Regarding an ultrasound beam produced by a single transducer: a. It i

1.	Regarding an ultrasound beam produced by a single transducer: a. It initially propagates as a plane wave with a diameter similar to the transducer diameter b. The length of the near field is proportional to the radius of the transducer and the ultrasound wavelengthc. The area where the beam starts to diverge is termed the Fresnel region d. The angle of divergence is proportional to the ultrasound wavelength e. A beam from a single transducer cannot be focused, as focusing is only possible in array transducers
Answer» a. True. This is because every point on the transducer surface produces a spherical wavelet (as described by Huygens’ principle); these wavelets undergo constructive and destructive interference producing a planar wave front. This part of the beam is called a ‘near field’. b. False. It is proportional to the squared radius of the transducer and inversely proportional to wavelength; the near field extends further in the case of big transducers emitting high-frequency ultrasound. c. False. The beam starts to diverge in the far field (Fraunhofer region). The Fresnel region is another name for the near field. d. True. The sine of this angle is proportional to the ratio of wavelength and transducer diameter. Therefore, a large transducer of high frequency has a less divergent beam in the far field. e. False. It cannot be focused electronically; however, it can be focused to one set depth using a curved piezoelectric crystal or a plastic acoustic lens at the transducer face.

Regarding an ultrasound beam produced by a single transducer: a. It initially propagates as a plane wave with a diameter similar to the transducer diameter b. The length of the near field is proportional to the radius of the transducer and the ultrasound wavelengthc. The area where the beam starts to diverge is termed the Fresnel region d. The angle of divergence is proportional to the ultrasound wavelength e. A beam from a single transducer cannot be focused, as focusing is only possible in array transducers

Answer»

a. True. This is because every point on the transducer surface produces a spherical wavelet (as described by Huygens’ principle); these wavelets undergo constructive and destructive interference producing a planar wave front. This part of the beam is called a ‘near field’.

b. False. It is proportional to the squared radius of the transducer and inversely proportional to wavelength; the near field extends further in the case of big transducers emitting high-frequency ultrasound.

c. False. The beam starts to diverge in the far field (Fraunhofer region). The Fresnel region is another name for the near field.

d. True. The sine of this angle is proportional to the ratio of wavelength and transducer diameter. Therefore, a large transducer of high frequency has a less divergent beam in the far field.

e. False. It cannot be focused electronically; however, it can be focused to one set depth using a curved piezoelectric crystal or a plastic acoustic lens at the transducer face.

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