Resonant conditions for Love wave guiding layer thickness

In this work we report a systematic investigation of polymer overlayer thickness in a Love wave device working at a fundamental frequency of 110MHz and at the 330MHz harmonic. At both frequencies we observe the initial reduction in insertion loss associated with a Love wave device. Significantly, we also observe a series of resonant conditions as the layer thickness is further increased. The separation of these resonances is attributed to an increase in thickness of half of the acoustic wavelength in the polymer

ST Quartz Acoustic Wave Sensors with Sectional Guiding Layers

We report the effect of removing a section of guiding layer from the propagation paths of ST-quartz Love wave sensors; this offers the ease of fabrication of a polymer guiding layer whilst retaining the native surface of the quartz which may then be used for the attachment of a sensitizing layer. Data is presented for rigid and viscous loading, which indicates a small reduction in mass sensitivity compared to a Love wave device. Biosensing capabilities of these discontinuous ‘sectional’ guiding layer devices are demonstrated using protein adsorption from solution

SU-8 Guiding Layer for Love Wave Devices

SU-8 is a technologically important photoresist used extensively for the fabrication of microfluidics and MEMS, allowing high aspect ratio structures to be produced. In this work we report the use of SU-8 as a Love wave sensor guiding layer which allows the possibility of integrating a guiding layer with flow cell during fabrication. Devices were fabricated on ST-cut quartz substrates with a single-single finger design such that a surface skimming bulk wave (SSBW) at 97.4 MHz was excited. SU-8 polymer layers were successively built up by spin coating and spectra recorded at each stage; showing a frequency decrease with increasing guiding layer thickness. The insertion loss and frequency dependence as a function of guiding layer thickness was investigated over the first Love wave mode. Mass loading sensitivity of the resultant Love wave devices was investigated by deposition of multiple gold layers. Liquid sensing using these devices was also demonstrated; water-glycerol mixtures were used to demonstrate sensing of density-viscosity and the physical adsorption and removal of protein was also assessed using albumin and fibrinogen as model proteins

Harmonic Love wave devices for biosensing applications

Simultaneous operation of a Love wave biosensor at the fundamental frequency and third harmonic, including the optimisation of IDT metallisation thickness, has been investigated. Data is presented showing a sequence of deposition and removal of a model mass layer of palmitoyl-oleoyl-sn-glycerophosphocholine (POPC) vesicles while frequency hopping between 110 and 330 MH

Field investigation of Love-waves in near-surface seismology

This is the publisher's version, also available electronically from "http://library.seg.org".We examine subsurface conditions and survey parameters suitable for successful exploitation of Love waves in near-surface investigations. Love-wave generation requires the existence of a low shear-velocity surface layer. We examined the minimum thickness of the near-surface layer necessary to generate and record usable Love-wave data sets in the frequency range of 5–50Hz . We acquired field data on a hillside with flat-lying limestone and shale layers that allowed for the direct testing of varying overburden thicknesses as well as varying acquisition geometry. The resulting seismic records and dispersion images were analyzed, and the Love-wave dispersion relation for two layers was examined analytically. We concluded through theoretical and field data analysis that a minimum thickness of 1m of low-velocity material is needed to record usable data in the frequency range of interest in near-surface Love-wave surveys. The results of this study indicate that existing guidelines for Rayleigh-wave data acquisition, such as receiver interval and line length, are also applicable to Love-wave data acquisition

Pulse mode operation of Love wave devices for biosensing applications

In this work we present a novel pulse mode Love wave biosensor that monitors both changes in amplitude and phase. A series of concentrations of 3350 molecular weight poly(ethylene glycol) (PEG) solutions are used as a calibration sequence for the pulse mode system using a network analyzer and high frequency oscilloscope. The operation of the pulse mode system is then compared to the continuous wave network analyzer by showing a sequence of deposition and removal of a model mass layer of palmitoyl-oleoyl-sn-glycerophosphocholine (POPC) vesicles. This experimental apparatus has the potential for making many hundreds of measurements a minute and so allowing the dynamics of fast interactions to be observed

Love wave tomography in Italy from seismic ambient noise

We estimate Love wave empirical Green's functions from cross-correlations of ambient seismic noise to study the crust and uppermost mantle structure in Italy. Transverse-component ambient noise data from October 2005 through March 2007 recorded at 114 seismic stations from the Istituto Nazionale di Geofisica e Vulcanologia (INGV) national broadband network, the Mediterranean Very Broadband Seismographic Network (MedNet) and the Austrian Central Institute for Meteorology and Geodynamics (ZAMG) yield more than 2 000 Love wave group velocity measurements using the multiple-filter analysis technique. In the short period band (5–20 s), the cross-correlations show clearly one-sided asymmetric feature due to non-uniform noise distribution and high local activities, and in the long period band (>20 s) this feature becomes weak owing to more diffusive noise distribution. Based on these measurements, Love wave group velocity dispersion maps in the 8–34 s period band are constructed, then the SH wave velocity structures from the Love wave dispersions are inverted. The final results obtained from Love wave data are overall in good agreement with those from Rayleigh waves. Both Love and Rayleigh wave inversions all reveal that the Po plain basin is resolved with low velocity at shallow depth, and the Tyrrhenian sea is characterized with higher velocity below 8 km due to its thin oceanic crust

A mathematical study of Voigt viscoelastic Love wave propagation

This research is a mathematical investigation of the propagation of a Love wave in a Voigt viscoelastic medium. A solution to the partial differential equation of motion is assumed and is shown to satisfy the three necessary boundary conditions. Velocity restrictions on the wave and the media are developed and are shown to be of the same form as those governing the elastic Love wave --Abstract, page ii

Love Wave Biosensors: A Review

In the fields of analytical and physical chemistry, medical diagnostics and biotechnology there is an increasing demand of highly selective and sensitive analytical techniques which, optimally, allow an in real-time label-free monitoring with easy to use, reliable, miniaturized and low cost devices. Biosensors meet many of the above features which have led them to gain a place in the analytical bench top as alternative or complementary methods for routine classical analysis. Different sensing technologies are being used for biosensors. Categorized by the transducer mechanism, optical and acoustic wave sensing technologies have emerged as very promising biosensors technologies. Optical sensing represents the most often technology currently used in biosensors applications. Among others, Surface Plasmon Resonance (SPR) is probably one of the better known label-free optical techniques, being the main shortcoming of this method its high cost. Acoustic wave devices represent a cost-effective alternative to these advanced optical approaches [1], since they combine their direct detection, simplicity in handling, real-time monitoring, good sensitivity and selectivity capabilities with a more reduced cost. The main challenges of the acoustic techniques remain on the improvement of the sensitivity with the objective to reduce the limit of detection (LOD), multi-analysis and multi-analyte detection (High-Throughput Screening systems-HTS), and integration capabilities. Acoustic sensing has taken advantage of the progress made in the last decades in piezoelectric resonators for radio-frequency (rf) telecommunication technologies. The so-called gravimetric technique [2], which is based on the change in the resonance frequency experimented by the resonator due to a mass attached on the sensor surface, has opened a great deal of applications in bio-chemical sensing in both gas and liquid media. Traditionally, the most commonly used acoustic wave biosensors were based on QCM devices. This was primarily due to the fact that the QCM has been studied in detail for over 50 years and has become a mature, commercially available, robust and affordable technology [3, 4]. LW acoustic sensors have attracted a great deal of attention in the scientific community during the last two decades, due to its reported high sensitivity in liquid media compared to traditional QCM-based sensors. Nevertheless, there are still some issues to be further understood, clarified and/or improved about this technology; mostly for biosensor applications. LW devices are able to operate at higher frequencies than traditional QCMs [5]; typical operation frequencies are between 80-300 MHz. Higher frequencies lead, in principle, to higher sensitivity because the acoustic wave penetration depth into the adjacent media is reduced [6]. However, the increase in the operation frequency also results in an increased noise level, thus restricting the LOD. The LOD determines the minimum surface mass that can be detected. In this sense, the optimization of the read out and characterization system for these high frequency devices is a key aspect for improving the LOD [7]. Another important aspect of LW technology is the optimization of the fluidics, specially the flow cell. This is of extreme importance for reducing the noise and increasing the biosensor system stability; aspects that will contribute to improve the LOD. The analysis and interpretation of the results obtained with LW biosensors must be deeper understood, since the acoustic signal presents a mixed contribution of changes in the mass and the viscoelasticity of the adsorbed layers due to interactions of the biomolecules. A better understanding of the transduction mechanism in LW sensors is a first step to advance in this issue; however its inherent complexity leads, in many cases, to frustration [8]. The fabrication process of the transducer, unlike in traditional QCM sensors, is another aspect under investigation in LW technology, where features such as: substrate materials, sizes, structures and packaging must be still optimized. This chapter aims to provide an updated insight in the mentioned topics focused on biosensors applications

Surface-wave attenuation and crustal anelasticity in Central North America

The southeastern Missouri earthquake of October 21, 1965 generated fundamental- and higher-mode Love and Rayleigh waves which were recorded at numerous North American stations. Love-wave amplitude radiation patterns were determined and found to be consistent with theoretical patterns predicted by a fault-plane solution previously inferred from Rayleigh-wave data. The radiation patterns were used to estimate the source spectrum and values for Love-wave attenuation coefficients for the mid-continent of North America by a least-squares iterative process. The source spectrum derived from Love-wave amplitudes exhibits a peak at periods between 5 and 9 sec and decreases to a lower DC level at longer periods, in agreement with the source spectrum determined previously for Rayleigh waves. The Love-wave attenuation coefficients decrease rapidly from about 0.0018 km^(−1) at a period of 4 sec to about 0.0001 km^(−1) at a period of 20 sec. At periods between 20 and 40 sec the values seem to remain nearly constant. The crust in the mid-continent of North America is characterized by relatively low Q_β values, 75 to 300, in its upper portion. At depths between 15 and 20 km, Q_β increases sharply and decreases again at greater depths. The decrease can be explained as being due to increasing temperature in a homogeneous material, but the sharp increase requires a change in the chemical constitution of the material at mid-crustal depths