• Korean Journal of Materials Research
• /
• v.20 no.12
• /
• pp.640-644
• /
• 2010

Information technology devices, such as cellular phones, MP3s and so on, due to restrictions of space, require thin and small micro-speakers to generate sound. The reduction of the size of micro-speakers has resulted in the decrease of sound quality, due to such factors as frequency range and sound pressure level. In this study, the acoustical properties of oval microspeakers has been studied as a function of pattern shape on the diaphragm. The other conditions of micro-speakers, except for the pattern, was not changed. When the pattern is present on the diaphragm and the shape of pattern was a whirlwind, the resonance frequency was reduced due to the decrease of tensile strength of diaphragm. The patterns presented in the semi-minor axis of diaphragm did not effect a change of resonance frequency. However, increasing the number of patterns in the semimajor axis of diaphragm became a reason for the decrease of resonance frequency on edge side. When the depth of pattern on edge side was increased, the resonance frequency was decreased due to reduction of geometrical stiffness. If the height of edge and dome were increased, the resonance frequency and geometrical stiffness rapidly increased. After reaching the maximum values, they began to decrease with the continuous increase of height.

• The Transactions of The Korean Institute of Electrical Engineers
• /
• v.57 no.7
• /
• pp.1213-1217
• /
• 2008

Poling is an important process in fabricating PZT ceramic devices such as filters and resonators and activates piezoelectricity to sintered PZT ceramics. Tolerance of the operating frequency of these devices is tightly required in applications. And a factor to attribute the tolerance is the temperature dependence of the resonance frequency of PZT ceramics. In this paper the relationship of poling strength and temperature dependence of resonance frequency of PZT specimens was studied. The $Pb(Zr_{0.53}Ti_{0.47})O_3$ ceramics were fabricated and the poling strengths were chosen to be 0.5, 1.5, 2.5 and 3.5 [kV/mm]. The dielectric constant of the specimen poled in poling strength 0.5 [kV/mm] was less than that of unpoled specimen and the specimen poled in higher electric field had the higher dielectric constant. (002) peak in X-ray diffraction patterns of the specimens increased as poling strength increased. And the change of resonance frequency of the specimens according to the variation of temperature was measured. Resonance frequency of all specimens increased as the temperature increased. The specimen poled in higher electric field had the smaller positive temperature coefficient of resonance frequency. The effect that temperature coefficient of resonance frequency becomes smaller is obtained when Zr mole in PZT composition equation increase. Controlling the poling strength is believed to be a method to adjust the temperature stability of resonance frequency of the PZT ceramic devices.

• Aerospace Engineering and Technology
• /
• v.4 no.2
• /
• pp.216-219
• /
• 2005

In this study, we will explain the design, test results and analysis of system for measuring the small mass in the microgravity environment. It is so difficult to measure the mass by sensing the gravity as the ground in the microgravity environment. The suggested method is to measure the resonance frequency of a sample. The resonance frequency may be measured as a function of mass. If we know the resonance frequency of the mass, we can guess the mass by detecting the resonance frequency. Piezoelectric ceramics have the characteristics that resonance frequency is changed by total mass which are its mass and the attached mass. This system have some problems but we verified that we can measure the unknown mass using the resonance frequency as the mass.

• Journal of KSNVE
• /
• v.2 no.2
• /
• pp.99-106
• /
• 1992

The complex Young's modulus of a viscoelastic material can be obtained as a function of frequency from the measurements of relative motion between the two ends of a bar-type specimen. Non-resonance method is usually used to obtain the complex Young's modulus over wide range of frequency including resonance points, while in resonance method information at resonance frequencies only is used. However, the complex Young's modulus obtained by the non-resonance method is often unreliable in the anti-resonance frequency regions because of the measurement noise problems. In this study, the effects of the random measurement errors on estimating the complex Young's modulus are studied in the aspect of sensitivity, and how to obtain the reliable frequency region for a given measurement error level is shown. The usable frequency regions in determining the complex Young's modulus are represented by a non-dimensional parameter formed with the wave length and specimen length.

• Proceedings of the KSME Conference
• /
• 2001.06d
• /
• pp.890-895
• /
• 2001

Pressure resonance frequency that is caused in the combustion chamber can be interpreted to acoustic analysis. Until now the pressure resonance has been assumed and calculated to a disc type combustion chamber that neglected the combustion chamber height because the knock occurs near the TDC(top dead center). In this research FEM(fine element method) has been used to calculate the pressure resonance frequency inside the experimental engine combustion. The reduce error of the resonance frequency obtained by FEM has decreased about 50% compared to the calculation of Draper's equation. Due to the asymmetry in the shape of the combustion chamber that was neglected in Draper's equation we could find out that a new resonance frequency could be generated. To make the experimental results equal we could know that the speed of sound that satisfies Draper's equation was selected 13% higher than all the pent-roof type combustion considered.

• Transactions of the Korean Society of Mechanical Engineers
• /
• v.18 no.12
• /
• pp.3202-3218
• /
• 1994

Mode shapes and natural frequencies of vibrating laminated composite plates are taken using real-time and time-average holographic interferometry. Debonds and delamination in the laminated plates are measured nondestructively. During holographic testing of composite plates, it has been found that the conditions for the local resonance in debonds are strongly dependent on the frequency of excitation. A membrane resonance model was proposed to describe this behavior. Relations between characteristic length according to the size, shape of debonds and membrane resonance frequency are presented. Several experiments were performed to verify the membrane resonance model. The agreements between the predicted excitation frequency and the observed resonance frequency are good. The experimental results show that higher stresses and strains due to local resonance lead to the debond detection.

• Journal of electromagnetic engineering and science
• /
• v.4 no.3
• /
• pp.113-118
• /
• 2004

As an application of ring filters, a new and simple method to determine an inherent-ring-resonance frequency is introduced. The ring filter consists of a ring and two short stubs. They are connected at 90$^{\circ}$ and 270$^{\circ}$ points of the ring and the ring filter may be seen in such way that two filters are connected in parallel. Therefore, if the two powers of the two filters are out-of-phase at the output, the power excited at the input can not be delivered. That can be done by making difference in length of the two short stubs, and when a certain condition is satisfied, a frequency exists where all the excited power is reflected. That is the very inherent-ring-resonance frequency. In the lossless case, the return loss with the condition reaches 0 dB at the inherent-ring-resonance frequency but does not with conductor, dielectric losses and so on. Therefore, the effective loss tangent at a frequency of interest may be obtained correctly. To verify the method, two ring filters have been fabricated in microstrip lines and the measured results show good agreement with the predicted ones.

• Journal of the Korean Society of Industry Convergence
• /
• v.24 no.4_2
• /
• pp.481-490
• /
• 2021

In the ultrasonic welding machine, when the load fluctuates, the L and C of the piezo element in the oscillation part change. As a result, the resonant frequency is changed, so it is necessary to match the operating frequency of the ultrasonic welding machine to the new resonant frequency. That is, in order to maximize the output of the oscillation unit of the ultrasonic welding machine, it is inevitable to follow the resonance frequency. Accordingly, many methods for following the resonant frequency are being actively studied. In addition, in order to check the effect of external inductance on the operation of the ultrasonic welding machine, The equivalent circuit of the piezo element was analyzed by including the external inductance for resonance in the equivalent circuit of the piezo element, and the method of selecting an appropriate inductance was described. In this paper, we propose a new system that allows the switching frequency of the inverter to tracking the resonance frequency even if the resonance frequency is changed due to the load of the ultrasonic welding machine.

• The Journal of the Acoustical Society of Korea
• /
• v.15 no.4E
• /
• pp.65-71
• /
• 1996

In shallow water with a thermocline, the characteristics of sound propagation strongly depend on the signal frequency. When only one of the source and the receiver is above the themocline, it is known that the intensity of the received signal changes largely and almost periodically as the signal frequency varies. This is the so-called channel resonance. By using the ray-mode approach, the formula relating the resonance frequency and the sound speed profile is obtained, and the resonance phenomenon is analyzed. Also this analysis is verified by numerical calculation.

• Proceedings of the KSME Conference
• /
• 2008.11a
• /
• pp.1613-1616
• /
• 2008

A Transcutaneous Energy Transmission System (TET) has been developed for the wireless energy transmission with two magnetically coupled coils. A resonance circuit is used to raise the induced voltage and current of the secondary coil. Its resonance frequency depends on the internal resistance of circuit and the transferred energy. Because the transferred energy usually changes in wide range, the output voltage is unstable and the energy transferring efficiency decrease. A push-pull class E amplifier is usedto generate high frequency AC voltage. To maintain proper resonance frequency, the voltage output of the amplifier was continuously monitored and adjusted to the optimized resonance frequency. Because of its high frequency (370 kHz), a phase lockedloop circuit and a comparator are used to monitor the output waveform. The results of experimentaldata show that the PLL circuit can increase the transmission efficiency and stabilize the output voltage of TET.