-Transducer
Characteristics
The sound field of
an ultrasonic transducer operating at a single frequency is
divided into a near field and a far field zone. The transition
between these zones occurs at a distance Yo+ (or
N) and is sometimes referred to as the "natural focus" of a
flat ( of unfocused ) transducer. The near/far distance Yo+
is significant because amplitude variations that characterize
the near field (and can make flaw evaluation difficult) change
to a smoothly declining amplitude as the distance from the transducer
increases.
The tables presented
here for unfocused and focused ultrasonic transducers represents
a range of typical transducers. An important column in the unfocused
tables, Normal Range of Focusing, shows the normal range
of focusing for immersion transducers in water for both spherical
and cylindrical lenses. The Down Field Focal Zone column
shows the start and end of the Yo+ maxima on the
transducer axis as the distance from the transducer increases.
Spherical or cylindrical
focusing changes the structure of the transducer field by "pulling"
the Yo+ point nearer the transducer, to the focal
point of the transducer. Again, the Down Field Focal Zone
column shows the beginning and end of the focal zone, where
the amplitude falls 6 dB below the maxima at the focal point.
It is important to
note that the driving excitation normally used in NDT applications
are either spike or rectangular pulsars, not single frequency.
They can significantly alter the results shown in both tables.
Nonetheless, the supporting analysis is widely used because
it represents a reasonable approximation and a good starting
point.
Unfocused
-
|
Frequency (MHz)
|
Diameter
(in.)
|
Focal Length
(in)
|
6 dB Spot Size
(in)
|
START
(in)
|
END (in)
|
Focal Gain SPHER. (dB)
|
CYL.
(in)
|
|
1.00
|
1.00
|
2.50
|
.146
|
1.9
|
4.10
|
11.80
|
9.3
|
|
|
|
|
|
|
|
|
|
|
2.25
|
.500
|
1.50
|
.078
|
1.10
|
2.50
|
10.00
|
7.5
|
|
2.25
|
.750
|
2.00
|
.069
|
1.50
|
2.80
|
24.00
|
21.5
|
|
2.25
|
.750
|
3.00
|
.104
|
2.20
|
4.90
|
13.30
|
1.8
|
|
2.25
|
1.000
|
3.00
|
.078
|
2.30
|
3.90
|
27.90
|
25.4
|
|
2.25
|
1.000
|
5.00
|
.130
|
3.80
|
7.90
|
15.00
|
12.5
|
|
|
|
|
|
|
|
|
|
|
5.00
|
.250
|
.75
|
.035
|
.60
|
1.20
|
12.90
|
10.4
|
|
5.00
|
.375
|
1.00
|
.031
|
.80
|
1.30
|
26.50
|
24.0
|
|
5.00
|
.375
|
2.00
|
.062
|
1.50
|
3.50
|
8.30
|
5.8
|
|
5.00
|
.500
|
1.50
|
.035
|
1.20
|
1.90
|
30.20
|
27.7
|
|
5.00
|
.500
|
3.00
|
.070
|
2.20
|
4.90
|
12.90
|
1.4
|
|
5.00
|
.750
|
2.00
|
.031
|
1.60
|
2.20
|
39.20
|
36.7
|
|
5.00
|
.750
|
4.00
|
.062
|
3.10
|
5.40
|
40
|
24.0
|
|
5.00
|
.750
|
6.00
|
.094
|
4.60
|
9.40
|
16.20
|
13.7
|
|
5.00
|
1.000
|
3.00
|
.035
|
2.50
|
3.30
|
41.40
|
38.9
|
|
5.00
|
1.000
|
4.00
|
.047
|
3.20
|
4.60
|
37.50
|
35.0
|
|
5.00
|
1.000
|
6.00
|
.070
|
4.70
|
7.60
|
3.20
|
27.7
|
|
|
|
|
|
|
|
|
|
|
10.00
|
.125
|
.38
|
.018
|
.30
|
.60
|
12.90
|
10.4
|
|
10.00
|
.250
|
.75
|
.018
|
.60
|
1.00
|
30.20
|
27.7
|
|
10.00
|
.250
|
1.50
|
.035
|
1.10
|
2.40
|
12.90
|
10.4
|
|
10.00
|
.375
|
1.00
|
.016
|
.80
|
1.10
|
39.20
|
36.7
|
|
10.00
|
.375
|
2.00
|
.031
|
1.50
|
2.70
|
26.50
|
24.0
|
|
10.00
|
.375
|
3.00
|
.047
|
2.30
|
4.70
|
16.20
|
13.7
|
|
10.00
|
.500
|
1.50
|
.018
|
1.20
|
1.60
|
41.40
|
38.9
|
|
10.00
|
.500
|
3.00
|
.035
|
2.30
|
3.80
|
30.20
|
27.7
|
|
10.00
|
.500
|
5.00
|
.059
|
3.80
|
7.60
|
17.90
|
15.4
|
|
10.00
|
.750
|
3.00
|
.023
|
2.50
|
3.20
|
42.80
|
40.3
|
|
10.00
|
.750
|
4.00
|
.031
|
3.20
|
4.50
|
39.20
|
36.7
|
|
10.00
|
.750
|
6.00
|
.047
|
4.70
|
7.40
|
32.50
|
30.0
|
|
|
|
|
|
|
|
|
|
|
15.00
|
.125
|
.50
|
.016
|
.40
|
.80
|
16.20
|
13.7
|
|
15.00
|
.250
|
.75
|
.012
|
.60
|
.90
|
37.50
|
35.0
|
|
15.00
|
.250
|
1.50
|
.023
|
1.20
|
2.10
|
23.70
|
21.2
|
|
15.00
|
.375
|
1.50
|
.016
|
1.20
|
1.70
|
39.20
|
36.7
|
|
15.00
|
.375
|
2.50
|
.026
|
2.00
|
3.20
|
30.40
|
27.9
|
|
15.00
|
.375
|
4.00
|
.042
|
3.10
|
6.00
|
19.30
|
16.8
|
|
|
|
|
|
|
|
|
|
|
20.00
|
.125
|
.50
|
.012
|
.40
|
.70
|
23.70
|
21.2
|
|
20.00
|
.125
|
.75
|
.018
|
.60
|
1.20
|
12.90
|
10.4
|
|
20.00
|
.250
|
.75
|
.009
|
.60
|
.80
|
41.40
|
38.9
|
|
20.00
|
.250
|
1.50
|
.018
|
1.20
|
1.90
|
3.20
|
27.7
|
|
20.00
|
.250
|
3.00
|
.035
|
2.20
|
4.90
|
12.90
|
10.4
|
Focused Transducers
|
Frequency
(MHz)
|
Dia.
(in)
|
Diameter/
wavelength
|
Beam
Spread
(Degrees)
|
6 dB Spot
Size at Yo+
(in)
|
Near Field
Yo+
(in)
|
Normal Range
of Focusing
|
Down Field
Focal Zone (6dB)
|
|
MIN
(in)
|
MAX
(in)
|
START
(in)
|
END
(in)
|
|
.50
|
.750
|
6.410
|
8.947
|
.188
|
1.202
|
Yo+
|
Yo+
|
.719
|
2.322
|
|
.50
|
1.000
|
8.547
|
6.707
|
.250
|
2.137
|
Yo+
|
Yo+
|
1.279
|
4.128
|
|
|
|
|
|
|
|
|
|
|
|
|
1.00
|
.750
|
12.821
|
4.470
|
.188
|
2.404
|
1.619
|
1.923
|
1.438
|
4.644
|
|
1.00
|
1.000
|
17.094
|
3.352
|
.250
|
4.274
|
2.158
|
3.419
|
2.557
|
8.255
|
|
|
|
|
|
|
|
|
|
|
|
|
2.25
|
.250
|
9.615
|
5.961
|
.063
|
.601
|
Yo+
|
Yo+
|
.360
|
1.161
|
|
2.25
|
.375
|
14.423
|
3.973
|
.094
|
1.352
|
.809
|
1.082
|
.809
|
2.612
|
|
2.25
|
.500
|
19.231
|
2.980
|
.125
|
2.404
|
1.079
|
1.9923
|
1.438
|
4.644
|
|
2.25
|
.750
|
28.846
|
1.986
|
.188
|
5.409
|
1.619
|
4.327
|
3.237
|
10.448
|
|
2.25
|
1.000
|
38.462
|
1.490
|
.250
|
9.615
|
2.158
|
7.692
|
5.754
|
18.574
|
|
|
|
|
|
|
|
|
|
|
|
|
5.00
|
.250
|
21.368
|
2.682
|
.063
|
1.335
|
.540
|
1.068
|
.799
|
2.580
|
|
5.00
|
.375
|
32.051
|
1.788
|
.094
|
3.005
|
.809
|
2.404
|
1.798
|
5.804
|
|
5.00
|
.500
|
42.735
|
1.341
|
.125
|
5.342
|
1.079
|
4.274
|
3.197
|
10.319
|
|
5.00
|
.750
|
64.103
|
.894
|
.188
|
12.019
|
1.619
|
9.615
|
7.192
|
23.218
|
|
5.00
|
1.000
|
85.470
|
.670
|
.250
|
21.368
|
2.158
|
17.094
|
12.786
|
41.276
|
|
|
|
|
|
|
|
|
|
|
|
|
10.00
|
.125
|
21.368
|
2.682
|
.031
|
.668
|
.270
|
.534
|
.400
|
1.290
|
|
10.00
|
.250
|
42.735
|
1.341
|
.063
|
2.671
|
.540
|
2.137
|
1.598
|
5.160
|
|
10.00
|
.375
|
64.103
|
.894
|
.094
|
6.010
|
.809
|
4.808
|
3596
|
11.609
|
|
10.00
|
.500
|
85.470
|
.670
|
.125
|
10.684
|
1.079
|
8.547
|
6.393
|
20.638
|
|
10.00
|
.750
|
128.205
|
.447
|
.188
|
24.038
|
1.619
|
19.231
|
14.385
|
46.436
|
|
10.00
|
1.000
|
170.940
|
.335
|
.250
|
42.735
|
2.158
|
34.188
|
25.573
|
82.553
|
|
|
|
|
|
|
|
|
|
|
|
|
15.00
|
.125
|
32.051
|
1.788
|
.031
|
1.002
|
.270
|
.801
|
.599
|
1.935
|
|
15.00
|
.250
|
64.103
|
.894
|
.063
|
4.006
|
.540
|
3.205
|
2.397
|
7.739
|
|
15.00
|
.375
|
96.154
|
.596
|
.094
|
9.014
|
.809
|
7.212
|
5.394
|
17.413
|
|
|
|
|
|
|
|
|
|
|
|
|
20.00
|
.125
|
42.735
|
1.341
|
.031
|
1.335
|
.270
|
1.068
|
.799
|
2.580
|
|
20.00
|
.250
|
85.470
|
.670
|
.063
|
5.342
|
.540
|
4.274
|
3.197
|
10.319
|
-