A Coin Detection System by Coupled Printed Spiral Inductors

Transcription

1 A Coin Detection Sstem b Coupled Printed Spiral Inductors Junichi Fukatani, Sho Yamaguchi, Masauki Yamauchi, Kazuhisa Yoshimatsu, Hisashi Aomori and Mamoru Tanaka Department of Electrical and Electronics Engineering, Sophia Universit 7- Kioi, Chioda-ku, Toko, , JAPAN Department of Electronics and Computer Engineering, Hiroshima Institute of Technolog Universit 2-- Miwake, Saeki-ku, Hiroshima-shi, Hiroshima, , JAPAN J.Fukata@gmail.com, amagus8@ahoo.co.jp, amauchi@ieee.org, oshimatsu.k@gmail.com, aomori@ieee.org, Mamoru.Tanaka@gmail.com Abstract: This paper describes a coin detection sstem using coupled Printed Spiral Inductors (PS-Inductors). In this research, the PS-Inductor is composed of copper foil spiral on the printed board. As an advantages, the PS- Inductor can be made easil and does not need the iron core. The eperimental measurement and the theoretical calculation of the inductance of the PS-Inductor are derived. This enables the easil realizable coin detection sstem using PS-Inductor. In this sstem, a coin can be identified as changes of the mutual inductance of coupled PS-Inductors. The mutual inductance is investigated b inserting the coin between two PS-Inductors. Ke Words: Coin detection, Mutual inductance, Printed Spiral Inductor, Combination inductance, Self-inductance Introduction A lot of spiral shape elements are used for RFID, IC, and so on [][2]. Especiall, the spiral shapes inductors are called spiral-inductor. The spiral inductor which is generated in an IC is often used [3]. The spiral inductor is not onl constructed on the chip but also on a printed board. The spiral inductors on the printed board have been easil used as a mutual inductor because the iron core does not need. That is, the mutual inductance can be easil achieved. In this paper, we propose a novel coin detection sstem using the mutual inductance changes of coupled printed spiral inductors (PS-Inductors). Since the elemental composition of each coin in the world is unique, the influence of the electro magnetic field generated b two PS-Inductors, strongl depends on the coin tpe. In other words, the coin can be identified b investigating the mutual inductance changes of two PS-Inductors. The advantage of the proposed method is that this method is better realizable than the conventional coin detection sstem using the natural frequenc of coin that requires the Fourier transform for detection [4]. Moreover, it can be said that the PS- Inductor generated b semicircular wiring pattern in the printed board is fit for the phsical characteristic of coins. The eperimental results of various coins suggest that the proposed method can identif coins correctl. This paper is organized as follows. In Section 2, the evaluation of the inductance of the PS-Inductor is described. The self inductance L is measured and calculated. In Section 3, the coin identification sstem is proposed. The coin can be distinguished b using the mutual inductance change effected b it. Section 4 shows the eperimental methods and results using two coupled PS-Inductors. The coin identification is eperimented using two tpes of PS-Inductors which have different diameter. Finall, in Section 5 the conclusion of this paper are drawn. 2 Printed Spiral Inductor The PS-Inductor is designed b combining hemiccles. In general, a spiral inductor in an IC is composed of a square wiring pattern that is combination of straight lines. The circle wiring pattern can provide the high Q value [5]. Therefore, PS-Inductor with circle wiring pattern is decided in this paper. Besides, its phsical form suits to form of coins ver well. The laout and inductance of PS-Inductor are decided b five parameters as shown in Fig. and Table. Also, two tpes of PS-Inductor α and β are used in this research (see Fig. 2). The PS-Inductors are created b combining semicircular patterns b using cutting machine (see Fig. 3). The length of the conductor shortens toward the center because the conductor rolls the hemiccle from the maimum radius to the center. ISSN: Issue 8, Volume 7, August 2008

2 R ma w PS-Inductor β Figure : Design of PS-Inductor. d PS-Inductor α Figure 2: Picture of PS-Inductor α and PS-Inductor β Table : Parameters of two kinds of PS-Inductor α β Greatest diameter R ma 36[mm] 0[mm] Pattern distance d 0.2[mm] 0.[mm] Pattern width w 0.[mm] 0.09[mm] Number of harf-turn TR 80[half-turn] 30[half-turn] Pattern thickness 35[um] 35[um] (single-sided) Pattern thickness 9[um] 9[um] (double-sided) Board material Glass epo Glass epo 2. Measurement of self-inductance of the PS-Inductor There are man methods of the measurement inductance. In this research, the inductance is measured b oscillating sstem which is built b combining arbitrar capacitors to a PS-Inductor. When the LC oscillation is caused, an inductance is obtained from an oscillation frequenc and the capacitances. The oscillation frequenc can be changed b changing values of capacitors. Therefore, the inductance of PS-Inductor can be determined b some eperiments. 2.. Eperimental measurement of selfinductance An inductance of high accurac can not be obtained without an oscillation frequenc and capacitances of high accurac. Therefore, when the inductance is measured, a parasitic impedance must be considered b all possible means in the eperiment circuit and the calculation obataining the inductance. The Col- cutting copper foil base material Figure 3: Fabrication of PS-Inductor pitts oscillator which uses onl one bipolar transistor is used because the influences of the parasitic impedances are reduced easil. Onl a digital oscilloscope is used for the frequenc measurements and waveform observations. Therefore, a circuit model with the measurement instrument can be drawn as like Fig. 4. An equivalent circuit of measuring impedance (see Table 2) is shown in the frame of Fig. 4. If oscillation waveform is sinusoidal shape, an inductance can be obtained from some capacitors, some resistors, an inductors, and an oscillation frequenc b using following equations. R2 R B L RL C3 A C4 C C2 R3 Measuring Impedance Oscillo- Probe Scope Figure 4: The circuit model with equivalent circuit of measurement equipments. c r r2 L' c2 Z Z2 Z3 Z4 ISSN: Issue 8, Volume 7, August 2008

3 L[uH] f 0 [MHz] Figure 5: The inductance L vs oscillating frequenc f 0 using PS-Inductor α where η = ωc 4 L = + 4η 2 R 2, () 2ωη ζ ε 2 + ζ 2, ε = αr 3 + ω 2 βδ α 2 + ω 2 β 2, ζ = ω ( C + C 3 ) + ω(αδ βγ) α 2 + ω 2 β 2 α = ω 2 (r + r 2 )R 3 c 2 (c + C 2 ) ω 2 c 2 L, β = R 3 (c + c 2 + C 2 ) + c 2 (r + r 2 ) ω 2 L R 3 c 2 (c + C 2 ), γ = R 3 ω 2 c 2 R 3 L, δ = (r + r 2 )c 2 R 3, The Eq. () can be obtained b following equations and the oscillation condition. Z =, jωc + r + jωl +r 2 + jωc 2 Z 2 = R 3 +, Z Z 3 = = γ + jωδ Z 2 + jωc 2 α + jωβ, Z 4 = + + = ε + jζ jωc jωc 3 Z 3 Y = R jωl R 2 + ω 2 L 2 + jωc 4 + Z 4 Im{Y} = 0. (2) The Y epresses an admittance of whole circuit. The oscillation frequenc f 0 is measured while changing Table 2: The value of parasitic element () model number () impedance oscilloscope SS-7804 C 2 = 25[pF] 454/L/VL C 2 = 6[pF] DS-9242A R = [MΩ] probe SS-00 C =70[pF] r + r 2 =66.73[Ω] L =40[uH] SS-0R C =2[pF] r + r 2 = [MΩ] L =40[uH] PP002i C = 5.5[pF] r + r 2 =9.05[MΩ] L =40[uH] transistor 2SC [pF] Table 3: The Inductance of PS-Inductor Parameter of Actual Calculated error PS-Inductor measurement value [%] α 3.944[uH] 3.265[uH] 2.7 β.77[uh].806[uh].94 the capacitors C, C 2, C 3, and C 4. Figure 5 shows the results using Eqs. () and (2). The inductance L is approached to the constant value. Therefore, the inductance using Eqs. () and (2) is assumed as the measurement value in this research Validation of eperimental measurement An inductance is calculated as follows: L = Φ(t) i(t) (3) In our previous stud, we developed a simulator which calculates the magnetic flu b using Biot- Savart Law and finite element method, and calculates an inductance of a PS-Inductor [6]. In this method, magnetic flu at an arbitrar domain AT of spacing is calculated from an arbitrar domain SC of conductor of the PS-Inductor below sequences.. Magnetic flu densit of a point a included domain AT, and magnetic flu densit of a point b ISSN: Issue 8, Volume 7, August 2008

4 Metal Magnetic field between these two dot lines is not calculated. Inside of PS-Inductor Outside of PS-Inductor a b AT SC Center Figure 6: Analsis of inside A Coin insertion Internal appearance Figure 7: Proposed coin detection sstem included domain AT are calculated from a point A included domain SC b using Biot-Savart Law (see Fig. 6). first side PSI first side PSI 2. An average of these magnetic flu densities is calculated. second side PSI (a) Forward direction second side PSI (b) Inverse direction 3. The magnetic flu of AT is calculated b multipling the average b a square measure of AT. The magnetic flu of AT is obtained b appling for whole conductor, and an inductance of the PS- Inductor is calculated b appling for whole spacing. In this method, the averages of magnetic flu are calculated, because computation time becomes short and accurac becomes good. The calculated values of self-inductances of PS-Inductor α and β are shown in Table 3. 3 Coin Identification Sstem The proposed coin detection sstem is shown in Fig. 7. The PS-Inductor is lapped over other PS-Inductor in same direction of the rotation (see Fig. 8), and the coin is passed between coupled PS-Inductors. In the proposed sstem, coins are detected b changes of mutual inductance of coupled PS-Inductors because each coin in the world is made from various materials and the sizes. Therefore, investigating the characteristics of the PS-Inductor is ver important task. Figure 8: How to overlap two PS-Inductors 3. Measurement of mutual inductance between two PS-Inductors 3.. Eperimental measurement The mutual inductance can be measured as follows.. The PS-Inductor is lapped over other PS- Inductor (see Fig. 8). 2. Two PS-Inductors are connected and a combination inductor L com is created. There are two kinds of L com b difference of connecting method (see Figs. 8, and 9). An inside terminal of the first PS-Inductor is coupled with an outside terminal of the second PS-Inductor (see Fig. 8(a)), and a L com of forward direction is constructed (see Fig. 9(a)). The inside terminal of the first PS-Inductor is coupled with an inside terminal of the second PS-Inductor (see Fig. 8(b)), and a L com of inverse direction is constructed (see Fig. 9(b)). The combination inductance L com of forward direction is ISSN: Issue 8, Volume 7, August 2008

5 Self-inductance (a) Forward direction (b) Inverse direction Figure 9: Combination inductance circuit second side PSI Mutual inductance given b di v = L dt + M di dt + L di 2 dt + M di dt = (L + L 2 + 2M) di dt, L com = L + L 2 + 2M, (4) and the combination inductance L com of inverse direction is obtained b di v = L dt M di dt + L di 2 dt M di dt = (L + L 2 2M) di dt, L com = L + L 2 2M. (5) Therefore, the mutual inductance M is described b M = L com L L 2. (6) 2 This proposed sstem uses the L com of forward direction, because the L com of forward direction is larger than that of inverse direction, and measurement of forward direction is easier than that of inverse direction. Therefore, we focus on onl L com of the forward direction. 3. The measurement circuit uses the Colpittsoscillator shown in Fig. 0. The distance between the first PS-Inductor and the second PS-Inductor is epressed as d. The thickness of PS-Inductor s base is epressed as t and t=0.005[m]. A Collpitts-oscillator is constructed using the L com. Two terminals of the L com are connected with a terminal A, and a terminal B. The combination inductance is measured b the oscillation method using a Colpittsoscillator. From Eq. (), the combination inductance is calculated as first side PSI Figure : Three dimensional calculation L com = + 4η 2 R 2 Lcom, (7) 2ωη where the R Lcom epresses a resistance including in the L com Theoretical approach In [7], Nukushida et.al. proposed a new method for theoretical calculation of the mutual inductance b using the Biot-Savart law and finite element method. The calculation method is changed to three dimensional calculation from previous simulator which is composed of two dimensional calculation (see Fig. ). The new simulator obtains the sum of a self inductance and a mutual inductance (L + M). The mutual inductance is calculated b subtracting self inductance L that is obtained b previous method Validation checking of eperimental measurement We eperiment using two coupled PS-Inductors (see Table ) and Colpitts-oscillator circuit (see Fig. 0). The distance d of coupled PS-Inductors α is changed into , , , and [m] and coupled PS-Inductors β is changed into 0.002, 0.003, 0.004, 0.005,0.006 and [m]. The mutual inductance M and combination inductance L com are measured in each distance. Then we compare actual measurement results with theoretical calculation results (see Figs. 2 and 3, and Tables 4, 5, 6 and 7). The relative error margin [%] of the combination inductance L com is smaller than that of the mutual in- ISSN: Issue 8, Volume 7, August 2008

6 R Measuring Impedance Oscillo- Probe Scope d R2 L RL C3 A L2 C4 RL2 C C2 R3 c r L' r2 c2 Z Z2 Z3 Z Z2 Z3 Z4 t B Lcom Figure 0: Coupled PS-Inductors and Colpitts-oscillator circuit Table 4: Error of the Combination inductance L com using PS-Inductor α ()eperimental measurement L com [μh] (2)theoretical calculation L cal [μh] distance d[m] () (2) error Table 5: Error of the Mutual inductance M of PS- Inductor α ()eperimental measurement M mea [μh] (2)theoretical calculation M cal [μh] distance d[m] () (2) error ductance M. In the PS-Inductor β, a large margin of error [%] especiall appears to the mutual inductance. As the reason, the mutual inductance of PS-Inductor β is small. Therefore, this sstem should be made in the range of which distance d is small. 4 Eperiments In order to evaluate the coin identification performance, we appl our sstem to 0 coins (see Fig. 4, and Table 8); JPY (500, 00, 50, 0, 5 and ) and USD (quarter, dime, nickel and penn). Firstl, the PS-Inductor α is used. The measurement conditions are set as follows. As shown in Figs. 5, coordinates are fied to the second side PS- Inductor. These coordinate are decided based on the side of the 500-en coin, because the 500-en coin has the largest radius in ten kinds of coins. The R ma, ma and d are fied as 0.08 [m], [m], and [m] respectivel, because the radius of 500-en coin is [m]. The center of the 500-en coin runs throw the origin coordinate of -ais and -ais. In Fig. 0, the resistances R, R 2, and R 3 are fied as 0 [kω], 0 [kω], and 3.3 [kω] respectivel. The capacitors C, C 2, C 3, and C 4 are changed as shown in Table 9 and measured at each parameter. Measurement values are assumed an average of three values. The epressing the position of coin is changed to , -0.08, -0.02, , , , 0, 0.003, 0.006, 0.009, 0.02, 0.08, and [m], and mutual in- ISSN: Issue 8, Volume 7, August 2008

7 Mutual inductance M, Combination inductance Lcom[μH] Distance d[m] Actual measurement(mutual) Simulation(Mutual) Actual measurement(combination) Simulation(Combination) Table 7: Error of the Mutual inductance M of PS- Inductor β ()eperimental measurement M mea [μh] (2)theoretical calculation M cal [μh] distance d[m] () (2) error Figure 2: Distance d v.s. Mutual inductance M and Combination inductance L com using PS-Inductor α ductance and combination inductance are measured at each position of the 500-en coin. As a result of Fig. 6, mutual inductance and combination inductance have a minimum value around =0. For this reason, the is changed to 0, 0.003, 0.006, 0.02, 0.08, and [m] (see Fig. 7), and mutual inductance is measured at each position b ten coins. Fig. 8 shows changing of mutual inductances b changed of position of each coin. Therefore, the coin can be predicted b this result. Especiall, man kind of the coin can be easil predicted around =0. Net, we use the PS-Inductor β. When the diameter of PS-Inductor is smaller than the average diameter of coins, we tr constructing coin detection sstem. Some measurement conditions are changed from above conditions as follows. The distance d is fied as [m] and [m]. In Fig. 0, the capacitors C, C 2, C 3, and C 4 are changed as shown Table 6: Error of the Combination inductance L com using PS-Inductor β ()eperimental measurement L com [μh] (2)theoretical calculation L cal [μh] distance d[m] () (2) error Mutual inductance M, Combination inductance Lcom[μH] Distance d[m] Actual measurement(mutual) Simulation(Mutual) Actual measurement(combination) Simulation(Combination) Figure 3: Distance d v.s. Mutual inductance M and Combination inductance L com using PS-Inductor β in Table 0 and measured at each value. Measurement values are assumed an average of four values. Other conditions are not changed from above conditions. Figure 9 and 20 show the results. The coin can be predicted onl d [m]. However, from the view point obtained b Fig.20, it is difficult to identif the coins. Because the diameter of the PS-Inductor is small, the mutual inductance is small. The coin can be predicted b the PS-Inductor especiall around =0. Furthermore, in other words, a position, a velocit, and a direction of the coin can be predicted b these results, if a kind of the coin is known, and when the coin is running through between PS-Inductors. ISSN: Issue 8, Volume 7, August 2008

8 Mutual inductance[μh] en en en en en en cent cent cent cent Coin position based on the 500-en coin: [m](=0) Coin identification is eas when a difference is great. Figure 8: Coins identification of mutual inductance using PS-Inductor α Table 8: Details of coin ()outside diameter[mm] (2)thickness[mm] Figure 4: 0coins (JPY (500, 00, 50, 0, 5, ) and USD (penn, nickel, dime, quarter)) 5 Conclusion In this paper, we proposed a novel coin detection sstem using coupled PS-Inductors. The eperimental results were shown that our method can identif the 0 coins correctl. This method can identif the coins in ver simple wa that transition of mutual inductance between PS-Inductors b inserting the coin is onl investigated. The coin identification was possible even b the PS-Inductor that is smaller than the coin. However, prediction of the kind of coin became eas b coin () (2) material 500en [%]Cu, 20[%]Zn, 8[%]Ni 00en [%]Cu, 25[%]Ni 50en [%]Cu, 25[%]Ni 0en [%]Cu, 3-4[%]Zn, -2[%]Sn 5en [%]Cu, 30-40[%]Zn en [%]Al cent [%]Zn, 2.5[%]Cu 5cent [%]Cu, 25[%]Ni 0cent [%]Cu, 8.33[%]Ni 25cent [%]Cu, 8.34[%]Ni using the PS-Inductor of diameter that is larger than diameters of coins. Moreover, prediction of the kind ISSN: Issue 8, Volume 7, August 2008

9 .6.4 Mutual inductance[μh] en 50en 5en cent 0cent 00en 0en en 5cent 25cent Coin position based on the 500-en coin: [m](=0) Figure 9: Coins identification of mutual inductance using PS-Inductor β d=0.003 Table 9: Combination of capacitors using parameter α ()Combination () C [pf] C 2 [pf] C 3 [pf] C 4 [pf] (γ) (δ) (ɛ) Rma Inside of the second side PS-Inductor Outside of the second side PS-Inductor Table 0: Combination of capacitors using parameter β ()Combination () C [pf] C 2 [pf] C 3 [pf] C 4 [pf] (ζ) (η) (θ) (ι) of coin became clear when the distance d between two PS-Inductor is short. It can be said that a ver small coin identification Figure 5: coordinates sstem at the stamp level can be constructed. Acknowledgment This research is supported b the fund of the Open Research Center Project from MEXT of the Japanese Government ( ). This research is supported b the Grants-in-Aid for Young Scientific Research(B) (No ) from the Japan Societ for the Promotion of Science. ISSN: Issue 8, Volume 7, August 2008

10 .3.2. Mutual inductance[μh] en 50en 5en cent 0cent 00en 0en en 5cent 25cent Coin position based on the 500-en coin: [m](=0) Figure 20: Coins identification of mutual inductance using PS-Inductor β d=0.005 Mutual inductance M, Combination inductance Lcom[μH] Combination inductance Mutual inductance Coin position based on the 500-en coin: [m](=0) Figure 6: Characteristic b the 500-en coin References: [] J. Park, Y. Park, Y. Kim, S. Jun, A Resistance Deviation-to-Time Interval Converter and its Application to a Passive RFID Tag for Securit, World Scientific and Engineering Academ and Societ(WSEAS) Circuits, Theor, and Applications, Vol., pp.26-30, Jul [2] A. Kabir, K. C. Huang, R. Wu, P. Rapajic, Net Generation Identit Card: RFID-based Automatic Access Control Sstem for Universities, World Scientific and Engineering Academ and Societ(WSEAS) Selected Topics on Circuits, Sstems, Electronics, Control and Signal processing, pp , December [3] K. Okada, Design Optimization Methodolog for On-Chip Spiral Inductors, IEICE Trans. Electron., Vol.E87-C, no.6, June, [4] M. Suzuki, Development of a simple and nondestructive eamination for counterfeit coins using acoustic characteristics, Forensic Science International, Vol.77, Issue, pp.e5-e8, Ma [5] S. S. Mohan, Simple Accurate Epressions for Planar Spiral Inductances, IEEE Journal of solid-state circuits., Vol.37, no.0, October, 999. [6] M. Motooshi, Y. Tanaka, M. Yamauchi and M. Tanaka, Measurement and Numeric Calculationfor Printed Spiral Inductors, Proc. of Nonlinear Theor and its Applications 2005, pp , [7] M. Nukushina, T. Kunihiro, T. Nanko, M. Yamauchi and M. Tanaka, Snchronization Phenomena of Coupled Colpitts Oscillators using Printed Spiral Inductors, Proc. of Nonlinear ISSN: Issue 8, Volume 7, August 2008

11 r [3] R. D. Lutz, Modeling of spiral inductors on loss substrates for RFIC applications, Radio Frequenc Integrated Circuits (RFIC) Smposium, 998 IEEE, pp.33-36, 7-9 June 998. =0 =0.003 =0.006 =0.02 =0.08 = Figure 7: Setting of coordinates based on the 500- en coin Theor and its Applications 2007, pp , [8] J. Fukatani, S. Yamaguchi, M. Yamauchi, H. Aomori and M. Tanaka, A Coin Detection Sstem b Coupled Printed Spiral Inductors, World Scientific and Engineering Academ and Societ(WSEAS) New aspects of circuits, pp.9-95, Jul 2008 [9] H.G. Dill, Designing Inductors for Thin Film Applications, Electronic Design, pp.52-59, 964. [0] S. Y. Y. Leung and D.C.C. Lam, Performance of Printed Polmer-Based RFID Antenna on Curvilinear Surface, IEEE CPMT Transactions in Electronic Packaging Manufacturing, Vol.30, no.3, pp , Jul [] F. J. Schmuckle, The method of lines for the analsis of rectangular spiral inductors [in MMICs], Microwave Theor and Techniques, IEEE Transactions on, Vol.4, Issue6, pp.83-86, June-Jul 993. [2] M. H. Chiou, A new wideband modeling technique for spiral inductors, Semiconductor Device Research Smposium, 2003 International, pp , December ISSN: Issue 8, Volume 7, August 2008