Ultrasonic generator

An ultrasonic generator which radiates sound waves toward a target space, comprising:

• a plurality of speaker elements which are piezoelectric micro electro mechanical systems ultrasonic transducers,
• wherein the plurality of speaker elements includes:
• a first speaker element having a first resonance frequency;
• and
• a second speaker element having a second resonance frequency adjacent to the first resonance frequency,
• wherein the first speaker element and the second speaker element are arranged apart from each other in a direction intersecting with a direction toward the target space, and
• wherein a distance between the first speaker element and the second speaker element is set so that a strengthening relationship of sounds having an intermediate frequency from the first speaker element and from the second speaker element appear at two or more positions on an object located in the target space, and
• wherein the strengthening relationship is created by strengthening a sound having the intermediate frequency between the first resonance frequency and the second resonance frequency from the first speaker element and a sound having the intermediate frequency from the second speaker element, and
• wherein the distance is set equal to or more than a value 2z obtained from an equation n=(SQRT ((z+x)2+y2)-SQRT ((z−x)2+y2))/λmid+½) where n is the natural number equal to or more than 1, z is a distance between a midpoint between two speaker element and one of the speaker elements, x is a width of the object, y is a distance between the midpoint and the object, and Amid is a wavelength of the intermediate frequency.