MEMS and sensors
Which statement correctly describes detecting very small masses by using the change in resonant frequency when material adheres to a tiny cantilever or a quartz crystal resonator?
- AAs adsorbed mass increases, the resonant frequency rises
- BAs adsorbed mass increases, the resonant frequency falls, and the mass is found from the change
- CThe resonant frequency is unrelated to mass
Show answer and explanation
Answer: B. As adsorbed mass increases, the resonant frequency falls, and the mass is found from the change
The resonant frequency is proportional to √(k/m), so when material adheres and the mass m increases, the frequency drops. The smaller and lighter the resonator, the larger the frequency change for a tiny mass change, so this is used to detect gas or biological molecules and to monitor film thickness (quartz crystal microbalance).
- A. Increasing mass lowers the resonant frequency.
- B. Correct. The adsorbed mass is found from the frequency drop.
- C. The resonant frequency depends on mass.