Blocking plate structure for improved acoustic transmission efficiency

An acoustic transducer comprising:

• 1) an acoustic matching structure for a transducer, the structure comprising:
• a cavity which, in use, contains a fluid, the cavity having a substantially planar shape;
• two end walls bounding the substantially planar shape of the cavity
• a side wall bounding the cavity and substantially perpendicular to the end walls;
• the structure defining an area Acavity given by an average cross-sectional area in a planar dimension in the cavity between the end walls
• wherein the cavity has an effective side wall radius rcavity defined as:
• rcavity=(Acavity/π)1/2;
• and
• at least one aperture placed in at least one of the end walls and side walls, wherein at least one aperture is located in an end wall within a distance less than rcavity/2 from the side wall;
• wherein the cavity height hcavity is defined as the average separation of the end walls;
• wherein rcavity and hcavity, satisfy the inequality:
• rcavity is greater than hcavity;
• wherein an area of one of the at least one aperture (Aaperture), and Acavity satisfy the inequality:
• Acavity/Aaperture is greater than 2;
• wherein, in operation, a transducing element acting on one of the cavity end walls generates acoustic oscillations in the fluid in the cavity;
• and whereby, in use, the acoustic oscillations in the fluid in the cavity cause pressure waves to propagate into a surrounding acoustic medium;
• and
• 2) an actuator, wherein, in use, the frequency of oscillatory motion of the actuator is within 30% of the lowest resonant frequency of radial acoustic oscillations in the cavity.