Surface Micromachined Resonant Force Transducers

This report covers a transduction scheme using surface micromachined tuning forks to measure small forces. This resonant sensing is done by applying an axial force to the tuning fork and measuring the resulting shift in natural frequency. The analysis of the tuning forks is carried out using simple linear dynamic methods. The suspension used to test the forks is analyzed using a spring-lever model that treats each structural stiffness in the system as an individual spring. Devices using the above models were fabricated in two surface micromachining technologies, one of which included on-chip circuitry. The tuning forks without electronics were used to characterize the dynamic behavior of the forks, and it is shown that the behavior is in excellent agreement with the dynamic model. The devices that contained on-chip amplifiers were used to characterize the entire sensor. Here, also, it is found that the models for the transducer and the actual results are in agreement.