Note: Descriptions are shown in the official language in which they were submitted.
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20661
METHOD AND APPARATUS FOR STRUCTURAL ANALYSIS AND/OR
FOR DETECTING THE POSITION OF STRATIFIED OBJECTS
The invention relates to an apparatus for structural
analysis and/or position detection of stratified objects by
means of ultrasonic waves, with one or more ultrasonic
generators and ultrasonic receivers, as well as a support
surface for the object.
Devices analyzing the structure of stratified objects
by means of ultrasound are already known, such as for
instance from the EP 0 262 186. The known devices are
based on the principle of reflection tomography. This
principle applied to fingerprints according to the
mentioned European Patent was presented at the Conference
of Acoustical Imaging in Florence in 1995 and published in
the respective Proceedings under the title" Ultrasonic
setup for fingerprint pattern detection and evaluation".
In the known references, the object placed on a support
plate is subjected to ultrasound waves coming from a
generator arranged oppositely thereto in a liquid filled
housing. Either several generators and several receivers
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are arranged on the housing wall opposite to the support
surface, or the generator and also the receiver are
movable on a carrier along a trajectory. This way the
finger tip or any other object on any point of the support
plate can be detected. The waves reflected and back-
scattered by the object are received by a receiver which
transmits the information about the intensity and/or the
phase of backscattering and reflection to a computer for
analysis and recording, optionally via an amplifier, a
timing device, possibly also a detector.
The ultrasonic waves to which the finger or other
objects are exposed are bulk waves originating from the
generator/generators in the same manner as the
backscattered and reflected sound waves, which are in the
range of 2 MEIz and above.
The production of devices of the known kind has proven
to be complicated, namely particularly because the housing
is filled with liquid. This requires the housing to be
perfectly sealed off and the arrangement of the transducers
in the liquid is also fraught with problems. Furthermore
due to the liquid-filled housing and the use of bulk waves,
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these devices are also relatively large, since a certain
size of the device can not be reduced. They also do not
allow for a large size of the support plate, which makes
impossible the analysis of objects with a large surface,
e.g. human hands.
Further devices used purely for position detection
have become known. Such a contact sensor is described in
the abstract of JP-A-2 195 289. The latter consists of a
tube serving as a wave guide, at whose open end an
ultrasound transducer serving a sender, respectively
receiver, to which a transmitting and time-measuring
circuit, as well as a distance calculator are connected.
Depending on the m~ch~nical pressure on the wave guide, the
reflection of the ultrasonic wave is determined and
therewith the pressure point is calculated. A structural
analysis can not be performed with the device of the
aforementioned application.
There are also other known device which detect the
position of an object, such as the position of a finger on
surface, e.g. a display (see also EP O 557 446 and 0 523
200). However these devices are not capable to analyze the
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structure of the object, e. g. the finger, since they have
a much too low resolution and also because they are not
intended for this purpose. Also their modus operandi is
different, since these devices use only the attenuation of
the ultrasonic waves which are generated by the object,
which in principle can not give information about the
structure.
The object of the invention consists in proposing a
method and an apparatus for the analysis of surface
structures, as well as of the areas close to the surface
and/or the position of objects, which permit a more compact
wave pattern and ma]ce possible a flatter and more compact
construction. Constructively the device should require
less technical effort for equal analysis results.
This object is achieved due to the characteristic
features defined in claims 1 and 2.
Surprisingly it has been established in tests that
also ultrasonic waves guided in this manner can deliver
clear and reproducible analyses of the structure and/or the
position of the objects. Thereby one starts with a plate
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of any desired dimensions, as defined in claim 2, with
laterally arranged senders or senders and receivers. One
sender or receiver can also be arranged underneath the
plate. According to the invention the exposure to sonic
waves takes place with shear waves (SH-waves)i.e. waves
which are horizontally polarized. As material for the
plate glass, metal or crystal with a low degree of
absorption are proposed. Of course it is also possible to
provide transducers on the plate sides, which at the same
time are senders and receivers, since also in the case of
ultrasonic waves generated and/or received laterally with
respect to the support plate, guided along the plate
surface, a reproducible and strong reflection and/or
scattering takes place at the structure adjoining the plate
surface.
At least one surface of the plate forms the limit
which guides the wave two-dimensionally. Thereby it does
not matter whether a guided or a normal wave is generated,
but the wave reflected and/or backscattered by the object
will be two-dimensionally guided by the limit or limits.
The plate can also be equipped with one or two
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channels, whereby a unidimensional wave is obtained and, at
the end of the channel, directed towards a receiver. The
channels are feasible by changing the plate structure, e.g.
the thickness. They can also be formed by using different
types of adjoining materials, namely in a manner similar to
optical wave guides, wherein the core of the guide and the
envelope surrounding the core can consist of different
materials.
The thickness of the plate equals 1/3 to 3 mm and
depends on the wave length. Namely it has been found that
the most favorable measurements for the plate thickness lie
within a range which is 5 - 10 bigger than the wave length
of the generated ultrasonic waves. If channels are
provided in the plate, their diameter has also to be kept 5
to 10 times bigger than the wave length of the used
ultrasonic waves. Furthermore the unidimensional guidance
has the advantage that the signals arrive one after another
and are also detected in this succession. It is also
possible to use thicker plates.
Compared to the known devices, the device of the
invention offers the advantage of a flat construction with
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reproducible and accurate analysis data. In addition the
construction is considerably simplified, since the liquid-
filled housing can be eliminated. The propagation of the
ultrasonic waves is guaranteed within the plate-shaped
solid body, so that additional steps become superfluous.
This fact makes also possible the use of small devices,
e.g. of the size of a key. Furthermore it is possible to
produce also devices with large ~i -n~ions, which can
analyze the structure of the object, as well as its
position, which can be advantageous for instance for the
control of computers, similar as in the known contact
fields (touch panels)and the detection of larger objects,
e. g. the whole hand.
Further details of the invention can be seen from the
attached drawing. Thereby show:
Fig. 1 a lateral view of the device in a schematic
representation,
Fig. 2 a top view of the embodiment shown in Fig. 1,
Fig. 3 the arrangement of a plate consisting of
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uni~; ?n~ional wave guides,
Fig. 4 the channel path through a plate,
Fig. S the spiral-shaped arrangement of two channels in
a plate.
In the represented example Fig. 1 shows a round plate
1 with transducers 3 arranged on the rim and a transducer 2
arranged underneath the plate. In the embodiment shown in
Fig. 2 in a top view, it can be seen that transducers 4 and
5 are arranged all around the plate. The transducers can
function as senders, as well as receivers. The optional
bottom transducer 2 can not be seen in Fig. 2.
In this device schematically represented in Fig. 1 and
2, shear waves in the ultrasonic range are used, which
propagate in the plate (the solid body) along one or also
both borders.
Consequently these are guided waves, i.e. of the type
which can not spread in all dimensions. In the plate of
the embodiment examples of Fig. 1 and 2, two-dimensional
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waves are produced, while plates with channels of any
origin, as for instance in Fig. 3, 4 and 5, show waves with
unidimensional spreading.
Similar to the known devices using bulk waves, the
electric signals are transmitted from the receiving
transducer, via an amplifier, and possibly a detector with
the assistance of a analog/digital converter to a computer
which, based on that, delivers the information about the
structure and/or the position of the analyzed stratum.
The method of analysis used in the case of two-
~; -n~ional waves corresponds to the one used in the
previously mentioned bulk-waves devices, e.g. the radon
transformation. Furthermore the version with channels
offers a simpler possibility, because it is only necessary
to summarize the signal, respectively signals which
correspond to the channel path.
Naturally these methods are only then necessary, when
it is desired to reproduce the image of the e~ ;ned layer.
For other purposes it is also possible to use other signal
processing methods, e.g. a simple signal comparison, other
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types of transformation, etc.
Moreover the flat solution of the device according to
the invention offers a simple possibility of structure
detection and of the therewith connected position
detection, since the plate also allows for a unidimensional
wave guidance. The advantage of an analysis with
uni~; ?~cional wave guidance consists in that it makes line
sc~nn~ng possible.
For producing unidimensional waves, as shown in Fig. 3
the plate has channels 6 running parallelly next to each
other, whose lateral walls are connected with neighboring
channels. At their ends the channels 6 have transducers,
which send in se~uence and transform the received
ultrasonic waves into signals.
In Fig. 4 a channel 8 is shown which covers the entire
surface of a plate 9 and which transmit to the transducer
10 the information of the object exposed to the ultrasonic
waves.
Fig. 5 shows two parallel channels 11 and 12, which
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follow an angular-spiral path and receive the backscattered
ultrasonic waves directing them to the transducers 13 and
14, which further transmit to the computer the signals
resulting therefromO
The represented shapes of the channel path are
indicated only as examples, because each path shape is
suited to transmit unimodally the backscattered waves to a
transducer.
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