T325: TECHNOLOGIES FOR DIGITAL MEDIA Second semester – 2010/2011 Tutorial 1 1

T325: TECHNOLOGIES FOR DIGITAL MEDIASecond semester – 2010/2011Tutorial 1

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Outline

General introduction to the T325 course Power for Digital Media

Introduction Battery technology Fuel cells. Power from the environment. Where does the energy come from?

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Arab Open University – Lebanon T325 - Spring 2011

Learning outcomes Course breakdown Assessments Study calendar Plagiarism

General introduction3

Learning outcomes of the Course

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To introduce you to the fundamental principles of selected technologies for digital media

To enable you to become a more independent learner, able to keep up to date in digital media technologies

To enable you to integrate knowledge from several sources in the presentation of an argument

To enable you to analyse, critique and synthesise examples of third-party material

To improve your understanding of the complexities of technological systems in terms of social, ethical and economic factors as well as the underlying technologies.


Course breakdown

Block 1: Enabling technologies You will be presented with materials on hardware,

such as disc drives, solid state (e.g. flash) memory, batteries, display screens and capture devices, and algorithms, such as error control coding and MPEG compression techniques.

Block 2: Intellectual property and security issues You will be presented with materials on the

technologies associated with digital rights management and watermarking.

Block 3: Mobile broadband You will be presented with materials on

developments designed to support broadband applications in a mobile world.

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Course Assessment

Continuous assessment (50% of the course grade) TMAs: Two TMAs worth 10% of course grade each MTA: One MTA worth 30% of course grade

Final Exam: One Final Exam worth 50% of course grade

You must obtain: At least 40% average on the Continuous

assessment At least 40% average on the final exam at least 50% overall in order to pass the course.

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Stu

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Week Start date Course block Course section(s) Assignments /due date

1 21/02/11Block 1: Enabling

technologiesPower for digital media

2 28/02/11 Information storage

3 07/03/11 Error control coding

4 14/03/11 Seeing and hearing:

multimedia

5 21/03/11 Video and audio coding

6 28/03/11

7 04/04/11Block 2: Intellectual property and security

issues

Intellectual property rights & Security

TMA0104/04/2011

8 11/04/11 Digital rights management &

Digital watermarking

9 18/04/11Block 3 Mobile

broadband Mobile evolution & Network architecture

MTA

10 25/04/11

11 02/05/11 Access and modulation

12 09/05/11 TMA02

09/05/2011

13 16/05/11 Better and beyond

14 23/05/11

15 30/05/11 Revision 7 Arab Open University – Lebanon T325 - Spring 2011

Plagiarism

Plagiarism is the act of taking some one else's work and passing it off as you own.

Using extracts, even those as short as phrases or single sentences, from another author (including authors of T325 course materials) without saying that you are doing so is plagiarism.

Plagiarism is not acceptable in any written material, because you are in effect stealing someone else's ideas.

When referring to or quoting from other people's work in your documents, the original source must always be properly cited.

Please refer to the T325 Course Guide for more information on how to avoid plagiarism

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Power for Digital Media9

Introduction

Power consumption is one of the main constraints on the design of electronic goods, and is a major consideration for mobile devices and even for mains-power equipment

most of the power consumed ends up as heat. overheating of electronic circuits damages the

components. Need to reduce energy consumption in order to

combat global warming.

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Introduction

Power needs of digital equipment have generally been increasing Powering consumer electronic and computer products alone in

the UK every year - that’s 23% of the average household electricity bill.

There is a vast amount of research and development effort being put into improving the technologies.

The lithium ion battery first commercialized by Sony in 1991, it stores energy a factor of 5 higher than that stored by the much older lead-acid batteries.

Receivers for digital audio broadcasting (DAB) available at the moment typically consume a lot more power than receivers for analogue radio broadcasts. In the extreme, it is possible to construct a receiver for analogue

AM broadcasts that requires no separate power source (‘crystal radio’ or ‘crystal set’).

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Introduction


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Battery technology13

Batteries produce electricity from a chemical reaction, called an electrochemical reaction.

You get a ‘battery’ when several cells are connected together


Battery technology


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The chemical reaction depends upon the material used to make the anode, the material used to make the cathode and the material used for the electrolyte.

Different combinations of chemical are used for different batteries: lead-acid batteries, alkaline batteries, nickel--cadmium (NiCd), nickel-metal hydride (NiMH), lithium and lithium-ion (Li-ion) batteries.

The chemistry, as well as the details of the physical construction, determines whether the batteries can be recharged or not.


Two categories of batteries Primary batteries

Manufactured to be used once Examples: alkaline and lithium batteries

Secondary batteries Rechargeable


Battery technology


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Chemistry-related terminology Elements: The purest substances of the physical

world are the elements (nickel, cadmium, zinc, potassium,).

Compounds: Most elements can join to other elements to form compounds. (hydrogen joined (in an appropriate way) to oxygen forms water.)

Chemical reaction: When elements combine to form a compound the process is called a chemical reaction. Chemical reactions can also take place between two or more compounds or between elements and compounds.

Atoms, molecules and ions: The basic building block of an element is an atom. An atom consists of a nucleus, which has a positive electrical charge, and electrons, which have a negative electrical charge.

Battery technology


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Voltage The voltage of a battery cell is determined

primarily by the materials used for the electrodes and the electrolyte.

To get higher voltages, cells are connected in series, with the result that the voltages add.

The voltage determined by the chemistry will only be found at its maximum when no current is being drawn from the battery.

If too much current is drawn, and also as the battery becomes discharged, the voltage at the battery terminals will reduce.

Battery technology


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Maximum current output The current drawn from the battery in any

application is determined by the load and by the battery voltage.

A battery that can deliver high currents will have a low internal resistance.

One that cannot deliver high currents will have a high internal resistance.



Battery technology


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Capacity (running time) The words ‘power’ and ‘energy’ are used

loosely in common speech Power is the rate at which energy is being

transferred. In SI units Energy is measured in joules (J) and power

in watts (W) 1W corresponding to energy being

transferred at a rate of one joule per second (1 J/s).

SELF-ASSESSMENT ACTIVITIES


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Activity 1.2 : Identify the misuse of terms such as energy, power or watts

in the following extract from a newspaper report. Rewrite it so that it is technically correct

“The company says that one of its typical phones needs a charge of 160 milliamps on Britain’s 240-volt electric grid. That means it is an appliance rated at 38 watts -- more than double the energy needed for a typical energy-saving light bulb. (Source: Alok Jha, 2005)”

21Arab Open University-Lebanon

TutorialI 2010



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Activity 1.2 : The rating of 38 W is a power rating, not energy. Also, the

160 mA is an electrical current, not a charge, so it would be better to write:

“The company says that one of its typical phones needs a charging current of 160 milliamps on Britain’s 240-volt electric grid. That means it is an appliance rated at 38 watts -- more than double the power needed for a typical energy-saving light bulb.”



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Activity 1.5 : (a) If the battery voltage is V volts and the load has a

resistance of R ohms, what current flows from the battery? (b) On a single graph, plot the current against resistance

for a 1.5V battery and a 3.6V battery, for a resistance range of 10 to 200 ohms.


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Activity 1.5 : (a) From Ohm’s law, the current is given by the voltage

divided by the resistance, V/R.

(b)


Capacity (running time) The length of time a battery can supply a

given power is determined by the amount of energy stored in the battery.

for example, a battery storing 10 kJ (10000 J) could ideally run for 10000 s delivering 1W.

Question: express the battery capacity in terms of amp-hours (Ah), amps multiplied by hours.

For example, a battery with a capacity of 1 Ah could supply 1 A for 1 h, or else it could supply 2 A for 0.5 h or 0.5A for 2 h. More generally, if a battery can run at a current i for t hours, then its capacity is capacity= i × t.




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Activity 1.7 A 1.2V battery has a capacity of 800

mAh. How long could it run if the load uses 50 mA?



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Activity 1.8 : A 1.2V battery has a capacity of 800

mAh. How long could it run if the load has a resistance of 30ohm?

The current drawn from the battery is 1.2/30 = 0.04 A, which is 40 mA.It could run for 800/40 = 20 h.


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Capacity (running time) The time t the battery can be used is given

by t=capacity/i. Small digital devices, such as mobile phones,

typically draw rather less than 1A, so it is more convenient to work in terms of milliamps (mA) rather than amps,

A 1.2V battery has a capacity of 800 mAh. How long could it run if the load uses 50 mA?.

power = current x voltage. Arab Open University – Lebanon

T325 - Spring 2011



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Activity 1.9

A 1.2V battery is specified to have a capacity of 800 mAh. What energy does the battery store? Give your answer in both watt-hours and joules.

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Activity 1.9 : 800mAh is 0.8 Ah. So the battery stores 1.2 x 0.8 = 0.96

Wh, which is 0.96 x 3600 = 3456 J. Since the 800 mAh specification for the battery capacity

can only be approximate, and the usable energy is anyway dependent upon factors such as temperature and the current being drawn from the battery, it would not be meaningful to express the energy stored in the battery to four significant figures. Without knowing any further details of variation that could be expected from the capacity, I would round the answer here to two significant figures, giving it as 3500 J


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Activity 1.10 :

What is 1kWh expressed in joules?

1000 x 3600 = 3 600 000 J, which is 3.6 MJ.

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Weight and size: figures of merit


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Comparing batteries: weight, size but also capacity An AAA battery is smaller and lighter than an AA

battery, but generally has a lower capacity. different technologies (different chemistries

and different physical constructions) can give different capacities for the same size or weight.

Figures of merit for battery technologies: numbers expressing how much capacity you can get for a given size or how much for a given weight.


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Volumetric energy density is the amount of energy stored per unit volume. It can be expressed in units of joules per metre cubed (J/m3);

Gravimetric energy density (also known as specific capacity) is the amount of energy stored per unit mass. Again, there are various units that might be used, such as joules per kilogram (J/kg), watt-hours per gram (Wh/g) and kilowatt-hours per kilogram (kWh/kg).



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Volumetric power density is the power that can be delivered, per unit volume. There are various units that could be used, such as watts per centimetre cubed (W/cm3) or watts per litre (W/L).

Gravimetric power density (also known as specific power) is the amount of power that can be delivered per unit mass. Again, there are various units that might be used, such as watts per kilogram (W/kg) or watts per gram (W/g).




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Activity 1.13 Suppose a battery has the following parameters:

voltage, 1.2V capacity, 800mAh weight, 24 g volume, 8.4cm3

Calculate the volumetric energy density and the gravimetric energy density of this battery.

For the volumetric energy density, give your answer in both J/cm3 and Wh/L, and for the gravimetric energy density give your answer in both J/kg and Wh/kg. Give all your answers to two significant figures.



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Activity 1.13 : Battery capacity = 1.2 x 0.8 = 0.96 Wh. In joules, this is 0.96 x 3600 = 3456 J.

To three significant figures, 3460 J (use three significant figures for intermediate results).

Volume = 8.4cm3, which is 0.0084 L. Volumetric energy density = 3460/8.4 = 410 J/cm3. Or, 0.96/0.0084 = 110 Wh/L. Mass = 24 g, which is 0.024 kg. Gravimetric energy density = 3460/0.024 = 140 000 J/kg. Or, 0.96/0.024 = 40 Wh/kg.


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Activity 1.13 Suppose the battery of Activity 1.13 can

deliver a current of 1A. Calculate its volumetric power density in W/L and its gravimetric power density in W/kg, assuming the battery voltage is 1.2V.

Drawing such a high current, the battery voltage will fall quite quickly. Calculate the same figures as in part (a) for when the battery voltage has dropped to 0.8V.



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Activity 1.14 : (a) 1 A at 1.2V is a power of 1.2W.

Volume (from previous activity) is 0.0084 L. So the volumetric power density is 1.2/0.0084 = 140 W/L.

The mass (from the previous activity) is 0.024 kg, so the gravimetric power density is 1.2/0.024 = 50 W/kg.

(b) 1 A at 0.8V is a power of 0.8W. So the volumetric power density is 0.8/0.0084 = 95 W/L.

The gravimetric power density is 0.8/0.024 = 33 W/kg.

Battery technology


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Number of recharge cycles Some batteries cannot be recharged at all.

These are known as primary batteries, contrasted with secondary batteries which can be recharged.

As the battery discharges there are chemical reactions taking place at the two electrodes, involving the material of the electrodes and the chemicals in the electrolyte.

To recharge the battery those reactions have to be reversed, which may not be possible, or may only be partially possible.


Number of recharge cycles Even a secondary battery, which can be

recharged, will be limited in the number of times it can be recharged before it deteriorates so that it no longer retains charge very effectively.

The way in which the battery is used and, especially, in which it is charged can have a significant influence on how effectively it can be recharged and, therefore, on how many cycles the battery can go through before it retains too little charge to be useful.



Battery charging and safety A battery is charged by passing an electrical

current through it in the opposite direction from the direction that current flows when it is in use.

General rules are that it is important not to attempt to charge a battery too fast and that the charging should stop once the battery is fully charged.

For some chemistries these rules are more strict than others. Li-ion batteries need careful charging, Care also needs to be taken over the discharging of Li-ion batteries.



Battery charging and safety Discharging a battery too fast -- such as if there

were to be a wire connecting the anode to the cathode directly (called a ‘short circuit’) -- can result in a battery overheating. and this can result in the battery exploding.

To ensure that none of these damaging or dangerous circumstances occur, Li-ion batteries are supplied packaged with control and protection electronics, which might even include ‘intelligence’: a microprocessor that controls the battery is referred to as a smart battery.



Shelf lifeThe shelf life of a battery is the length of time a

battery can be stored, even if it is not being used.

shelf life can be very important in some applications – ( example of military applications)

When not in use, all batteries gradually lose charge, a process referred to as self-discharge.

Standard NiMH batteries can lose as much as 20--30% of their charge in a month, and Li-ion batteries of the order of 5% per month.


Battery technology


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Environmental issues Of considerable importance, but not a topic that we shall

be covering in any detail, is the impact that battery manufacture, use and disposal have on the environment.

Primary batteries are very inefficient in the use of energy. The amount of energy used to manufacture a battery is

much greater than the amount of energy that will be usefully delivered to the equipment.

Secondary batteries are generally more efficient in these terms than primary batteries, but it still takes substantially more energy to recharge a battery than you get out of it from the charging.

Disposing of used batteries can damage the environment.


Battery comparisons At the time of writing (2008), the main types of

battery in common use for digital equipment, such as personal radios, laptop computers, mobile telephones and MP3 players, etc., are alkaline primary batteries, NiMH secondary batteries and Li-ion secondary batteries.



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Fuel cells47

The idea that fuel cells might be used to generate electricity for small portable devices like laptops is a relatively recent development.

Until now, fuel cells have tended to be used for more specialised applications -- providing electricity for use in space rockets

However, with the increasing demand for power by digital devices, and the inability of batteries to keep up, the attraction of being able to revive a laptop by pouring in a cupful of liquid fuel has led to a substantial research effort aimed at producing a small, cheap and safe fuel cell for electronic devices.


Fuel cells48

A fuel cell is an electrochemical energy conversion device.

It produces electricity from various external quantities of fuel (on the anode side) and oxidant (on the cathode side). These react in the presence of an electrolyte.

Fuel cells are different from batteries in that they consume reactant, which must be replenished, whereas batteries store electrical energy chemically in a closed system.


Power from the environment

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there is a lot of interest in finding ways of picking up power from the environment, removing the need for providing an energy supply ‘up front’, or at least reducing the amount of energy being drawn from a battery. This is referred to as energy scavenging or energy harvesting.

Though at first sight this idea might sound exotic, solar-powered calculators are in fact harvesting energy from the ambient light and have been around for decades.

One application for which energy scavenging or harvesting might become very important is in providing power for wireless sensor networks.


Performance comparisons50

For batteries, the figures of merit were important in assessing the performance. Similar measures can be used for other sources of power.

Tables 1.6 and 1.7 are taken from a paper (Flipsen, 2006) comparing a range of power sources, including batteries, fuel cells and even the human body.


Performance comparisons51


Where does the energy come from?


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The energy always has to come from somewhere, however, and Figure 1.10 traces it back to its original source.

Where does the energy come from?

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At present, most energy for digital devices, as for all electrically powered equipment, ultimately can be traced back to fossil fuels.

One solution is to find alternatives to fossil fuels, but the particular responsibility of the information and communication technology (ICT) industry is to attack the problem from the other direction and work to reduce energy consumption.

Indeed, concern about the growth of energy use has led to the issuing of a directive by the European Union, establishing a framework for the setting of ecodesign requirements for energy using products




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Activity 1.20 : Read the following announcement from Samsung, and use

the information in it to answer the following questions. (a) Estimate the assumed running power of the laptop,

averaged over a month (assume there are four weeks in a month).

(b) How many litres of fuel must there be in the docking station?

(c) Approximately how many litres of fuel does the writer assume are contained in a coffee cup?



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Activity 1.20 :



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Activity 1.20 : (a) It uses 1200Wh to run for 8 h a day, 5 days a week, for a

month (which we take to be 4 weeks). At 5 days per week that is 20 days, and 8 h a day gives 160 h. So the power drawn must be 1200/160 = 7.5W.

(b) 1200Wh with a volumetric energy density of 650 Wh/L means it must use 1200/650 = 1.85 L.

(c) It is supposed to be able to run for 15 h on ‘a coffee cup’s worth of fuel’. So 15 h would need 15 x 7.5 = 112.5 Wh. This would need 112.5/650 = 0.173 L. (This is about 1/3 of a pint, which is reasonable.)

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T325: TECHNOLOGIES FOR DIGITAL MEDIA Second semester – 2010/2011 Tutorial 1 1