Patent ID: 7213460

Claim:
An ultrasonic sensor, comprising: conversion devices for at least one of: converting a first ultrasonic signal to an electric signal after receiving the first ultrasonic signal; and transmitting a second ultrasonic signal after converting an electric signal to the second ultrasonic signal, wherein sizes of the conversion devices are uneven and primary resonance frequencies of the conversion devices are uneven, wherein each conversion device of the conversion devices has a shape of a flat rectangular plate having a certain surface which functions as at least one of a reception surface for receiving the first ultrasonic signal and a transmission surface for transmitting the second ultrasonic signal; wherein the conversion devices are arranged one-dimensionally on a plane so that: the certain surfaces of the conversion devices face the same direction; the conversion devices are aligned in width directions of the conversion devices; and certain longitudinal ends of the conversion devices at a certain longitudinal side of the conversion devices are aligned in a generally straight line; wherein widths of the conversion devices are even and thickness of the conversion devices are even; wherein longitudes of the conversion devices are uneven; wherein both longitudinal ends of every conversion devices are fixed to prevent the longitudinal ends from vibrating; wherein resonance values Q of the conversion devices are the same; wherein a first primary resonance frequency f 1 of a first one of the conversion devices which is next highest to a second primary resonance frequency f 2 of a second one of the conversion devices is represented by a following equation: f 1 =f 2 −n×f 2/ Q, wherein the coefficient n is either of 7 and 8.