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Over the past century as the understanding of the physical universe has grown, one of the areas that have received a lot of attention is the phenomenon of sound. Just like in the case of other wave-like phenomena, studying sound has resulted in massive technological advancement.
Today, many industries rely on sound for their operations. They leverage the unmatched properties of sound with the most notable being that it can travel to places where light cannot. Moreover, we have now delved deeper into ultrasonics – this refers to the sound that is not within the audible frequencies. Anything over 20,000 Hz is under this category.
Since they fall outside the realm of human auditory perception, you cannot produce ultrasonic sound in the same way that we do for other sounds. That is where ultrasonic transducers come in. These convert electric energy to acoustic energy and vice versa. Usually, this conversion is a function of a piezoelectric element.
Transducer testing essentially refers to the process of performing a series of operations on your transducer to ensure that it is working correctly and optimally. Just like other electrical components, transduces are prone to wear out or take a performance hit after extended use or physical damage.
Considering how vital they are to many modern systems, transducer testing is very important. This is the only way to guarantee their accuracy and efficiency. Ideal, testing and calibration should be carried out periodically across all areas where they are used.
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Ultrasonic transducers are found in several sectors. While each of them will have very specific use cases for the technology within their systems, its working principle is the same across the board. Generally speaking, the applications of ultrasonic transducer testing can be divided into two broad categories. These are:
Medical Applications. – Ultrasonic transducer testing has been key to many medical breakthroughs of the past century. It is used for diagnostic testing, internal organ testing and fetal screening. Not only has it made non-invasive testing and care easier but it has also made medical services more accessible and affordable.
Industrial Applications. – Across several industrial fields, ultrasonic transducers testing has a wide range of use cases. All these have been monumental to industrial growth and continue to revolutionize various aspects of industrial operations. The most common applications in this regard include object detection, liquid level control, detection of wire breaks, product line management in factories, thickness detection and flaw detection among other things.
Depending on factors ranging from frequency, the piezoelectric crystal arrangement, or even the component’s footprint, different manufacturers will have different ways of testing ultrasonic transducers. These are based on the time and frequency domain plots that are provided by the manufacturers.
That said, if you are looking to increase your confidence in both the reliability and the performance of your ultrasonic transducers, there are three types of testing to consider:
For applications that require a high level of accuracy when it comes to beam positioning, this is the best kind of ultrasonic transducer testing. That is simply because it gives you data on the degree of alignment between the transducer housing and the axis of the sound beam. This is with respect to a mechanical reference surface.
This is the best kind of test if what you are looking for is data revolving around the characteristics of the transducer sound field. It works by scanning across a target to create transverse beam profiles at a distance from the transducer face. The profiles are then used to determine the beam’s symmetry and the focal spot size.
For axial beam profiles, the pulse-echo amplitude of the sound field is recorded as a function of distance from the transducer’s face. These profiles give you data on both the focal length and the depth of field.
These tests are great for obtaining vital information about such things as the design and the construction of an ultrasonic transducer. With that, you can easily source electrically similar transducers elsewhere.
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Once you have all the necessary knowledge about ultrasonic transducers, performing actions such as testing should be straightforward. When testing ultrasonic transducers, you should start with the basic physical dimension measurements. You should then follow this with tests to the continuity, shorts and opens of the transducer. Also, to ensure that your transducer does not have any major defect, be sure to test capacitance and loss.
Once done with the basic testing, the next step should be functional testing. Ideally, this should be at ambient conditions which are usually the most optimal. Functional testing often consists of pulse-echo measurement at a specified distance and reflecting off a specified predetermined target.
It involves driving the transducer with a wave from an industry-standard pulse receiver. An oscilloscope is used to monitor the pulse and return signal. Numerical measurements you can make from this include the ring-down, bandwidth and sensitivity. Also measured during functional testing is Total Acoustic Power (TAP) output.
When it comes to determining both the electrical and the acoustic properties of an ultrasonic transducer, there are specific steps you should follow. According to the ASTM E1065 Standard Guide for Evaluating Characteristics of Ultrasonic Transducers, the procedures you should pay attention to are:
There are two procedures that you can use to obtain the frequency. These are sinusoidal burst and shock excitation. Both procedures work well but some manufacturers may specify an optimal procedure for their transducers. This is defined by the peak frequency and the range of frequencies within which the transducer operates. The choice of transducer sensitivity and bandwidth is made based on the application’s needs.
You can also obtain value from the sinusoidal burst procedure’s frequency response data. Typically, the relative pulse-echo sensitivity comes from the relationship of the applied voltage’s amplitude and the specified target’s pulse-echo signal.
This is a way of describing the radio frequency response of the waveform and is obtained using a shock excitation, pulse-echo procedure. Depending on the type of ultrasonic transducer under evaluation, specific targets provide the time or waveform responses.
The value of the complex electrical impedance may provide the magnitude and the impedance of the search unit over its operating frequency range. You may also obtain the value of the magnitude of this characteristic using values gotten from the sinusoidal burst. These measures are made using commercial impedance measuring instruments often in accordance with manufacturer specifications.
You can achieve this by scanning the sound field using a hydrophone transducer to map the sound field in a three-dimensional space. The goal is to create important parameters like the on-axis and transverse sound beam profiles for immersion. It applies to both flat and curved transducers.
Hopefully, this detailed overview of ultrasonic transducers and how to test them is enough to get you started. You will find several basic types of transducers falling under different classifications. As such, you will get to choose the one that suits your application best. That can be based on either the energy source or the medium into which the ultrasonic waves are being generated.
Here is the top ultrasonic transducer manufacturers guide, click to read more if you are looking for the suppliers.
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