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ABSTRACT: Attenuation alpha<sub>n</sub> versus viscosity eta of adjacent liquid is measured for each normal mode n generated in 30 different plates of commercially available, piezoelectric crystals with thickness-to-wavelength ratio in the range h/lambda = 0.6-2.5. Two modes with an optimal combination of sensitivity (0.1 dB/mmmiddotcP), insertion loss (<35 dB), and stop-band rejection (>15 dB) are found in liquid-loaded 128degY, X + 90deg-LiNbO<sub>3</sub> with h/lambda = 1.67. Both modes are suited for viscosity measurements and other sensing tasks in viscous liquids. They have predominantly longitudinal displacement and large propagation velocity v<sub>n</sub> about 15,000 m/s
IEEE Transactions on Ultrasonics Ferroelectrics and Frequency Control 09/2006; · 1.69 Impact Factor
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ABSTRACT: A simple method is developed for measurements of the distribution of the energy flow density of elastic waves using piezosemiconductor transducers and an acoustoelectric probe. The method permits to investigate piezoelectric and nonpiezoelectric crystals. Orientation dependences of the energy flow directions of acoustic surface waves on x y and y z planes of quartz and (111) planes of germanium were investigated. On these surfaces the regions were discovered, in which pseudo surface waves exist. The experimental results are compared with theory.[Russian text ignored].
physica status solidi (a) 02/2006; 14(1):339 - 346. · 1.21 Impact Factor
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ABSTRACT: The shear horizontal modes that occur in a quartz plate are studied both theoretically and experimentally. These modes are
shown to possess a wide variety of temperature properties, including the characteristic behavior of the temperature coefficient
of delay, which can take on negative, zero and record-breaking high positive values up to 350×10−6/°C. The dependence of this coefficient on the mode number is explained by the varying partial contributions of three elastic
moduli, c
12, c
14, and c
44, to this coefficient.
Acoustical Physics 12/2001; 48(1):8-11. · 0.70 Impact Factor
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ABSTRACT: It is shown how the performances of SAW gas sensors can be optimized based on pure acoustic peculiarities of SAW propagation in anisotropic single crystals. For a given gas and sensitive membrane, the calibration curve (dependence of the response R versus gas concentration n), the sensitivity S (slope of the calibration curve: S = dR/dn), the detection limit nth, (cut-off of the curve at the threshold Pthr), and the resolution deltan of the sensor (recognition of two close concentrations) can be controlled by a proper choice of the substrate material and its crystallographic orientation (cut and direction of the SAW propagation). An experimental test of this property is performed on SAW devices implemented on different substrate materials and crystallographic orientations, both uncoated or coated, with a sorbent membrane of polycrystalline Pd or Pd:Ni film, upon exposure to humid air as a test analyte.
IEEE Transactions on Ultrasonics Ferroelectrics and Frequency Control 10/2001; 48(5):1413-8. · 1.69 Impact Factor
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ABSTRACT: By considering the 6 most popular planes of quartz and LiNbO<sub>3
</sub>, a multi-channel SAW analytical tool for sensing is optimized.
The best anisotropy conditions for the SAW velocity, elastic
displacement, electric coupling, and temperature sensitivity are found
to be on the ST-plane of the former and 128°Y-rotated plane of the
latter with orientation of the channels at 0°, -33°, +47°
and θ = 0°, 46°, 80°, 115° off x-axis
respectively. Based on the optimized orientations, two novel prototypes
were fabricated using photomasks integrating all the channels on a
single plate. The anisotropy of different channels of the tools was
tested for uncoated and PVA coated substrates, both for humid air, as
the example. The difference in SAW responses and in the calibration
curves of the channels was found to be sufficient to make an appropriate
analysis of gas-phase adsorption. The largest number of channels on a
substrate was found to be 5
Ultrasonics Symposium, 2001 IEEE; 02/2001
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ABSTRACT: On considering 13 modes with shear horizontal (SH) polarization,
propagating perpendicular to the x-axis in a ST quartz plate, it is
experimentally shown and theoretically verified how the temperature
coefficient of delay (TCD) and its behavior vs. temperature depend
monotonically on the order n of the mode. This property is attributed to
the different sensitivities of the modes towards temperature variations
in c<sub>12</sub>, c<sub>14</sub> and c<sub>44</sub> elastic moduli. The
modes sensitivities towards density ρ, elastic moduli
c<sub>11</sub>, c<sub>13</sub>, c<sub>33</sub> and plate thickness h are
either temperature independent or negligibly small. The best thermal
stability (TCD≈0) over the widest temperature range (2-92°C) has
been detected for the 6<sup>th</sup> mode, while the largest one (350
ppm/°C) has been measured for the 13<sup>th</sup> mode, at 47°C.
For comparison, five Lamb modes, propagating along the x-direction in
the same quartz plate, show a non monotonic dependence of the thermal
coefficient on the mode number, a temperature independent TCD in the
range 2-92°C, a minimum and maximum value of the TCD (≈0.7
ppm/°C and ≈100 ppm/°C) for the 0<sup>th</sup> symmetric mode
and for the 1<sup>st</sup> anti-symmetric mode, respectively
Ultrasonics Symposium, 2001 IEEE; 02/2001
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ABSTRACT: An analytical expression for the SAW sensor gas response versus
gas concentration (calibration curve) is deduced, at low gas
concentrations, on using the perturbation approach. The calibration
curve, the sensitivity (its slope) and the detection limit (threshold
value) for a given gas and sorbent membrane, can be controlled by a
proper choice of the substrate material and its crystallographic
orientation. We show how this property takes place from the anisotropy
of the SAW propagation on piezoelectric single crystals, allowing to
change the partial contributions to the SAW response through mechanical
displacements, coupling constant and temperature coefficient of velocity
(TCV). The theoretical predictions are experimentally verified on
devices implemented on different orientations of quartz and LiNbO<sub>3
</sub> substrates, using Pd, Pd:Ni and polyvinyl alcohol (PVA) as
sorbent films and humid air as analyte. The lowest threshold value of RH
(0.01%) and the highest sensitivity (49 ppm/%) are detected in the
PVA/yz-LiNbO<sub>3</sub> structure, whose sensitivity is about two
orders of magnitude higher than that observed in uncoated LiNbO<sub>3
</sub>
Ultrasonics Symposium, 1999. Proceedings. 1999 IEEE; 02/1999
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ABSTRACT: Surface acoustic wave (SAW) sensors have been successfully exploited for the detection of both chemical and physical quantities. In this paper we report more recent results on SAW sensors for the detection of relative humidity (R.H.). Different chemical interactive materials (CIMs), of both organic and inorganic compounds, are tested and their performances in the R.H. range between 10 and 80% are reported and compared. All the devices analysed have been shown to operate in a reversible way, with a fairly good repeatibility and fast response times. The CIMs have been shown to produce a variety of different behaviours versus R.H. percentage, with respect to both the amplitude and linearity of the response. The response to R.H. has also been investigated for different orientations of both quartz and lithium niobate bare substrates. These data can be useful in order to investigate the effect of the R.H. of the surroundings on the performances of SAW based devices. In addition this test is of great importance in order to know how humidity influences the response of both chemical and physical sensors. The response of organic CIMs has also been tested toward hydroxylated molecules such as acetone and ethanol, and the relative calibration curves are reported.
Smart Materials and Structures 12/1998; 6(6):707. · 2.09 Impact Factor
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ABSTRACT: The gas sensing properties of organic polypyrrole (PPS) film, deposited onto LiNbO/sub 3/ substrate by Langmuir-Blodgett (LB) technique, have been monitored by surface acoustic wave (SAW) delay lines and studied with respect to sensitivity, selectivity, response time, stability, repeatability, and aging. The SAW PPy elements demonstrate high sensitivity toward NH/sub 3/ gas with high selectivity against CH/sub 4/, CO, H/sub 2/, and O/sub 2/. The detectable threshold concentration has been estimated as 20 ppm NH/sub 3/ in air; the response time is in the 10s range, and the recovery time is about 15 min; the repeatability of the SAW response toward eight sequential NH/sub 3/ gas exposures is within 6%; the aging of the PPy film is within 4% over a month; and the effect of humidity on SAW NH/sub 3/ gas response is negligible for the typical conditions at room ambient air. Partially reversible SAW response recognizing NH/sub 3/ gas as one component of an interfering gases-mixture has been observed. Simultaneous chemoresponses of SAW phase and insertion loss have been performed in order to investigate the sensing mechanisms. By merging with electrical conductivity gas response, the dominant SAW sensing effects for NH/sub 3/ gas detection are defined as elastic loading.
IEEE Transactions on Ultrasonics Ferroelectrics and Frequency Control 10/1998; · 1.69 Impact Factor
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ABSTRACT: A new surface acoustic wave multi-channel sensor array suitable
for pattern recognition purposes has been implemented and tested on an
ST-cut quartz substrate using one single palladium sorbent film for all
the channels. The different response of each channel towards the same
gas components is provided by the dependence of the mechanical
displacement components of the acoustic wave on the propagation
direction
Electronics Letters 07/1998; · 0.96 Impact Factor
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ABSTRACT: A new approach, based on the properties of SAW devices, is used to
integrate an array of gas sensors into a single substrate, using a
single chemical membrane. The different response of each individual
device to the same set of gases is provided by different acoustic
propagation conditions, only. Three four-sensor prototypes have been
implemented on ST-cut quartz substrates, using different Pd films as
membrane. Their response upon exposure to concentrations of
H<sub>2</sub>, N<sub>2</sub>O and CO in N<sub>2</sub> and to water
humidity have been tested. A strong dependence of the response versus
the acoustic propagation direction has been demonstrated for all the
prototypes analyzed
Ultrasonics Symposium, 1998. Proceedings., 1998 IEEE; 02/1998
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ABSTRACT: Novel attractive properties of SAW gas sensing are theoretically predicted and experimentally verified. The response upon gas exposure of SAW-based gas sensors can be increased, decreased, reversed, cancelled, speeded up, aged down, and selected for a given sensitive layer, simply by changing the substrate material and orientation. When utilized as a tool for analytical chemistry, the steady-state and kinetic properties of adsorption, desorption, and diffusion, together with other related processes, can be simply deduced from pure acoustic measurements. These new properties are shown to be produced by the change of the components of the elliptic polarization of the wave, varying with the propagation direction and the substrate material. Experimental results, obtained for quartz substrates coated with polycrystalline palladium and palladium-nickel films exposed to H(2), CO, N(2)O, and different concentrations of relative humidity in air are presented as an example.
IEEE Transactions on Ultrasonics Ferroelectrics and Frequency Control 02/1998; 45(5):1347-54. · 1.69 Impact Factor
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ABSTRACT: An analytical expression for the magnitude of the “response” of surface acoustic waves (SAWs) to gases is obtained. It is
tested experimentally. The main features of the detection of gases by means of SAWs are predicted theoretically and confirmed
experimentally. The SAWs in coated and uncoated gas sensors are compared. A technique for using SAWs to determine the relative
changes in the density (Δρ/ρ) and the elastic moduli (ΔC
11/C
11 and ΔC
44/C
44) of films upon the adsorption (desorption) of gases is proposed. The possibility of using this technique to analyze adsorption
and desorption processes is demonstrated. The adsorption properties of polycrystalline, thermally deposited palladium films
before and after low-temperature vacuum annealing, as well as unannealed Pd and Pd:Ni films, are compared. The prospects of
using SAWs to detect gases and to study surface processes induced by them are discussed.
Technical Physics 01/1998; 43(2):201-208. · 0.50 Impact Factor
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ABSTRACT: Quantitative characterization of the surface acoustic field radiated forward, backward, and in orthogonal directions by the grooved transducer, implemented onto a glass substrate, is accomplished by a scanning laser acoustic microscope (SLAM) operating at 31 MHz. The surface acoustic wave (SAW) amplitude is measured as a function of the number of grooves and the position of the bulk acoustic wave (BAW) transducer. The number of the operating grooves efficiently contributing to the SAW response is estimated. Remarkable reflection of the SAW beam between two identical gratings is observed.
IEEE Transactions on Ultrasonics Ferroelectrics and Frequency Control 12/1997; · 1.69 Impact Factor
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ABSTRACT: Adsorption of water vapors on single crystal and polycrystalline
substrates is analyzed using the propagation of surface acoustic waves
as an experimental tool. The perturbation in the SAW velocity
(Δv/v<sub>0</sub>), the number N of adsorbed species as well as
the changes in the density Δρ/ρ and in the elastic moduli
Δc<sub>ij</sub>/c<sub>ij</sub> of the sorbent materials, are
deduced in terms of the normalized SAW displacements A<sub>x</sub>, A
<sub>y</sub>, A<sub>z</sub> and of the unperturbed SAW velocity v<sub>0
</sub>. Vapour adsorption on polished plates of single crystal quartz
and polycrystalline films of Pd and Pd:Ni is experimentally
investigated. Results of the measurements clearly show that humidity
adsorption gives rise to effects whose amplitude is larger and whose
time duration is longer in the films than in the plates. These effects
are also dependent on the orientation of the quartz, allowing to monitor
the value and the rate of the effect by proper selection of a substrate
material
Ultrasonics Symposium, 1997. Proceedings., 1997 IEEE; 11/1997
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ABSTRACT: Novel attractive properties of SAW gas sensing are theoretically predicted and experimentally verified. It is demonstrated that the SAW response can be increased, decreased, reversed, cancelled, speeded up, aged down and selected without changing the sensitive layer, simply by properly selecting the acoustic substrate material and its crystallographic orientation. These new properties are shown to come from the elliptic polarization of the acoustic wave and from its dependence on the propagation conditions. An experimental verification of the theoretical predictions is carried out on SAW H<sub>2</sub> sensors using both Pd and Pd:Ni sensitive films, deposited on ATx-, STx- and yx-quartz substrates upon exposure to 1% H<sub>2</sub>+N<sub>2</sub>, 1% CO+N<sub>2</sub> and 1% N<sub>2</sub>O+N <sub>2</sub> gas mixtures. These new peculiarities will make possible to develop a new generation of SAW sensors
Ultrasonics Symposium, 1997. Proceedings., 1997 IEEE; 11/1997
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ABSTRACT: Surface acoustic wave (SAW) delay lines without gas-sensitive coatings are used as thermal sensors for the thermoconductometric
detection of gases and gas flows. The forced convection of 13 gases is analyzed in the linear approximation without regard
for their interaction with the environment. Quartz, LiNbO3, Bi12GeO20, and Bi12SiO20 delay lines are used to detect H2, He, Ar, CH4, NH3, N2, and O2 at frequencies f=21–263 MHz and temperatures T=25–165 °C. The SAW “response” is measured as a function of the gas concentration n, the flow rate U, the temperature coefficient of the SAW velocity (TCV), and the working temperature T
p
. The feasibility of controlling the level of the gas “response” and imparting selectivity to the choice of TCV and T
p
is demonstrated. The threshold gas concentrations are 0.35% for CH4 and 0.1% for H2 and NH3 in nitrogen. A linear response is obtained in the interval U=20–200 ml/min.
Technical Physics 04/1997; 42(5):564-568. · 0.50 Impact Factor
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ABSTRACT: A modification of the matrix formalism for studying acoustic wave
propagation in anisotropic piezoelectric multilayers is developed. The
modification is based upon the use of the compound matrices, well known
from the theory of the matrices. Using the modified method, analytical
expressions for the relationship between the real and imaginary parts of
the determinant of the boundary conditions are derived. One of the
advantages of the method is demonstrated for thick plates and thick film
structures. On considering the dispersion curves for thick multilayers,
the slow dispersion regions inherent for anisotropic materials are
discovered. The regions are related with the cutoff velocities of the
bulk waves in the film materials
Ultrasonics Symposium, 1996. Proceedings., 1996 IEEE; 12/1996
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ABSTRACT: The magnitude and time variations of the SAW propagation velocity
Δv/v, of the mass and elastic loading, and of the fractional
changes in the density Δρ/ρ and in the elastic modulii
Δc<sub>ij</sub>/c<sub>ij</sub> of Pd films are experimentally
evaluated at room temperature and atmospheric pressure for 0.1, 0.5, 1%
H<sub>2</sub>, 1% CO, 1% N<sub>2</sub>O and 1% NO gas mixtures in pure
nitrogen. Two different thermally evaporated Pd films have been tested:
one as evaporated, the other one after annealing at 423°K and
10<sup>-5</sup> Pa for 15 hours. The annealing is shown to change all
set of the parameters. For not annealed films, hydrogen gives rise to
large variations in the elastic constants (≃5-40%) and to an
increase in the phase velocity; while for annealed films, it produces
small variations in the elastic constants (≃1-2%) and a decrease in
the phase velocity. The difference is attributed to weakly and strongly
coupled oxygen preadsorbed in the film. The results obtained can allow
an improvement of Pd-based sensors
Ultrasonics Symposium, 1996. Proceedings., 1996 IEEE; 12/1996
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ABSTRACT: A SAW delay line, without any absorbent film between the
interdigital transducers, has been developed as a thermal gas detector.
The change of the thermal conductivity of the ambient atmosphere
produces a change of substrate temperature thereby causing a SAW phase
variation (SAW response) at the output of the device. Different effects
contribute to the SAW response such as the thermal conductivity
Δλ, flow rate Δu, dynamic viscosity Δμ, and
the density Δρ of the test ambient and they are numerically
analysed for each test gas. Uncoated SAW delay lines operating at 41-263
MHz are implemented on SiO<sub>2</sub>, LiNbO<sub>3</sub>, Bi<sub>12
</sub>GeO<sub>20</sub>, and Bi<sub>12</sub>SiO<sub>20</sub> substrates.
The gases under test (H<sub>2</sub>, He, Ar, CH<sub>4</sub>, NH<sub>3
</sub>, N<sub>2</sub>, O<sub>2</sub>, dry air) are used within
concentrations of 0.1-100% and flow rates of 50-2000 mL/min at
20-150°C and atmospheric pressure. The SAW response
Δφ/φ, is measured as function of Δλ,
Δu, operating temperature, and gas concentration. The SAW
prototype has a good sensitivity: Δφ/φ≡15 ppm to
0.7% CH<sub>4</sub> in N<sub>2</sub> for a Bi<sub>12</sub>SiO<sub>20
</sub> delay line heated at 120°C; Δφ/φ≡15 ppm
to 0.4% NH<sub>3</sub> in N<sub>2</sub> for a YZ-LiNbO<sub>3</sub> delay
line heated at 120°C. Some selective SAW gas responses are discussed
Electrotechnical Conference, 1996. MELECON '96., 8th Mediterranean; 06/1996
