A Design of Mobile Phones Using Design Support Software for Compact Acoustic Systems Makoto KAJIWARA , Yoshinobu KAJIKAWA and Yasuo NOMURA Department of Electronics, Faculty of Engineering, Kansai University mktkj,kaji,
[email protected]
Abstract Black Box 3
Z0
Pin(s) Diaphragm
Front Cavity
Back Cavity
Black Box 2
Pout(s)
Black Box 1
Ear Piece Hole
Coupler
In this paper, we design mobile phones by using the design support software we have constructed for compact acoustic systems. It is difficult to design mobile phones whose frequency response using the ITU-T P.57 Type3.2 High-leak coupler is within the GSM mask. In other words, it is very difficult to satisfy the request with existent diaphragms, sounder, structure, sizes, and so on. Hence, we study ideal structure and sizes satisfying the request by using the design support software in this paper. Moreover, we analyze the obtained design results and then study a guideline for the design of mobile phones satisfying the above request.
Figure 1: Acoustic equivalent circuit.
1. Introduction In recent years, spread level of mobile phone is remarkably high and improvement in sound quality of mobile phone is called for. In case mobile phone is used, space is generated between ear and receiver, consequently sound often leaks. The leak causes deterioration of sensitivity and call quality. Therefore, in case mobile phone is designed, you have to design in consideration of leak. Generally, analysis by acoustic equivalent circuit is used to design of acoustic systems. However, in order to design acoustic parameter value and circuit structure, the present condition is depending on experience of designer, and then improvement of call quality and curtailment of cost have been a very difficult problem. Therefore, this paper introduces an effective guideline for improvement in sound quality by using the design support software which can automatically design some realizable size values and circuit structures satisfying given design conditions.
2. Transfer Function The definition of transfer function used in case of analyses on acoustic equivalent circuit is shown below. The parameters of acoustic equivalent circuit is defined as the system parameter vector X, and is expressed as follows. X = [X 1 X 2 L X i L X
N
]
T
(1)
where N is number of parameters and Xi is R, L, or C.
Mo.P2.21
Figure 2: Main window. The transfer function is expressed as follows in order to take the output sound pressure to input voltage. H (X, s) =
Pout ( s ) E in ( s )
(2)
Moreover, sound pressure response is expressed as follows. G C ( X , s ) = 20 log 10 H ( X , s ) × E in ( s )
s = jω
(3)
Figure 1 shows the acoustic equivalent circuit used in this paper. In Fig. 1, the Black Boxes 1~3 show designed parameters. In the Black Boxes 1~3, holes, cavities, or/and so on are generated and the optimal
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acoustic equivalent circuit and its acoustic parameter values are derived in order to satisfy a given design target. Cavities are needed in the front or back of the diaphragm because of the vibration so that the Front Cavity and Back Cavity are prepared from the start. From the same point of view, the Ear-Piece Hole is also prepared because holes are definitely needed in the surface of the ear-piece. The above constraints prevent the design of unrealizable structures.
2. [ Generating of an initial individual ] One equivalent circuit is chosen from the whole search space S at random and M size vectors Y1m (m=1~M) on the acoustic structure derived from the chosen circuit are generated. Then these are added to partial group S’.
3.1. Outline of Software
3. [ Generating of an individual ] One equivalent circuit is chosen from the whole search space S at random and M size vectors Y2m (m=1~M) on the acoustic structure derived from the chosen circuit are generated. Then these are added to partial group S’.
Figure 2 shows the main window of developed software. The items to be taken into account in the use of the software are the following seven points.
4. [ Determination of parents ] Two kinds of circuits are chosen from partial group S’ and defined as parents P1 and P2.
• Search ranges of types and size values of the elements generated in the Black Boxes.
5. [ Creation of children ] Crossover and mutation of parents P1 and P2 are performed. Consequently, let the generated individuals be children C1 and C2.
3. Design Support Software
• Search ranges of size values of ear piece, front cavity and back cavity. • Search ranges of parameter values of diaphragm. • GA parameters used for design. • Standard used for design (GSM or EIA). • Coupler used for design (ITU-T P.57 type3.2 Lowleak or High-leak).
6. [ Change to acoustic parameter value ] Size vector Y is converted into acoustic parameter vector X by the acoustic theoretical formula. 7. [ Calculation of Fitness ] Fitness is calculated by the following formula.
• Allowable range of design. (Termination condition) In Black Boxes 1 and 2, “anything”, “series hole”, “parallel hole”, “cavity”, “parallel hole and cavity”, or “nothing” can be selected. In Black Box 3, “anything”, “hole”, or “nothing” can be selected. The above options allow users to design acoustic systems at their requests. Moreover, if “anything” is selected, then various elements are generated and the best element is automatically determined so as to satisfy a given design target (that is, the best sound pressure response). 3.2. Method of Design In this section, we describe a design method of acoustic equivalent circuit and its parameters (sizes) whose sound pressure responses with and without leak are adjusted to a standard used as a design target [1]. This design method uses the Michalewicz’s [2] genetic program and the PfGA [3] for designing sizes and acoustic equivalent circuits, respectively. 1. [ Initial setting ] Users setup search range, standard, and so on, only the initial allowable range is fixed to plus or minus 15[dB] of a selected standard.
Fitness
=
N N
∑ {G
t
(4)
( X , ω ) − G c ( X , ω )}
2
k =0
where N is the number of evaluation frequency, Gt (X, ω ) the target sound pressure response, and Gc (X, ω ) the calculation sound pressure response. 8. [ Selection of individuals ] In the circuits P1, P2, C1, and C2, the circuits and the corresponding size vectors (individuals) satisfying the present allowable range remain in the partial group S’ and the others are removed. If all of the circuits and the corresponding size vectors (individuals) can not satisfy the present allowable range, then the individuals having higher fitness remain in the partial group S’. 9. [ Addition of individuals ] New individuals whose number is that of the removed individuals at the procedure 8 are added to the partial group S’ in the Michalewicz’s GA and then the number of individuals returns to M. 10. [ Update of allowable range ] The present allowable range is updated according to
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Table 1: Design Conditions Iteration 4000 Population size 40 13 The number of the genes of equivalent circuit The number of the genes of acoustic parameters 39 1.00 Crossover rate in Michalewicz’s GP 0.05 Mutation rate in Michalewicz’s GP 3 The number of elements in Black Boxes 1,2
L10 R10 L1 R1
R2 Z0
whether all of the present individuals satisfy or not the present allowable range.
Pout(s)
L2
LD RD CD R4 L4 C4
L8
Pin(s) C5
R8
R7 L7
C6
C7
Figure 3: Obtained acoustic equivalent circuit.
SPL[dB]
11. [ Termination conditions ] If the number of circuits in the partial group is less than 2, the algorithm returns to procedure 3, if not, returns to procedure 4. The above procedures are repeated until given termination conditions are satisfied.
4. Design of mobile phone It is difficult to design mobile phones whose frequency response using the ITU-T P.57 Type3.2 High-leak coupler is within the GSM mask. In other words, it is very difficult to satisfy the request with existent diaphragms, sounder, structure, sizes, and so on. Hence, we study ideal structures and those sizes satisfying the request by using the design support software in this paper.
130 120 110 100 90 80 70 60 100
Low-Leak
High-Leak
GSM standard 1000 Frequency [Hz]
4000
Figure 4: SPL after the design.
Impedance[dB]
4.1. Design Conditions The conditions used for the design are shown in Table 1. The search range of size value is as follows. Sounder is R = 2.10×106 ~ 2.10×108, L = 1.02×103 ~ 1.02×105, C = 5.49×109 ~ 5.49×1011, length and radius of holes is 0.1 ~ 5.0 [mm]. Total capacity is Maximum 2.4 [cc]. Under the condition, we tried to design mobile phones 30 times. 4.2. Design Result Various characteristics were acquired as a result of the design. One of the designed models is shown in Fig. 3. This result is the model having the best characteristic. Moreover, the size values of this model are shown in Table 2, and the SPL is shown in Fig. 4. These results show that structures whose frequency responses are within GSM mask cannot be obtained, that is, the difficulty of the design. However, the frequency responses in Low-leak and High-leak are within plus or minus 3.5[dB] of GSM mask. Hence, this result shows that the structure whose frequency response is independent of leaks can be obtained, that is, independent of the way using mobile phones. From Fig. 4, flat frequency responses are realized over range
L3 R3
150 145 140 135 130 125 120 115 110 105 100 100
Low-Leak
High-Leak 1000 Frequency [Hz]
4000
Figure 5: Acoustic impedance, re 1Pa s/m3. of low and middle bands in both of Low-leak and Highleak. However, the frequency responses deteriorate in the range of 2~3[kHz]. This is due to impedance characteristics of artificial ears (see Fig. 5). It is therefore difficult to compensate this frequency band. Since many design guidelines are obtained as the above, the efficiency of the design support software is demonstrated.
5. Conclusions In this paper, we have shown the outline of the constructed design support software and some design guidelines. As a result, although the obtained frequency
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C9
responses cannot satisfy the GSM mask, those are within plus or minus 3.5[dB] of the GSM mask. This result has shown that the structure whose frequency response is independent of leaks can be obtained, that is, independent of the way using mobile phones. Since many design guidelines have been obtained as the above, the efficiency of the design support software has been demonstrated. We plan to examine various design guidelines obtained by using this software.
Table 2: Acoustic parameters after the design. Parameters
Values
RD
3.90×106
LD
1.02×103
CD
5.49×109
Length
2.54
Radius
0.28
Capacity
0.12
Length
3.02
Radius
0.63
Capacity
0.30
Length
4.10
Radius
2.03
2nd back cavity
Length
0.16
1st front cavity
Capacity
0.30
Length
1.08
Radius
2.30
Capacity
0.13
Length
4.17
Radius
1.41
Length
0.10
Radius
5.00
Length
0.10
Radius
5.00
Sounder
Diaphragm hole
6. Acknowledgements
1st back cavity
The authors would like to thank Mr. Takashi Miyakura from Hoshiden Ltd. for his useful discussions.
Hole and Cavity
7. References [1] Y. Nomura, T. Nakatani, Y. Kajikawa, “An Automatic Design Technique Using Genetic Algorithm for the Acoustic Component of Mobile Phones”, 17th International Congress on Acoustics, Rome, Italy, Sep. 2001. [2] Zbigniew Michalewicz, Genetic Algorithms + Data Structures = Evolution Programs, Springer Verlag, 1992. [3] S. Kizu, H. Sawai, and S. Adachi, “Parameter-free Genetic Algorithm (PfGA) Using Adaptive Search with Variable Size Local Population and Its Extension to Parallel Distributed Processing”, IEICE Trans. Fundamentals (Japanese Edition) Vol.J82-D-ⅱ, No,3, pp.512-521, March, 1999.
1st back hole
Hole and cavity
1st front hole
2nd front hole
Receiver hole
Length[mm], Radius[mm], Capacity[cc]
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