ARDMS (American Registry for Diagnostic Medical Sonography) Practice Test

A given frequency of sound is 4.5 MHz, and it has a wavelength of 0.8 mm. How thick should a manufacturer design the matching layer of a transducer in this scenario?

1. 0.4 mm

2. 0.16 mm

3. 0.2 mm

4. 0.6 mm

The correct answer is: 0.2 mm

A) 0.4 mm is too thick because it is twice the wavelength, which is not ideal for sound transmission. B) 0.16 mm is too thin because it is only one fifth of the wavelength, which would lead to inefficient sound transmission. D) 0.6 mm is too thick because it is three quarters of the wavelength, which would also lead to decreased sound transmission efficiency. The matching layer of a transducer should generally be between one quarter to one half of the wavelength in order to efficiently transmit sound waves. In this scenario, the wavelength is 0.8 mm, so the matching layer should be approximately half that length, which is 0.4 mm. Therefore, option C, 0.2 mm, is the most appropriate answer as it falls within the ideal thickness range.