Acoustic wave device and filter device

An acoustic wave device comprising:

• a piezoelectric substrate including a piezoelectric layer;
• and
• an IDT electrode on the piezoelectric layer;
• wherein
• the IDT electrode includes a first busbar and a second busbar facing each other, a plurality of first electrode fingers each including one end connected to the first busbar, and a plurality of second electrode fingers each including one end connected to the second busbar, the plurality of first electrode fingers and the plurality of second electrode fingers being interdigitated with each other;
• a virtual line connecting tip ends of the plurality of second electrode fingers is defined as a first envelope, a virtual line connecting tip ends of the plurality of first electrode fingers is defined as a second envelope, and a region between the first envelope and the second envelope in the IDT electrode is an intersection region;
• each of shapes of the plurality of first electrode fingers and the plurality of second electrode fingers in a plan view includes a shape of at least two circular or substantially circular arcs or elliptical or substantially elliptical arcs and includes at least one inflection point;
• the intersection region includes at least two curved regions in which each of the shapes of the plurality of first electrode fingers and the plurality of second electrode fingers in a plan view is a shape of a single circular or substantially circular arc or an elliptical or substantially elliptical arc;
• the intersection region includes a first edge region including the first envelope, a second edge region including the second envelope, and a central region interposed between the first edge region and the second edge region;
• a low acoustic velocity region with an acoustic velocity lower than an acoustic velocity in the central region is provided in at least one of the first edge region and the second edge region;
• and
• when a center of a circle including the circular or substantially circular arc in shapes of a first electrode finger and a second electrode finger or a midpoint of two focal points of an ellipse including the elliptical or substantially elliptical arc in each of the curved regions is defined as a fixed point, and a portion on any straight line passing through the fixed point in a region located in the central region of each of the curved regions is defined as an excitation portion, as the excitation portion is closer to the first envelope or the second envelope, a value of at least one of a duty ratio, an electrode finger pitch, or thicknesses of the plurality of first electrode fingers and the plurality of second electrode fingers changes in one of a direction in which the value increases and a direction in which the value decreases.