Patent ID: 8042398

Claim:
An ultrasonic receiver comprising: a wave propagating portion, which defines a first opening and a waveguide that makes an ultrasonic wave, coming through the first opening, propagate in a predetermined direction; a propagation medium portion, which has a transmissive interface and which is arranged with respect to the waveguide such that the transmissive interface defines one surface of the waveguide in the direction in which the ultrasonic wave propagates, the transmissive interface being designed and arranged with respect to the waveguide such that as the ultrasonic wave propagates along the waveguide, each portion of the ultrasonic wave is transmitted into the propagation medium portion through the transmissive interface and then converged toward a predetermined convergence point; and a sensor portion, which is arranged at the convergence point to detect the ultrasonic wave converged, wherein the propagation medium portion includes a propagation medium that fills a space between the transmissive interface and the convergence point, and wherein the waveguide is filled with an environmental fluid and acoustic velocities C n and C a of the ultrasonic wave propagating through the propagation medium and the environmental fluid, respectively, satisfy C n C a < 1 and wherein if a distance from the first opening of the waveguide to a point P, which is set at an arbitrary location on the transmissive interface, is L a as measured in the ultrasonic wave propagating direction and if a distance from the point P to the convergence point is L n , then L a /C a +L n /C n is always constant irrespective of where the point P is located.