Phased array ultrasonics

Key takeaways

Phased array ultrasonics belongs to science; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Phased array ultrasonics to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Phased array ultrasonics from memory before moving on to harder problems.

Reference excerpt

Phased array ultrasonics (PA) is an advanced method of ultrasonic testing that has applications in medical imaging and industrial nondestructive testing. Common applications are to noninvasively examine the heart or to find flaws in manufactured materials such as welds. Single-element (non-phased array) probes, known technically as monolithic probes, emit a beam in a fixed direction. To test or interrogate a large volume of material, a conventional probe must be physically scanned (moved or turned) to sweep the beam through the area of interest. In contrast, the beam from a phased array probe can be focused and swept electronically without moving the probe. The beam is controllable because a phased array probe is made up of multiple small elements, each of which can be pulsed individually at a computer-calculated timing. The term phased refers to the timing, and the term array refers to the multiple elements. Phased array ultrasonic testing is based on principles of wave physics, which also have applications in fields such as optics and electromagnetic antennae.

Principle of operation The PA probe consists of many small ultrasonic transducers, each of which can be pulsed independently. By varying the timing, for instance by making the pulse from each transducer progressively delayed going up the line, a pattern of constructive interference is set up that results in radiating a quasi-plane ultrasonic beam at a set angle depending on the progressive time delay. In other words, by changing the progressive time delay the beam can be steered electronically. It can be swept like a search-light through the tissue or object being examined, and the data from multiple beams are put together to make a visual image showing a slice through the object.

Use in industry Phased array is widely used for nondestructive testing (NDT) in several industrial sectors, such as construction, pipelines, and power generation. This method is an advanced NDT method that is used to detect discontinuities i.e. cracks or flaws and thereby determine component quality. Due to the possibility to control parameters such as beam angle and focal distance, this method is very efficient regarding the defect detection and speed of testing. Apart from detecting flaws in components, phased array can also be used for wall thickness measurements in conjunction with corrosion testing. Phased array can be used for the following industrial purposes:

Inspection of welds Thickness measurements Corrosion inspection PAUT Validation/Demonstration Blocks Rolling stock inspection (wheels and axles) PAUT & TOFD Standard Calibration Blocks

Features

The method most commonly used for medical ultrasonography. Multiple probe elements produce a steerable and focused beam. Focal spot size depends on probe active aperture (A), wavelength (λ) and focal length (F). Focusing is limited to the near field of the phased array probe.

Focal spot size = F λ / A {\displaystyle {\text{Focal spot size}}=F\lambda /A}

Near Field = A 2 / 4 λ {\displaystyle {\text{Near Field}}=A^{2}/4\lambda }

Produces an image that shows a slice through the object. Compared to conventional, single-element ultrasonic testing systems, PA instruments and probes are more complex and expensive. In industry, PA technicians require more experience and training than conventional UT technicians.

Standards European Committee for Standardization (CEN)

prEN 16018, Non destructive testing - Terminology - Terms used in ultrasonic testing with phased arrays ISO/WD 13588, Non-destructive testing of welds – Ultrasonic testing – Use of (semi-) automated phased array technology

See also Phased array (general theory and electromagnetic telecommunications). Phased array optics

References

Books ASME Boiler and Pressure Vessel Code. American Society Of Mechanical Engineers, 2013. Section V — Nondestructive Examination. [See Article 4 — Ultrasonic Examination Methods for Welds. Para E-474 UT-Phased Array Technique]

External links FOCUS - Fast Object-oriented C++ Ultrasound Simulator [MATLAB routines for creating and simulating phased arrays] Phased array animated simulator [registration required after 5 minutes' use]

Illustrations

Phased array ultrasonics: Animation showing the principle of an ultrasonic scanner used in medical ultrasonic imaging. It consists of a beamforming oscillator (TX) that produces an electronic signal consisting of pulses of sine waves oscillating at an ultrasonic frequency, which is applied to an array of ultrasonic transducers (T) in contact with the skin surface that convert the electric signal into ultrasonic waves traveling through the tissue. The timing of the pulses emitted by each transducer is controlled by programmable delay units (φ) that are controlled by a microprocessor control system (C). The moving red lines are the wavefronts of the ultrasonic waves from each transducer. The wavefronts are spherical, but they combine (superpose) to form plane waves, creating a beam of sound traveling in a specific direction. Since the pulse from each transducer is progressively delayed going up the line, each transducer emits its pulse after the one below it. This results in a beam of sound waves emitted at an angle (θ) to the array. By changing the pulse delays, the computer can scan the beam of ultrasound in a raster pattern across the tissue. Echoes reflected by different density tissue, received by the transducers, build up an image of the underlying structures. — Animation showing the principle of an ultrasonic scanner used in medical ultrasonic imaging. It consists of a beamforming oscillator (TX) that produces an electronic signal consisting of pulses of sine waves oscillating at an ultrasonic frequency, which is applied to an array of ultrasonic transducers (T) in contact with the skin surface that convert the electric signal into ultrasonic waves traveling through the tissue. The timing of the pulses emitted by each transducer is controlled by programmable delay units (φ) that are controlled by a microprocessor control system (C). The moving red lines are the wavefronts of the ultrasonic waves from each transducer. The wavefronts are spherical, but they combine (superpose) to form plane waves, creating a beam of sound traveling in a specific direction. Since the pulse from each transducer is progressively delayed going up the line, each transducer emits its pulse after the one below it. This results in a beam of sound waves emitted at an angle (θ) to the array. By changing the pulse delays, the computer can scan the beam of ultrasound in a raster pattern across the tissue. Echoes reflected by different density tissue, received by the transducers, build up an image of the underlying structures.

Worked examples

Example 1 — a first encounter with Phased array ultrasonics

Start with the simplest possible case. Write down what Phased array ultrasonics claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In science, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Phased array ultrasonics before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Phased array ultrasonics ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Phased array ultrasonics

In research: Phased array ultrasonics appears in science research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Phased array ultrasonics in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Phased array ultrasonics is common in secondary-school and first-year university syllabi. It links to neighbouring topics Medical ultrasonography, Nondestructive testing, Ultrasound, so understanding it makes those chapters shorter.
In everyday life: Look for Phased array ultrasonics outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

How to study Phased array ultrasonics in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Phased array ultrasonics means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Phased array ultrasonics out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Phased array ultrasonics in simple terms?

Phased array ultrasonics (PA) is an advanced method of ultrasonic testing that has applications in medical imaging and industrial nondestructive testing. Common applications are to noninvasively examine the heart or to find flaws in manufactured materials such as welds.

Why does Phased array ultrasonics matter?

Because it connects several science ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Phased array ultrasonics?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Phased array ultrasonics.