Admittance Curves Research Articles

An improved cymbal transducer with combined piezoelectric ceramic ring and metal ring

An improved cymbal transducer with a combined piezoelectric ceramic ring and metal ring is presented and analyzed. The cymbal transducer is composed of metal caps in flexural vibration, a piezoelectric ceramic ring and a metal ring in radial vibration. The radial vibration of the radial combination of a piezoelectric ring and a metal ring is analyzed and its electro-mechanical equivalent circuit is obtained. By means of numerical method, the relationship between the resonance/anti-resonance frequency, the effective electro-mechanical coupling coefficient and the geometrical dimensions is studied. The vibrational modes of the cymbal transducer are analyzed; the admittance–frequency curve and vibrational displacement distribution are given. Two cymbal transducers are designed and manufactured, and their frequency characteristics are measured. It is shown that the simulated resonance/anti-resonance frequencies and the admittance curve of the cymbal transducer are in good agreement with the measured results. The improved cymbal transducer is expected to be used in high power underwater sound projector and ultrasonic radiators in air and liquid.

Damage Detection Using Piezoelectric Admittance Approach with Inductive Circuitry

The impedance/admittance-based damage detection has been recognized to be sensitive to small-sized damage due to its high frequency measurement capability. Low-cost measurement circuit has previously been explored to extract the piezoelectric impedance/ admittance curves by using a resistor that is serially connected with the piezoelectric transducer, which enables a self-contained sensor unit. In this research, an innovative admittance-based damage detection scheme is proposed, which combines the key features of the low-cost impedance/admittance measurement circuit with those of the piezoelectric circuitry dynamics. In the new scheme, the piezoelectric transducer is integrated with an inductive circuit. The resonant effect of the inductive circuitry can greatly increase the measurement amplitude. Moreover, when the inductance is properly tuned, very significant dynamic interaction between the mechanical structure being monitored and the electrical circuitry will occur. This results in an order-of-magnitude amplification of the admittance change upon the occurrence of damage, which can yield much increased damage detection sensitivity. Extensive numerical and experimental investigations are carried out to demonstrate the new sensing system development.

Design of thin cross type ultrasonic motor

This paper proposes a newly designed structure for a thin ultrasonic rotary motor. A thin brass plate is used as a cross-shaped vibrator and sixteen ceramic plates are attached to the top and bottom sides of the brass plate. To find the optimum size for the prototype motor, the stator motions were simulated using ATILA by changing the length and thickness of the ceramics. In the results, the stators commonly had three resonance peaks on the admittance curve; the contact tips of the stator moved at trajectories tangential or normal to these resonance peaks. Elliptical displacements of the tips were obtained at off-resonance frequencies. The maximum displacements at the resonance peaks were compared and the maximum displacements of the contact tips were obtained at a length, width, and thickness of 18, 3, and 1.8 mm respectively. With the fabricated prototype motor, high rotational speeds were obtained by applying relatively low voltages. Speed and torque were increased linearly by increasing the voltage. However, torque decreased when the input voltage went over 24 V.

Broadband characteristics of piezoelectric transducer bonded to a thick plate resonator.

The piezoelectric transducer bonded to a thick plate resonator wholly vibrates as a single transducer. Since the distribution of stress in the thickness direction is asymmetric, the transducer resonates at even order harmonic frequencies as well as odd order ones. The back of the resonator is bonded to a quarter‐wavelength matching layer to transmit backward the fundamental frequency wave through the layer. The front of piezoelectric transducer is bonded to another matching layer to transmit forward the ultrasonic wave of higher order frequencies. If both the piezoelectric transducer and the resonator are made of low Q materials, the admittance curve including troughs among resonance peaks is flattened and shows broadband characteristics. Such broadband characteristic transducers made of one to three composite piezoelectric materials were experimentally studied. The thickness of the piezoelectric transducer and the resonator were designed for resonance frequencies of 7 and 1 MHz, respectively. The back of matching layer was bonded to the absorbing material not to reflect forward the ultrasonic waves of 1 MHz. As a result, the ultrasound of center frequency of 5 MHz and fractional bandwidth of 100% were transmitted from the transducer driven by an impulsive signal.

Vibration damping with negative capacitance shunts: theory and experiment

This paper analyzes in detail the enhancement of piezoelectric stack transducers bymeans of the well known ‘negative’ capacitive shunting. The stability is thoroughlystudied: starting from the electrical admittance curve of the transducer, a method isintroduced that quantifies the stability margins of the shunted structure. Two differentimplementations (series vs parallel) are investigated, and the lack of robustness of theparallel one is demonstrated.Next, this technique is experimentally applied on a truss structure. Its performances arecompared with those of passive shunt circuits and with those of an active control law, theso-called Integral Force Feedback or IFF. As expected, the damping introduced by thenegative capacitance shunt is larger than the damping obtained with the passive shunts; itremains, however, one order of magnitude smaller than that obtained with the IFF.

Perceptual thresholds for detecting modifications applied to the acoustical properties of a violin

This study is the first step in the psychoacoustic exploration of perceptual differences between the sounds of different violins. A method was used which enabled the same performance to be replayed on different "virtual violins," so that the relationships between acoustical characteristics of violins and perceived qualities could be explored. Recordings of real performances were made using a bridge-mounted force transducer, giving an accurate representation of the signal from the violin string. These were then played through filters corresponding to the admittance curves of different violins. Initially, limits of listener performance in detecting changes in acoustical characteristics were characterized. These consisted of shifts in frequency or increases in amplitude of single modes or frequency bands that have been proposed previously to be significant in the perception of violin sound quality. Thresholds were significantly lower for musically trained than for nontrained subjects but were not significantly affected by the violin used as a baseline. Thresholds for the musicians typically ranged from 3 to 6 dB for amplitude changes and 1.5%-20% for frequency changes. Interpretation of the results using excitation patterns showed that thresholds for the best subjects were quite well predicted by a multichannel model based on optimal processing.

Psychoacoustic experiments with virtual violins

This study is the first step in the psychoacoustic exploration of why some violins sound better than others. A method was used that enabled the same performance to be replayed on different ‘‘virtual violins,’’ so that the relationships between acoustical characteristics of violins and perceived qualities could be explored. Recordings of real performances were made using a bridge-mounted force transducer, giving an accurate representation of the signal from the violin string. These were then played through filters corresponding to the admittance curves of different violins. Initially, the limits of performance in detecting changes in acoustical characteristics have been characterized. Thresholds were measured for the detection of different modifications of a violins acoustical response, such as a shift in frequency or an increase in amplitude of one or several modes, using a three-interval forced-choice discrimination task. Thresholds were higher for an input of a musical phrase than for a single note, but depended strongly on the choice of the note. The lowest threshold corresponded to a simultaneous shift in frequency of 1.5%, or an increase in level of 3 dB, of several modes, but thresholds appear to be dependent on the musical training of the listeners.

A General-Purpose Online Measurement System for Resonant BAW Sensors

A novel general-purpose online measurement system for the resonant piezoelectric bulk-acoustic-wave sensors is presented. The system supports the various sensor types for the different physical measurands, such as the temperature, humidity, the viscosity, density, and speed of sound of liquids, and the film thickness. The measurement principle is based on the determination of the locus of the admittance curves of the respective sensors for one or several resonances (fundamental and/or overtones). The measurement results are calculated from the measured resonance frequencies or quality factors by applying the appropriate sensor function or calibration data for each sensor. The system covers sensors with resonance frequencies ranging from 30 kHz to 30 MHz. Special electronics have been developed to transform the sensor-admittance values (real and imaginary parts) to voltage signals that are acquired by the computer system. The disturbing effects caused by the capacitance of the sensor connecting cable are minimized by a special electronic circuitry. System performance was tested successfully in combination with two different types of temperature sensors (30-MHz quartz crystal and 6-MHz GaPO4 crystal) and two different types of viscosity sensors (56-kHz torsional mode and 2.8-MHz thickness-shear-mode quartz crystals)

Nanostructuring of Langmuir‐Blodgett Films Containing a Novel Thiomacrocyclic Ionophore on Si3N4/SiO2/Si for Copper Ion Recognition

In its ionic form, copper is a potentially toxic substance, thus, there is a need for developing a sensor to detect low levels of copper in environmental samples. A new capacitive biosensor sensitive to copper(II) was developed. This was achieved by the deposition of the new synthesized ionophore 4‐phenyl‐4‐sulfide‐11‐(1‐oxodecyl)‐1,7‐dithia‐11‐aza‐4‐phosphacyclotetradecane using the Langmuir‐Blodgett (LB) technique. The LB films formed on the Si3N4/SiO2/Si substrate were characterized using X‐ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), and electrochemical impedance spectroscopy (EIS). The shift of the admittance curves owing to the variation of the Cu2+ concentration shows that the device is sensitive to this ion.

Numerical simulation of impedance and admittance of OLEDs

AbstractThe electrical characteristics of organic light‐emitting devices are calculated for the dc and ac regimes by numerically solving the basic semiconductor equations under steady‐state and small‐signal conditions. For a given structure, the dc and ac electric potential and electric field, the electron and hole concentrations, as well as the different components of the current density are obtained as function of the one‐dimensional spatial coordinate. This approach allows a detailed microscopic description of the dependencies of these quantities on the applied steady‐state voltage V0 and the frequency of the modulating voltage. The final output consists in the frequency‐dependent complex admittance and impedance of the device, the real and imaginary parts of which are the experimentally‐available data. As a typical example, we show the results for a two‐layer structure where α‐NPD is the hole‐transporting material and Alq3 the electron‐transporting material. The anode is made of ITO and Al/LiF composes the cathode. The admittance and impedance curves, yielded by the numerical simulation as functions of the modulation frequency, are fitted by an equivalent electrical circuit, the elements of which are resistances and capacitances. The number of components depends on the structure composition and on the applied steady‐state voltage. We show that each element can be associated with a particular region of the device. This allows to correlate the dependence of each feature of the admittance and impedance curves with one or several parameters describing the material system. Such an analysis can be useful for the inverse approach, where, starting from measurements of the electrical ac characteristics, the aim is to get information on the microscopic mechanisms which contribute to the electrical conduction of the device. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Optimization algorithm for transformer admittance curves

This paper describes a fitting algorithm suitable for simultaneously approximating the real and imaginary parts of transformer admittance curves. The algorithm follows a unique strategy to determine the best initial guess. It optimizes the parameters one group at a time. This technique allows the fitting routine to find the best solution even when the number of optimization parameters is large. Since the optimization of each group of parameters is well controlled at each stage, the algorithm is suitable for constrained optimization. Another advantage is that the starting point for each stage can be very simple. Examples demonstrate that the algorithm produces good results for a variety of transformer admittance curves.

A Wireless Surface Acoustic Wave Temperature Sensor Using Langasite as Substrate Material for High-Temperature Applications

A wireless surface acoustic wave (SAW) temperature sensor was produced using langasite single crystal as a piezoelectric substrate. The properties of both solid-electrode and split-electrode interdigital transducers (IDTs) were studied by fitting the admittance curves. A miniature antenna was used and the impedance matching technique between the antenna and the IDT was investigated. The temperature characteristic in the temperature range of 20–700°C was measured. The results showed that both the SAW chip and the antenna functioned in this temperature range.

A Supplemental Method for Evaluating Quartz Transducers

A supplemental method, called double balanced bridge (DBB), is proposed to measure the quality of piezoelectric transducers. The DBB consists of a power divider, two RF bridges with device under test (DUT) terminals and a combiner, which form a doubly balanced bridge with upper and lower arms. In the DBB, the effect of parallel capacitance C0 is directly canceled by a hardware, whereas the phase information is collected with a network analyzer employed in the standard method. The DBB seems to be useful because it gives a symmetrical admittance curve which is proportional to the amplitude of the particle velocity of the transducer. Reproducibility is found to be better than that obtained using the Japanese Industrial Standard method even for the transducers with spurious modes. It can be concluded that the DBB method provides a compatible testing tool for the piezoelectric transducers.

Harmonic admittance and dispersion equations--the theorem.

The harmonic admittance is known as a powerful tool for analyzing the excitation and propagation of surface acoustic waves (SAWs) in periodic electrode arrays. In particular, the dispersion relationships for open- and short-circuited systems are indicated, respectively, by the zeros and poles of the harmonic admittance. Here, we show that a strict reverse relationship also exists: the harmonic admittance of a periodic system of electrodes may always be expressed as the ratio of two determinants, which have been specifically constructed to describe the eigen-modes of the open- and short-circuited systems. There is no need to solve these equations to find the admittance. The existence of a connection between the excitation and propagation problems was recognized within the coupling-of-modes theory by Chen and Haus and was recently used to model surface transverse waves by Koskela et al., but a rigorous mathematical proof was only found later by Biryukov. Here, we reproduce this theorem in detail, give some examples of calculations based on this theorem, and compare the results with measured admittance curves.

Experimental and theoretical investigations of the electrical properties of undoped and magnesium-doped GaN layers

The ac characteristics of GaN : Mg and undoped GaN layers, grown by MOVPE on sapphire substrates, are measured for a wide range of temperature and bias conditions, in order to investigate the effect of the magnesium-related level on the transport properties. Two peaks, whose height and position depend on the measurement temperature, are observed in the admittance curves ( G/ ω versus frequency) of the Mg-doped samples, whereas only one peak appears in undoped samples. The study of the frequency dependence of the impedance, with a model including the two metallic Au/GaN junctions, the GaN layer itself, shows that, besides the effect of the differential resistance of the layer which plays a role in both sample types, the presence of a Mg-related deep level contributes to the observed variations of the peaks in the admittance curves of the p-doped samples. Results of a theoretical steady-state and small-signal analysis based on numerical modelling of the Au/GaN/Au heterostructure complete our analysis.

Elastic Thickness Estimates for Venus Using Line of Sight Accelerations from Magellan Cycle 5

The elastic thickness, T e, for various regions of Venus is estimated by comparing the observed line of sight (LOS) acceleration of the Magellan spacecraft with that predicted using a spherical harmonic representation of the topography, to degree and order 360. At long wavelengths (typically longer than about 500 km) the transfer function between the topography and gravity, or admittance, usually has a flat spectrum with a magnitude of between 20 and 50 mGal Km −1, which is most likely due to convective support. In particular, the topographic highs associated with Beta, Phoebe, Bell, and Eistla are thought to be dynamically supported. At shorter wavelengths, the admittance increases, suggesting a component of flexural support. The elastic thicknesses are constrained by fitting theoretical admittance curves to the observed short wavelength values for the admittance. Results from Magellan cycle 5 show evidence of regional variations in elastic thickness between about 19 and 29 km, with a mean value of around 21–23 km, assuming a crustal thickness of 16 km and a density of 2670 kg m −3. The observed variations in admittance between different regions are unlikely to be due to differences in crustal thickness or density, and probably represent real variations in T e. The values obtained are similar to those from an identical analysis using cycle 4 data. Estimates of the elastic thickness of the Ovda and Alpha regions are unreliable, probably because the topography is not well determined. No reliable estimates of elastic thickness could be made from cycle 6 data where the altitude of the spacecraft was higher than about 300 km, due to the reduction in short wavelength signal amplitude with altitude.

Evolution of the vibrational behavior of a guitar soundboard along successive construction phases by means of the modal analysis technique

The crucial piece of a craft guitar is the soundboard since it determines the quality of the sound given by the instrument. From the initial phase (the gross plate with no hole) until the last construction phase (the plate with the full structure) several stages are followed to modify the dynamic behavior of the structure and hence the acoustic response of the final guitar. The aim of this work is to analyze the effect of each modification on the vibrational response of the plate. With this in mind, an experimental modal analysis of all the construction phases has been performed in the low frequency range under free conditions. The response of the plate in each stage is defined by vibration patterns, resonance frequencies, quality factors, and admittance curves.

Acoustic behavior of chimney pipes

The objective of this work is to study the acoustic behavior of chimney organ pipes. The working hypothesis is that its role is to reinforce the fifth harmonic of the tone of a stopped pipe. According to Helmholtz, the chimney should have the length of an open pipe resonating at the frequency of the fifth harmonic. This design appears to be the least favorable one, except if the chimney is placed half inside and half outside the main pipe, and should therefore be avoided. The ratio of the modulus of the admittance of the different harmonics appears to describe, for the chimney pipe used in this study, the dependency of the ratio of the measured amplitude of the fifth, third, and first harmonic with the geometry of the chimney. The admittance curve can therefore be used to determine the effects of the geometry of the chimney on the timbre of the organ pipe. This result is used in order to determine the optimal diameter of the chimney as a function of its length.

Electromechanical characterization and modelling of piezoelectric thick films

Polycrystalline Pb(Zr x Ti 1-x )O 3 thick films have been prepared by spin-on and rapid sintering in a conventional oven. The remanent polarization and coercive field of a 80 μm thick film are studied versus the applied field. Modellings from the admittance curves and from a modified Mason circuit can explain that the weaker electromechanical characteristics of the PZT layer against the bulk material are due both to the porosity and to the existence of an inactive layer. A characterization by the beam method shows a good correlation between the theoretical and experimental resonance frequencies.

Multiple Frequency Tympanometry

Three methods for compensating multiple frequency acoustic admittance measurements for ear canal volume were studied in 26 men with normal middle ear transmission systems. Peak compensated static acoustic admittance (magnitude of y) and phase angle (phi) were calculated from sweep frequency tympanograms (226-1243 Hz in 113 Hz increments). Of the procedures used to compensate for volume in rectangular form, the ear canal pressure used to estimate volume had the largest effect on the estimate of middle ear resonance. Median resonance was 800 Hz for admittance measurements compensated at 200 daPa versus 1100 Hz for measurements compensated at -350 daPa. The remaining two methods, compensation of susceptance only versus both susceptance and conductance and compensation using the minimum volume versus separate volumes at each frequency, did not affect estimates of middle ear resonance. Estimates of middle ear resonance from compensated phase angle measurements also were compared with estimates of resonance from admittance and phase difference curves. Although resonance could not be estimated from the phase difference curve, resonance estimated from the admittance difference curve agreed with the estimate from compensated phase angle.