A novel Love-plate acoustic sensor utilizing polymer overlayers

Gizeli, Electra; Stevenson, Alice; Goddard, N J; Lowe, Christopher R.

doi:10.1109/58.156185

Cited by 128 publications

(76 citation statements)

References 13 publications

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“…Examples of surface acoustic wave device types with a dominant shear horizontal polarization include surface transverse waves 14 (STWs), leaky SAWs 15 , surface skimming bulk waves 16 (SSBWs) and Love waves 17,18 . The Love wave configuration has been reported as having one of the highest mass sensitivities 19 . In aqueous phase sensing, one difficulty with these devices is the need to have an IDT on the same face of the substrate as the liquid.…”

Section: Introductionmentioning

confidence: 99%

Layer guided shear horizontally polarized acoustic plate modes

McHale

Newton

Martin

2002

Journal of Applied Physics

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The theoretical basis describing Love waves propagating on a finite thickness substrate covered by a finite thickness solid layer having a lower shear acoustic speed is considered. A generalized dispersion equation is derived for shear horizontally polarized acoustic waves in this system. Two types of solutions to the dispersion equation, both satisfying stress free boundary conditions at the free surfaces, are shown to exist.The first type of solution has a displacement that decays with depth into the substrate whilst the second does not. Analytical approximations to the solutions for a thin solid guiding layer show that these solutions can be considered as generalizations of Love waves and resonant shear horizontally polarized acoustic plate modes (SH-APM), respectively. Numerical solutions to the dispersion equation are developed and the spectrum of modes for thick guiding layers is examined with particular reference to sensor applications. As expected, increasing the thickness of the guiding layer leads to multiple Love wave modes. However, each of these Love wave modes is found to possess a set of shear horizontally polarized acoustic plate modes. As the guiding layer thickness is increased the Love wave speed decreases until at approximately v l /4f , where v l is the shear acoustic speed of the layer and f is the frequency, a sharp transition occurs in the Love wave speed from a value close to the shear acoustic speed of the substrate, v s , to one close to the shear acoustic speed of the layer, v l . A similar pattern is observed for the layer guided SH-APM's with an increase in the guiding layer thickness resulting in a sharp transition in the speed of the SH-APM towards a value close to that of the next lower SH-APM. It is shown that the appearance of the second Love wave mode is a result of a continuation of the lowest SH-APM associated with the previous Love wave mode. A physical interpretation is developed for the Love waves on the finite substrate and for the layer guided SH-APM's and from this interpretation it is suggested that layer guided SH-APM sensors could provide significantly enhanced mass sensitivity.

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Section: Introductionmentioning

confidence: 99%

Layer guided shear horizontally polarized acoustic plate modes

McHale

Newton

Martin

2002

Journal of Applied Physics

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“…The second approach is to use an acoustic wave mode that has surface parallel displacements. Examples of such waves, in approximate order of mass sensitivity, include the thickness shear mode of the quartz crystal microbalance, 4,5 a shear horizontal acoustic plate mode ͑SH-APM͒, 6-8 a shear horizontal surface acoustic wave ͑SH-SAW͒, 9 a layer-guided SH-SAW, 10 a surface transverse wave, 11 or a Love wave, [12][13][14] which is a SH mode with a wave guiding layer. 15 The difference in the sensitivity between these devices is enormous with the mass sensitivity of Love waves, and more recently the layer guided SH-SAWs, being several orders of magnitude greater than that of SH-APMs.…”

Section: Introductionmentioning

confidence: 99%

Theoretical mass sensitivity of Love wave and layer guided acoustic plate mode sensors

McHale

Newton

Martin

2002

Journal of Applied Physics

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A model for the mass sensitivity of Love wave and layer guided shear horizontal acoustic plate mode ͑SH-APM͒ sensors is developed by considering the propagation of shear horizontally polarized acoustic waves in a three layer system. A dispersion equation is derived for this three layer system and this is shown to contain the dispersion equation for the two layer system of the substrate and the guiding layer plus a term involving the third layer, which is regarded as a perturbing mass layer. This equation is valid for an arbitrary thickness perturbing mass layer. The perturbation, ⌬ , of the wave speed for the two-layer system by a thin third layer of density, p and thickness ⌬h is shown to be equal to the mass per unit area multiplied by a function dependent only on the properties of the substrate and the guiding layer, and the operating frequency of the sensor. The independence of the function from the properties of the third layer means that the mass sensitivity of the bare, two-layer, sensor operated about any thickness of the guiding layer can be deduced from the slope of the numerically or experimentally determined dispersion curve. Formulas are also derived for a Love wave on an infinite thickness substrate describing the change in mass sensitivity due to a change in frequency. The consequences of the various formulas for mass sensing applications are illustrated using numerical calculations with parameters describing a ͑rigid͒ poly͑methylmethacrylate͒ wave-guiding layer on a finite thickness quartz substrate. These calculations demonstrate that a layer-guided SH-APM can have a mass sensitivity comparable to, or higher, than that of Love waves propagating on the same substrate. The increase in mass sensitivity of the layer guided SH-APMs over previously studied SH-APM sensors is of significance, particularly for liquid sensing applications. The relevance of the dispersion curve to experiments using higher frequencies or frequency hopping and to experiments using thick guiding layers is discussed.

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“…For this reason lithium tantalate (LTO) and rotated Y-cut quartz have remained the primary material for leaky SAW propagation despite their higher temperature coefficient factors (TCF). 6 LGS (0°,θ,90°) (0°,22°,90°) 2790 SH SH 1 lithium tantalate [10] calculated 2 potassium niobate [11] 3 [12] 4 calculated 5 LGT: Langatate (La 3 Ga 5.5 Ta 0.5 O 14 ) [13,14] 6 LGS: Langasite (La 3 Ga 5 SiO 14 ) [15] …”

Section: General Piezoelectric Problem and Shear-horizontal (Sh) Wavementioning

confidence: 99%

“…It also serves to provide a mechanism for stable chemical attachment through covalent linkage of antibodies, DNA, or other biomolecules to achieve the required selectivity. Waveguide materials such as polymers [6], silicon dioxide (SiO 2 ) [7], and more recently zinc oxide (ZnO) [8] This work is based on the leaky SH-type wave propagating on 36° Y-cut lithium tantalate (LTO) along the x-axis which exhibits strong coupling (K 2 = 6.6%). The strong coupling on LTO provides advantages over substrates such as ST-Quartz where exquisite care in the fluidic packaging is required to prevent excessive wave damping and hence high insertion losses.…”

Section: Introductionmentioning

confidence: 99%

Shear horizontal surface acoustic wave microsensor for Class A viral and bacterial detection.

Branch¹,

Huber²,

Brozik³

et al. 2008

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The rapid autonomous detection of pathogenic microorganisms and bioagents by field deployable platforms is critical to human health and safety. To achieve a high level of sensitivity for fluidic detection applications, we have developed a 330 MHz Love wave acoustic biosensor on 36° YX Lithium Tantalate (LTO). Each die has four delay-line detection channels, permitting simultaneous measurement of multiple analytes or for parallel detection of single analyte containing samples. Crucial to our biosensor was the development of a transducer that excites the shear horizontal (SH) mode, through optimization of the transducer, minimizing propagation losses and reducing undesirable modes. Detection was achieved by comparing the reference phase of an input signal to the phase shift from the biosensor using an integrated electronic multi-readout system connected to a laptop computer or PDA. The Love wave acoustic arrays were centered at 330 MHz, shifting to 325-328 MHz after application of the silicon dioxide waveguides. The insertion loss was −6 dB with an out-of-band rejection of 35 dB. The amplitude and phase ripple were 2.5 dB p-p and 2-3° p-p, respectively. Time-domain gating confirmed propagation of the SH mode while showing suppression of the triple transit. Antigen capture and mass detection experiments demonstrate 4 a sensitivity of 7.19 ± 0.74 ° mm 2 / ng with a detection limit of 6.7 ± 0.40 pg / mm 2 for each channel.5 CONTENTS

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A novel Love-plate acoustic sensor utilizing polymer overlayers

Cited by 128 publications

References 13 publications

Layer guided shear horizontally polarized acoustic plate modes

Layer guided shear horizontally polarized acoustic plate modes

Theoretical mass sensitivity of Love wave and layer guided acoustic plate mode sensors

Shear horizontal surface acoustic wave microsensor for Class A viral and bacterial detection.

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