• Proceedings of the KIEE Conference
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• 2005.07c
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• pp.1870-1872
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• 2005

In this study, an ultrasonic level limit sensor with a new structure utilizing the acoustic impedance matching is proposed to be able to check it out a change of water-level. 2 PZT resonators with the same property are bonded directly on the polyethylene plate. One resonator is for transmitter as an ultrasonic transducer, the other one is for receiver. In this case, a polyethylene plate will operate as an acoustic guider to transmit a transverse wave between 2 PZT resonators in air. While in the water, a polyethylene plate having a similar acoustic impedance with the water will be emitted an acoustic energy into the water as a longitudinal wave. According to this mechanism, there was a wide difference of acoustic signal output between underwater and in air. As a summary, this proposed level limit sensor could be used as a strong candidate with low cost and more stable one.

• Journal of the Korean Society for Nondestructive Testing
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• v.36 no.3
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• pp.217-224
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• 2016

This paper presents a new technique for monitoring the concrete curing process using embedded piezoelectric transducers via admittance measurements. When a piezoelectric transducer is embedded in a structure, the electrical impedance (admittance) of the transducer is coupled with the mechanical impedance of the host structure, which allows monitoring of the structural condition. In this study, the admittance signatures are used for monitoring the concrete curing process. This new method is based on an admittance-based sensor diagnostic process, in which the capacitance values of the piezoelectric transducers are dependent on the strength of the host structure. We numerically and experimentally investigated the variations in capacitive value during the curing process. The results demonstrate that there is a clear relationship between the concrete curing status and the slope, this indicates that the proposed method could be efficiently used for monitoring the curing status of a concrete structure.

• The Journal of the Acoustical Society of Korea
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• v.26 no.2
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• pp.80-86
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• 2007

We have investigated on the development of 2-2 type piezocomposites that have better piezoelectric activity and lower acoustic impedance than those of conventional piezoceramics. In this study, we have investigated the piezoelectric and acoustic properties of 2-2 type piezocomposites sensor which was fabricated using dice-and-fill technique for the different volume fraction of PZT. The specific acoustic impedance of 2-2 type piezocomposites decreased linearly when PZT volume fraction was decreased. The resonance characteristics measured by an impedance analyzer(HP4194A) were similar to the analysis of finite element method (FEM). The resonance characteristics and the electromechanical coupling factor were the best when the volume fraction PZT was 0.6. It also showed the highest result from the standpoint of sensitivity, bandwidth and ring-down property and so on at the same condition. The specific characteristics show that the 2-2 type piezocomposites turned out to be superior to the ultrasonic sensor composed by single phase PZT.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.15 no.12 s.91
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• pp.1123-1130
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• 2004

In this paper, a technique is presented f3r the design of a structurally simple narrow-band orthomode transducer (OMT) operating at 12/14 GHz frequency bands. The proposed OMT has such a structure that a horizontally polarized wave incident on the circular waveguide of the common port is directed to the rectangular waveguide of the straight port, while the vertically polarized wave is directed to the rectangular waveguide of the side port. Firstly methods are developed f3r designing individual parts of the OMT based on the waveguide theory and the theory of impedance matching. Secondly based on developed methods the whole OMT structure is designed using a commercial electromagnetic field analysis software. The validity of the proposed design technique is confirmed by fabricating and testing the designed OMT.

• The Transactions of the Korean Institute of Power Electronics
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• v.14 no.5
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• pp.343-354
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• 2009

In this paper, a magnetic-less dc-dc switching converter realizing an integrable power conversion system is described. Instead of magnetic devices, the inductive impedance range of piezoelectric transducers is utilized to store and resonate the energy for soft-switching. Piezoelectric devices have no windings and deliver the power by the electrodes, which lead to mass product through semiconductor-manufacturing process. This paper presents a resonant-type step-up dc-dc power converter employing a disk-type piezoelectric transducer, analyzing the operation principles and the frequency control characteristics. Also, a topology extension of the single stage converter into cascaded multi-stage is presented and analyzed with the operation principles and control characteristics. For verification of the analysis, a 10W output dc-dc power converter hardware was implemented. The hardware experiments shows a good frequency control and power efficiency greater than 96% in the single stage. A hardware prototype of the extended multi-stage one was also realized and tested. The results shows that the converter has the same frequency control performance and high efficiency such as 93%.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.11 no.10
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• pp.1916-1923
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• 2007

We have studied to obtain the SAW filter for the passband was formed on the Langasite substrate and was evaporated by Aluminum-Copper alloy and thin we performed computer-simulated by simulator. We cm fabricate that the block weighted type IDT as an input transducer of the filter and the withdrawal weighted type IDT as an output transducer of the filter from the results of our computer-simulation. Also, we have performed to obtain the properly design conditions about phase shift of the SAW filter for WCDMA. We have employed that the number of pairs of the input and output IDT are 50 pairs and the thickness and the width of reflector are $5000\;{\AA}$ and $3.6{\mu}m$ respectively. And we have employed that the distances from the hot electrode to the reflector are $2.0{\mu}m$, $2.4{\mu}m$ and the distance from the hot electrode to the ground is $1.5{\mu}m$ respectively. Frequency response of the fabricated SAW filter has the property that the center frequency is about 190MHz and bandwidth at the 3dB is probably 7,8MHz. And we could obtain that return loss is less then -18dB, ripple characteristics is probably 3dB and triple transit echo is less then -25dB after when we have matched impedance.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.8 no.8
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• pp.1705-1712
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• 2004

This paper presents a new low-cost RF Built-In Self-Test (BIST) circuit for measuring transducer voltage gain, noise figure and input impedance of 5.25GHz low noise amplifier (LNA). The BIST circuit is designed using 0.18${\mu}{\textrm}{m}$ SiGe technology. The test technique utilizes input impedance matching and output transient voltage measurements. The technique is simple and inexpensive. Total chip size has additional area of about 18% for BIST circuit.

• Smart Structures and Systems
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• v.25 no.4
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• pp.423-432
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• 2020

In this paper, a novel but practical approach named series/parallel multi-sensing technique was proposed to evaluate the bolt looseness in a bolt group. The smart washers (SWs), which were fabricated by embedding a Lead Zirconate Titanate (PZT) transducer into two flat metal rings, were installed to the bolts group. By series connection of SWs, the impedance signals of different bolts can be obtained through only one sweep. Therefore, once the loosening occurred, the shift of different peak frequencies can be used to locate which bolt has loosened. The proposed multi input single output (MISO) damage detection scheme is very suitable for the structural health monitoring (SHM) of joint with a large number of bolts connection. Another notable contribution of this paper is the proposal of 3-dB bandwidth root mean square deviation (3 dB-RMSD) which can quantitatively evaluate the severity of bolt looseness. Compared with the traditional naked-eye observation method, the equivalent circuit based 3-dB bandwidth can accurately define the calculation range of RMSD. An experiment with three bolted connection specimens that installed the SWs was carried out to validate our proposed approach. Experimental result shows that the proposed 3 dB-RMSD based multi-sensing technique can not only identify the loosened bolt but also monitor the severity of bolt looseness.

• The Transactions of the Korean Institute of Electrical Engineers C
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• v.48 no.4
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• pp.241-246
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• 1999

In this study, the piezoelectric ceramics PZT powders were synthesized by Wet-Dry combination method. And the flexible 1-3-0 type composites were favricated with piezoceramic PZT and Eccogel polymer matrix embedded 3rd phase. Dielectric constant of 1-3-0 type composites was lower than that of single phase PZT ceramics. Thickness mode coupling factor $k_t$ which was comparable with single phase PZT ceramics, and Mechanical Quality factor $Q_m$ were about 0.65 and 6 respectively. These composites are considered as a good candidates for broad-band type transducer applications. The acoustic impedance for 1-3-0 type composites was lower than that of single phase PZT ceramics. Therefore, these composites would be better used for hydrophone applications.

• The Transactions of the Korean Institute of Electrical Engineers B
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• v.50 no.9
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• pp.453-458
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• 2001

This paper presents a new vector control algorithm of the surface mounted permanent magnet motor (SMPMM) without any rotational tranceducer. Originally, SMPMM does not have any magnetic saliency in structure, but it has a little magnetic saliency due to the saturation by the flux of the permanent magnet. Moreover, it varies according to the load conditions and the control performance of schematics using the saliency can be easily degraded. To prevent it and to improve the performance of the proposed algorithm, the saliency of a SMPMM under various load conditions is analyzed. In the proposed algorithm, the saliency or the impedance difference related to the saliency is utilized in order to estimate the position and speed of the rotor. And the high frequency signal is injected into the motor to measure the impedance difference and also to enhance the control performance of the system. The experimental results verify the performance of the proposed sensorless algorithm.