Classifications

• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
  • G01N29/00—Investigating or analysing materials by the use of ultrasonic, sonic or infrasonic waves; Visualisation of the interior of objects by transmitting ultrasonic or sonic waves through the object
  • G01N29/02—Analysing fluids
  • G01N29/022—Fluid sensors based on microsensors, e.g. quartz crystal-microbalance [QCM], surface acoustic wave [SAW] devices, tuning forks, cantilevers, flexural plate wave [FPW] devices
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
  • G01N2291/00—Indexing codes associated with group G01N29/00
  • G01N2291/02—Indexing codes associated with the analysed material
  • G01N2291/025—Change of phase or condition
  • G01N2291/0256—Adsorption, desorption, surface mass change, e.g. on biosensors
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
  • G01N2291/00—Indexing codes associated with group G01N29/00
  • G01N2291/04—Wave modes and trajectories
  • G01N2291/042—Wave modes
  • G01N2291/0423—Surface waves, e.g. Rayleigh waves, Love waves

Definitions

• interdigital transducers For exciting such waves and recovering again electri ⁇ cal vibrations, use can be made of so-called interdigital transducers.
• the latter comprise two comb-shaped electrodes made of metal foil on the surface of a piezo-electric wafer, the teeth of said electrodes being intercaleted said teeth having a width which is equal to 1/4 of the pitch of the teeth.
• An elastic wave is produced then which is directed perpendicularly to the teeth, the wave-length thereof being equal to said pitch.
• the amplitude of said vibration and the sharpness of resonance increase with the number of teeth.
• the latter can, for instance, be included in an oscillator circuit which,because of a change - 2 - in the condition of the layer, and, hus, of the transit time of the elastic wave, will be more or less detuned.
• Information in respect , ⁇ f the character of the adsorbed substance can be derived therefrom.
• Such an apparatus can also be used for other changes in condition of the surface layer, or for mutual ⁇ ly comparing different kinds of surface layers.
• the apparatus according to the invention for de ⁇ termining the condition of a material, and in particular the adsorption of a gas or liquid on this material comprises a substrate with a plane surface possessing, at least near said surface, piezo-electric characteristics, an electrode assembly provided on said surface and consisting of thin metallic layers in the form of two combs with mutually intercalated teeth, said assembly being adapted for applying thereto an electrical alternating voltage with an adapted frequency, in order to produce an elastic wave in the piezo-electric material directed transversely to said teeth, and at least one surface layer of the material of which the condition is to be determined, which is arranged laterally of said assembly on said surface, said apparatus being characterised in that, at both sides of the comb-shaped electrode assembly.
• a mirror for the elastic waves produced by said assembly is arranged, said mirrors being, formed by substantially rectilinear surface variations extending parallel to the teeth of the electrodes, and being situated at such a distance from said electrode assembly that the waves reflected between said mirrors are in phase at said electrode assembly if the surface layer is in a given reference condition, said layer being provided at least between said - 3 - electrode assembly and one of said mirrors.
• This structure is comparable to an interferometer known from optrics, and is extremely sensitive for small transit time differences between the electrode assembly and the mirrors. At a variation of the transit time, so that the different waves are no longer in phase, the energy storage in this system will change, which is sensed as an impedance variation by the electrical circuit causing the elastic vibration, and such variation can be easily detected. It is also possible to provide a second and similar electrode assembly at such a distance from the first one that, in the reference condition, the different waves will be in phase also there, which second assembly is connected with an electric measuring circuit. When, in this respect, reference is made to distances and points in which vibrations are in phase, this holds, of course, for points of the electrode assemblies which can be considered as a centre of vibration.
• Said mirrors consist, in particular, of a plurality of parallel lines having a mutual distance of a whole number of quarter wave-lengths of the elastic wave in the reference condition of the surface layer, said number being chosen so that a substantially complete reflection is obtained.
• Said mirror lines can consist of metallic layers provided on the piezo-electric surface, or of shallow grooves formed in said piezo-electric surface.
• the piezo-electric surface can be in the form of a cover layer on a semiconductor substrate in which the associated circuits are integrated.
• Fig. 1 a diagrammatic view of the basic shape of the apparatus of the invention
• FIG. 2 a view at a larger scale of a portion of Fig. 1 ; and Fig. 3 a corresponding representation of a modified embodiment .
• the apparatus of the invention comprises a wafer 1 of a piezo-electric material, or at least a piezo-electric covering layer on a suitable substrate, said covering layer 1 - 4 - having a sufficient thickness for being adapted to form there ⁇ in so-called Rayleigh-waves with a penetration depth of several ⁇ m.
• interdigital electrode assembly 2 On this wafer 1 a so-called interdigital electrode assembly 2 is provided. A portion of such an assembly is shown in Fig. 2 at a larger scale. Beyond the portion of the wafer 1 below said assembly, said wafer 1 does not need to be piezo- electrical, so that, if the wafer 1 is not piezo-electrical itself, only at said assembly 2 a piezo-electric covering layer is to be provided.
• the assembly 2 consists of two electrodes 3 and 4 each comprising a number of teeth 5.
• the width of said teeth 5 is equal to the width of the interspaces between two teeth 5 of different electrodes 3 and 4. If a suitable alternating voltage is applied to said electrodes, in the surface portion of the wafer 1 an elastic wave is pro ⁇ quizd having a propagation direction which is directed per ⁇ pendicularly to the direction of the teeth 5.
• the excitation frequency should be such that the wave-length, in view of the propagation velocity in the piezo-electric material, will be equal to four times the tooth width or the tooth pitch, and, in this respect, reference can be made to the literature, e.g. the publication of A.
• the distance between the lines nearest to the assembly 2 and the centre point of this assembly 2 - 5 - equals a whole number ⁇ f half wave-lengths, and the distance between the parallel lines of each set equals a whole number of quarter wave-lengths.
• Said lines operate as a mirror for the elastic wave.
• a single line 7 will not produce a complete reflection, but a number of parallel lines at a distance of a whole number of quarter wave-lengths will provide an accor ⁇ dingly better reflection. In practice some tens of lines can provide a substantially complete reflection.
• the elastic waves emitted by the electrode assembly 2 return, after reflection against the mirror lines 7, in phase with the emitted waves in the centre of the assembly 2. This will, then, operate as an interferometer, in which, in the tuned condition, a maximum energy storage occurs. However, as soon as the reflected waves do not arrive in phase in the centre point of the assembly 2, this energy is sharply reduced, which, in the electric circuit supplying the electrode assembly 2, will be sensed as a cor ⁇ responding impedance change, which can be detected in a simple manner.
• the assembly 2 is shown in Fig. 2 half-way between the line assemblies 7; this is, of course, not necessary, as long as the distances in respect both line assemblies 7 are a whole multiple of the half wave-length.
• a surface layer 8 is provided which is adapted to influence the elastic behaviour of the piezo-electric material.
• the said interferometer tuning is, of course, adapted to the wave-length which occurs in the piezo-electric material provided with this layer.
• Fig. 3 shows still an other embodiment in which a second electrode assembly 2' is provided satisfying the same phase requirements as the first assembly 2.
• the assembly 2' is connected with an electric measuring circuit, and the assembly 2 only serves for excitation of the elastic vibration.
• a piezo- electric layer 1 provided on a semiconductor substrate, which semiconductor substrate can be used, then, for forming therein integrated circuits which can be used for generating the electric vibrations and for measuring the occurring deviations.

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• Physics & Mathematics (AREA)
• Biochemistry (AREA)
• Health & Medical Sciences (AREA)
• Life Sciences & Earth Sciences (AREA)
• Chemical & Material Sciences (AREA)
• Analytical Chemistry (AREA)
• Acoustics & Sound (AREA)
• General Health & Medical Sciences (AREA)
• General Physics & Mathematics (AREA)
• Immunology (AREA)
• Pathology (AREA)
• Measurement Of Mechanical Vibrations Or Ultrasonic Waves (AREA)
• Investigating Or Analyzing Materials By The Use Of Ultrasonic Waves (AREA)
• Surface Acoustic Wave Elements And Circuit Networks Thereof (AREA)

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• 1985
  • 1985-09-26 NL NL8502634A patent/NL8502634A/nl not_active Application Discontinuation
• 1986
  • 1986-09-26 WO PCT/NL1986/000030 patent/WO1987002134A1/en not_active Application Discontinuation
  • 1986-09-26 JP JP50512386A patent/JPH01500052A/ja active Pending
  • 1986-09-26 EP EP19860905945 patent/EP0239608A1/de not_active Withdrawn

Non-Patent Citations (1)

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