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Phased Arrays for NDT: Adding Delay Laws to 2D Array Simulations

By Chloe Allison 12 December 2019

Ultrasonic phased array testing is a powerful non-destructive testing (NDT) technology which is growing rapidly.

A phased array system is based around a specialized ultrasonic transducer that contains many individual elements, which are sequentially pulsed. In NDT the number of elements can range from 16-256. The shapes of the elements can be square, rectangular, or round with test frequencies ranging between 1-10MHz.

Phased arrays pulse and receive from multiple elements generating waves that combine to form a single wave front that is propagating in a desired direction, whilst cancelling components that travel in other directions.

NDTFigure 1. Diagram of a phased array working principle. The wavefronts from each elements combine to create a plane wave. The array of elements is powered by a transmitter (Tx). The computer (c) controls the phase shifter (?)

Phasing technology enables the generation of a vast number of different ultrasonic beam profiles through electronically steering and shaping of the beam.

However, phased arrays cost more for equipment and operator training. Although the cost is offset by their greater flexibility and a reduction in inspection time. More than one scan be performed from a single probe location with various inspection angles.

OnScale enables the design and simulation of phased array probes and thanks to the limitless compute power of cloud supercomputers, massive sweeps of these various inspection angles can be executed in parallel.

How do you accurately simulate a phased array?

Firstly, you need a simulation software like OnScale that can handle the 2-way coupling between voltage, mechanical strain, and acoustic waves.

Moreover, the main solver available in OnScale is a time-domain nonlinear explicit solver. Anything you input and simulate using the software is exactly what you would expect to see from a phased array controller during real-time use of the probe.

OnScale can also simulate signals in the frequency-domain. This can be done postprocessing the time-dependent simulation results through a Fast Fourier Transform (FFT)

Why use a phased array device

An additional benefit of phased arrays over single element (non-phased array) probes technically known as monolithic probes that emit a beam in fixed direction is the ability to radiate multiple beams simultaneously. This means that multiple targets can be tracked at any given time depending on the aperture size of your array.

Typically, with monolithic probes if you wanted to focus the beam at a different location you would need to physically move the probe. With phased array technology more than one scan be performed from a single probe location. Lets imagine we have one probe and know the location of a defect in a steel test piece or the location of a point of interest in a water load we can calculate the necessary delay laws needed to steer and focus the ultrasonic beam to that location. This is what we are going to show you today.

Simulating a phased array making use of delay laws

We will consider a 2D simulation of a phased array where we have placed some steel arbitrarily into a water load. Based on the location of the steel component we will calculate the appropriate delays needed to steer and focus our beam to that location. The probe we are simulating has 16 elements.

Each probe element is being excited individually whilst the delay corresponding to that element is also being applied appropriately.Phased Array

The OnScale model allows the following design variables to be adjusted:

  • Piezoelectric thickness
  • Element thickness
  • Matching thickness

From it we can obtain the following simulation results:

  • Electrical impedance
  • Mode shapes
  • Maximum acoustic pressure
  • Analyze electrical crosstalk on adjacent elements
ElectrodeFigure 2. Results obtained from the 2D phased array simulation. viewport 1 (top left) shows the wave coming into contact with the steel circle in the water, viewport 3 (bottom) shows the electric charge recorded on the top electrode of the first element of the array, viewport 2 (top right) shows the maximum acoustic pressure in the model this shows how the energy from the array is focused towards the point of interest

You can run the simulation yourself by downloading the files available from OnScale’s Help Center here!

If you are new user of OnScale, please get the software by creating your account on our website!

Chloe Allison
Chloe Allison

Chloe Allison is an Application Engineer at OnScale. She received her MA in Electrical and Electronics Engineering from the University of Strathclyde. As part of our engineering team Chloe assists with developing applications, improving our existing software and providing technical support to our customers.

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