Difference betwwen SAW & BAW Filters

Hi,
What is the differrence between surface acoustic wave filter and Bulk acoustic wave filter How we are getting the electrical equalent of these

surface acoustic wave means that the wave flows over the surface of the material and the conversion to electic is done at the same side of the acoustic material; bulk acoustic wave means that the wave flows through the acoustic material and conversion from acoustic to electric happens at the opposite sides of the material.