Acoustic wave element, acoustic wave filter device, and multiplexer

An acoustic wave element comprising:

• a piezoelectric substrate;
• an interdigital transducer (IDT) electrode on the piezoelectric substrate and including a plurality of comb-shaped electrodes;
• and
• a reflector adjacent to the IDT electrode in an acoustic wave propagation direction;
• wherein
• the comb-shaped electrodes include a plurality of comb-shaped electrode fingers extending in a direction intersecting the acoustic wave propagation direction;
• the reflector includes a plurality of reflecting-electrode fingers extending in a direction intersecting the acoustic wave propagation direction;
• when, in the a plurality of electrode fingers included in the IDT electrode and the reflector, a center-to-center distance between ones of the electrode fingers adjacent to each other in the acoustic wave propagation direction is defined as an electrode-finger pitch:
• an electrode-finger pitch of the plurality of reflecting-electrode fingers is greater than an electrode-finger pitch of the plurality of comb-shaped electrode fingers;
• and
• a center-to-center distance in the acoustic wave propagation direction between a reflecting-electrode finger closest to the IDT electrode of the plurality of reflecting-electrode fingers and a comb-shaped electrode finger closest to the reflector of the plurality of comb-shaped electrode fingers is equal to or less than about 0.9 times the electrode-finger pitch of the plurality of reflecting-electrode fingers;
• when a reflecting-electrode finger counted from one of the reflecting-electrode fingers which is closest to the IDT electrode in a direction away from the IDT electrode is designated as a k-th reflecting-electrode finger in order, where k is an integer equal to or greater than 1;
• one of the reflecting-electrode fingers farthest from the IDT electrode is defined as an (n+1)-th reflecting-electrode finger, where n is an integer greater than k;
• an electrode-finger pitch between the k-th reflecting-electrode finger and a (k+1)-th reflecting-electrode finger is defined as a k-th electrode-finger pitch;
• and
• a value of electrode-finger pitches from a first electrode-finger pitch to the k-th electrode-finger pitch is less than a value of electrode-finger pitches from the (k+1)-th electrode-finger pitch to an n-th electrode-finger pitch.