigation instruments

-- Air speed indicator, depth gauge, gyroscope, turn coordinate, …

Position, angle, displacement, distance, speed, acceleration

-- Accelerometer, position sensor, tilt sensor, ultrasonic sensor, …

Optical, light, imaging

-- Colorimeter, electro-optical sensor, infra-red sensor, photodiode, …

Pressure

-- Barometer, boost gauge, pressure gauge, tactile sensor, …

Force, density, level

-- Force gauge, level sensor, load cell, hydrometer, …

Thermal, heat, temperature

-- Heat sensor, radiometer, thermometer, thermistor, …

Proximity, presence

-- Motion detector, occupancy sensor, touch switch, ...

A list of various kinds of sensors in Wikipedia

Sensor Performance Range

maximum and minimum values that can be measured

Resolution or discrimination smallest discernible change in the measured value

Linearity

maximum deviation from a ‘straight-line’ response

Sensitivity

a measure of the change produced at the output for a given change

Error – Accuracy/Precision difference betw. measured & actual values Random/System Errors

SystemError

Temperature Sensors Resistive Thermometers

- typical devices use platinum wire, linear but has poor sensitivity

Thermistors

- use materials with a high thermal coefficient, sensitive, highly non-linear

pn junctions

- a semiconductor device, linear, easy to use, limited range (-50C to 150 C)

Thermometer Thermistor pn junction

Force Sensors Strain gauge

- stretching in one direction increases the resistance of the device,

while stretching in the other direction has little effect

- can be bonded to a surface to measure strain

- used within load cells and pressure sensors

A strain gauge

Direction of sensitivity

A force sensor videoPressure sensing principle

Motion Sensors

Motion sensors measure quantities such as velocity and acceleration

can be obtained by differentiating displacement

differentiation tends to amplify high-frequency noise

Alternatively can be measured directly

some sensors give velocity directly

e.g. measuring frequency of pulses in the counting techniques described earlier gives speed rather than position

some sensors give acceleration directly

e.g. accelerometers usually measure the force on a mass

Accelerometer Principles of Motion Sensing

Acceleration Sensor

Sound Sensors

Microphones

a number of forms are available

e.g. carbon (resistive), capacitive, piezoelectric and moving-coil microphones

moving-coil devices use a magnet and a coil

Ultrasonic Sensor

Ultrasonic sensors are used for position measurements

Sound waves emitted are in the range of 2-13 MHz

Sound Navigation And Ranging (SONAR)

Radio Detection And Ranging (RADAR) –ELECTROMAGNETIC WAVES !!

15° - 20°

Infrared Source IR Detector

CO2 Gas Sensor

CO2 sensor measures gaseous CO2 levels in an environment

Measures CO2 levels in the range of 0-5000 ppm

Monitors how much infrared radiation is absorbed by CO2

molecules

Biosensors A biosensor is an analytical device for the detection of an analyte

that combines a biological component with a physicochemical

detector component. (Wikipedia)

Health check, environment monitoring, food analysis, …

Incorporation of a biomolecule in order to detect something

Species to be detected (analyte)

Filter Recognition Layer

Transducer Electronics Signal

Recognition Layer

Electronic Tongue using Biosensors

Taste cell

Nerve cell

Taste compounds

Electric

responses

Brain

Taste

reception

Biological taste system

Artificial liquid system - electronic tongue

Sensor

responses ComputerSensor

arrayPattern

recognition

Y. Vlasov, A. Legin, A. Rudnitskaya, Anal. Bioanal. Chem. 2002, 373, 136.

Nanosensors

Nanosensors are any biological, chemical, or sugery sensory points

used to convey information about nanoparticles to macroscopic world.

Their uses mainly include various medicinal purposes and as gateways

to build other nanoproducts, such as computer chips that work at

nanoscale and nanorobots. (Wikipedia)

Medicinal uses of nanosensors to accurately identify particular cells

or places in the body.

Using nanosensors to build smaller integrated circuits, as well as

incorporating them in other chip/devices

Nanosesnors are new, ongoing research,

potential huge applications

MEMS and NEMS MEMS (Micro-Electro-Mechanical System) is the technology of

very small mechanical devices driven by electricity. (Wikipedia)

Range from 1 to 1000 micrometres in size (i.e. 0.001 to 1 mm)

Micromachines (in Japan), or Micro Systems Technology - MST (Europe)

NEMS (Nano-Electro-Mechanical System), similar but smaller (<100nm)

MEMS perform 2 basic types of functions: sensors or actuators.

- both act as transducers converting one signal into another.

MEMS actuators: electrical signal

physical phenomena to move or control mechanisms.

MEMS Sensors work in reverse to actuators

~ 1mm

MEMS and NEMS (cont.)

MEMS comprising mechanical and discrete electronic components

MEMS design is different from macro devices

MEMS design are based upon Silicon IC chips design

Micro-actuators: micro-motor, micro-mirror, micro-fluid pump, etc.

Micro-sensors: micro-accelerometer, micro-gyroscope, etc.

Electrostaticmotor

Hinge

Actuator Gyroscope

MEMS Gyroscope Chip

Video for Introduction to MEMS

A gyroscope is a device for measuring or maintaining orientation

Popular Sensors in Smart Phones

Android Sensor Java Development APIs

Sensors in Automotive Applications

Suspension Systems

Position Sensing

Chassis height

Electronic Power Steering

Position Sensing

Motor Commutation

Current Sensing

Safety Systems

Airbag Diagnostics & Control

Occupant Sensing

ABS/Traction - Wheel Speed Sensing

Convenience Systems

Door lock Position Sensing

Window Position/Speed Sensing

Window/Sunroof Direction

Sensing for anti-pinch

Seating Systems

Various Contactless Switches

Motor Controllers/Drivers

Wiper Systems

LCD screens

Powertrain Applications

Cam/Crank Sensors

Transmission Speed

Sensors

Throttle Position Sensors

EGR Valve Position

Sensors

Valve Position Sensors

Current Sensing

Google Self-Driving Car Project

Sensor Networks A sensor network (SN) is consisted of multiple interconnected sensors.

A wireless sensor network (WSN) consists of spatially distributed

autonomous sensors (called sensor nodes) to cooperatively monitor

physical or environmental conditions Sensors + Wireless Networks

San Fransisco’s Moscone Center equipped with sensor network

Traditional Networks vs WSN

An Introduction Video about Wireless Sensor Networks

Sensor Nodes

A sensor node, also called a mote in North America, is a WSN node that is capable of performing some processing, gathering sensory information and communicating with other connected nodes in the WSN.

Examples for Wireless Sensor Nodes

MICA Mote

Rene Mote

weC Mote

Dot Mote

Laser diodeIII-V process

Passive CCR comm.MEMS/polysilicon

SensorMEMS/bulk, surface, ...

Analog I/O, DSP, ControlCOTS CMOS

Solar cellCMOS or III-V

Thick film batterySol/gel V2O5

Power capacitorMulti-layer ceramic

1-2 mm

Example: Berkeley Motes, Smart Dust

• 4 KB RAM, 4 MHz CPU• 19.2 Kbps, 12m

Sensors in a Berkeley Mote

General Features of Sensor Node

Small Size : few mm to a few inches

Limited processing and communication

MHz clock, MB flash, KB RAM, 100’s Kbps (wireless) bandwidth

Limited power (MICA: 7-10 days at full blast)

Failure prone nodes and links (due to deployment, fab, wireless medium, etc.)

But easy to manufacture and deploy in large numbers

Need to offset this with scalable and fault-tolerant OS’s and protocols

Sensor-node Operating System

Issues

Size of code and run-time memory footprint

Embedded System OS’s inapplicable: > 100KB ROM

Workload characteristics

Continuous ? Bursty ?

Application diversity

Want to reuse sensor nodes

Tasks and processes

Scheduling, hard and soft real-time

Power consumption

Communication

Representative OS TinyOS, Contiki, NanoPK, LiteOS

TinyOS Layers and Functions

RFM

Radio byte

Radio Packet

i2c

Tempphoto

Messaging Layer

clocksbit

byte

packet

Routing Layer

sensing applicationapplication

HW

SW

ADC

messaging

routing

TinyOS Language and Size

0

500

1000

1500

2000

2500

3000

3500

Byte

s

InterruptsMessage DispatchInitilizationC-RuntimeLight SensorClockSchedulerLed ControlMessaging LayerPacket LayerRadio InterfaceRouting ApplicationRadio Byte Encoder

Scheduler:

144 Bytes code

Totals:

3430 Bytes code

226 Bytes data

• Event-driven execution (reactive mote)

• Use a variant of language C called NesC

Limited power they can harvest or store

Ability to withstand harsh environmental conditions

Ability to cope with node failures

Mobility of nodes

Dynamic network topology

Communication failures

Heterogeneity of nodes

Large scale of deployment

Unattended operation

Nodes are scalable, only limited by bandwidth of gateway node

WSN Characteristics

Typical Multiple WSN Architecture

A sensor network normally constitutes a wireless ad-hoc network,

and each sensor supports a multi-hop routing algorithm where

nodes function as forwarders, relaying data packets to a base station.

WSN Topologies

Sensor Network System

Interface electronics, radio

and microcontroller

Soil moisture probe Senor

Node

Antenna

Gateway

Server

Internet

Communications barrier

Sensor field

Sensor Network System

Gateway

Server

Internet

Sensor fieldWatershed

Multiple Sensor Networks System

S

S

S

S

SS

S

SSS

S S

S

S

Sensor net

Internet

Access

Node

Storage

Distribution field of

phenomena that

can be detected

measured

Physical

Phenomena

User

Sensors that

detect event Sensors that

notify access

node

Sensor

net

Sensor

net

40

WSN System Issues

Applications

service

network

system

architecture

data mgmt

Monitoring & Managing Spaces and Things

Technologies

MEMS

sensingPower

Comm. uRobots

actuate

Miniature, low-power connections to the physical world

Proc

Store

WSN System Platforms

OS

Hardware

Application

Signal Proc.Detection

Power Supply

StorageNetworkingClassificationTracking

RoutingFiltering Transport

Link Layer

TimersTime Sync

SensorsMCU

Radio Storage

Scheduler

Storage

OTAP

Query Processing

Heap FilesIndicesDissemination

Interrupts

Arbiters Queues

ZigBee, 802.15.4, EnOcean, IETF PRL, etc

Time Sync

Sensor

router

– “the software”

– Network, Security &

Application layers

– Brand management

IEEE 802.15.4

– “the hardware”

– Physical & Media Access

Control layers

Wireless Sensor Network Standards IEEE 802.15.4 & ZigBee

PHY

868MHz / 915MHz / 2.4GHz

MAC

Network

Star / Mesh / Cluster-Tree

Security32- / 64- / 128-bit encryption

Application

API

ZigBeeAlliance

IEEE 802.15.4

Customer

Sensor Data Management

phenomena

sensors

observer

Observer interested in phenomena with certain tolerance

Accuracy, freshness, delay

Sensors sample the phenomena

Sensor Data Management

Determining spatio-temporal sampling schedule

Difficult to determine locally

Data aggregation

Interaction with routing

Network/Resource limitations

Congestion management

Load balancing

QoS/Realtime scheduling

Sensor Data Query

Sink

Select temp from

Fully aggregated queries Un-aggregated queries Partially aggregated queries

Sensing Information Fusion One sensor is (usually) not enough

- Noisy, limited accuracy, unreliable – failure, environment restriction, etc.

Sensor fusion - Combine readings from several sensors into a better one

Fusion Interpretation

Sensor 2

Sensor 3

Sensor N

Sensor 1

Sensing Perception

Preprocessing

Preprocessing

Preprocessing

Preprocessing

(1.10, 1.06) 1.08

(0.92, 0.96) 0.94

(0.30, 0.36) 0.33

(0.94, 0.96) 0.95

1.08+0.94+0.953 0.99

ObjIgnore 0.43

0.33?

Sensing Information Fusion

Preprocessing

- 'Cleanup’ the sensor readings before using them, e.g.,

noise reduction, re-calibration, unify the format, etc.

Data Fusion

- Combine data from different sources

- Measurements from different sensors

- Measurements from different positions

- Measurements from different times

Techniques that take into account uncertainties in data sources

- Discrete Bayesian methods

- Neural networks

- Kalman filtering

Sensor Web

Sensor Web - Wikipedia

Semantic Sensor Web

Sensor Web (Cont.)

Access the following websites to learn more about

various sensors, sensor networks, and their features,

technologies, applications, etc.

Sensor - Wikipedia

List of sensors - Wikipedia

MEMS – Wikipedia

Android Sensor Java Development APIs

Wireless sensor network – Wikipedia

TinyOS – Wikipedia

An Introduction Video about Wireless Sensor Networks

Others you like Important to get materials from Web!!

Homework