Series Resonant Frequency Research Articles

Problems associated with driving an efficient Tonpilz transducer with broadband signals

A symmetrical piezoceramic-stack-driven Tonpilz makes a very efficient underwater loudspeaker for use in any body of water where human activity takes place. The large variation of impedance with frequency makes driving this type of transducer a unique problem. Transformer leakage inductance together with stack capacitance causes excessive current to be drawn at the series resonant frequency, which must be controlled with an appropriately sized series resistor. This paper presents measured and computed frequency responses and impedance magnitude versus frequency graphs for several of Lubell Labs.’ underwater acoustic transducers. Included are recent calibrations made at the USN Dodge Pond facility. These are used to determine suitable values of leakage inductance and series resistance. A reasonable size series resistance is one that will not cause excessive loss at the fundamental transducer resonance. Excessive leakage inductance must be avoided because of its effect on high frequency response. An expression for the current drawn when the transducer is driven with bandlimited pink noise has been derived by the author and will be given herein.

A Study of Depletion Layer Effects on Equivalent Circuit Parameters Using an Electrochemical Quartz Crystal Impedance System

An electrochemical quartz crystal impedance system (EQCIS) was used to investigate depletion layer effects on equivalent circuit parameters of piezoelectric quartz crystal resonance in electrochemical processes of CoSO4 aqueous solutions containing 0.4 mol/L ethylenediamine + 0.5 mol/L Na2SO4, 0.2 mol/L 1,10-phenanthroline + 0.5 mol/L Na2SO4 and K3Fe(CN)6, or K4Fe(CN)6 aqueous solutions containing 1.0 mol/L KCl in potential cycling experiments, respectively. The impedance data were analyzed according to Martin's model. For the former two systems, motional resistance R1, series resonant frequency fs, and motional inductance L1 changed reversibly with potential, and the observed values of ΔR1, ΔL1, and Δfs roughly satisfied equations reflecting liquid loading effects, suggesting that changes in these parameters might be mainly governed by local variations in solution density and viscosity near the electrode surface. For the latter two systems, reversible changes in R1 with potential coincided well with the simulated results from variations in solution density and viscosity near the electrode surface; however, besides reversible changes of ΔL1 and Δfs with potential, rising drifts of fs and decreasing drifts of L1 were found at oxidation potentials. The drifts of fs and L1 observed are believed to result from mass changes of the gold electrode, and cyanide and chloride corrosion of the gold electrode at oxidation potentials may play an important role for the drifting phenomena. It is concluded that quantitative analyses of ΔR1, ΔL1, and Δfs obtained from the EQCIS provide the possibility for differentiating the net depletion layer effect with the change in electrode mass, and the ΔR1 response may be well used for evaluating local changes in liquid loading inside the depletion layer compared with responses of Δfs and ΔL1.

Interactions of HIV-1 TAR RNA with Tat-derived peptides discriminated by on-line acoustic wave detector.

The human immunodeficiency virus type I is strongly regulated at the transcriptional level through the interaction of an 86-amino acid protein (Tat) with a viral messenger RNA transcript. Accordingly, the binding of this protein and other cellular factors to the RNA has constituted a significant target for the development of anti-HIV drugs. In the present work, we describe the detection of the binding of two Tat-derived peptides, of 12 and 40 amino acids in length, with chemically synthesized RNA by an acoustic wave sensor. Immobilization of the nucleic acid to the sensor surface, which was incorporated in an on-line system, was effected using the biotin-neutravidin interaction. As expected, the changes in series resonance frequency and motional resistance for the two peptides indicate reversible interactions in both cases that can be further characterized by the calculation of kinetic off-rates. Of particular interest is the nature of the two frequency-based signals, which are in opposite directions for the two peptides. These results together with those obtained for the surface interactions of neutravidin and biotinylated RNA confirm that the thickness shear mode sensor, mass-response model involving the well-known Sauerbrey expression is invalid when applied to operation in liquids.

Interfacial Properties of Biotin Conjugate−Avidin Complexes Studied by Acoustic Wave Sensor

The adsorption of avidin, neutravidin, and biotin-labeled dextran 10,000, dextran 70,000, bovine albumin, and insulin to the gold electrodes of thickness-shear-mode acoustic wave devices was studied in a flow injection analysis configuration. Electrodes with different surface rugosity and free energy were also examined. Changes in series resonance frequency for the various molecules as a result of electrode adsorption cannot be explained in terms of the conventional mass-response effect. Perturbation of the properties of the protein and polysaccharide layers, such as their viscosity, and acoustic coupling phenomena offer a more reasonable basis to evaluate the results. In an analogous fashion, the acoustic wave sensor signals obtained for the formation of the various avidin− and neutravidin−biotin conjugate samples do not correspond to the additional mass deposited on the device surface. The responses for the binding of biotinylated insulin to avidin and to the nonglycosylated form of the parent molecule were completely different. This result is ascribed to a difference of surface free energy associated with the two protein-based interfaces. The acoustic wave sensor was also employed to investigate the formation of avidin−biotin conjugate multilayer structures on the surface of the device. Multilayer buildup is detectable for several pairs of avidin−biotin interactions, but the corresponding shifts in series resonance frequency gradually diminish in magnitude. Finally, the introduction of biotin itself appears to result in structural changes in the multilayer deposit, causing alterations in viscoelastic properties.

The study of diffusion of media in the organic coating films by BAW admittance analysis

The permeation of water and corrosive species in coating films is very important for the corrosion protection by organic coatings. As a new method for the study of diffusion of media in coating films, bulk acoustic wave (BAW) admittance analysis has been proposed in this article. Real-time information on the change of the film mass, mechanic property of the layer, and the permeation process of the media can be provided simultaneously by the parameters of BAW admittance analysis, fs (series resonant frequency), ΔL1 (inductance variance), R1 (resistance), Q (quality factor), and Cs (film capacitance). The diffusion behavior of media and the corresponding film stability can be described by the following parameters: D (diffusion coefficient), P (permeation coefficient), S (the solubility of media), and SC (the swelling coefficient of the coating layer). © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 70: 2283–2290, 1998

Coated-quartz crystal resonator (QCR) sensors for on-line detection of organic contaminants in water

Coated-quartz crystal resonators (QCRs) with enhanced surface mass sensitivity profile are investigated as chemical sensors for the detection of volatile organic compounds (VOC) in water. Various polymers that show stability in water and sensitivity to the VOCs are used as coating materials. These include poly(ethyl acrylate) (PEA), poly(epichlorohydrin) (PECH), and poly(octadecyl methacrylate) (PODMA). The main detection mechanism investigated in this study is the mechanical loading considered primarily as mass loading. Under appropriate experimental conditions (e.g., liquid cell, coating thickness, oscillator circuit), lower detection limits for VOCs can be achieved using QCRs, provided that noise in the sensor signal is minimized. Inherent noise is introduced by the decrease in the crystal Q, the parasitic elements within the oscillator circuit, and the liquid flow on the crystal surface. Using PEA-coated QCRs operating at the series-resonant frequency, detection limits of 150 ppb and 500 ppb are found for tetrachloroethane and trichloroethene, respectively. Results also are presented and discussed for other polymer coatings with different organic compounds, Using results of the mass loading effect (i.e., the measured frequency shifts), the partition coefficients, K/sub L/, of the analyte molecules in the composite load are discussed in order to analyze the detection process.

Piezoelectric resonant sensor for sound velocity of liquids

The sensor consists of two circular piezoelectric plates with the liquid in between. Each piezoelectric plate is a bulk resonator with two electrodes driven in thickness extensional modes. The two resonator plates are electrically connected in parallel and the total admittance is measured in the vicinity of two quasiharmonic series resonance frequencies by a PC-controlled electric admittance measurement system. The extensional thickness mode purity was checked directly by corresponding mode pattern measurements using a laser speckle vibration amplitude measurement system. The sensor element is mounted in a thermostated aluminum housing to avoid temperature effects and to obtain the sound velocity of the liquid at a defined temperature. Two quasiharmonic resonance frequencies are used to allow the elimination of the unknown density of the liquid. The sound velocity is calculated out of a rigorous one-dimensional theoretical model of the three-layer sensor arrangement. In addition to the determination of the sound velocity of the liquid, the mass density of the liquid can be obtained from the same primary measurements. However, at present the accuracy of the density value is one order of magnitude lower than that of the velocity (typically 0.1% for water, acetone, glycerin).

A transverse shear model of a piezoelectric chemical sensor

This model of a transverse shear-mode piezoelectric quartz-crystal chemical sensor is based on the fundamental equations of motion and piezoelectricity. The geometry includes the crystal as well as a metal electrode and a polymeric sensing layer immersed in a fluid medium. All of these are considered to be viscoelastic materials, and slip at the three interfaces is included. The model is shown to agree well with both experimental data and published correlations of the series resonant frequency and equivalent series resistance under both mass and liquid loading. In addition, the mechanical resonant behavior is also calculated. The interfacial slip parameter and the complex shear viscosity are shown to be mathematically interchangeable but not physically equivalent. Negative elastic coefficients obtained from the slip parameters for less viscous fluids suggests that interfacial slip is an important process, which dominates viscoelastic effects for these fluids.

Protein adsorption to organosiloxane surfaces studied by acoustic wave sensor.

Surfaces of the two organosiloxanes, polymercaptopropylmethylsiloxane and octaphenylcyclotetrasiloxane, were prepared on the gold electrodes of thickness-shear mode acoustic wave sensors. Compounds containing the siloxane bond are important in the fabrication of medical implants. The flow-through adsorption of the proteins: human serum albumin, alpha-chymotripsinogen A, cytochrome c, fibrinogen, hemoglobin, immunoglobulin G and apo-transferrin to the two siloxane surfaces and a gold electrode were detected by acoustic network analysis. With the exception of minor wash-off by buffer flow, the adsorption of all proteins to the three surfaces is irreversible. Differences observed for the magnitudes of adsorption for the various cases are ascribed to the role played by molecular interactions at the liquid/solid interface. The results confirm that changes in series resonant frequencies caused by macromolecular adsorption differ significantly from the widely accepted "mass based" model usually employed to characterize the response of this type of acoustic wave device.

Response of a thickness-shear mode quartz crystal resonator upon hydrogel formation

The response of an AT-cut quartz crystal piezoelectric resonator operating in the thickness shear mode (TSM) during polymer gel formation has been examined by acoustic network analysis. The series and parallel resonant frequencies as well as the amplitude and phase of the impedance of the TSM resonator were monitored in real-time when a layer of polyacrylamide gel was formed on one side of the sensor. Various concentrations of radical initiator and crosslinking agents were used to control the rates of polymerization and crosslinking during the hydrogel formation. The increase in the magnitude of the minimum impedance and the decrease in the maximum phase angle were observed as a result of the damping of both the magnitude-frequency and phase-frequency curves, caused by the transformation of the contacting medium from a viscous liquid to a viscoelastic hydrogel. Significant difference was observed between the responses of series and parallel resonant frequencies. The series resonant frequency increases while the parallel resonant frequency decreases during gel formation, and the magnitude of change in the parallel frequency is several times that in the series frequency. Small variations in the gelforming solutions such as the depletion of buffer and addition of double-stranded DNA cause distinct changes in the response profiles of the quartz resonator.

Adhesion of human platelets to collagen detected by 51Cr labelling and acoustic wave sensor

Selective adhesion of human platelets to layers of collagen Type I, immobilized on silicon wafers, has been confirmed using 51Cr radiolabelling of platelets. Corresponding experiments conducted with collagen-treated thickness-shear mode acoustic wave sensors resulted in changes in series resonant frequency in the range 35–43 Hz. Control experiments with sensors, coated with bovine serum albumin, displayed significantly reduced response. Similar reduced values were also obtained when EDTA was present and Mg 2+ was absent from the assay-buffer solution. Direct correlation of the sensor results with 51Cr labelling experiments confirms that the conventional quartz crystal microbalance description is completely inadequate to explain the magnitude of the sensor response, which is 200 times less than that predicted by the well-known Sauerbrey expression.

Polymer-coated quartz crystal resonators for multi-information sensing

A study of polyphosphazene-coated QCRs gas sensors using both mass and electrical loadings has been performed. In addition to the device series resonance frequency, the parallel resonant frequency was measured in an attempt to characterise the changes in the dielectric properties of the coating during the detection process. The result is a sensor with an additional parameter to improve selectivity.

Polymer-coated QCR sensors for the detection of organic solvents in water

Poly(ethyl acrylate) (PEA), poly(epichlorohydrin) (PECH) and a silicon-based copolymer of trimethoxypropylsilane/octadecyltrimethoxysilane (TMPS/ODTMS) were used as sensitive materials for the detection of organic solvent molecules in water. Quartz crystal resonators (QCR) with modified electrode configurations are used to monitor the changes in mass and in electrical properties by measuring the shifts in series resonance frequency ( f s), parallel resonance frequency ( f p), and frequency of maximum admittance ( f m), respectively. The result is a multi-information chemical sensor. The sensor signals are completely reversible at room temperature with the response and recovery time in the order of minutes under our measurement conditions. The sensitivities obtained from the measurements of f m for all organic solvents investigated are generally larger than those obtained from f s and f p. It is also found that there is no correlation between the measured sensitivities of the series resonance frequency and the boiling point temperatures of the organic solvents investigated in the liquid phase under our experimental conditions, as is generally obtained in the gas phase.

A simple setup to simultaneously measure the resonant frequency and the absolute dissipation factor of a quartz crystal microbalance

An experimental setup is described that can simultaneously measure the absolute dissipation factor and the resonant frequency of a short-circuited quartz crystal microbalance. The crystal is driven at approximately its resonant frequency by a signal generator which is intermittently disconnected by a relay, causing the crystal oscillation amplitude to decay exponentially. The decay is measured using a ferrite toroid transformer. One of the crystal leads is fed through the center of the ferrite toroid and thereby acts as the primary winding of the transformer. The secondary winding of the transformer is connected to a digitizing oscilloscope which records the decay of the crystal oscillation. From the recorded decay curve, the absolute dissipation factor (calculated from the decay time constant) and the series resonant frequency of the freely oscillating crystal are obtained. Alternatively, the dissipation factor and resonant frequency can be measured for the crystal oscillating under open-circuit conditions, i.e., in the parallel mode. The measurements are automated.

QCM Operation in Liquids: An Explanation of Measured Variations in Frequency and Q Factor with Liquid Conductivity

Recently, several reports have shown that when one side of a quartz crystal microbalance (QCM) is exposed to a liquid, the parallel (but not the series) resonant frequency is influenced by the conductivity and dielectric constant of the liquid. The effect is still controversial and constitutes a serious complication in many applications of the QCM in liquid environments. One suggestion has been that acoustically induced surface charges couple to charged species in the conducting liquid. To explore this effect, we have measured the parallel and the series mode resonance frequencies, and the corresponding Q factors, for a QCM with one side facing a liquid. These four quantities have all been measured versus liquid conductivity, using a recently developed experimental setup. It allows the simultaneous measurement of the resonant frequency and the Q factor of an oscillating quartz crystal, intermittently disconnected from the driving circuit. Based on these results, a simple model together with an equivalent circuit for a quartz crystal exposed to a liquid is presented. The analysis shows that it is not necessary to infer the existence of surface charges (or other microscopic phenomena such as electrical double layers) to account for the influence of the liquid's electrical properties on the resonant frequency. Our results show that the contacting conductive liquid, in effect, enlarges the electrode area on the liquid side and thereby changes the parallel resonant frequency. By proper design of the QCM measurement, perturbing effects due to the liquid's electrical properties can be circumvented.

Rheological and interfacial properties of nucleic acid films studied by thickness – shear mode sensor and network analysis

Complete characterization of the thickness – shear mode (TSM) acoustic wave sensor coated with films of nucleic acid and subjected to conductive solution loading is achieved through network analysis of impedance measurements. The responses of coated sensors with respect to series resonant frequency can be separated into two regions. When 0 < σ < 0.5Ω−1 m−1 the frequencies for sensors with films of single strand (ss) DNA or polycytidylic (5′) (Poly C) in place rise significantly with increasing conductivity. The motional resistances for sensors coated with both species peak at the same value of conductivity where the frequency has the most rapid shift. In the second region (0.5 < σ < 12Ω−1 m−1), the frequency response for the ss DNA system exhibits a bell-shaped curve, with a minimum at σ = 4Ω−1 m−1. The motional resistances for both nucleic acid layers show reversible behaviour, whereas TSM sensors with bare PdO and Au electrodes yield little change. Models that consider only the bulk properties of solutions fail to explain the observed changes in frequency. On the other hand, an equivalent circuit model incorporating the rheological properties of nucleic acid layers on the sensor surface is successful in explaining the various responses. Key words: DNA sensor, network analysis, thickness – shear mode sensor, DNA interfacial properties.

Interfacial Hybridization of RNA Homopolymers Studied by Liquid Phase Acoustic Network Analysis

Hybridization of RNA homopolymers has been employed to verify the possibility of developing a biosensor for nucleic acid based on the thickness-shear mode (TSM) acoustic wave device. The results clearly show that RNA homopolymers can be successfully immobilized onto a PdO electrode surface by chemisorption and that sequence-specific hybridization can be detected. The characterization of TSM sensors upon hybridization of immobilized nucleic acid is achieved through the network analysis of impedance measurements. Multidimensional chemical information regarding nucleic acid hybridization at the interface through correlation with such parameters as the series and parallel resonant frequencies, frequencies at the maximum and minimum impedance, and equivalent circuit elements was obtained. The effect of temperature on RNA homopolymer hybridization has also been examined. The results show that the series resonant frequency increases when single strand Poly C hybridizes to complementary Poly G from solution at lo...

Platinum anticancer drug binding to DNA detected by thickness-shear-mode acoustic wave sensor.

Nucleic acid has been attached to the electrodes of thickness-shear-mode acoustic wave devices to produce a biosensor for platinum-based drugs. The decreases in series resonant frequency for interactions of DNA with both cis- and transplatin are indicative of two distinct kinetic processes. The results of a kinetic analysis are interpreted in terms of nucleic acid binding of the hydrolysis products of the two drugs. Concentration-dependent decreases of series resonant frequency show that the limit of detection for the drugs is approximately 10(-7) M. Motional resistance changes for nucleic acid-drug interactions also convey information regarding the chemistry of the macromolecules at the interface.

Kinetics of interfacial nucleic acid hybridization studied by acoustic network analysis

A novel acoustic network analysis technique has been developed to study DNA hybridization kinetics at a sensor-solution interface. The series resonant frequency change is related to the DNA hybridization process through the DNA concentration-dependent viscosity change in the acoustic wave decay length region. The kinetics of hybridization of pPT-2 cDNA probe to ss DNA immobilized on thickness-shear-mpde (TSM) acoustic wave sensors has been examined. The process measured by this device does not conform to the generally assumed theoretical second order reaction in solution and one-step mechanism on a typical membrane filter. The pseudo-first order effective rate constants are (8·0 ± 0·5) × 10 −5 s −1 when hybridization is performed in solution without the presence of moieties employed to prevent non-specific effects (blocking reagents), and (3·8 ± 0·1) × 10 −5 s −1 with them. The calculated Mark-Houwink constant, α, is 1·8, and the intrinsic viscosity is 9·0 × 10 4 (M −1) under the hybridization conditions. Inflection points due to the formation of intermediate hybrids are observed during continuous measurement of series resonant frequency with time.

Analysis of electrical equivalent circuit of quartz crystal resonator loaded with viscous conductive liquids

An electrical equivalent circuit of quartz crystal resonator (QCR), with modified electrodes, loaded with a viscous conductive liquid is proposed. The electrode in contact with the liquid is modified so as to create an unmetallized crystal surface in contact with the liquid and thus to introduce an acoustoelectric interaction at the crystal | liquid interface. The admittance—impedance characteristics of the equivalent circuit of the loaded QCR are analyzed to obtain expressions for the changes in the series and parallel resonant frequencies in terms of the liquid viscosity η L, density ϱ L, dielectric constant ϵ L, and conductivity σ, as well as the quartz parameters and electrode area geometry. Using a network analyzer, the S parameters of the equivalent circuit of various conductive liquid-loaded QCRs are measured and analyzed. It is shown that in addition to being a well-known detector of mechanical properties of liquids, a QCR, when properly designed, can be used to monitor the electrical properties of dilute ionic solutions.