EP0419900A1

EP0419900A1 - Antenna apparatus

Info

Publication number: EP0419900A1
Application number: EP90117062A
Authority: EP
Inventors: Shigeyuki C/O Mitsubishi Denki K.K. Yoshida; Toshiya C/O Mitsubishi Denki K.K. Inubushi; Manabu C/O Mitsubishi Denki K.K. Hasegawa; Atsushi C/O Mitsubishi Denki K.K. Musha
Original assignee: Mitsubishi Electric Corp
Current assignee: Mitsubishi Electric Corp
Priority date: 1989-09-26
Filing date: 1990-09-05
Publication date: 1991-04-03
Also published as: NO176417B; JPH03110901A; AU6202990A; AU624732B2; CA2025882A1; NO176417C; NO903822D0; CA2025882C; NO903822L

Abstract

An antenna apparatus to be used in a wireless equipment is which an element part (9) of an external atenna is made of work hardening alloy and even if a large external force is applied to the element part, a removal of this external force causes the antenna to be recovered to its original state. A bending or breaking of the element part are prevented to reduce a deterioration of electrical characteristics of the external antenna. The element part can be bent and stored in a box of the wireless equipment, thereby the box of the wireless equipment can be reduced in size.

Description

BACKGROUND OF THE INVENTION

Field of the Invention

This invention relates to an antenna apparatus used in a portable wireless equipment, for example.

Description of the Prior Art

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 tranceiver 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 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 λ/2 (λ: 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 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.

SUMMARY OF THE INVENTION

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 work hardening alloy.

BRIEF DESCRIPTION OF THE DRAWINGS

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.
FIG. 4 is an illustrative view for measuring a restoring angle ϑ′ in respect to a bending angle ϑ 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.
FIG. 8 is a diagram showing elasticity of work hardening alloys in respect to temperature conditions.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

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 350°C to 400°C 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 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 350°C to 400°C 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 (about 4%) larger than a normal metal which is work hardened.
FIG. 3 is a load-deflection diagram (practically measured at 20°C) 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 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 ϑ′ and a restoring rate η in respect to a bending angle ϑ 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 ϑ and a restoring angle ϑ′ 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.
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 η is calculated as a ratio of a restoring angle ϑ′ with respect to a bending angle ϑ, i.e. (ϑ′/ϑ).
As apparent from Table 1, if the bending angle ϑ 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 η 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 η is 100%. In this case, the restoring rate η 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 η 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 ϑ, a polarization A generated by the element 9 in perpendicular to its axial direction is distributed into one polarization a₁ generated in perpendicular to a length ℓ₁ from its bending point to the fixed point and the other polarization b₁ generated in perpendicular to a length ℓ₂ 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 µΩ-cm which is slightly larger than 10 µΩ-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 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 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 L₁ 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 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 within 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).
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 18°C, a shape memory alloy having a transformation point Af of -15°C and work hardening alloy. As shown in the stage (a) of FIG. 8(B), the shape memory alloy having a transformation point Af of 18°C generates a shape memory effect in a range of 0°C to -20°C of environmental temperature, and as shown in the stage c) of FIG. 8(B), the shape memory alloy having a transformation point Af of -15°C may generate a shape memory effect in a range of -20°C of environmental temperature, and further generates a permanent strain in a range of 40°C to 60°C of environmental temperature.
To the contrary, the work hardening alloy merely generates a slight shape memory effect at an environmental temperature of -20°C in a range of -20°C to 60°C 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 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, 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. Table 2

E′ [kgf/mm²] Y′ [kgf/mm²]

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, -20°C to 60°C. 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.

Claims

1. An antenna apparatus characterized in that an element part of an external antenna arranged in a wireless equipment is made of work hardening alloy.

2. An antenna apparatus as set forth in claim 1, wherein the work hardening alloy is of Ni-Ti alloy.

3. An antenna apparatus as set forth in claim 1, wherein the work hardening alloy contains at least one metal in addition to Ni-Ti.

4. An antenna apparatus as set forth in claim 1, wherein the work hartening alloy is wound in a helical form to get the element part of the external antenna.

5. An antenna apparatus characterized in that an element part of an external antenna arranged in a wireless equipment is made of work hardening alloy, and a bent storing part for bending said element part and storing it is arranged within a box of said wireless equipment.

6. An antenna apparatus as set forth in claim 1 or 5, wherein said element part of the external antenna is used in an environmental temperature of -20°C to 60°C.