Applications of Waves
In 1971, the first MRI scanner at Royal Adelaide Hospital used radio waves to image human tissue, with zero radiation and no incision needed.
β Know
- How X-rays, ultrasound and MRI are used in medicine
- How radio waves, microwaves and optical fibre are used in communication
- How waves are used in remote sensing and astronomy
β Understand
- Why different wave types are chosen for different applications
- How Aboriginal and Torres Strait Islander Peoples use wave knowledge
- The trade-offs between benefits and risks of wave technologies
β Can do
- Evaluate wave technologies using scientific evidence
- Compare medical imaging techniques for different situations
- Communicate scientific arguments about wave applications
A doctor pressing an ultrasound probe against a pregnant patient's abdomen in 2024 is using 3β10 MHz sound waves that reflect off tissue boundaries, safe enough to image a developing baby. A radiographer using X-rays in the next room is using electromagnetic waves 1,000 times shorter that pass straight through soft tissue. Choosing the right wave for an application means matching wave properties, wavelength, energy, and what it interacts with, to the task's specific requirements.
Penetration depth: Higher energy waves penetrate deeper but may be more hazardous. X-rays penetrate soft tissue to image bones. Gamma rays penetrate everything and require thick shielding. Ultrasound reflects at tissue boundaries and does not penetrate bone well.
Resolution: Shorter wavelengths give better resolution. Visible light microscopes resolve features down to about 200 nm (limited by diffraction). Electron microscopes use much shorter electron wavelengths to resolve atomic structures. Medical ultrasound uses MHz frequencies (mm wavelengths) to resolve features millimetres in size.
Safety: Non-ionising radiation (ultrasound, MRI, visible light) is safer for repeated use. Ionising radiation (X-rays, CT, nuclear medicine) carries cancer risk and must be used judiciously.
Contrast mechanism: Different waves interact with tissue differently. X-rays are attenuated by dense materials (bone). Ultrasound reflects at density boundaries. MRI detects hydrogen nuclei in water and fat. The best imaging method depends on what property you need to visualise.
A pregnant woman has multiple imaging options, each with different trade-offs:
Ultrasound: Safe, real-time, shows fetal movement and heartbeat. Limited resolution and cannot penetrate bone (skull blocks brain imaging). Used routinely throughout pregnancy.
MRI: No ionising radiation, excellent soft tissue contrast. Can image fetal brain through the skull. Expensive and not always available. Used for complex cases where ultrasound is insufficient.
X-ray: Avoided in pregnancy due to ionising radiation risk to the fetus. Only used if absolutely necessary and benefits outweigh risks.
This case illustrates how wave properties (safety, penetration, resolution) determine clinical choices.
Australian medical imaging: Australia has world-class medical imaging infrastructure, including MRI machines in most major hospitals, PET-CT scanners in cancer centres, and ultrasound in virtually every medical practice. The Australian Nuclear Science and Technology Organisation (ANSTO) produces radioisotopes for nuclear medicine at the Lucas Heights reactor in Sydney. Australian researchers develop new imaging techniques, including hyperspectral imaging for wound assessment and photoacoustic imaging that combines light and ultrasound for high-resolution deep tissue imaging.
More powerful radiation always gives better medical images. This is false. The best image is obtained with the minimum radiation dose that provides diagnostic information. This is the ALARA principle (As Low As Reasonably Achievable). Higher doses increase cancer risk without necessarily improving diagnostic accuracy. Modern imaging systems use sophisticated algorithms to extract maximum information from minimal dose. For example, digital X-rays use 10-20% of the dose of film X-rays while providing better image quality. Safety and image quality must be balanced.
Match each imaging technology to the wave type it uses and why.
Beyond medicine, waves are essential tools for navigation, communication, and remote sensing.
Sonar (Sound Navigation and Ranging): Uses sound pulses to detect underwater objects. Active sonar emits a pulse and listens for the echo. Passive sonar listens for sounds made by vessels. Sound travels well through water (about 1,500 m/s), while radio waves are absorbed. Sonar is used for submarine detection, fish finding, seabed mapping, and measuring ocean depth.
Radar (Radio Detection and Ranging): Uses radio pulses to detect aircraft, ships, and weather. The round-trip time of the pulse gives distance; the Doppler shift gives speed. Radar works through clouds and darkness where visible light cannot.
Lidar (Light Detection and Ranging): Uses laser pulses for extremely precise distance measurement. Lidar creates detailed 3D maps of terrain, buildings, and vegetation. It is used in autonomous vehicles, archaeology, forestry, and atmospheric monitoring.
Autonomous vehicles like Tesla use a combination of sensors: cameras (visible light), radar (radio waves), and increasingly lidar (laser light). Cameras provide rich visual information but struggle in poor light. Radar works in all weather and measures speed accurately via Doppler shift but has lower resolution. Lidar creates precise 3D point clouds of the surroundings but can be affected by rain and dust. By fusing data from all three wave-based sensors, the vehicle builds a robust understanding of its environment. This sensor fusion is essential for safe autonomous driving in diverse conditions.
Australian lidar mapping: Geoscience Australia uses airborne lidar to map the entire Australian continent with unprecedented detail. The Elevation Information System (ELVIS) provides high-resolution elevation data for flood modelling, infrastructure planning, and environmental management. Australian lidar data revealed previously unknown archaeological sites, including ancient Aboriginal fish traps and ceremonial structures. Lidar has also mapped bushfire fuel loads by measuring vegetation density, helping fire agencies predict fire behaviour and plan hazard reduction burns.
Radar detects objects by bouncing radio waves off them, so stealth aircraft are invisible. This is false. Stealth technology reduces radar detectability but does not eliminate it. Stealth aircraft use shape design (angled surfaces that reflect radar away from the transmitter), radar-absorbent materials (that convert radio wave energy to heat), and active cancellation (emitting signals that interfere with reflected radar). These techniques reduce the radar cross-section by factors of 100-1000, making detection much harder but not impossible. At short ranges or with powerful radar, stealth aircraft are still detectable. Stealth is about reducing signature, not invisibility.
Modern communication encodes information onto electromagnetic waves through modulation.
Amplitude Modulation (AM): The amplitude of the carrier wave varies with the signal. Simple but susceptible to noise.
Frequency Modulation (FM): The frequency varies with the signal. Better noise immunity than AM, hence higher sound quality.
Digital modulation: Modern systems encode digital data onto carriers using phase shifts, frequency shifts, or amplitude changes. Techniques include QAM (Quadrature Amplitude Modulation) and OFDM (Orthogonal Frequency Division Multiplexing).
Trade-offs: Higher frequency carriers can carry more data (wider bandwidth) but have shorter range and poorer penetration through obstacles. This is why 5G uses higher frequencies than 4G for dense urban areas but lower frequencies for rural coverage. Wi-Fi at 5 GHz is faster than 2.4 GHz but has shorter range and worse wall penetration.
When you stream a video on your phone, the data is encoded onto radio waves using complex digital modulation. A 4G LTE connection might use 64-QAM, encoding 6 bits per symbol by varying both amplitude and phase. The base station allocates frequency bands dynamically, adjusting modulation based on signal quality. In a strong signal area, 256-QAM (8 bits per symbol) gives higher throughput. At the cell edge, simpler QPSK (2 bits per symbol) provides robustness against noise at the cost of speed. This adaptive modulation is invisible to users but essential for reliable mobile broadband.
Australian telecommunications: The NBN uses a mix of technologies: fibre optic (light waves), fixed wireless (microwaves), and satellite (radio waves). The choice depends on geography and population density. Australian mobile networks (Telstra, Optus, Vodafone) operate across multiple frequency bands, balancing coverage and capacity. The Australian Communications and Media Authority manages spectrum allocation, ensuring that different services (broadcasting, emergency services, aviation, scientific) do not interfere. Understanding wave properties is essential for designing networks that serve Australia vast and sparsely populated landscape.
5G towers emit dangerous radiation that causes cancer and COVID-19. This is completely false and conspiracy theorising. 5G uses non-ionising radio waves at frequencies similar to existing 4G and Wi-Fi. The photon energy is billions of times too low to damage DNA. Decades of research have found no health effects from mobile phone signals at permitted exposure levels. The COVID-19 claim is biologically nonsensical - viruses cannot be transmitted by electromagnetic waves. These conspiracy theories have led to real-world harm, including arson attacks on telecommunications infrastructure during the pandemic.
Tap each card to flip. Mark Got it when you can recall the answer without flipping.
Aboriginal and Torres Strait Islander Peoples have deep, sophisticated knowledge of wave phenomena developed over tens of thousands of years. This knowledge is practical, empirical and closely tied to survival and culture.
Sound and vibration: Many Aboriginal cultures use sound for communication over long distances. The didgeridoo produces low-frequency sound waves that travel far across flat terrain. Traditional knowledge also includes interpreting vibrations in the ground, reading seismic signals from distant events to understand what is happening in the landscape.
Light and astronomical observation: Aboriginal astronomy is among the oldest in the world. Indigenous observers track the movement of stars (light waves from distant suns) to create calendars, predict seasons and navigate across the continent. The Emu in the Sky, a dark constellation recognised by many Aboriginal groups, demonstrates deep understanding of how light and dark regions in the Milky Way can be interpreted.
Water waves and coastal knowledge: Aboriginal coastal peoples have intimate knowledge of ocean swells, tides and currents, all wave phenomena. This knowledge was used for fishing, travel and predicting weather. Before European arrival, Aboriginal people navigated between islands and across open water using wave patterns, star positions and seasonal wind patterns.
Aboriginal and Torres Strait Islander Peoples used knowledge of ocean wave patterns for navigation and fishing. Which statement best describes this knowledge system?
Wrong: "MRI uses X-rays." No οΏ½ MRI uses magnetic fields and radio waves. It does not involve ionising radiation, which is why it is safe for repeated use and for imaging sensitive tissues like the brain.
Right: MRI (Magnetic Resonance Imaging) uses radio waves and a strong magnetic field, not X-rays. Because it involves no ionising radiation, MRI is safe for repeated use and is the preferred tool for imaging soft tissues such as the brain, spinal cord and joints where X-rays provide poor contrast.
Wrong: "Ultrasound is dangerous because it uses radiation." No οΏ½ ultrasound uses high-frequency sound waves (mechanical waves), not electromagnetic radiation. It is considered safe for pregnant women and developing fetuses.
Right: Ultrasound uses high-frequency mechanical sound waves, not electromagnetic radiation of any kind. The waves bounce off internal tissues and the reflected echoes are used to build an image. There is no ionising radiation involved, which is why ultrasound is routinely used to monitor fetal development during pregnancy.
Wrong: "Traditional knowledge is just stories, not real science." No οΏ½ Aboriginal and Torres Strait Islander knowledge systems are based on rigorous observation, testing and prediction, just like Western science. They represent a different but equally valid way of understanding natural phenomena including waves.
Right: Aboriginal and Torres Strait Islander knowledge systems are built on meticulous observation, pattern recognition and knowledge refined over tens of thousands of years, the same foundations as Western science. They reliably predict seasons, navigate vast distances and interpret environmental signals. Calling them "just stories" misrepresents a sophisticated empirical tradition.
Waves in Australian Life
The NBN and rural connectivity: Australia's National Broadband Network uses a mix of optical fibre, fixed wireless (microwaves) and satellite to deliver internet across the continent. In remote areas like the Kimberley or central Australia, satellite is often the only practical option. Understanding which wave technologies work best in different environments is essential for equitable access.
Bushfire monitoring: During the 2019-20 Black Summer bushfires, satellite remote sensing was crucial for tracking fire spread across millions of hectares. Infrared sensors detected fire fronts through smoke, and microwave sensors measured vegetation dryness to predict where fires might spread next. This technology saved lives by giving firefighters real-time information.
Medical imaging access: Australia has world-class medical imaging, but access is uneven. Urban hospitals have MRI machines, while rural clinics may only have X-ray and basic ultrasound. The Royal Flying Doctor Service uses portable ultrasound and satellite communication to deliver emergency diagnostics to remote communities, demonstrating how wave technologies combine to overcome distance.
β Copy Into Your Books
βΎMedical Imaging
- X-rays: ionising EM waves, good for bones, limited exposure needed
- Ultrasound: high-frequency sound waves, safe for pregnancy
- MRI: magnetic fields and radio waves, detailed soft tissue images
Communication
- Radio and microwaves: broadcasting, mobile phones, Wi-Fi
- Optical fibre: light pulses in glass, fast internet (NBN)
- Satellite: essential for remote areas
Remote Sensing and Indigenous Knowledge
- Satellites use infrared, visible and microwave to monitor Earth
- Radio telescopes detect waves from space (Parkes, SKA)
- Aboriginal knowledge includes sound, seismic, light and water wave understanding
Choose the Right Tool
Wave Technology Evaluation
At the start of this lesson you were shown the Bureau of Meteorology's Doppler radar detecting a raindrop 400 km away and measuring its speed using only microwave pulses and the wave equation.
Now that you've worked through the lesson, how has your thinking shifted? Can you explain that hook idea more precisely using what you've learned today?
Q1. 1. Explain how optical fibre works and why it can carry more data than copper wire. 4 MARKS
Q2. 2. A rural community in outback Queensland needs reliable internet and emergency medical diagnostics. Describe two wave-based technologies that could help, and explain why each is suitable for this remote location. 4 MARKS
Q3. 3. Aboriginal and Torres Strait Islander Peoples have used knowledge of sound, light and water waves for tens of thousands of years. Describe one example of traditional wave knowledge and explain how it demonstrates the same principles as modern wave science. 4 MARKS
Revisit Your Thinking
Go back to your Think First answer. Has your understanding changed?
- Can you now explain three different ways doctors use waves to see inside the body?
- Can you describe how Aboriginal knowledge of waves parallels modern science?
Model answers (click to reveal)
Answers
βΎMCQ 1
BUltrasound uses high-frequency sound waves (mechanical waves) to create images. X-rays and CT scans use ionising electromagnetic radiation, and MRI uses magnetic fields and radio waves.
MCQ 2
COptical fibre carries data as pulses of light through thin glass fibres. The light reflects off the inner walls (total internal reflection) and can travel long distances with very little loss, allowing extremely fast data transmission.
MCQ 3
AUltrasound is the safest choice for pregnant women because it does not use ionising radiation. X-rays and CT scans use ionising radiation that could harm the developing fetus. While MRI does not use ionising radiation, it is expensive and not routinely used for pregnancy checks.
MCQ 4
DRadio waves have much longer wavelengths than visible light, allowing them to pass through dust and gas clouds in space that block visible light. This means radio telescopes can detect objects and regions that optical telescopes cannot see.
MCQ 5
BThe claim is incorrect because it oversimplifies the situation. While MRI has advantages (no ionising radiation, excellent soft-tissue detail), it is expensive, takes longer, requires specialised facilities and cannot be used on patients with certain metal implants. X-rays remain faster and more accessible for many applications, especially bone imaging.
Short Answer 1
Model answer: Optical fibre works by sending pulses of light through a thin glass fibre. The light reflects off the inner walls of the fibre through total internal reflection, staying inside even when the fibre bends. Because light has a much higher frequency than electrical signals, optical fibre can carry vastly more data than copper wire. A single optical fibre can carry millions of phone calls simultaneously, whereas copper wire is limited by electrical resistance and interference. This is why optical fibre forms the backbone of the NBN.
Short Answer 2
Model answer: Two suitable technologies are satellite internet and portable ultrasound. Satellite internet uses microwave signals sent to and from satellites in orbit, making it ideal for remote areas where laying cables is impractical. It provides reliable connectivity for telehealth and emergency services. Portable ultrasound uses high-frequency sound waves to create images of internal organs and is safe, relatively inexpensive and can be operated by trained staff in remote clinics. The Royal Flying Doctor Service uses both technologies to deliver healthcare across outback Australia.
Short Answer 3
Model answer: One example is Aboriginal astronomical knowledge. Aboriginal observers have tracked star positions and light from distant stars for tens of thousands of years to create calendars, navigate and predict seasons. This demonstrates the same principle as modern astronomy, that light is an electromagnetic wave that travels from distant sources and carries information about those sources. Another example is the use of the didgeridoo for long-distance communication: the low-frequency sound waves travel further than high-frequency sounds, which parallels the physics of sound propagation studied in modern acoustics.