Thicker active elements create which combination of wavelength and frequency?

Thicker active elements create which combination of wavelength and frequency?

• A. Shorter wavelength, Higher frequency
• B. Longer wavelength, Higher frequency
• C. Shorter wavelength, Lower frequency
• D. Longer wavelength, Lower frequency

Answer: (D)

When the active element operates in a thickness mode, its thickness sets the resonant frequency. For the fundamental mode, the frequency scales roughly as f ≈ v/(2t), where v is the speed of sound in the material and t is the thickness. So making the element thicker lowers the resonant frequency. Since wavelength in the material is λ = v/f, a lower frequency means a longer wavelength. In short, thicker active elements produce longer wavelengths and lower frequencies.

When the active element operates in a thickness mode, its thickness sets the resonant frequency. For the fundamental mode, the frequency scales roughly as f ≈ v/(2t), where v is the speed of sound in the material and t is the thickness. So making the element thicker lowers the resonant frequency. Since wavelength in the material is λ = v/f, a lower frequency means a longer wavelength. In short, thicker active elements produce longer wavelengths and lower frequencies.