"Hands-on science with radio waves"

Transcription

1 "Hands-on science with radio waves" WSE187 project: Sudden Ionospheric Disturbance (SID) VLF monitor Joanna Kiryluk Contact: Office: C109 (physics building) 04/02/2016

2 "Hands-on science with radio waves" Radio detection techniques are widely used in science and engineering, in areas ranging from object detection with radar to searches for the most energetic and elusive particles in the universe. In this course students will learn a method to detect Solar Flares - a sudden large energy release on the Sun's surface using Very Low Frequency (VLF) antennas. The laboratory component offers a hands-on experience with this technique. Every student will build her own antenna, use a laptop as a data acquisition system, and SpectrumLab software to collect and analyze the data.

3 The Sun and the Solar Flares

4 The Sun Diameter: 1,390,000 km (Earth 12,742 km or ~100 times smaller) Mass: x kg (333,000 times Earth s mass) Temperature: 5800 K (surface) 15,600,000 K (core) The Sun contains more than 99.8% of the total mass of the Solar System (Jupiter contains most of the rest). Chemical composition: Hydrogen 92.1% Helium 7.8% Rest of the other 90 naturally occurring elements: 0.1% (0:55)

5 The Sun Energy is created in the core when hydrogen is fused to helium. This energy flows out from the core by radiation through the radiative layer, by convection through the convective layer, and by radiation from the surface of the photosphere, which is the portion of the Sun we see.

6 The Sun Activity: e.g. Sunspots

7 The Sun Activity: Climate on Earth? Solar Cycle (Solar magnetic activity cycle) powered by a hydromagnetic dynamo process, driven by the inductive action of internal solar flows The Maunder Minimum coincided with a period of lower-than-average European temperatures.

8 The Sun Activity: Climate on Earth? Solar Cycle (Solar magnetic activity cycle) powered by a hydromagnetic dynamo process, driven by the inductive action of internal solar flows Increase in number of sunspots, solar flares etc 2015/2016 great time to make observations!

9 The Sun Activity: Solar Flares In this course students will learn a method to detect Solar Flares - a sudden large energy release on the Sun's surface using Very Low Frequency (VLF) antennas.

10 The Electromagnetic Waves

11 The Electromagnetic Waves Visible Light

12 The Electromagnetic Waves Visible Light

13 The Electromagnetic Waves Radio waves: first predicted by mathematical work done in 1867 by James Clerk Maxwell Maxwell noticed wavelike properties of light and similarities in electrical and magnetic observations. He then proposed equations that described light waves and radio waves as waves of electromagnetism that travel in space, radiated by a charged particle as it undergoes acceleration. y E x B z Every charge that accelerates emits light that indicates how it has been accelerating. This can be used for radio and other long-range communications!

14 The Electromagnetic Waves What is a wavelength? wavelength λ = c ν frequency

15 The Electromagnetic Waves ν λ λ = c ν c m s [ ]

16 The Electromagnetic Waves Source:

17 Source: Radio frequencies

18 Radio waves: The Electromagnetic Waves In 1887, Heinrich Hertz demonstrated the reality of Maxwell's electromagnetic waves by experimentally generating radio waves in his laboratory (every charge that accelerates emits light that indicates how it has been accelerating) Many inventions followed, making the use of radio waves to transfer information through space. Electromagnetic Spectrum: Radio Waves 9:50 (propagation)

19 How to detect solar flares? Make use of - the Earth atmosphere and - man-made radio waves transmitter(s)

20 Layers of the Atmosphere Energy from the Sun affects the Earth ionosphere (> 60 km above the Earth surface)

21 Man-made Radio Signals on Earth Free electrons in the ionosphere have strong influence on the propagation of radio signals. Radio frequencies of long wavelength (or very low frequency, VLF) bounce off there free electrons in the ionosphere allowing radio communication over horizon and around curved Earth.

22 (indirect) detection of Electromagnetic Waves The VLF (very low frequency) receiver (antenna we re going to build) can't detect radio waves directly from space because Earth's Ionosphere is opaque to wavelengths longer than about 20 m Solar flare During solar flares, the Sun emits bursts of X-rays that enhance the ionization of the D layer. VLF transmitter (antenna we re going to build) This results in a measurable change in the strength of received VLF signals.

23 VLF (Very Low Frequency) Transmitters VLF: frequency 3-30 khz, wavelength km We ll use the VLF Transmitter located in Cutler, Maine 24kHz US Navy s VLF radio station High power (1MW), signals can be received thousands of miles away (across the US) Low bandwidth, no audio (submarine communication)

24 This Experiment Idea (SID Monitor) The primary parts of your instrument will be: an antenna and a computer with a sound card software (program) to process signals

25 This Experiment Idea (SID Monitor) The primary parts of your instrument will be: an antenna and a computer with a sound card software (program) to process signals Antenna: The antenna receiver collects radio energy from its surroundings and converts it into an oscillating electrical signal. A loop antenna is needed to pick up radio signals reflected from the ionosphere. These signals typically are very small, only ~0.1 millivolts (a preamplifier will amplify the signal, but is not needed in the right environment)

26 This Experiment Idea (SID Monitor) The primary parts of your instrument will be: an antenna and a computer with a sound card software (program) to process signals PC with a sound card: Signal will be with a PC sound card, which converts the signal from analog to digital. Software: A program running on your computer, tracks the VLF transmission signal strengths and processes the data. SpectrumLab free download: Spectrum Lab runs under Windows only (not linux/unix/mac osx) plotting program (matlab or excel or something else of your choice)

27 Fake solar flares (this rotation section) Real solar flares (need to go outside, find VLF signal and monitor it for a longer period of time)

28 This Experiment Idea (SID Monitor) The primary parts of your instrument will be: an antenna and a computer with a sound card software (program) to process signals 2013 WSE187 Radio Antenna rotation Since the reflected radio signals are strongly influenced by the Sun s radiation, plotting the signal strengths over time should tell us when there is a solar flare on the Sun. In the lab we ll use a function generator as a VLF transmitter and by changing the signal amplitude we ll mimic solar flares effect.

29 Construction of the multi-turn small loop antenna A. Antenna wire Magnet wire - is a copper or aluminium wire coated with a very thin layer of insulation. It is used in the construction of transformers, inductors, motors, speakers, electromagnets, and other applications which require tight coils of wire. AWG (American wire gauge) - is a standardized wire gauge system used since 1857 predominantly in the United States and Canada for the diameters of round, solid, nonferrous, electrically conducting wire. In this experiment we need 24 AWG magnet enameled copper wire (~0.5 mm diameter), about 185m long

30 Construction of the multi-turn small loop antenna B. Antenna frame 1. Cut a piece of wood 57 cm long from a piece of 20 mm square wood (upright of a cross) 2. Cut a piece of wood 52 cm long from a piece of 20 mm square wood (horizontal section of the cross) 3. Cut two pieces of wood (bottom part) 4. Cut 4 pieces of wood 5-6 cm long long from a piece of 20 mm square wood. Mark a line across each of them 1 cm from one end and make a saw cut to a depth of half of the thickness, completing the cut down from the end to remove the piece, leaving a tongue 1 cm long and half the thickness of the wood on all four short pieces. 5. Next mark the center of the 52-cm-long cross member, then make two more marks across the width of the material 10 mm either side of the center line. 6. Put two saw cuts down carefully to half the thickness of the wood, taking care to cut on the inside (towards the center) of your pencil lines. Using a small sharp wood chisel cut away the material between the saw cuts leaving a flat bottomed notch. Do the same on the longer upright, but don't forget it's not now in the center but offset 50 mm towards one end.

31 7. By now fitting the two long sections together in the center and gluing the joint you have a cross framework. 8. The small pieces are now glued to the tips of cross with the cutaway section on the inside forming a groove to carry the copper wire loop. 9. In a similar way construct the bottom part (a cross of two wooden sticks) C. Putting the wire and the frame together: 1. Wind 125 turns of copper wire on the frame. 2. Strip both ends of the wire (remove enamel, ~1.5cm) - a wire stripping tool (wear eye protection!) - Sand paper Make sure the insolation is removed (e.g. measure the resistance) 3. The two ends of the loop can now be soldered to a Phono or a 3.5mm jack socket. Basic soldering (many videos) e.g. Congratulations: Your VLF antenna is ready for testing!

32 Practice soldering, by building a circuit (light switch) using the following components: LED: Light Emitting Diode LEDs are diodes which means that current can only flow through an LED from the anode to the cathode and not the other way around. If an LED is connected the wrong way around in a circuit (anode to negative and cathode to positive) it is said to be "reverse biased" and will not emit light. Never connect an LED directly across a battery or other power source it will burn out. LEDs must always be connected in series with a resistor.

33 Perfboard (material for prototyping electronic circuits (DOT PCB) Soldering practice:

34 See you next week!