Ultrasonic Transducer Types: How to Choose Your Right Ultrasonic Transducer?

Won’t you be relieved if you had a formula that simply helps you choose the right ultrasonic transducer that meets your inspection needs?

As an essential element in an ultrasonic testing device, your transducer should not just be left to a trial-and-error process to decide. You should critically think through your choice of a transducer and only select after following essential steps to ensure that you choose the right transducer that meets inspection requirements.

This guide gives you all the types of transducers available in the market today and what you need to out for when selecting a transducer for your inspection needs.

Are you ready to learn more? Then, let’s dive in together.

What are the Types of Ultrasonic Transducers?

Ultrasonic transducers come in different shapes, sizes, and formations. The type you choose has a lot to do with the inspection requirements you’re looking at and the level of accuracy you seek. However, you might also want to consider other features unique to certain ultrasonic transducer types. These features may give them an advantage over other types for specific inspection requirements. So, let’s look at these ultrasonic transducers in greater depth and their various uniqueness, including their applications. 

• Linear Transducers

The linear arrangement of the piezoelectric crystals have earned these transducers their name. Linear transducers have universal applications and are used for almost all ultrasonic testing. These Piezoelectric crystals are Rochelle salt, ceramics, and quartz crystals.

• Standard Transducers

These transducers are also known as convex transducers due to their possession of curved piezoelectric crystals. Where there is a need for in-depth examination, these transducers have been very effective. 

• Phased Array Transducers 

Having several elements housed within a case, with each functioning separately but as a unit within a larger unit, is the unique feature of the phased array transducer. Sometimes the number of elements can be 16 or as high as 256. Still, their arrangement enables a programmed pattern of pulse projection. The versatility of the phased array transducer is such that it can serve for both contact and immersion inspection, and it can also use different wedge types. 

More importantly, phased array transducers can test frequencies within 1 and 10 MHz Their pulse shapes can be circular, square, or rectangular. Yet they offer numerous benefits, which technicians often attribute to their steering ability and the number of elements functioning as a pulse generator unit. The possibility of sweeping the beam from a single position increases inspection speed, mainly where the test sample has limited space for physical scanning. 

• Immersion Ultrasonic Transducers

This transducer is suitable for automated inspection as it is very effective when there is a need to carry out a contactless assessment. With the immersion ultrasonic transducer, a column of water is often used to project sound energy to the object. The single-element transducer’s piezoelectric element receives and converts the sound energy to electrical pulses. One advantage of this transducer is its quick coupling speed, which makes it fast for the inspector to carry out their assessment of the test sample. 

Also, a focused immersion transducer is an option that ensures that critical parts of a test sample receive maximum benefits with higher sensitivity and increased performance from the transducer. Consequently, applications of immersion transducers are often typical with complex shapes and objects with grooves, contours, and channels where inspectors need to optimize sound couplings. Additionally, it is effective for in-process and automated scanning, amplitude-based imaging, and transmission testing. 

• Dual Element Ultrasonic Transducers

For this transducer, two crystal elements are involved (as the name implies) divided into two compartments using an acoustic barrier but within the same container. However, they function differently, with one element producing the sound waves while the other receives the sound signal. Still, the inspector must position both elements in a V-shaped formation for the test sample’s sound path. 

Nonetheless, there is an enhancement of the focal zone resolution, which occurs as the sound waves pass under the sample’s surface. This feature makes this transducer very effective in corrosion measurements, especially for ascertaining the wall thickness left. It is also very effective for inspecting welding quality, porosity, cracks, inclusions, and lamination integrity. 

• Angle Beam Ultrasonic Transducers

The generation and projection of refracted shear waves into the test sample is the purpose of using an angle beam ultrasonic transducer for quality assessment tests. Likewise, it can also project a longitudinal wave through a test sample with the help of a wedge. All the same, the sound wave produced is usually at an angle, and it doesn’t matter if you use an integral or a removable wedge. 

The standard industrial application of an angle beam ultrasonic transducer is for a weld integrity inspection, which requires an angle projection of sound waves. Similarly, it is effective for identifying defects such as cracks and porosity. On the other hand, the available options of wedges needed for this type of transducer are numerous. These wedges include both short-distance wedges and high-temperature befitting wedges. What’s more, some of the wedges are customizable. 

• Delay Line Ultrasonic Transducer 

While this single element transducer pulses and receives the signal through the same element, it is in no way limited in precision. It is designed to work with a delay line which is replaceable but with an introduction of a delay from projection to the reception of the sound waves. This delay improves the near-surface resolution of the waves for increased result accuracy. Some typical applications of the delay line ultrasonic transducer include thickness gauging, an inspection of parts with limited access, and flaw detection. 

• Ultrasonic Contact Transducer

For testing scenarios in a well-spaced environment without any hindrance to accessing the test sample, a contact ultrasonic transducer can come in handy. This transducer comes in direct contact with the test sample and transmits the sound waves through the material surface. However, because it has a single element makeup, it sends and receives signals using the same element. It then converts to electric signals for analysis. Also, it is made to withstand very rugged use as its surface is made with surface-resistant optimized material. So, this property makes it ideal for testing industrial components where the environment is a bit rough. All the same, there are different forms and styles available for this transducer giving individuals many options. Some Common applications for contact ultrasonic transducers include thickness gauging, velocity measurements, and flaw detection. 

• High-Temperature Transducers

In cases where high temperature is a worry since temperature instability can negatively impact testing accuracy, a special ultrasonic transducer is always the best option. The high-temperature transducer is a special transducer that can effectively assess the quality of a test sample even in the extremes of the temperature of more than 50° C or 125° F, as obtainable with conventional transducers. The damage on conventional transducers can be permanent once the test sample temperature exceeds 50° C or 125° F. Hence, it is best to employ other specialized testing methods, including using high-temperature transducers to avoid internal disbanding of the elements of a conventional transducer. Still, high-temperature transducers are highly applicable in thickness gauge and corrosion measurements.

How to Choose the Right Ultrasonic Transducer?

One important reason you should be acquainted with ultrasonic transducers is to know the benefits they offer and select a suitable one that fits your peculiar inspection requirements. However, choosing a suitable ultrasonic transducer also involves critically assessing the factors, with the most important ones highlighted below. 

• Application – The type of testing application is the first factor you should consider when choosing the right ultrasonic transducer for your testing. For instance, if your application involves corrosion testing of wall thickness gauge measurement, your choice of the ultrasonic transducer will differ from another individual looking to weld cracks. 
• Material geometry – This factor is sometimes erroneously overlooked by some technicians when deciding on the right ultrasonic transducer for their testing. However, awkward shapes and irregular geometries often hamper direct access to some parts of the test sample leading to an inaccurate test result. 
• Environmental factors – while ultrasonic transducers have shown to be an accurate quality assessment device, it has also been susceptible to changes in environmental parameters, especially temperature. The high sensitivity of transducers to a change in temperature often gives inaccurate results. Hence, considering this will help you select the most suitable ultrasonic transducer, primarily if you work in an environment with fluctuating temperatures. 
• The level of accuracy – Some tests require a high level of precision and often require an ultrasonic transducer with unique features and abilities. Ensuring you are familiar with the test and the necessary level of accuracy will give you the essential criteria to select the best-suited ultrasonic testing for your testing requirements. 
• The manufacturer – Various ultrasonic transducer manufacturers, exist. While they all claim to produce the best ultrasonic transducer, not all will meet your expectation. It is critical that you choose your transducer manufacturer carefully, considering their reliability, customer service, after-sales service, and track record of quality product and delivery over the years. 

➤ Related Article: Top 8 Ultrasonic Transducer Manufacturers

Conclusion

In conclusion, choosing the right ultrasonic transducer isn’t that difficult once you are clear on what you must do. As highlighted in this post, the first is an understanding of the available options of ultrasonic transducers that you can find in the market. This first step is critical to match your testing requirements with the available solutions. But then there is more.

You will also need to consider some critical criteria when choosing from the available options you have collated. The most important criteria will include the geometry and properties of the material you want to test, stability of weather conditions like temperature, the level of accuracy, and the supplier’s credibility.

Follow the information given in this post. Choosing the right ultrasonic transducer should be a walk in the park for you.