Classifications

• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
  • G01R23/00—Arrangements for measuring frequencies; Arrangements for analysing frequency spectra
  • G01R23/16—Spectrum analysis; Fourier analysis
  • G01R23/17—Spectrum analysis; Fourier analysis with optical or acoustical auxiliary devices
• • 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
  • G01N29/36—Detecting the response signal, e.g. electronic circuits specially adapted therefor
  • G01N29/42—Detecting the response signal, e.g. electronic circuits specially adapted therefor by frequency filtering or by tuning to resonant frequency
• • 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
  • G01N29/44—Processing the detected response signal, e.g. electronic circuits specially adapted therefor
  • G01N29/46—Processing the detected response signal, e.g. electronic circuits specially adapted therefor by spectral analysis, e.g. Fourier analysis or wavelet analysis
• • 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
  • G01N2291/0426—Bulk waves, e.g. quartz crystal microbalance, torsional waves

Definitions

• the present invention relates to spectrum analyzers which use to separate the different spectral lines the propagation of volume acoustic waves inside a suitable material.
• spectrum analyzers which use to separate the different spectral lines the propagation of volume acoustic waves inside a suitable material.
• FIG. 1 Devices of this kind known up to now are constituted as shown diagrammatically in FIG. 1.
• a body 101 of parallelepiped shape made of a material capable of transmitting microwave volume waves, generally monocrystals.
• an electroacoustic transducer 102 On one of the small lateral faces of this body, an electroacoustic transducer 102 has been fixed which emits the electrical signal to be analyzed.
• This electroacoustic transducer is produced in a known manner so as to be able to emit inside the body 101 volume acoustic waves, which are both deflected towards one of the large lateral sides of the body and focused on this side.
• This can be done very simply, for example by segmenting the transducer and spacing the segments in such a way that the space between two consecutive elements varies progressively along the transducer, which corresponds to the technique known under English terminology. Saxon from "Shirped Transducer”.
• the volume acoustic waves are focused at a pre-point.
• c is of the reception plane formed by this large lateral face. The position of this point depends on the frequency.
• To analyze a given frequency band there is then arranged on this reception face a set of N reception transducers 103, each corresponding to one of the sub-bands of the band analyzed. In other words, a bank of N filters has thus been produced.
• Another technique which is not fundamentally different, consists, as shown in FIG. 2, of producing the transmitting antenna 202 so as to obtain only the deflection.
• the segments of the antenna 202 are then equidistant.
• the volume waves are then reflected on the face 204 of the body 201 opposite to the emission face supporting the transducer 202, towards the reception transducer 203 carried by the same face as this transducer 202.
• the reflecting face 204 has a curved shape which makes it possible to focus the volume waves in the manner of a concave mirror.
• the input and output transducers have hitherto been produced using a technology commonly used to excite volume waves in a material, and which is shown diagrammatically in section in FIG. 3.
• a conductive metallic layer 305 is deposited on the body 101, which forms an electrode, generally of mass.
• segments 306 made of piezoelectric material are fixed, and one finishes by covering these segments with electrodes 307 on which the connections with the outside are fixed.
• the seg- The piezoelectric elements 306 vibrate normally on the surface of the body 101, which causes the appearance therein of volume waves which propagate towards the interior of the body from the electrodes thus produced.
• the segments 306 and the electrodes 307 are produced from continuous layers which are then cut by a known process, photolithography for example.
• This technology has a certain number of drawbacks, in particular it requires several levels of masking, and welds of which neither the dimensions nor the quality are well controlled.
• the invention proposes a volume wave spectrum analyzer, of the type comprising a body intended to transmit volume waves, an input transducer making it possible to inject into the body volume waves of which the direction of propagation depends on the frequency of an input signal applied to this transducer, and a set of output transducers intended to receive the volume waves emitted by the input transducer, each of these output transducers being located on one face of the body at a place where the volume wave corresponding to a determined frequency comes to focus, mainly characterized in that at least one of these transducers is a transducer in interdigitated combs.
• FIG. 1 a schematic view of a disposi ⁇ tif according to the prior art
• FIG. 2 a schematic view of a variant of the device according to Figure 1;
• - Figure 3 a schematic sectional view of the transducers of the devices according to the prior art
• - Figure 4 a partial sectional view and limited to the essentials of the invention of a device according to the invention
• FIG. 8 is a plan view of two reception transducers according to the invention.
• transducers are used, having the form of interdigitated combs and whose dimension makes it possible to excite and receive volume waves inside the body on which they are deposited.
• the transmitting and receiving transducers are produced, as well, but one could only have one or the other according to this technique.
• This body will be made of a material itself piezoelectric, so that these combs can be produced by simple metallization of the surface on which they rest and then etching of this metallization by any process, photoli ⁇ thographic for example.
• This technique very similar to that used for the production of surface wave filters, uses only one level of masking and makes it possible to obtain electrodes which are very adherent to the surface on which they rest.
• the device according to the invention shown in FIG. 4, comprises a body 401 of which it has been shown that the part implementing the invention, the rest being of any shape. This part comprises two faces forming between them an angle A. According to the invention, it is obtuse and its value is therefore greater than 90 °.
• This body is formed of a piezoelectric material making it possible to propagate volume waves in a satisfactory manner, such as lithium niobate for example.
• an emission transducer 402 formed by two interdigitated combs has been produced, as described above.
• FIG. 6 shows an enlarged portion of this transducer 402 corresponding to the circle shown in FIG. 4.
• the cut is made along the axis of the combs and perpendicular to the fingers thereof.
• the electric field between these fingers allows the material of the body 401 to contract alternately by piezoelectric effect, and to obtain the emission of a volume wave propagating with an angle ⁇ from the surface where the electrodes rest.
• this angle ⁇ varies and the beam therefore goes to different locations on the surface of the body 401 forming the other side of the angle A.
• FIG. 5 shows an enlarged view of one of the reception transducers 403.
• This transducer is formed by two nested combs each having teeth 414 and 415 respectively, shown in cross section in the figure.
• the beam from both the face supporting the emission transducer 402 with an angle ⁇ arrives on the face supporting the receiving transducer 403 with an angle ⁇ .
• the pitch between the teeth of the combs of the reception transducer corresponding to ⁇ is approximately constant and its value is calculated so that the acoustic wave comes to excite these successive teeth in phase.
• This wavelength ⁇ is shown in the figure in a very schematic manner in the form of a series of lines, corresponding for example to the bellies or to the pressure nodes of the wave which spreads. The phase agreement is illustrated in this figure by the fact that these lines each intercept a tooth of the combs.
• Such a transducer with interdigitated combs introduces in itself filtering on the received wave, since of course and contrary to the simplified diagram of the figure, a reception transducer does not receive only the volume wave exactly adapted in phase to the spacing of his fingers.
• the frequencies to be analyzed in the input signal of the transmission transducer have no reason to be distributed over pure lines, each corresponding to a reception transducer, and it is necessary to consider for each of these transducers receiving a certain bandwidth; all the bandwidths of the reception transducers covering the frequency band of the signal to be analyzed.
• the focusing is not done as in the ideal manner represented in FIG. 4, but according to a ray diagram showing a main lobe of a certain width which can possibly excite a lower level the adjacent transducers, and possibly secondary lobes which can randomly excite other receiving transducers.
• the filtering function specific to the individual receiving transducers is added to the filtering function due to the ba- layout of the main beam, which allows the latter to be improved.
• FIG. 7 shows the transfer function corresponding to an isolated reception transducer whose central frequency, for which the phase agreement is perfect, is fixed at 2000 MHz.
• the overall response curve is that shown in solid lines. It has fast undulations corresponding to a function substantially in 0 sine x / x, which corresponds to filtering by deflection from the emission transducer.
• This function is added to another function in sine x / x, denoted F in the figure, whose undulations are much wider and which corresponds to the
• the efficiency of the filtering can be further increased by weighting, in a known manner, the combs of the reception transducers, so as to reduce the level of the secondary lobes thereof.
• each comb includes fingers which
• FIG. 8 shows two contiguous transducers comprising, one two buses 801 and 802, and the other two buses 811 and 812.
• These buses are connected on one side to earth and on the other side to the output connection of the transducer and according to the invention these connections are killed alternately on one side and on the other by a transducer to the next transducer.
• half of the output connections are on one side and the other half are on the other side. This facilitates the connection of these connectors to the connection wires with the outside.
• the number of these connections can be very numerous depending on the resolution desired for the analyzer, and this way of proceeding makes it possible to separate by a factor of 2 the connection points to be made, by welding for example.
• the angle A determined by the angles ⁇ and ⁇ , has a value greater than 90 ° and is therefore obtuse. So This value is preferably between 95 ° and 120 °, which makes it possible to obtain an optimal result for the separation of the channels of the analyzer thus described.
• the invention has been described in the context of a spectrum analyzer of the type of that of FIG. 1, where the emission transducer makes it possible to obtain scanning and focusing simultaneously. It also extends to the case of the analyzer of the type of FIG. 2, where the emission transducer only serves to obtain the scanning, the focusing being obtained by reflection on a concave face.

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• Spectroscopy & Molecular Physics (AREA)
• Surface Acoustic Wave Elements And Circuit Networks Thereof (AREA)

Applications Claiming Priority (2)

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Citations (4)

• 1992
  • 1992-05-05 FR FR9205499A patent/FR2690994A1/fr active Granted
• 1993
  • 1993-05-04 WO PCT/FR1993/000427 patent/WO1993022832A1/fr active Application Filing

Patent Citations (4)

Non-Patent Citations (1)

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