Focusing Characteristics of a Transcranial Ultrasonic Lens of a Point-like Scatterer Array Partially Covering the Head

Abstract

This lens can focus an incident plane wave to the diffraction limit in the direction perpendicular to the incident direction, but the peak width in the propagation direction is more than five times that. This phenomenon is a characteristic of Fresnel lenses, and this lens, which is a kind of lens, is also not avoided. It can be improved by increasing the width of the lens, whereas it is not practical. In this work, as an alternative method, we propose to arrange a point-like scatterer so as to partially cover the head. It is shown that the proposed method can suppress the spread of the focal spot at the focal point in the propagation direction.