EN 61828:2001

INTRODUCTION
1 Scope
2 Normative references
3 General
   3.1 Focusing methods
   3.2 System and measurement requirements
   3.3 General focused field descriptions
4 Focusing definitions
   4.1 Background information
   4.2 Definitions
5 List of symbols
6 Measurement procedures
   6.1 General
   6.2 Finding the beam axis
   6.3 Determining if transducer is focusing
   6.4 Measuring other focal parameters of a focusing transducer
Annex A (informative) Background for the transmission/Characteristics
        of focusing transducers
Annex B (informative) Methods for determining the beam axis for
        well-behaved beams
   B.1 Comparisons of beam axis search methods
   B.2 Beamwidth midpoint method
Annex C (informative) Methods for determining the beam axis for beams
        that are not well-behaved
Annex ZA (normative) Normative references to international publications
         with their corresponding European publications
Figure 1 - Transducer options - Top: Transducer with a radius of
           curvature R and a focal length equal to R - Middle:
           Transducer with a plano-concave lens - Bottom: Transducer
           with a plano-convex lens
Figure 2 - Definitions for focusing measurements when the transducer
           geometry is unknown
Figure 3 - Field parameters for non-focusing and focusing transducers
Figure 4 - Beam contour plot - Contours at -6, -12, and -20 dB for
           a 5 MHz transducer with a diameter of 25 mm and a radius
           of curvature of 50 mm centred at location 0,0 (bottom
           centre of graph)
Figure 5 - Parameters for describing a focusing transducer of a known
           geometry
Figure 6 - Path difference parameters for describing a focusing
           transducer of a known geometry
Figure 7 - Beamwidth focus in a principal longitudinal plane
Figure 8 - Types of geometric focusing
Figure 9 - Pressure focus in a principal longitudinal plane
Figure B.1 - X-axis scan at 9 cm depth for the first focal zone with
           beam centre
Figure B.2 - X-axis scan at 4,4 cm depth for the second focal zone
Figure C.1 - Asymmetric beam showing beamwidth midpoint method
Table B.1 - Standard deviations for x and y scans using three
             methods of determining the centre of the beam
Table B.2 - -dB beamwidth levels for determining midpoints