Basic Phased Array Introduction (V1)

Basic Phased Array Introduction

April, 2007

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Introduction To Ultrasonic Testing (UT) Ultrasonic test instruments have

been used in industrial applications for more than sixty years. Since the 1940s, the laws of physics that govern the propagation of high frequency sound waves through solid materials have been used to detect hidden cracks, voids, porosity, and other internal discontinuities in metals, composites, plastics, and ceramics, as well as to measure thickness and analyze material properties.

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Conventional UT Basic Theory Sound waves are simply organized mechanical vibrations

traveling through a medium. These waves will travel through a given medium at a specific speed or velocity, in a predictable direction, and when they encounter a boundary with a different medium they will be reflected or transmitted according to simple rules.

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Phased ArrayProbe Configuration

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Conventional UT Probe Configuration With a conventional UT probe, a single piezoelectric

element converts an electrical signal into a mechanical vibration.

Source: NDT Resource Center(www.ndt-ed.org)

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Phased Array Probe Configuration Essentially, a phased-array probe is a long

conventional probe

cut into many small elements, which are individually excited.

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Phased Array Probe Configuration It is like having many small conventional UT

probes integrated inside a single probe.

…

128 elements !

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Phased Array Probe Configuration PA probes are based on

composite technology. The signal-to-noise ratio

obtained from composite transducers is typically 10 to 30 dB greater compared with piezoceramic probes.

A metallic layer is deposited on the piezocomposite.

This metallic layer conforms to the element pattern and provides electrical contacts for each element.

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Phased Array Beam Forming

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How Does Phased Array Work?

Ultrasonic phased arrays consist of a series of individual elements, each with its own connector, time delay circuit, and A/D converter.

Elements are acoustically insulated from each other.

Elements are pulsed in groups with precalculated time delays for each element (i.e., “phasing”).

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Beam Forming – Emission

Appropriate delays introduced electronically during emission to generate a specific beam

Beam forming requires precise pulsing and time delays

Acoustic beam generated by Huyghens principle

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Beam Forming – Reception

Receiving is the opposite of pulsing. Appropriate delays are introduced electronically

during reception. Only signals satisfying the delay law shall be in

phase and generate a significant signal after summation.

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Beam Forming When no time delay is applied between each element

(elements in the array are yellow and the delay applied to each element is in green), a PA probe becomes like a conventional UT probe.

Conventional UT probe(contact probe)

Phased array probe(simulating a conv. UT contact probe)

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Beam Steering Provides the capability to modify the refracted angle of the beam

generated by the array probe. Allows for multiple angle inspections, using a single probe Applies symmetrical (e.g., linear) focal laws.

Conventional UT probe(angle beam probe)

Phased array probe(simulating a conv. UT angle beam probe)

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Beam Focusing Provides the capability to converge the acoustic energy onto a small

focal spot. Allows for focusing at several depths, using a single probe. Applies a symmetrical (e.g., parabolic) focal law for a normal beam.

Conventional UT probe(Focused probe)

Phased array probe(simulating a conv. UT focused probe)

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Beam Steering + Focusing By combining both steering and focusing focal laws (delay

applied to each element is in green), the focal point can be angled.

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Summary of Beam Forming Types Using a single group of elements, on the same probe,

different beam configurations can be performed:

No time delay Steering Focusing Steering + focusing

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Phased Array Scanning Types

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Linear Electronic Scan

The movement of the acoustic beam is along the axis of the array, without any mechanical movement.

The beam movement is performed by time multiplexing of the active elements. Arrays are multiplexed using the same focal law.

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Sectorial Scan The ability to scan a

complete sector of volume without any probe movement.

Useful for inspection of complex geometries, or geometries with space restrictions.

Combines the advantages of a wide beam and/or multiple focused probes in a single phased array probe.

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Depth Focusing Scan Instead of requiring one focal law for each depth position,

the DDF (dynamic depth focusing) algorithm allows the use of a single pulsed focal law by dynamically changing the focusing depth at reception of the signal.

DDF is an excellent way of inspecting thick components with a single pulse.

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Summary of Scan Types Electronic pulsing and receiving allows a great

variety of scan patterns using the same probe.Linear Electronic Scan Sectorial Scan Depth Focusing Scan

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Phased Array Imaging

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Conventional UT A-Scan An A-scan is a simple RF waveform representation

showing the time and amplitude of an ultrasonic signal, as commonly provided by conventional ultrasonic flaw detectors.

An A-scan waveform represents the reflections from one sound beam position in the test piece.

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Color-Encoded A-Scan Signal Additional imaging capability is provided for the rectified A-scan signal

by color encoding the amplitude. This allows the representation of various phased array views, which is to be explained in later slides.

Color-encodedA-scan (beam)

83% = Red

50% = Green

20% = Blue

Ultrasonic path / TOF

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Imaging – Linear Electronic Scan By using the electronic

scanning capability of the phased array technology, imaging becomes possible without mechanical movement.

Arrays are multiplexed using the same focal law and the resulting A-scan of each beam is color-encoded and displayed in a linear S-scan.

Beams

1 2 3 4 5 6 7 8 9 10111213Beams

1 2 3 4 5 6 7 8 9 101112 13

d

d

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Imaging – Linear Electronic Scan Because of the short distance between each element in a

phased array probe, the electronic scan resolution is very precise.

Linear S-scan

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Imaging – Linear Electronic Scan A linear electronic scan can also be performed with a

steering angle (15° in the image below).

Linear Angle S-scan

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Imaging – Sectorial Scan A typical Sectorial Scan sweeps through a range of angles

using the same focal distance and elements.

Beams 12

3

4

Beams 1

2

3

4

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Imaging – Sectorial Scan Using a small angle step value, the sectorial scan

resolution is very precise.

Thank you!