Answer :
Final answer:
False
The statement is false because the beam diameter only increases by a factor of √2 at one Rayleigh range from the beam waist, so it would take more than twice the near zone distance for the beam to be as wide as the transducer.
Explanation:
The statement that at a depth of twice the near zone, the beam is as wide as the transducer is false. In the context of ultrasound and beam formation, near zone, also known as Fresnel zone, refers to the area close to the transducer where the beam converges to its narrowest point. This point is called the focal point or beam waist. Beyond the near zone begins the far zone or Fraunhofer zone, where the beam starts to diverge slowly. According to diffraction theory, at one Rayleigh range (ZR) from the minimum beam radius, the beam diameter increases by a factor of √2. Therefore, it would take more than two near zones for the beam to become as wide as the transducer itself. The near and far fields, beam divergence, and focal point are all critical concepts in understanding how ultrasonic beams propagate through different media.
