With a 1D linear array, where is the beam narrowest in the out-of-plane dimension?

With a 1D linear array, where is the beam narrowest in the out-of-plane dimension?

• A. It is at the point of mechanical focusing
• B. It is at the point of electronic focusing
• C. The beam is the same width throughout the image
• D. It is in the far field

Answer: (A)

In 1D ultrasound arrays, the out-of-plane (elevation) beam width is determined by the transducer’s physical focusing. Mechanical focusing—using the curved shape of the element or a lens—concentrates energy in the elevation direction, producing the narrowest beam at that focal point. Electronic focusing mainly affects the plane of the array (the imaging plane) and doesn’t reduce the elevation width in a 1D array, so the tightest cross-section in the out-of-plane dimension occurs where the transducer is mechanically focused. Away from that focus, the beam diverges and widens, and in the far field it’s widest due to diffraction.

In 1D ultrasound arrays, the out-of-plane (elevation) beam width is determined by the transducer’s physical focusing. Mechanical focusing—using the curved shape of the element or a lens—concentrates energy in the elevation direction, producing the narrowest beam at that focal point. Electronic focusing mainly affects the plane of the array (the imaging plane) and doesn’t reduce the elevation width in a 1D array, so the tightest cross-section in the out-of-plane dimension occurs where the transducer is mechanically focused. Away from that focus, the beam diverges and widens, and in the far field it’s widest due to diffraction.