The ornamental design for the ultrasound transducer, as shown and described.
1.1 is a front perspective view of an ultrasound transducer showing our new design;
1.2 is a front plan view thereof;
1.3 is a rear plan view thereof;
1.4 is a left plan view thereof;
1.5 is a right plan view thereof;
1.6 is a top plan view thereof; and
1.7 is a bottom plan view thereof.
The portions of the ultrasound transducer shown in broken lines are included for the purpose of illustrating unclaimed portions of the ultrasound transducer and form no part of the claimed design.