to view how Phased Arrays works - DE-TECT Unit Inspection

How Phased Arrays Work 

and What Can They do? 

Houston Open House 

January 15-17, 15 17, 2003

Phased arrays – a definition 

✦ A mosaic of transducer elem ents in which 

the timing of the elem ents' excitation can 

be individually controlled to produce certain 

desired effects, such as steering the beam 

axis or focusing the beam . 

Source: NDT On-line

Illustration -Beam Beam Generation and Focusing 

Beam shaping is 

performed by pulsing 

the elements with 

different time delays. 

This picture shows the 

elements in the array, 

and the delay applied 

to each element 

These time delays 

(green histogram) 

generate a focused 

normal beam, from the 

symmetrical 

“parabolic” time 

delays

For shear waves, 

the time delay 

pattern has a 

“slant” as shown 

here. 

Focusing can be 

performed by 

using “parabolic” 

time delays (see 

previous slide), 

as well as the 

slant. 

Illustration -Beam Beam Deflection

Illustration -Beam Beam Deflection and Focusing 

The picture shows the 

generated beams in very 

early, mid-stage, late and 

at focus. 

For angling and focusing, 

we use a combined slant 

and parabola.

Beam Generation

Physics of Phased Arrays


✦ Ultrasonic phased arrays consist of a series of 

individual elem ents, each with its own connector, 

time delay circuit, and A/D converter. 

✦ Elem ents are acoustically insulated from each 

other. 

✦ Elem ents are pulsed in groups with pre-calculated 

time delays for each elem ent, i.e. “phasing”. 

✦ For econom ic reasons, pulsersare usually 

multiplexed. Instrum entation nom enclature such 

as a FO CU S 32/128 refers to an instrum ent with 

32 multiplexed pulsersand a total of 128 

ultrasonic channels.


✦ The elem ents are purchased as an “array” with 

known geom etry. 

✦ These arrays are manufactured using several 

“designs”, and each array is specifically built for 

the application, as with conventional ultrasonic 

transducers. 

✦ Typical array designs are: 

–Linear 

–Matrix 

–Circular 

–Sectorial-annular

Y=4.4 

Y=8.0 

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 

X=-7.9, Y=-8.0 --> X=7.9 

X=-4.4, Y=-4.4 --> X=4.4 

1 

45678910111213141516 

3 

2 

Common Probe Geometry’s 

✦ Linear 

–1 D linear 

array 

–2 D matrix 

• Circular 

– 1 D annular 

array 

– 2 D sectorial 

annular 

Y=1.9 

4 

3 

2 

1 

8 

7 

6 

5 

12 

11 

10 

9 

X=-3.9, Y=-1.9 --> X=3.9 

Y=6.5 

51 

52 

50 

53 

33 

34 

49 

32 

35 

54 

19 

20 

48 

31 

18 

21 

36 

55 

9 

10 

X=-6.5, Y=-6.5 --> X=6.5 

47 

30 

17 

8 

3 

16 

15 

14 

13 

1 

46 

29 

16 

7 

2 

4 5 

11 12 

22 23 

37 38 

56 57 

20 

19 

18 

17 

6 

13 

45 

28 

15 

24 

39 

58 

14 

25 

24 

23 

22 

21 

44 

27 

40 

59 

26 

41 

43 

60 

28 

27 

26 

25 

42 

61 

32 

31 

30 

29

Phased-array 

Phased array probe 

Basically, a phased-array is a long conventional probe 

Cut into many elements


✦ Linear arrays are the most common type, and can 

perform scanning in one dimension only. Linear 

arrays typically minimize the num ber of elem ents 

required, and hence cost. 

✦ Matrix arrays can scan in two dimensions, and 

offer considerably more flexibility, albeit at a price. 

✦ Circular and sectorial-annular arrays are specific 

for normal beam inspections, e.g. billets, forgings.


✦ The operator inputs the focal depth(s), inspection 

angle(s) and/or couplant, plus how many and 

which elem ents are to be fired. 

✦ The operator also must input details on the array 

and wedge. (T his information is engraved on the 

side of the array and wedge.) 

✦ The phased array calculator calculates what time 

delays to apply to each elem ent. 

✦ The operation of the calculator is shown in the 

next slides. 

✦ For standard scans (e.g. electronic or sectorial), 

the set-up is essentially straightforward.

Operator defines depth and refracted angle 

The calculator searchs the Snell point. It considers the center of the active aperture 

(from elements2 to 7 in this example). 

Then, the X, Z point of the focal point is determined 

The wedge delay is calculated and the focal law is offset accordingly 

Depth 

law scan offset 

Snell point 

Angle 

Xaxis or Scan axis 

interface 

Focal point(X,Z)


✦ The calculator produces a file called a 

FO C A L LA W , which defines the elem ents 

to be fired, time delays, voltages, for both 

the transmitter and receiver functions. 

✦ This is an ASCII file, and can be edited, emailed 

etc. as required.

Phased Array Basics 

•For linear scans, arrays are multiplexed using the same Focal Law. 

•For sectorial scans, the same elements are used, but the Focal Laws are 

changed. 

•For DDF, the receiver Focal Laws are changed in hardware.

Phased Array Beamforming 

Beamforming requires precise pulsing and time delays. 

Receiving is the reverse of pulsing.

UT Phased-Array 

Phased Array 

Principles & Capabilities

Introduction 

✦ Phased-array technology is the ability to modify 

electronically the acoustic probe characteristics 

✦ Probe modifications are performed by introducing 

time shiftsin the signals sent to (pulse) and 

received from (echo) individual elem entsof an 

array probe. 

✦ Any UT technique for flaw detection and sizing 

can be applied using phased-array probes.

Conventional Waveform ing 

Excitation pulse 

Crystal 

A B C 

Wave front 

Wedge 

Material 

Delay 

A B C 

Location 

✦ Beam steering using conventional UT probe (EM ISSION) : 

– acoustic beam generated by Huyghensprinciple 

– angled wedge introduces appropriate delays during em ission to 

generate angle beam

Phased-Array 

Phased Array Waveform ing 

Time 

Wave front 

Delay 

Focal law 

Element 

✦ Beam steering using phased-array probe (EM ISSION) : 

– acoustic beam generated by Huyghensprinciple 

– appropriate delays introduced electronically during em ission to 

generate angle beam



S 

✦ Beam steering using phased-array probe (R EC EPT ION) : 

– appropriate delays introduced electronically during reception 

– Only signals “satisfying” delay law shall be “in phase” and generate 

significant signal after sum m ation 

∑



Global overview of phased-array signal processing

Design Param eters of Phased-Array Phased Array Probes 

e 

A 

p g 

H

Beam Focusing 

✦ Is the capability to converge the acoustic energy 

into a small focal spot 

✦ Allows for focusing at several depths, using a 

single probe 

✦ Sym m etrical (e.g. parabolic) focal law s (time delay 

vs. elem ent position) 

✦ Is limited to near-field only 

✦ Can only perform ed in the steering plane, when 

using a 1D -array

Beam Steering 

✦ Is the capability to modify the refracted angleof 

the beam generated by the array probe. 

✦ Allows for multiple angle inspections, using a 

single probe 

✦ Applies asym m etrical (e.g. linear) focal law s 

✦ Can only be perform ed in steering plane, when 

using 1D -arrays 

✦ Can generate both L (com pression) and SV (shear 

vertical) waves, using a single probe

Electronical(Linear) Electronical(Linear) 

Scanning 

✦ Is the ability to move the acoustic beam along the 

axis of the array without any m echanical movement. 

✦ The beam movement is performed by time 

multiplexing of the active elem ents 

✦ Scanning extent is limited by : 

–number of elem ents in array 

–number of “channels” in acquisition system

Combined Beam Processing 

✦ The phased-array technique allows for 

almost any com bination of processing 

capabilities : 

–focusing + steering 

–linear scanning + steering 

–…

Other Types of Array Probes 

DUAL-ARRAY PRO BES : 

✦ Consist of separate transmitter (T ) and 

R eceiver (R ) arrays 

✦ In side-by-side configuration, all considerations for 

conventional TRL probes rem ain valid : 

–Pseudo-focusing effect 

–Absence of interface echo 

–Improved SN R in attenuating materials 

✦ In addition, all advantages of the PA technique 

are available

What Phased Arrays Can Do


✦ This section illustrates typical scans that can be 

performed using phased arrays: 

–Electronic (linear) scans 

–Sectorial (azimuthal) scans 

–Transverse scans 

–Dynamic Depth Focusing 

–Time-Of-Flight Diffraction 

✦ With the Tomoview software, operators can 

custom -design their own scan patterns, displays 

and output.

Electronic or Linear Scanning 

Multiplex A Single Focal Law 

Across the Array

✦ The ability to move the beam 

along one axis of an array without 

any m echanical movement. 

✦ The movement is perform ed only 

by time multiplexing the active 

elem ent 

✦ The beam movement depends on 

the probe geom etry and could be 

–linear scanning 

–sectorial scanning 

–lateral scanning 

–a com bination 

Electronic Scanning

Electronic Scanning 

This animation shows a conceptual weld inspection using electronic 

(linear) scanning. This approach can easily emulate typical ASMEtype 

45 and 60 shear wave inspections, and is much faster than raster 

scanning. 

Typical weld inspection requires two or more angles with implied 

raster size, step size etc. Need to cover weld, HAZ, any position 

errors => significant amount of scanning.

Electronic (linear) Scanning on 

Circular Components 

Electronic scanning permits very rapid scanning of components 

with constant geometry, e.g. tubes, pipes.

Tandem Probes for Vertical Defects

Sectorial (A zimuthal) Scanning 

Changing the Inspection Angle 

without M oving the Array

Illustration of Sectorial Scanning

Sectorial Scanning 

✦ Sectorial scanning is the ability to scan a 

com plete sector of the volum e without any 

probe movement. 

✦ Useful for inspection of com plex geom etry’s or 

those with space restrictions 

✦ Combines the advantage of wide beam and/or 

multiple focused probes in a single phased array 

probe 

1 

2...... 

N

Sectorial (A zimuthal) Scans 

Sectorial scanning – by changing the 

incident angle without changing position – 

can be used for a variety of inspections.

This illustration 

shows a turbine blade 

root being inspected 

using S-scans 

(sectorial scanning). 

Sectorial Scanning Animation

Turbine Welded Rotor Inspection 

Phased-array inspection: 

•Sectorial scan 30-60 SW 

•Step of 1 degree 

•Mechanical scan along the 

circumferential axis 

Phased-array probe: 

5 MHz, 16 elements, 16 mm x 

16 mm 

mounted on a wedge 

Calibration block: 

EDM notches 2 mm x 0.5 mm

Electronic/Sectorial Scanning Animation

Combined S-Scan S Scan and Linear Scan 

✦ Combined scans 

offer unique 

imaging 

possibilities

Dynamic Depth Focusing 

Extending the Focal Range 

Electronically

DDF is an 

excellent way 

of inspecting 

thick 

components in 

a single pulse. 

The beam is 

re-focused 

electronically 

on its return 

Schematic Representation of 


Beam displacement 

c = velocity in material 

Mechanical Displacement 

FOCUS DEPTH (PULSER) 

DYNAMIC FOCUSING (RECEIVER)


Standard phased 

array 

Phased A rray with 

Dynamic Depth 

Focusing

Dynamic Depth Focusing Animation

Time-Of TimeOf-Flight 

Flight Diffraction 

Optimum Sizing Technique for 

Thicker Components

Transmitter 

TOFD using Phased Arrays – 

sam e as conventional UT 

LW 

Lateral wave 

Upper tip Lower tip 

Back-wall reflection 

Receiver 

BW

What Do TOFD Scans Look Like? 

Lateral wave is clearly 

seen in a good TOFD 

scan (top signal). 

Backwall signal is 

strong (bottom signal). 

Both typically used 

for calibration. 

On clean material, 

defects show up well. 

Backwall is always 

strong. Watch for 

perturbations due to 

surface-breaking 

defects (also on lateral 

wave).

R/D Tech Products 

Hardware and Software Available for 

Your Application

Leader in Phased Array Technology 

✦ First system on site 

1993 

✦ More than 400 PA units 

sold 

✦ Improved technology 

4 th generation 

✦ Advanced PA 

technology 

✦ DDF-VFT-TRM

FO C U S Phased Array System 

FOCUS Phased Array 

System 

◗ PC interface 

◗ Up to 128 channels 

◗ 20 kHz PRF and 

◗ 20 MHz bandwidth

An economical 

solution for 

industrial 

requirements, e.g. 

in-line inspections 

on production plant. 

Rack-mounted. 

Similar capabilities 

to FOCUS, but less 

flexible. 

Industrial Product Line 

QuickScan PA

Menu 

ACCEPT 

Start/ 

Stop 

---> 

1 

CONFIG 

ABC 

4 

TOOLS 

JKL 

7 

USER 

STU 

+/- 

CHANNEL 

_ %# 

2 

FILE 

DEF 

5 

Utilities 

MNO 

8 

FREEZE 

VWX 

0 

. * 

Omniscan – Portable PA Unit 

Function keys and knob interface for field used 

Cursors 

ESC 

Store / 

Print 

Instrum entation Nomenclature 

✦ Phased array units (FO C U S or Quickscan) 

are defined as two num bers divided by a 

backslash, e.g. 32/128. 

✦ This refers to an instrum ent with 32 

multiplexed pulsersand 128 individual 

channels. 

✦ R/D Tech instrum ents are supplied in binary 

sizes, e.g. 16/64, 16/128, 32/256 …. 

✦ Instrum ents are custom -built for the 

application.

Software 

Tomoview : phased array software, 

which can be set-up or tailored to 

your requirem ents.

TomoView 

PC-based UT software 

◗ Real-time, multichannel, 

angle-corrected top, side, 

and front view s 

◗ Pulse-echo and TOFD functions 

◗ Logarithm ic and linear 

12-bit data 

◗ RF, com pressed,and C-scan data 

◗ Weld overlays 

◗ User-defined screen and report 

layouts 

◗ Handles GB-size data files 

◗ Online and offline modes

C orrected S-scan scan View

Merging of data 

✦ Raw UT data generated by different focal 

law s (angles, focusing depths) can be 

merged off-lineto generate new UT data 

✦ Merged data contain maximum am plitude 

of the different focal law s 

✦ Merged data can be treated as regular data, 

and visualised as VC Top (C -scan), Side (Bscan) 

and End (D -scan) View s 

✦ Time-saving during data analysis

Sum m ary – FO C U S, Quickscan & Tomoview 

✦ FO CU S: 

–Commercial system , ~four years old 

–Over two hundred and fifty sold 

–In service 24/7 in several industries 

✦ Quickscan: 

–Industrial version of FO CU S 

– 19” rack-mounted 

–Less flexible than FO CU S, but cheaper 

✦ Omniscan: 

–New, portable phased array system 

✦ Tomoview : 

–Established commercial software 

–Widely used on hundreds of system s 

–Very flexible for inspections, displays, windows etc.

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