Ultrasonic testing is a highly effective non-destructive testing application (NDT). It uses high-frequency ultrasonic sound waves for various purposes that include flaw detection, thickness gauging among several others. These high-frequency sound waves are generated by small ultrasonic probes also known as ultrasonic transducers. These probes are the starting and an essential part of any ultrasonic testing device and come in a wide range of frequencies, sizes, and case styles for different inspection purposes ranging from flaw detection in bridges and other big structures to thickness measurement of ultra-thin paint coatings.
An ultrasonic probe or a transducer is a device that converts the pulse of electric energy generated from the equipment to mechanical energy i.e., high-frequency sound waves that travel through the tested material. These sound waves after bouncing back from the test subject are captured and converted by the probes into an electrical energy pulse. This in turn is processed and displayed in the testing instrument. In simple words, an ultrasonic probe acts like a speaker and receiver that is generating and receiving the pulses of high-frequency sound waves much above the range of human beings.
Ultrasonic Probes-Elements Used
Usually, the active elements of an ultrasonic probe are a thin disk, square, or rectangle of piezoelectric ceramic or composite. The size of these elements varies from as small as 0.125 in. (3 mm) to 1.5 in. (38 mm). They perform the function of converting electrical energy into mechanical energy and vice versa. These elements are also called crystals as earlier, they were made of quartz crystals. Ceramics like lead meta-niobate and lead zirconium titanate have replaced the quartz crystals as elements but the name “crystal” has stuck. Now, composite elements are used in ultrasonic probes for increased bandwidth and improved sensitivity for detecting flaws.
Ultrasonic probes are precision devices and as such require great care and precision in their design, composition material, and manufacturing so to ensure accurate and consistent performance. The transducers or probes commonly used for ultrasonic testing are described below. These are classified as per their design and intended use.
1. Contact Probes
As the name suggests, these probes have to be used in direct contact with the testing material. A thin and hard wear-plate protects the element from damage. These probes are used in flaw detectors using straight beam tests. The tests include checking for voids in metal ingots, gauging thickness, and inspecting de-laminations in composites.
2. Angle Beam Probes
These are similar to contact probes but optimized to be used with angle beam wedges so that they can generate sound waves tilted at an angle to the coupling surface. Wedges are usually configured so that they can generate refracted shear waves at 45, 60, and 70 degrees. These ultrasonic probes are required in most weld inspections. As ultrasonic testing in most of the common weld geometries requires aiming the waves at an angle.
3. Delay Line Probes
Delay line probes have a delay line between the active element and the test object. This delay line is made of a cylinder of epoxy, plastic, or fused silica. Delay lines are used when testing thin and hot objects. In thin test objects like spot welds in sheet metals, the delay line separates the excitation pulse recovery from back wall echoes. For hot test objects, the delay line works as a thermal insulator to protect the heat-sensitive elements in the probe from direct contact with heat. Delay lines are also altered or contoured in confined or sharply curved spaces so to improve the sound coupling.
4. Immersion Probes
Immersion probes are designed to be immersed in liquid or water. They use a column or bath of water to propagate sound waves in the test object. These probes frequently include an acoustic lens that focuses the sound waves into a small spot, thus increasing sensitivity to small-sized reflectors. These ultrasonic probes are generally used for scanned tests, for on-line or in-process tests on moving parts, and for optimizing sound waves propagating into sharp grooves, radiuses, or channels in test objects that have complex geometry.
5. Dual Element Probes
Dual element probes are commonly known as “duals”. These probes have separate elements for transmitting and receiving sound waves. These elements are mounted on a delay line at a small angle. This is done to focus sound waves at a selected distance beneath the surface of the test object. These probes are used generally for testing rough and corroded surfaces as they have a higher sensitivity to pitting with good near-surface resolution. These are also used for high-temperature testing and detecting flaws in rough-surfaced castings.
Precautions while Using Ultrasonic Probes
Though ultrasonic probes from quality manufacturers like Modsonic are sturdy and reliable equipment yet take these precautions for their lasting use.
a. Protect them from excessive shock and vibration.
b. Avoid scraping them against rough surfaces to prevent abrasion.
c. Avoid exposure to corrosive liquids.
d. Protect from overheating (more than 52 degrees Celsius) unless specified.
Importance and Functions of Ultrasonic Probes
These probes are used for various purposes in a wide range of industrial applications. Their importance can be gauged by the fact that they are vital for so many industries for maximizing efficiency and streamlining the production process through precise measurement and control. Let us look at some of the uses of ultrasonic probes.
a. In Manufacturing and Other Industries
Ultrasonic probes are used in production line management, for counting of a large workforce, for detecting broken down wires and threads, detecting vehicles for automotive assembly and car wash, stacking height control, assessment of liquid levels, robotic sensing, irregular parts detection for feeder bowls and hoppers, and for measuring the distance between objects among countless other functions.
b. In Health Care & Medical Field
Ultrasonic probes are used for a wide range of functions in the health care sector. These include diagnostic tests, testing of internal organs like eyes, heart, and uterus, and for detecting tumors helpful in cancer detection. Ultrasound waves generated by these probes help reduce joint pains. These waves also cauterize tumors requiring localized heating. Their vibrations also help remove bladder and kidney stones.
c. In Chemical Industry
Ultrasonic waves produce cavitation (form bubbles) that results in an electric discharge. It acts as a catalyst in chemical reactions including oxidation and reduction, polymerization and depolymerization, molecular rearrangement, and hydrolysis. Catalytic activity results in efficient and fast chemical reactions at low or room temperature. Therefore, ultrasonic probes are used in several industries that utilize chemicals. It results in larger savings and reduced adverse effects on the environment.
d. For Cleaning Sensitive and Precious Items
Ultrasonic probes are used for cleaning sensitive and precious objects. As we explained above, ultrasonic waves create cavitation, bubbles, and vibrations. These probes are placed in a liquid medium along with the objects to be cleaned. The vibrations caused by the probes result in the cleaning of the object. The objects meant for cleaning include small machinery, jewelry, dentures, and other surgical instruments.
6. With Ultrasonic Flaw Detectors
Ultrasonic probes are an essential component of flaw detectors. Due to the waves generated by them, the flaw detectors can detect corrosion in pipes and pressure vessels, inspect welding bonds, and check the integrity of critical and essential structures like railroad rails, metal towers, and beams and pins of bridges.
Ultrasonic probes are an essential part of any ultrasonic testing equipment. These are used for a variety of purposes in a wide range of industries. Modsonic is the leading ultrasonic probe manufacturer in India. They also manufacture other Ultrasonic testing devices like flaw detectors, reference and calibration blocks, and ultrasonic thickness gauges among several others. Browse their site for purchasing high-quality and reliable ultrasonic testing equipment.