Which design choice is typical for achieving higher-frequency operation in transducers?

Which design choice is typical for achieving higher-frequency operation in transducers?

• A. Use thicker PZT crystals
• B. Use thinner PZT crystals
• C. Use larger diameter crystals
• D. Use lower speed PZT material

Answer: (B)

Higher-frequency operation in transducers is achieved by using thinner piezoelectric crystals because the resonance in the thickness mode depends on the crystal’s thickness. The resonant frequency is determined by how fast sound travels through the material divided by twice the thickness, so when you reduce thickness, the frequency goes up. The speed of sound in PZT is fixed for a given material, so making the crystal thinner pushes the thickness-mode resonance to higher values. Using a larger diameter mainly changes the aperture and beam focusing, not the fundamental thickness-mode frequency. A lower-speed PZT material would lower the frequency, not raise it. Therefore, thinning the PZT crystal is the standard way to achieve higher-frequency transducers.

Higher-frequency operation in transducers is achieved by using thinner piezoelectric crystals because the resonance in the thickness mode depends on the crystal’s thickness. The resonant frequency is determined by how fast sound travels through the material divided by twice the thickness, so when you reduce thickness, the frequency goes up. The speed of sound in PZT is fixed for a given material, so making the crystal thinner pushes the thickness-mode resonance to higher values.

Using a larger diameter mainly changes the aperture and beam focusing, not the fundamental thickness-mode frequency. A lower-speed PZT material would lower the frequency, not raise it. Therefore, thinning the PZT crystal is the standard way to achieve higher-frequency transducers.