Herbert Behlow

Direct measurement of shear properties of microfibers.

As novel fibers with enhanced mechanical properties continue to be synthesized and developed, the ability to easily and accurately characterize these materials becomes increasingly important. Here we present a design for an inexpensive tabletop instrument to measure shear modulus (G) and other longitudinal shear properties of a micrometer-sized monofilament fiber sample, such as nonlinearities and hysteresis. This automated system applies twist to the sample and measures the resulting torque using a sensitive optical detector that tracks a torsion reference. The accuracy of the instrument was verified by measuring G for high purity copper and tungsten fibers, for which G is well known. Two industrially important fibers, IM7 carbon fiber and Kevlar(®) 119, were also characterized with this system and were found to have G = 16.5 ± 2.1 and 2.42 ± 0.32 GPa, respectively.

Deconvolution of damping forces with a nonlinear microresonator

We report a fully electrical microcantilever device that utilizes capacitance for both actuation and detection and show that it can characterize various gases with a bare silicon microcantilever. We find the motion of the cantilever as it rings down when the oscillating force is removed, by measuring the voltage induced by the oscillating capacitance in the microcantilever∕counterelectrode system. The ringdown waveform was analyzed using an iterative numerical algorithm to calculate the oscillator motion, modeling the cantilever∕electrode capacitance to calculate the electrostatic force. We find that nonlinearity in the motion of the cantilever is not necessarily a disadvantage. After calibration, we simultaneously measure viscosity and density of several gaseous mixtures, yielding viscosities within ±2% and densities within ±6% of NIST values.

Harmonic detection of resonance method

Electromechanical resonators in the micro (MEMS) and nano (NEMS) regimes have emerged as promising tools for use in diverse applications such as ultrasensitive physical, chemical, and biological sensors, with detection limits as low as a single molecule. The advent of state-of-the-art micro-fabrication techniques has enabled a high throughput platform for commercialization. However, the sensitivity and reliability of such devices are highly dependent on the employed detection technique. We present a highly useful yet simple electrical detection scheme: the Harmonic Detection of Resonance (HDR) method. The prominent HDR features will be discussed and applications ranging from the use of micro-cantilevers as sensors to probing mechanical properties in nano-cantilever systems will be presented.

A low-cost approach for measuring electrical load currents in triboelectric nanogenerators

Abstract Research into the development of triboelectric nanogenerators (TENGs) has exponentially expanded over the last 5 years with TENGs expected to be a prominent alternative energy-harvesting source in the near future. Notwithstanding the rapid progress in TENG development and their applications, the start-up cost of required research equipment and components remains high for new entrants into the field. A substantial portion of that cost is for the preamplifier, which is needed for measuring the output current of a TENG. Here, an ultra-low-cost device is presented that can measure the TENG output current, which is a crucial parameter in the characterization of TENG electrical performance. This alternative approach is expected to enable research groups in the future to partially offset the initial expense of instrumentation necessary for TENG research, and accelerate the development and applications of TENGs.

Ringdown sensing method

Miniaturization of devices into lab-on-chip designs is a dominating field of current scientific research. While the technology to build these devices is continuing to develop, the practical realization of such devices remain elusive, mainly due to lack of techniques that bridge the macroscopic world to the mechanical motion and/or the electronic signals generated on the micro- or nano-sized scale. Hence, there is an increasing need for sensitive detection techniques that can not only be implemented on such small scale systems but also be integrated with the current CMOS technology. In this regard, a fully electrical microcantilever-based ringdown method will be presented. We show that detection technique can be employed to precisely analyze the composition of gas mixtures. The viscosity and density can be measured simultaneously, which is illustrated for multiple gases yielding viscosities within ± 2% and densities within ± 6% of NIST values.