FLAUT: A mutual sensitivity improvement through matched pipe, cavity and thin plate resonance

Electrostatic transducers promises a great potential in alternative to piezoelectric transducer based on certain advantages such as inherently wide bandwidth and good acoustic matching to air due to the membrane’s low acoustics impedance. There are two basic designs that are popular among electrostatic ultrasonic transducer developer – rigid backplate and micromachine backplate. This paper presents a methodology for improving the sensitivity of an air-coupled ultrasonic transducer by coupling the resonating thin plate, cavity and pipe in a single cell. The proposed device is termed Fluidically Amplified Ultrasonic Transducer (FLAUT) for an air-coupled application. Investigation of the concept of matched thin plate, cavity and pipe, of which the individual geometry is expected to mutually enhance one another. Analytical modelling is utilized to the matched thin plate, cavity and pipe. The analytical modelling identifies the required geometry for the FLAUT based on the matched operating resonant frequency of 25 kHz. At the end of the paper the prototype of FLAUT is presented where the device was fabricated using additive manufacturing process (3-D printing) which consist of a 50 µm Kapton thin film over a micro stereolithography designed backplate. Here aluminum is coated as the electrode utilizing the thermal evaporation process for both the Kapton film and the backplate. A laser interferometer is utilized to measure FLAUT thin plate displacement which indicates the device is running at 25 kHz fundamental mode. A 30 dB difference is also observed between the deformation velocity of the cavity active region and its surrounding.

On the Lateral Instability Analysis of MEMS Comb-Drive Electrostatic Transducers

This paper investigates the lateral pull-in effect of an in-plane overlap-varying transducer. The instability is induced by the translational and rotational displacements. Based on the principle of virtual work, the equilibrium conditions of force and moment in lateral directions are derived. The analytical solutions of the critical voltage, at which the pull-in phenomenon occurs, are developed when considering only the translational stiffness or only the rotational stiffness of the mechanical spring. The critical voltage in a general case is numerically determined by using nonlinear optimization techniques, taking into account the combined effect of translation and rotation. The influences of possible translational offsets and angular deviations to the critical voltage are modeled and numerically analyzed. The investigation is then expanded for the first time to anti-phase operation mode and Bennet’s doubler configuration of the two transducers.

Characterization of Nanoscale Ultrasonic Transducer Elements as Effective Acoustical Devices

The generation and detection of ultrasound in air has many applications in the field of ranging, non-destructive evaluation, microscopy and the most impactful in medical imaging. Conventional designs of electrostatic transducers have large electrode spacing of 50-100 μm which reduces the sensitivity of these capacitors. In the last one and a half decade silicon micromachining is used to define capacitors with gap spacing as small as 500Å, making it possible highly efficient capacitive micromachined ultrasonic transducers (CMUTs). In this paper a CMUT element is analytically characterized and FEM simulated. The observations are compared with published experimental results and excellent agreement is found between them.