Recommended Focal Lengths
This table lists the near-field lengths of minimum and maximum practical focal lengths in water (inches). Customers should only request focal lengths within these limits to achieve good focal performance. SNI is aware that some customers have experience with transducers focused longer than the recommended maximum (sometimes called “Beam Correction” since the transducer cannot achieve a focal point that long). These are available on a best-effort basis.
- N = Near-field practical focal length
- Min = Minimum practical focal length
- Max = Maximum practical focal length
N = (Dia)2 x (Freq.) / 4 x Velocity
When ordering immersion transducers, please include the part number followed by type of focus and focal length in inches (if applicable).
(ex. 00-011321 NF, 00-011321 6.0S, 00-011321 8.0C)
- NF = Non-focused (flat)
- S = Spherical focus
- C = Cylindrical focus
| Frequency (MHz) | Element Ø (Inches) | ||||||
|---|---|---|---|---|---|---|---|
| 1 | 0.75 | 0.5 | 0.375 | 0.25 | 0.125 | ||
| 1 | Near | 4.3 | 2.4 | 1.1 | |||
| Min | 2 | 1.5 | 1 | ||||
| Max | 3 | 2 | 1 | ||||
| 2.25 | Near | 9.5 | 5.4 | 2.4 | 1.4 | 0.6 | |
| Min | 2 | 1.5 | 1 | 0.8 | 0.5 | ||
| Max | 6 | 4 | 2 | 0.8 | 0.5 | ||
| 3.5 | Near | 15 | 8.4 | 3.7 | 2.1 | 0.9 | |
| Min | 2 | 1.5 | 1 | 0.8 | 0.5 | ||
| Max | 8 | 6 | 2.5 | 0.5 | 0.5 | ||
| 5 | Near | 21 | 12 | 5.4 | 3 | 1.3 | 0.3 |
| Min | 2 | 1.5 | 1 | 0.8 | 0.5 | 0.3 | |
| Max | 8 | 8 | 4 | 1 | 0.8 | 0.3 | |
| 10 | Near | 12 | 10.7 | 6 | 2.7 | 0.7 | |
| Min | 1.5 | 1 | 0.8 | 0.5 | 0.3 | ||
| Max | 8 | 6 | 4.5 | 1.5 | 0.3 | ||
| 15 | Near | 16 | 9 | 4 | 1 | ||
| Min | 1 | 0.8 | 0.5 | 0.3 | |||
| Max | 6 | 6 | 2 | 0.5 | |||
| 25 | Near | 6.7 | 1.7 | ||||
| Min | 0.5 | 0.3 | |||||
| Max | 2 | 1 |
