325: Technologies for Digital Media

Transcription

1 T325: 325: Technologies for Digital Media Second semester 2011/2012 Tutorial 1

2 Presentation of the T325 course Power for Digital Media Introduction Battery technology Fuel cells. Power from the environment. Where does the energy come from? Outline 2

3 Learning outcomes Course breakdown Assessments Study calendar Plagiarism General introduction 3

4 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 analyze, critique and synthesize 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. Learning outcomes of the Course 4

5 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. Course breakdown 5

6 Continuous assessment (50% of the course grade) TMA: One TMA worth 20% of course grade 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. Course Assessment 6

7 Start date Course block Course section(s) 1 20-Feb-12 Block 1: Enabling technologies Power for digital media 2 27-Feb-12 Information storage 3 5-Mar-12 Error control coding 4 12-Mar-12 Seeing and hearing: multimedia 5 19-Mar-12 Assignments /due date Study calendar Week Video and audio coding 6 26-Mar Apr Apr Apr Apr Apr-12 Block 2: Intellectual property and security issues Intellectual property rights & Security Digital rights management & Digital watermarking Block 3 Mobile broadband Mobile evolution & Network architecture Access and modulation 12 7-May May-12 Better and beyond May May-12 Revision TMA 11/12/2011 7

8 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 Plagiarism 8

9 POWER FOR DIGITAL MEDIA 9

10 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. Introduction 10

11 Power needs of digital equipment have generally been increasing Miscellaneous contains smaller electronics such as chargers, home audio equipment, game consoles, etc. Also contain non-electronics such as portable fans, irons, etc. Powering consumer electronic and computer products alone in the UK every year - that s 23% of the average household electricity bill. Introduction 11

12 Introduction 12

13 Typical power (W) Crystal radio Portable analogue FM radio DAB radio Mobile telephone on standby Mobile telephone in use Laptop computer Introduction 3 Desktop computer in use Desktop TV with liquid TV with liquid Low energy Car, driven at computer in crystal display crystal display light bulb for a 50 mph and (in use) (on standby) small room consuming 50 sleep mode mpg 13

14 Batteries produce electricity from a chemical reaction, called an electrochemical reaction. You get a battery when several cells are connected together Battery technology 14

15 The chemical reaction depends upon: the material used to make the anode the material used to make the cathode 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. Battery technology 15

16 Two categories of batteries Primary batteries Manufactured to be used once Examples: alkaline and lithium batteries Secondary batteries Rechargeable Battery technology 16

17 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 17

18 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 18

19 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. Internal resistance is a characteristic of the battery itself Battery technology 19

20 Battery technology 20

21 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 the International System of Units (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). Battery technology 21

22 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) SELF-ASSESSMENT ACTIVITIES 22 22

23 Activity 1.2 : 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) 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: SELF-ASSESSMENT ACTIVITIES 23

24 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. SELF-ASSESSMENT ACTIVITIES 24 24

25 Activity 1.5 : a) From Ohm s law, the current is given by the voltage divided by the resistance, V/R. a) SELF-ASSESSMENT ACTIVITIES 25

26 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 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. Battery technology 26

27 Activity 1.7 A 1.2V battery has a capacity of 800 mah. How long could it run if the load uses 50 ma? Answer: Capacity = I * t => t = capacity / I = 800 / 50 = 16 h SELF-ASSESSMENT ACTIVITIES 27

28 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 30 ohm? Answer 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. SELF-ASSESSMENT ACTIVITIES 28

29 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, power = current x voltage. Battery technology 29

30 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. SELF-ASSESSMENT ACTIVITIES 30 30

31 Activity Answer 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 SELF-ASSESSMENT ACTIVITIES 31 31

32 Activity 1.10 : What is 1kWh expressed in joules? 1000 x 3600 = J, which is 3.6 MJ. SELF-ASSESSMENT ACTIVITIES 32

33 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. Weight and size: figures of merit 33

34 Volumetric energy density is the amount of energy stored per unit volume. In SI units, 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. Gravimetric energy density SI unit is joules per kilogram (J/kg), Other units can be used such as watt-hours per gram (Wh/g) and kilowatt-hours per kilogram (kwh/kg). Weight and size: figures of merit 34

35 Volumetric power density is the power that can be delivered, per unit volume. The volumetric power density SI unit is W/m3 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. The gravimetric power density SI unit is W/Kg Other units might be used, such Watt per gram (W/g), Kilo-Watt per Kg (KW/Kg), etc. Weight and size: figures of merit 35

36 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. SELF-ASSESSMENT ACTIVITIES 36

37 Activity Answer 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 L. Volumetric energy density = 3460/8.4 = 410 J/cm3. Or, 0.96/ = 110 Wh/L. Mass = 24 g, which is kg. Gravimetric energy density = 3460/0.024 = J/kg. Or, 0.96/0.024 = 40 Wh/kg. SELF-ASSESSMENT ACTIVITIES 37 37

38 Activity 1.14 a) 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. b) 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. SELF-ASSESSMENT ACTIVITIES 38

39 Activity 1.14 Answer a) 1 A at 1.2V is a power of 1.2W. Volume (from previous activity) is L. So the volumetric power density is 1.2/ = 140 W/L. The mass (from the previous activity) is 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/ = 95 W/L. The gravimetric power density is 0.8/0.024 = 33 W/kg. SELF-ASSESSMENT ACTIVITIES 39

40 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. Battery technology 40

41 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 technology 41

42 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 technology 42

43 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. Battery technology 43

44 Shelf life The 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) Self-Discharge When not in use, all batteries gradually lose charge, a process referred to as self-discharge. Standard NiMH batteries can lose as much as % of their charge in a month, and Li-ion batteries of the order of 5% per month. Battery technology 44

45 Environmental issues Primary batteries 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 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 technology 45

46 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 specialized applications; providing electricity for use in space rockets Interest for research in fuel cell batteries Increasing demand for power by digital devices Inability of batteries to keep up The attraction of being able to revive a laptop by pouring in a cupful of liquid fuel Aims of research in fuel cells batteries Producing a small, cheap and safe fuel cell for electronic devices Fuel cells 46

47 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. Fuel cells 47

48 Energy scavenging or energy harvesting Finding ways of picking up power from the environment Removes the need for providing an energy supply up front, Reduces the amount of energy being drawn from a battery. Examples: solar-powered calculators are in fact harvesting energy from the ambient light and have been around for decades. A very important area of application of energy harvesting: providing power for wireless sensor networks. Power from the environment 48

49 Figure of merits can be applied for other sources of power (than batteries) Performance comparisons 49

50 Where does the energy come from? 50

51 At present, most energy for digital devices, as for all electrically powered equipment, ultimately can be traced back to fossil fuels. Solutions find alternatives to fossil fuels reduce energy consumption (responsibility of the ICT industry) European Union established a framework for the setting of eco-design requirements for energy-using products Where does the energy come from? 51

52 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? SELF-ASSESSMENT ACTIVITIES 52

53 Activity 1.20 SELF-ASSESSMENT ACTIVITIES 53

54 Activity Answers 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 = Wh. This would need 112.5/650 = L. (This is about 1/3 of a pint, which is reasonable.) SELF-ASSESSMENT ACTIVITIES 54

55 TEST YOUR KNOWLEDGE QUESTIONS FROM PREVIOUS EXAMS 55

56 In a fuel cell battery, the substance that makes it easier for a reaction to take place by lowering the activation energy is called Compound Barrier Reactor Catalyst Fuel (Fall 2011 Final Exam) 56

57 The batteries that have the property to be rechargeable are called: Primary batteries Primitive batteries Secondary batteries Alkaline batteries Tertiary batteries (Fall 2011 MTA) 57

58 The amount of energy stored per unit volume is defined as Volumetric energy density Gravimetric power density Volumetric power density Gravimetric energy density Voltage (Fall 2011 MTA) 58

59 What are the environmental issues related to the manufacture and use of batteries? Highlight those related to primary and secondary batteries Explain briefly how the battery works. Give examples of different batteries. (Fall 2011 MTA) 59

60 A 1.2V battery has a capacity of 1700 mah. How long could it run if the load has a resistance of 50ohm? What energy does the battery store? Give your answer in both watt-hours and joules. (Fall 2011 MTA) 60

61 Suppose a battery has the following parameters: Voltage: 1.2V Capacity: 600 mah Weight: 24 g Volume: 9 cm3 Current delivered: 1A Calculate the volumetric energy density and the gravimetric power density in SI units. (Fall 2011 MTA) 61

62 The chemical reaction inside a battery depends upon: The material used to make the anode The material used to make the cathode The material used for the electrolyte All of the above None of the above (Fall 2011 MTA) 62

63 Why power consumption constitutes an issue even for the mains-powered equipment? Overheating of electronic circuits damages the components. Need to reduce energy consumption in order to combat global warming To minimize the cost of production of the equipment a&b a, b & c (Fall 2011 MTA) 63

64 The following numbers appears on the back of a battery: 1.5 Volts, 12 grams, 10 cm3, 10 Ohms, 600 mah. Calculate the volumetric and gravimetric energy density of this battery in SI units This battery is connected to a 30 Ohm resistance What time this battery can last with this load? Calculate the volumetric and gravimetric power density in SI units. (Fall 2011 MTA) 64

65 A 6V battery have the following characteristics: Volumetric power density = 7.5 W/L Energy supplied = 6J Current delivered = 10 ma Calculate the volume of this battery in cm3 (3 marks) Calculate the capacity of this battery in Ah (3 marks) Supposing that the battery delivers the current mentioned when connected to a 580 Ohms external resistance. What is the internal resistance of this battery? (2 marks) (Fall 2011 Final exam) 65