Note: Descriptions are shown in the official language in which they were submitted.
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ANTENNA APPARATUS
This invention relates to an antenna apparatus used
in a portable wireless equipment, for example.
It is an object of this invention to provide a new
antenna apparatus in which the element part of the
external antenna is prevented from being bent or broken
when a substantial external force is removed even if it
is applied to it and then a deterioration of
characteristics of the external antenna is improved.
It is another object of this invention to provide a
small-sized antenna apparatus.
The antenna apparatus of this invention is
constructed such that the element part of the external
antenna arranged in the wireless equipment is made of
lS work hardening alloy.
The present invention will be described in detail
hereinbelow with the aid of the accompanying drawings, in
which:
FIG. 1 is a perspective view for showing a main body
of a wireless equipment to which a prior art antenna
apparatus is applied;
FIG. 2 is a structural view for showing the antenna
apparatus of one preferred embodiment of this invention;
FIG. 3 is a diagram of a deflection-load
characteristic of a work hardening alloy;
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FIG. 4 is an illustrative view for measuring a
restoring angle 0' in respect to a bending angle ~ of a
work hardening alloy;
FIG. 5 iS an illustrative view for showing an
electrical influence caused by a bending of the element
part of the external antenna;
FIG. 6 is a structural view for showing the antenna
apparatus of another preferred embodiment of this
invention;
FIG. 7 (a) and (b) is a structural view for showing
the antenna apparatus of still another preferred
embodiment of this invention; and
FIG. 8 is a diagram showing elasticity of work
hardening alloys in respect to temperature conditions.
As a configuration of this type of antenna apparatus
a system disclosed in a gazette of Japanese Utility Model
Laid-Open No. 62-21636/1987 has been provided.
FIG. 1 is a view of configuration for showing an
antenna apparatus used in the conventional type of
portable wireless equipment, wherein 1 denotes a main
body of the wireless equipment, 2 denotes an internal
antenna arranged at an upper part of the main body 1 of
the wireless equipment, 3 denotes a battery pack set at a
side surface of a transceiver section 4, 5 denotes an
element part of the external antenna which is made of
stainless steel for a spring in the prior art and used
~1 .__,)
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while being pulled out of its stored state in the main
body 1 of the wireless equipment.
A length of the external antenna is required to
extend about 17 cm of A/2 (~: a wave length) if an
applied frequency is about 800 MHz.
6 denotes a cap part arranged at an extreme end of
the element part 5, this cap constitutes the external
antenna 8 together with the element part 5 and is used in
such a way as it may easily be pulled out when the
external antenna 8 stored in the main body 1 of the
wireless equipment is pulled out of it. 7 denotes a
holder part for the cap 6.
In the prior art, in case of performing a wireless
communication through the external antenna 8, when the
external antenna 8 is pulled out of the main body 1 of
the wireless equipment, a changing-over switch (not
shown) arranged within the main body 1 of the wireless
equipment is automatically changed over from the internal
antenna to the external antenna 8 and the equipment can
be used.
In case of such a wireless equipment as described
above, if a substantial force is applied to the external
antenna 8 due to accidental troubles such as a striking
of the external antenna 8 against an obstacle article
during its use or its dropping as well, the element 5 of
the external antenna 8 is sometimes kept in its bent
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condition even after its external force is removed.
This type of system had a problem that a
predetermined length of the external antenna 8 may not be
assured, a desired electrical characteristic as the
external antenna 8 and a function of the external antenna
8 may not be sufficiently attained.
Referring now to the drawings, some preferred
embodiments of this invention will be described in
detail. In FIG. 2, reference numeral 9 denotes an
element of an external antenna made of work hardening
alloy. The work hardening alloy is heat treated under a
low temperature of 350C to 4DQC and a cold working
.. ...... .
dislocation is substantially remained to apply
_
elasticity. It shows less variation in characteristic
caused by an environmental temperature. As the-work
hardening alloy, there are Ni-Ti alloys and ternary
~ -- . ..~ .
alloys including Ni, Ti added_with Co, for example.
In the drawings, 10 denotes a resin tube for
covering the element 9. 11 denotes a cap which is press
fitted to one end of the element 9, i.e. an upper end of
the element 9. 12 denotes a rigid member integrally
formed with the cap 11. 13 denotes a holder which is
fixed to a box of the wireless equipment so as to cause
the element 9 of the antenna to be freely passed and to
hold the element 9. 14 denotes a stopper arranged at the
other end of the element 9 and engaged with the lower end
of the holder 13 so as not to be
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pulled out of it. As illustrated in FIG. 2, this
stopper 14 has a slight round corner at its extreme
corner part.
The work hardening Ni-Ti alloy to be used in the
element 9 of the antenna will be described. In case of
a general type of metallic material, application of the
external force (stress) exceeding its elastic limit
causes dislocations among its atoms to produce a plastic
deformation and even if the external force is removed,
the metal does not recover its original shape. However,
in case of material called as a work hardening Ni-Ti
alloy, application of the external force exceeding its
elastic limit under its normal state causes its
deformation and its dislocations due to the deformation
is prevented by heat treating it at a low temperature
of 350C to 400C and increasing its dislocation
density, resulting in getting an elastic member and
then if the external force is removed by this elastic
member, the alloy may return to its original state.
The work hardening Ni-Ti alloy shows its maximum
recovering strain tabout 4%) larger than a normal metal
which is work hardened.
FIG. 3 is a load-deflection diagram (practically
measured at 20C) showing that a sample piece of the
work hardening Ni-Ti alloy is measured under a
condition shown in FIG, 8(A). As apparent from FIG. 3,
in case of the work hardening material, as its stress
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or load is increased, its deflection or strain is
gradually increased and in turn as its load is
decreased, its deflection is also decreased and finally
if its load is completely removed, its deflection shows
at last a zero value.
For example, a comparison between a spring steel
used as an element of the prior art antenna and the work
hardening Ni-Ti alloy shows the following results.
Table 1 is a comparison table of a restoring angle
~' and a restoring rate n in respect to a bending angle
~ of a prior art spring steel and the work hardening
Ni-Ti alloy of the preferred embodiment (Ni 48: Tu 50:
Co 2).
FIG. 4 is an illustrative view for getting data
shown in Table 1, wherein one end of the antenna 15 is
defined as a fixed point 16, an external force is
applied at a point spaced apart by about 7 cm from the
fixed point 16 to bend the antenna up to a bending
angle ~ and a restoring angle ~' attained when the
external force is removed is measured. In FIG. 4, a
dotted line indicates a position of the antenna to
which the external force is applied and an alternate
long and short dash line indicates a position of the
antenna from which the external force is removed.
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Table 1
= Bending
15 30 45 60 75 90
Restoring
angle 15 30 43 54 61 65
Spring
steel Restoring
raten 100% 100% 95% 90% 81% 72%
Restoring
Work angle 15 30 45 60 75 90
hardening
aNlloTy rate 100% 100% 100% 100~ 100% 100%
n
In this case, the antenna 15 is made of prior art
spring steel and work hardening Ni-Ti alloy to be
compared to it, a length of the antenna 15 is about 14
cm and a diameter of it is about 2 mm. A restoring
rate n is calculated as a ratio of a restoring angle ~'
with respect to a bending angle ~, i.e. (~'/~).
As apparent from Table 1, if the bending angle ~
is about 30, both spring steel and work hardening Ni-Ti
alloy have a restoring rate of 100%. However, if the
bending angle is more than 45, a certain difference is
generated in the restoring rate n between them.
It is an important thing that in case of the work
hardening Ni-Ti alloy, even if the bending angle is 90,
the restoring rate n is 100%. In this case, the
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restoring rate n of the prior art spring steel is 72%
and has a remarkable difference with respect to it.
In this way, the presence of substantial difference
of the restoring rate n between the work hardening Ti-Ni
alloy and the prior art spring steel may influence a
substantial antenna height and its direction and further
it may provide a further influence against an electrical
characteristic of the antenna.
For example, as shown in FIG. 5, in case that a
bending is generated from the point P of the element 9
at an angle ~, a polarization A generated by the
element 9 in perpendicular to its axial direction is
distributed into one polarization al generated in
perpendicular to a length Ql from its bending point to
the fixed point and the other polarization bl generated
in perpendicular to a length Q2 of the element 9 from
the bending point to the free end, thereby the
characteristics of antenna (a radiation efficiency) is
reduced.
An electrical resistance of the work hardening
Ni-Ti alloy is 50 to 100 ~Q-cm which is slightly larger
than 10 ~Q-cm of the prior art spring steel and even if
this fact, in view of its electrical resistance, this
invention can be applicable practically as an antenna
apparatus without any difference at all.
FIG. 6 is a structural view showing another
preferred embodiment of the antenna apparatus of this
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invention. In FIG. 6, 17 denotes an element of the work
hardening Ni-Ti alloy wound helically and 18 denotes a
resin tube for use in covering the helical element 17.
11 denotes a cap, 12 denotes a rigid part, 13
denotes a holder and 14 denotes a stopper in the same
way as that shown in FIG. 2.
In case of a still further preferred embodiment,
since the element 17 of the antenna is constructed by
the helical work hardening Ni-Ti alloy, the restoring
rate n in respect to the element 17 is larger than that
shown in FIG. 2.
Then, in FIG. 7(a), even if a length of element L2
of the antenna is larger than a size Ll of a box 20 of
the wireless equipment, the antenna is constructed such
that the element 9 of the antenna can be stored
completely in the box 20 of the wireless equipment. In
the preferred embodiment shown in FIG. 7(a), 21 denotes
a storing tube arranged in the box 20 of the wireless
equipment, the tube extends from a head part 20a to a
bottom part 20b of the box 20 of the wireless equipment.
A bending part 22 is arranged at the bottom part 20b
and further the tube extends at the bottom part 20b.
The element 9 of the antenna is made of work
hardening Ni-Ti alloy as described above, and as
indicated by a dotted line of FIG. 7(a), it is bent at
the bending part 22 of the storing tube 21 due to an
ultra-elastic feature and it is stored within the
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storing tube 21. A length of the storing tube 21 is
slightly longer than a length of the element 9 of the
antenna.
In case that the element 9 of the antenna is
applied to perform a wireless communication, the element
9 of the antenna is pulled out of the box 20 of the
wireless equipment and even if the element 9 is pulled
out of the box 20 of the wireless equipment, the element
9 is constructed by the work hardening Ni-Ti alloy, so
that it rises in a straight line as shown by a solid line
of FIG. 7(a).
In FIG. 7(a), 24 denotes rigid parts fixed to the
element 9 of the antenna which are arranged at a
forward part and a rearward part of the bending part 22
while being stored in the box 20 of the wireless
equipment. This arrangement is made so as to enable
the element 9 of the antenna to be easily slid witKin
the storing tube 21. In addition, since the stopper 14
arranged at the element 9 of the antenna is formed in
an arcular form at its extreme end, its sliding in the
storing tube 21 can more easily be performed.
In FIG. 7(b), it shows a case in which the box 25
of the wireless equipment has a special shape of circle.
26 denotes a storing tube arranged within the box 25 of
the wireless equipment and this tube has a large bent
part 27. Other elements are the same as those shown in
FIG. 7(a).
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FIG. 8(B) illustrates load-deflection curves for
use in comparing a mechanical performance of each of a
shape memory alloy having a transformation point Af of
18C, a shape memory alloy having a transformation point
Af of -15C and work hardening alloy. As shown in the
stage (a) of FIG. 8(B), the shape memory alloy having a
transformation point Af of 18C generates a shape memory
effect in a range of 0C to -20C of environmental
temperature, and as shown in the stage c) of FIG. 8(B),
the shape memory alloy having a transformation point Af
of -15C may generate a shape memory effect in a range
of -20C of environmental temperature, and further
generates a permanent strain in a range of 40C to 60C
of environmental temperature.
To the contrary, the work hardening alloy merely
generates a slight shape memory effect at an
environmental temperature of -20C in a range of -20C
to 60C of the environmental temperature and it is
effective as the element material for the external
antenna.
It is of course apparent that the antenna
apparatus of this invention can be applied to the
external antenna in a wireless equipment in which the
internal antenna and the external antenna are provided
and when the external antenna is pulled out of the box
of the wireless equipment, the internal antenna is
automatically changed over to the external antenna by
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using the antenna changing-over device disclosed in the
gazette of Japanese Patent Laid-Open No. 62-21636/1987,
for example.
At this time, a rigid part is arranged at a lower
end of the element of the antenna, this rigid part may
operate the changing-over switch and then the internal
antenna can be changed over to the external antenna.
In the preferred embodiments described above, the
work hardening Ni-Ti alloy has been described, and as
shown in FIG. 8(C) and 8(D), the ternary alloy including
Ni and Ti together with Co r for example, has a higher
elastic modulus and elastic limit than those of a binary
metal having only Ni and Ti and is particularly suitable
for the element member of the external antenna.
FIG. 8(C) shows load-deflection characteristics of a
ternary alloy in comparison with the binary alloy
(dotted lines) shown in the stage (b) of FIG. 8(B). As
seen from FIG. 8(C)~ the ternary alloy has a higher
elastic limit and a smaller residual deformation in a
low temperature range than the binary alloy does.
FIG. 8(D) shows tension-strain curves of the binary and
ternary alloys as results of tension tests, in which
the elastic moduli and elastic limits thereof are read
as follows.
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Table 2
E' [kgf/mm ] Y' [kgf/mm ]
Ni-Ti ALLOY 4,400 56.0
Ni-Ti-Co ALLOY 5,150 66.2
Where E' and Y' are an apparent elastic modulus and an
apparent elastic limit, respectively, in the strict
sense of terms in this case. As seen from FIG. 8(D),
an alloy having a lower transformation temperature has
greater values in apparent elastic modulus E' and
limit Y'.
Even in case of the work hardening alloy, each of
the characteristic values has a thermo-sensitivity and
at a low temperature, a residual strain is left or a
bending load is decreased. Accordingly, it is
effective to use material having a low transformation
temperature.
As described above, according to this invention,
since the element part of the external antenna of the
wireless equipment is made of work hardening alloy,
even if a large external force is applied to the
external antenna, upon removal of the external force it
can easily return back to its original state, so that
it may reduce the bent state as found in the prior art
even if it is used in a wide range of applied
environmental temperature, for example, -20C to 60C.
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As a result, a deterioration of electrical
characteristics of the external antenna can be improved.
In addition, since the element part of the external
antenna is arranged to be inserted into or taken out of
the box of the wireless equipment, this invention has
an effect that the box of the wireless equipment can be
made small in size.
