Sound energy is used in a surprisingly wide range of applications, from breaking apart kidney stones inside your body to mapping the ocean floor thousands of meters below the surface. While we experience sound as something we hear, engineers and scientists treat it as mechanical energy, pressure waves that can penetrate solid materials, generate heat, move objects, and carry detailed information back to a sensor. Here’s how that energy gets put to work.
Medical Imaging and Diagnosis
The most familiar use of sound energy in medicine is the ultrasound scan. Medical ultrasound devices send high-frequency sound waves (typically between 2 and 40 MHz, far above the range of human hearing) into the body and listen for the echoes that bounce back from organs, bones, and fluid. A computer translates the timing and strength of those echoes into a real-time image.
There’s a core tradeoff built into the physics. Higher frequencies produce sharper, more detailed images but can’t penetrate very deep into tissue. Lower frequencies reach deeper structures but sacrifice resolution. That’s why a scan of a superficial tendon uses a different frequency than one of a deep abdominal organ. Doctors also use a technique called Doppler ultrasound, which detects shifts in the frequency of returning echoes to measure blood flow through vessels in real time.
Breaking Up Kidney Stones
One of the most dramatic medical uses of sound energy is extracorporeal shock wave lithotripsy, a procedure that breaks kidney stones into passable fragments without surgery. A device outside the body generates focused shock waves that travel through tissue and converge on the stone. The pressure waves fragment it through several overlapping mechanisms: tiny gas bubbles form around the stone and collapse violently, sending jets of fluid into its surface; stress cracks develop along internal layers; and reflected energy bouncing inside the stone creates fracture points from within.
For stones smaller than 2 centimeters, this approach achieves stone-free rates approaching 75%. Success drops off for larger stones, and some patients need repeat sessions, but the procedure remains a first-line treatment because it’s entirely noninvasive.
Destroying Tumors With Focused Ultrasound
High-intensity focused ultrasound (HIFU) takes sound energy a step further by concentrating it tightly enough to heat tissue above 55°C, a temperature that kills cells within seconds through a process called coagulative necrosis. Think of it like using a magnifying glass to focus sunlight, except the energy source is sound and it can reach targets deep inside the body.
HIFU is currently used or being actively studied for cancers of the prostate, breast, liver, kidney, pancreas, and bone. Its roles vary by situation. For early-stage, localized tumors, the goal can be complete destruction. For advanced cancers that can’t be surgically removed, HIFU can shrink the tumor or relieve pain, particularly in patients with painful bone metastases. The FDA approved a focused ultrasound system in 2020 for treating a specific benign bone tumor (osteoid osteoma) in the arms and legs. Researchers are also exploring how focused sound waves can temporarily open the blood-brain barrier to allow chemotherapy drugs to reach brain tumors more effectively.
Mapping the Ocean Floor
Sonar, short for “sound navigation and ranging,” uses sound energy to explore underwater environments where light can’t reach. Active sonar works by emitting a pulse of sound into the water and measuring the echo. The time it takes for the pulse to return reveals the distance to the seafloor or an object, while the strength of the echo provides information about what reflected it. This is how researchers map seamounts, shipwrecks, and geological features across vast stretches of ocean.
Passive sonar takes a different approach: it emits nothing and simply listens. This makes it valuable for military submarines that don’t want to reveal their position, and for scientists studying marine life. A single passive sensor can detect a sound source like a whale or a ship engine, but it can’t determine the distance on its own. Multiple passive sensors working together can triangulate a source by comparing the slight differences in when the sound reaches each one. Some sonar systems trade resolution for coverage, scanning large areas at lower detail, while others image small sites like archaeological shipwrecks in high resolution.
Inspecting Materials Without Damaging Them
Industries that depend on structural safety, including aerospace, oil and gas, power generation, and manufacturing, use ultrasonic testing to find hidden flaws inside solid materials. The principle is the same as medical ultrasound: send sound waves into the material and analyze what comes back. When a sound wave hits an internal crack, a pocket of trapped gas, or an inclusion of foreign material, part of the wave reflects back to the sensor. By measuring the timing and amplitude of that reflection, a trained operator can determine how deep the flaw is and what type of defect it represents.
Industrial ultrasonic testing typically uses frequencies above 1 MHz and works on nearly all solid materials, from aluminum and steel alloys to composites and plastics. In the energy sector, it’s a standard method for assessing corrosion in pipelines and pressure vessels, detecting cracks in equipment before they cause failures, and verifying the quality of welds during construction. The technique is less effective on materials that scatter or absorb sound heavily, such as concrete, certain stainless steel castings, and soft materials like rubber.
Harvesting Electricity From Noise
Researchers are developing devices that convert ambient sound into small amounts of electrical power using piezoelectric materials, substances that generate a voltage when they vibrate. When sound waves hit a thin piezoelectric membrane, the pressure fluctuations cause it to flex back and forth, producing a tiny current.
The power levels are still very small. One advanced nanogenerator design achieved a peak power density of about 11.6 milliwatts per square meter under a 115-decibel sound source at 150 Hz. For context, 115 decibels is roughly the volume of a rock concert or a chainsaw. Another prototype using specialized nanofibers generated up to 6 volts of open-circuit voltage at 110 decibels. These outputs are far too low to power a home, but they could eventually trickle-charge sensors in noisy industrial environments or inside machinery where replacing batteries is impractical.
Levitating Objects in Midair
Acoustic levitation uses carefully controlled sound waves to suspend small objects, typically liquid droplets, in midair without any physical contact. Opposing speakers create a standing wave pattern with fixed points of high pressure that can trap a droplet in place. This creates a completely containerless environment, which turns out to be extremely useful in pharmaceutical research.
When developing new drugs, scientists often need to study how proteins crystallize or how chemical compounds behave without contamination from container walls. Acoustic levitation eliminates that variable entirely. Researchers have used it to perform X-ray crystallography on levitated protein samples, a technique critical for understanding molecular structures used in drug design. The contactless setup also opens possibilities for manipulating artificial cells, loading drugs into delivery vehicles, and automating sample handling that currently requires tedious manual work.
Refrigeration Without Chemicals
Thermoacoustic refrigeration is a cooling technology that uses sound waves instead of conventional chemical refrigerants. Inside a sealed tube, a loudspeaker or similar driver generates intense sound waves. As the gas molecules in the tube compress and expand with each pressure cycle, they heat up and cool down in predictable ways. A porous material called a “stack” inside the tube exploits this effect: gas parcels deposit heat at one end and absorb it at the other, gradually building a temperature difference that can be used for cooling.
The appeal is environmental. Traditional refrigerators rely on chemical refrigerants that can be potent greenhouse gases if they leak. A thermoacoustic system uses only inert gas and has no moving parts beyond the speaker, meaning less mechanical wear and no harmful chemicals. Efficiency remains a challenge compared to conventional systems, and most current designs are experimental or used in niche applications. But the technology is being actively developed, with some projects pairing thermoacoustic coolers with solar energy as the heat source that drives the sound waves.