High enough to hear the sound - what is the use of ultrasound?
The sound with frequencies above 20,000 Hz is commonly known as ultrasound. As the frequency increases, the wavelength becomes shorter. In most solid materials, sound waves travel at speeds ranging from 1,000 to 10,000 meters per second. Frequencies can reach up to 10^8 to 10^12 Hz, which falls into the microwave region of the electromagnetic spectrum. By leveraging the propagation properties of ultrasound in solids and the effects of cavitation and radiation pressure from high-intensity ultrasound, a variety of useful applications have been developed, such as ultrasonic cutting, grinding, and drilling.
**1. Non-Destructive Testing**
In manufacturing, solid components like metal parts may develop internal cracks or voids due to material defects or production processes. These issues can weaken the structure or lead to leaks, posing serious risks. To detect these without damaging the part, non-destructive testing methods have been developed, including X-ray, radiography, electromagnetic techniques, and ultrasonic testing. Each method has its own range of applications, and often multiple techniques are used together.
Ultrasonic pulses are sent from the surface of the object. If there are flaws or holes along the path, they reflect the signal back. By comparing the reflected signal with the signal from the bottom of the object, the depth of the defect can be determined. Moving the probe allows for mapping the location of the flaw. This technique, called reflection detection, is one of the oldest and most widely used. Another method, transmission testing, involves sending an acoustic signal from one end of the object and receiving it at the other, allowing for the assessment of internal damage.
When two or more parts are bonded together, measuring the acoustic impedance from one surface can help identify poor bonding. A single probe with two piezoelectric crystals can emit and receive continuous sound waves. If there’s a weak bond, the structural response will change, helping to identify the issue.
Large infrastructure like highways, runways, and railways require constant monitoring during construction and use to ensure safety. Probes are often placed on trains or vehicles for real-time monitoring, and specialized ultrasonic instruments are used to measure road surface conditions.
**2. Ultrasonic Hardness Testing**
An ultrasonic transducer with a longitudinal vibration tip is pressed against the object’s surface, creating a small indentation. The object’s hardness affects the transducer’s vibration, changing its resonant frequency. Softer materials create deeper indentations, leading to greater frequency shifts. This allows the hardness of the surface to be measured based on the frequency change.
**3. Thickness Measurement**
When ultrasound is applied to a material, it resonates at a specific frequency, causing large amplitude vibrations. Knowing the sound velocity in the material allows the thickness to be calculated. Conversely, if the thickness is known, the speed of sound can be determined. This method, called resonance, achieves accuracy up to 0.1%–1%. The pulse echo method is widely used in industry for measuring plate thickness, where the time it takes for a pulse to travel through the material and return is measured.
**4. Level and Liquid Level Measurement**
Ultrasound is also used to measure the level of liquids in large containers. This is typically done by measuring the round-trip time of the pulse. However, because sound absorption in air or liquid is significant, lower frequency ultrasound is usually used for this purpose.
**5. Ultrasonic Thermometer**
For extremely high-temperature environments, such as steam turbine intakes or rocket exhaust, traditional thermometers are not suitable. An ultrasonic thermometer measures the speed of sound in the medium, which is related to temperature. It functions as a sound speed meter and can respond quickly. When measuring high temperatures, the transducer must be protected with a water jacket to prevent overheating.
**6. Flow Rate Measurement**
In industries like oil and chemical processing, flow rate can be measured using ultrasound. The speed of sound in a flowing liquid changes depending on the direction of flow. Two pairs of transducers are placed on either side of a pipe, and the time difference between signals traveling with and against the flow is measured to determine the flow rate. The Doppler effect can also be used, where the frequency shift of sound waves in the fluid relates to the flow rate.
**7. Ultrasonic Viscometer**
The viscosity of a liquid affects its shear resistance. By placing a transducer in the liquid and measuring the changes in voltage and current caused by resistance, the viscosity can be determined. Differences in sound velocity between substances like kerosene and diesel allow for their identification and separation, which is crucial in pipeline transportation.
**8. Phacoemulsification**
High-powered ultrasound can mix immiscible liquids like oil and water, forming stable emulsions. This process is widely used in food, pharmaceutical, and cosmetic industries. Emulsifying fuel with water using ultrasound can improve combustion efficiency and reduce pollution.
**9. Ultrasonic Cleaning**
Small or complex mechanical parts with internal channels can be cleaned effectively using ultrasound. The cavitation bubbles created by the sound waves break down dirt, remove it from surfaces, and enhance the cleaning process.
**10. Ultrasonic Pulverization**
Ultrasonic energy can produce finer and more uniform particles than traditional grinding methods, making it ideal for producing high-quality powders.
**11. Ultrasonic Tinning**
Aluminum surfaces have a tough oxide layer that makes soldering difficult. Applying ultrasonic vibrations in molten tin helps remove the oxide layer, allowing tin to adhere properly. The transducer is protected with a cooling system during this process.
**12. Ultrasonic Humidifier**
Ultrasonic humidifiers convert water into fine mist, improving air quality without heating. The tiny droplets stay suspended in the air for longer periods, making them ideal for dry environments.
**13. Ultrasonic Welding**
This technique is used to weld metals and plastics, especially rare metals like titanium and tantalum. It offers advantages like no heat distortion, minimal residual stress, and precise control, making it ideal for delicate electronics.
**14. Ultrasonic Motor**
These motors convert electrical energy into mechanical vibrations, using friction between the stator and rotor to rotate. They offer high torque, fast response, and compact design, making them ideal for robotics, computers, and precision instruments.
Shanghai Janetec Electric Co., Ltd. , https://www.janetecelectric.com