• Journal of Sensor Science and Technology
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• v.17 no.4
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• pp.267-272
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• 2008

Energy harvesting from the vibration through the piezoelectric effect has been studied for powering the small wireless sensor nodes. As piezoelectric uni-morph cantilever structure can transfer low vibration to large displacement, this structure was commonly deployed to harvest electric energy from vibrations. Through our previous results, when stress was applied on the cantilever, stress was concentrated on the certain point of the ceramic of the cantilever. In this study, for miniaturing the energy harvester, we investigated how the size of ceramics and the stress distribution in ceramic affects energy harvester characteristics. Even though the area of ceramic was 28.6 % decreased from $10{\times}35{\times}0.5mm^3$ to $10{\times}25{\times}0.5mm^3$, both samples showed almost same maximum power of 0.45 mW and the electro-mechanical coupling factor ($K_{31}$) of 14 % as well. This result indicated that should be preferentially considered to generate high power with small size energy harvester.

• Transactions on Electrical and Electronic Materials
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• v.13 no.5
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• pp.215-220
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• 2012

Miniature ultrasonic and tactile sensors on Si substrate have been proposed, fabricated and characterized to detect objects for a dexterous robot. The ultrasonic sensor consists of piezoelectric PZT thin film on a Pt/Ti/$SiO_2$ and/or Si diaphragm fabricated using a micromachining technique; the ultrasonic sensor detects the piezoelectric voltage as an ultrasonic wave. The sensitivity has been enhanced by improving the device structure, and the resonant frequency in the array sensor has been equalized. Position detection has been carried out by using a sensor array with high sensitivity and uniform resonant frequency. The tactile sensor consists of four or three warped cantilevers which have NiCr or $Si:B^+$ piezoresistive layer for stress detection. Normal and shear stresses can be estimated by calculation using resistance changes of the piezoresitive layers on the cantilevers. Gripping state has been identified by using the tactile sensor which is installed on finger of a robot hand, and friction of objects has been measured by slipping the sensor.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.15 no.12
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• pp.1060-1064
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• 2002

We have studied the effect of crystallization temperature, composition and film thickness, which are the fundamental processing parameters of lead zirconate titanate(PZT) thin film fabrication, in the respect of the piezoelectric properties by our pneumatic loading method(PLM). A great deal of research has been done in the field of characterization for piezoelectric thin films after the first report on the measurement for the piezoelectric coefficient of thin films in 1990. Even though the piezoelectric properties of thin films are very critical factors in the micro-electro mechanical system(MEMS) and thin film sensor devices, a few reports for the piezoelectric characterization are provided for the last decade unlikely the bulk piezoelectric devices. We have found that the piezoelectric properties of thin films are improved as the increase of crystallization temperature up to 750$\^{C}$ and this behavior can be also explained by the analysis of dielectric polarization hysteresis loop, X-ray diffraction and scanning electron microscopy. The effect of Zr/Ti composition has been also studied. This gives us the fact that the maximum piezoelectricity is found near Morphotropic Phase Boundary(MPB) as bulk PZT system does.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2007.05a
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• pp.943-946
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• 2007

In-plane piezoelectric charge constant of Electro-Active paper (EAPap) was investigated based on direct and converse piezoelectric effects. EAPap samples were made with cellulose film with very thin gold electrode coated on both sides of the film. To characterize direct piezoelectricity of EAPap, induced charge was measured when mechanical stress was applied to EAPap. In-plane piezoelectric charge constant was extracted from the relation between induced charge and applied in-plane normal stress. To investigate converse piezoelectricity, induced in-plane strain was measured when electric field was applied to EAPap. Piezoelectric charge constant was also extracted from the relation of induced in-plane strain and applied electric field. Piezoelectric charge constants obtained from direct and converse piezoelectricity are 31 pC/N and 178 x 10-12m/V for 45 degree sample, respectively. Measured piezoelectric charge constants of EAPap provide promising potential as a piezoelectric material.

• Journal of Mechanical Science and Technology
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• v.16 no.10
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• pp.1222-1228
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• 2002

This research is the development of a flexible tactile sensor array for service robots using PVDF (polyvinylidene fluoride) film for the detection of a contact state in real time. The prototype of the tactile sensor which has 8${\times}$8 array using PVDF film was fabricated. In the fabrication procedure, the electrode patterns and the common electrode of the thin conductive tape were attached to both sides of the 281$\mu\textrm{m}$ thickness PVDF film using conductive adhesive. The sensor was covered with polyester film for insulation and attached to the rubber base for a stable structure. The proposed fabrication method is simple and easy to make the sensor. The sensor has the advantages in the implementing for practical applications because its structure is flexible and the shape of the each tactile element can be designed arbitrarily. The signals of a contact force to the tactile sensor were sensed and processed in the DSP system in which the signals are digitized and filtered. Finally, the signals were integrated for taking the force profile. The processed signals of the output of the sensor were visualized in a personal computer, and the shape and force distribution of the contact object were obtained. The reasonable performance for the detection of the contact state was verified through the sensing examples.

• Journal of Sensor Science and Technology
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• v.27 no.4
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• pp.269-274
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• 2018

High-sensitivity signal-to-noise ratio (SNR) microphones are essentially required for a broad range of automatic speech recognition applications. Piezoelectric microphones have several advantages compared to conventional capacitor microphones including high stiffness and high SNR. In this study, we designed a new piezoelectric membrane structure by using the finite elements method (FEM) and an optimization technique to improve the sensitivity of the transducer, which has a high-quality AlN piezoelectric thin film. The simulation demonstrated that the sensitivity critically depends on the inner radius of the top electrode, the outer radius of the membrane, and the thickness of the piezoelectric film in the microphone. The optimized piezoelectric transducer structure showed a much higher sensitivity than that of the conventional piezoelectric transducer structure. This study provides a visible path to realize micro-scale high-sensitivity piezoelectric microphones that have a simple manufacturing process, wide range of frequency and low DC bias voltage.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2003.06a
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• pp.251-255
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• 2003

This paper presents the design, fabrication, and calibration of a piezoelectric polymer-based sensorized microgripper. Electro discharge machining technology is employed to fabricate super-elastic alloy based micro gripper. It is tested to present improvement of mechanical performance. For integration of force sensor on the micro gripper, the sensor design based on the piezoelectric polymer PVDF film and fabrication process are presented. The calibration and performance test of force sensor integrated micro gripper are experimentally carried out. The force sensor integrated micro gripper is applied to perform fine alignment tasks of micro opto-electrical components. It successfully supplies force feedback to the operator through the haptic device and plays a main role in preventing damage of assembly parts by adjusting the teaching command.

• Composites Research
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• v.15 no.5
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• pp.7-13
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• 2002

The piezoelectric thin film sensor has good characteristics to observe the impact responses of composite structures. The capabilities for monitoring impact behavior of Gr/Ep laminates subjected to damage-induced impact using the PVDF(polyvinylidene fluoride) film sensor were examined. For a series of low-velocity impact tests from low energy to damage-induced energy, simulated sensor signals were compared with measured signals and the PVDF film sensor. Local impact damages(matrix cracking and delamination) were found at three impact tests, but the measured signals agreed well with the simulated sensor signals based on the linear relationship between the impact forces and the PVDF film sensor signals. And the inverse technique was applied to reconstruct the impact forces using the PVDF film sensor signals. Most of reconstructed impact forces had good agreement with the measured forces. The comparison results showed that the local damage due. to low-velocity impact didn't disturb the global impact responses of composite laminates and the reconstruction of impact forces from PVDF sensor signals wasn't affected by the local damage.

• Proceedings of the Materials Research Society of Korea Conference
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• 2003.03a
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• pp.34-34
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• 2003

Piezoelectric or magnetostrictive materials, known as smart materials, have been researched widely for sensors or actuators in micro system technology. In our research, thick sol-gel lead zirconate titanate(Pb(Zr$\sub$1-x/Ti$\sub$x/)O$_3$) films were fabricated and their characteristics were investigated f3r angular rate sensor applications. The thickness of the PZT films is 1.5${\mu}$m, which is required by a vibration angular rate sensor for a good actuation and sensing. The remnant polarization of the PZT flms is 12.0 ${\mu}$C/$\textrm{cm}^2$. The electromechanical constants of PZT thin film showed the value of susceptance(B) of 4800${\mu}$ s at capacitance of 790pF. The PZT films were applied to the vibration angular rate sensor structure and the vibration of 1.78 ${\mu}$m in amplitude at the resonant frequency of 35.8㎑ was obtained by driving voltage of 5V$\sub$p-p/ of bulk piezoelectric materials with out of phase signal through voltage and inverting amplifier.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.19 no.9
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• pp.915-921
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• 2009

Cellulose based electro-active paper(EAPap) is considered as a new smart material which has a potential to be used for biomimetic actuators and sensors. Beside of the natural abundance, cellulose EAPap is fascinating with its biodegradability, lightweight, high mechanical strength and low actuation voltage. When the external stress is applied to EAPap, it can generate the electrical output due to its piezoelectric property. Using piezoelectric behavior of EAPap, we studied the feasibility of EAPap as mechanical strain sensor applications and compared to commercial strain sensor. By measuring the induced output voltage from the thin piezoelectric cellulose EAPap under static and dynamic force, we propose cellulose EAPap film as a potential strain sensor material.