Gi-Woo Kim

Hysteresis Compensation of Piezoresistive Carbon Nanotube/Polydimethylsiloxane Composite-Based Force Sensors

This paper provides a preliminary study on the hysteresis compensation of a piezoresistive silicon-based polymer composite, poly(dimethylsiloxane) dispersed with carbon nanotubes (CNTs), to demonstrate its feasibility as a conductive composite (i.e., a force-sensitive resistor) for force sensors. In this study, the potential use of the nanotube/polydimethylsiloxane (CNT/PDMS) as a force sensor is evaluated for the first time. The experimental results show that the electrical resistance of the CNT/PDMS composite changes in response to sinusoidal loading and static compressive load. The compensated output based on the Duhem hysteresis model shows a linear relationship. This simple hysteresis model can compensate for the nonlinear frequency-dependent hysteresis phenomenon when a dynamic sinusoidal force input is applied.

Measurement of flexoelectric response in polyvinylidene fluoride films for piezoelectric vibration energy harvesters

This study presents an investigation on the measurement of flexoelectric response in β-phase polyvinylidene fluoride (PVDF) films attached on cantilever beam-based flexible piezoelectric vibration energy harvesters (PVEHs). The flexoelectric response associated with negative strain gradients was simulated through harmonic response analysis by using the finite element method (FEM). The polarization frequency response functions (FRFs) modified by direct flexoelectric effect of PVDF films was experimentally validated by multi-mode FRFs. From quantitative comparisons between experimental observations and simulated estimation of FRFs, it is demonstrated that the direct flexoelectric response can be observed in PVDF films attached on PVEHs.

On-line estimation of effective bulk modulus in fluid power systems using piezoelectric transducer impedance

The effective bulk modulus of working fluids plays an important role in the control of hydraulic actuation systems because of its effect on the system response time and performance. Therefore, to ensure good control, monitoring the effective bulk modulus of the working fluids is an important task. Current methods normally require precision test equipment consisting of many complex components. The size of these devices is large and thus makes online measurement impractical. In this research, we develop a new on-line technique to estimate effective bulk modulus of the working fluids based on measurements of the impedance of piezoelectric transducers. The idea is to generate a sensitivity curve characterizing the relationship between the effective bulk modulus and the impedance resonant frequency via either off-line numerical simulation or off-line experimental calibration; the curve can then be used for monitoring the working fluids bulk modulus in an online manner. In this article, a simulation model is utilized to predict the peak resonance frequency of the impedance function and identify its dependency on the variation of the fluid bulk modulus. The new approach is then illustrated and a sensitivity curve is generated through comparing the simulation results with experimental data.

Variable stiffness actuator based on fluidic flexible matrix composites and piezoelectric-hydraulic pump

Recently, a new biological-inspired fluidic flexible matrix composite (in short, F2MC) concept has been developed for linear/torsional actuation and structural stiffness tailoring. Although the actuation and the variable stiffness features of the F2MC have been successfully demonstrated individually, their combined functions and full potentials were not yet manifested. In addition, the current hydraulic pressurization systems are bulky and heavy, limiting the potential of the F2MC actuator. To address these issues, we synthesize a new variable stiffness actuator concept that can provide both effective actuation and tunable stiffness (dual-mode), incorporating the F2MC with a compact piezoelectric-hydraulic pump (in short, PHP). This dual-mode mechanism will significantly enhance the potential of the F2MC adaptive structures.

Helmholtz resonance in a piezoelectric–hydraulic pump-based hybrid actuator

This paper demonstrates that a hydraulically acting Helmholtz resonator can exist in a piezoelectric‐hydraulic pump (PHP) based hybrid actuator, which in turn affects the volumetric efficiency of the PHP. The simulation and experimental results illustrate the effect of Helmholtz resonance on the flow rate performance of the PHP. The study also shows how to shift the Helmholtz resonant frequency to a higher value through changing parameters such as the cylinder diameter and the effective bulk modulus of the working fluid, which will improve the volumetric efficiency and broaden the operating frequency range of the PHP actuator. (Some figures in this article are in colour only in the electronic version)

Hysteresis compensation of photoluminescence in ZnS:Cu for noncontact shaft torque sensing

This paper presents a preliminary investigation of loading rate-dependent hysteresis of photoluminescence (PL) by phosphorescence quenching of copper-doped zinc sulfide (ZnS:Cu) microparticles in response to dynamic torsional loading. Precision sinusoidal torque waveforms in the frequency range of 0.5-3 Hz are used to identify the loading rate-dependent (i.e., frequency-dependent) nonlinear hysteresis phenomenon. The potential of the application of PL is demonstrated by successfully measuring the sinusoidal torque applied to a rotational shaft by evaluating the loading rate-dependent PL intensity signature using a photomultiplier tube. In addition, the potential of noncontact shaft torque sensing is demonstrated successfully by the simple compensation derived from ad hoc heuristic characterization.

Fluid-structure coupled acoustic analysis of vibrating Basilar membrane within the cochlea of inner ears

This paper presents the preliminary study on the dynamic characteristics of the basilar membrane (BM) within the cochlea of inner ear. The BM is a vibrating element that varies in width and stiffness like a string on an instrument. While low frequency sounds vibrate near the apex (at the maximum length), high frequency sounds vibrate near the base of the cochlea (near the round and oval windows). Over the last decades, this frequency selectivity has been utilized for acoustic transducers by mimicking the cochlea tonotopy: passive frequency selectivity and transform from acoustic sound into frequency signal of hair cells in the organ of Corti. In previously reported studies, the frequency selectivity was simply achieved by physical parameters, such as length and thickness of beam array although the motion of the BM is generally described as a traveling wave. In this study, fluid-structure coupled acoustic analysis of vibrating BM within the cochlea of inner ear is performed to describe the actual motion of BM. The new approach different from the cantilever beam array –based approach will be then investigated for improved frequency selectivity.

A styrene-butadiene rubber (SBR)/carbon nanotube-based smart force sensor for automotive tire deformation monitoring

This paper provides a preliminary study on the piezoresistive effect of a styrene-butadiene Rubber (SBR), one of the main ingredients of automotive tire, dispersed with carbon nanotubes (CNTs) to explore its feasibility as a force sensor embedded in automotive tires. Typically, the application of CNTs has been successfully applied to the mechanical sensing technology such as a stress/strain and impact sensor. In this study, the potential of using the SBR/CNT as a force sensor for monitoring automotive tire deformation is evaluated for the first time. Experimental results show that the electrical resistance of the SBR/CNT composite changes in response to the sinusoidal loading, as well as static compressive load. These piezoresistive responses of the SBR/CNT composite will be used for sensing the tire deformation caused by the vehicle loading or cracks of tires.

Road roughness estimation based on discrete Kalman filter with unknown input

ABSTRACT The road roughness acts as a disturbance input to the vehicle dynamics, and causes undesirable vibrations associated with the ride and handing characteristics. Furthermore, the accurate measurement of road roughness plays a key role in better understanding a vehicle dynamic behaviour and active suspension control systems. However, the direct measurement by laser profilometer or other distance sensors are not trivial due to technical and economic issues. This study proposes a new road roughness estimation method by using the discrete Kalman filter with unknown input (DKF-UI). This algorithm is built on a quarter-car model and uses the measurements of the wheel stroke (suspension deflection), and the acceleration of the sprung mass and unsprung mass. The estimation results are compared to the measurements by laser profilometer in-vehicle test.

Design analysis of a magnetorheological elastomer based bush mechanism

This paper deal with a semi-active type bush design and magnetic analysis associated with the magnetorheological elastomer. It is focused on the magnetic field intensity analysis with 3 coil structure. The bush design consists of 3 coil structure of the bush in order to apply the magnetic field. As a result of first investigation, it is found that MRE thickness and electric current are most important parameters to design an effective bush. From the magnetic analysis, it is identified that the magnetic permeability of the MRE is lower than MR fluid. In addition, the bush model is formulated to have the uniformity of the magnetic flux and intensity field distribution.