Modeling and characterization of the electrostatic coupling intra-body communication based on Mach-Zehnder electro-optical modulation

Yong Song; Kai Zhang; Qun Hao; Jannick P. Rolland

doi:10.1364/OE.20.013488

1. Introduction

Intra-body communication (IBC) is a technology using the human body as a transmission medium for electrical signals [1]. Compared with short distance wireless communication, such as Zigbee and Bluetooth, it has the characteristics of high information security, low energy consumption, and high data transmission rate [2]. Therefore, it is believed that IBC technology will offer significant advantages in Personal Area Network (PAN) [1,3],biomedical monitoring [4], and interaction between the humans and their environments [5,6].For instance, IBC technology can be used to build a biomedical monitoring network consisting of on-body sensors and implanted sensors, as shown in Fig. 1 , in which biomedical data collected from the different parts of the human body transmit within the human body, and eventually arrive at the cell phone or hospital by using a link sensor attached on the wrist. Therefore, the patients and their doctors can achieve the biomedical data of the human body almost anytime and anywhere.

Fig. 1 The biomedical monitoring based on IBC technology.

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The detection of signals transmitting within the human body is important for achieving reliable and high-speed IBC. Two related methods have been proposed, as shown in Fig. 2 . One is the electrical detection method shown in Fig. 2(a), in which a signal transmitting within the human body is directly detected by electrical sensors [1,7]. Given the comparatively low input impedance of electrical sensors, the signal transmission is susceptible to interference and the signal transmission rate is limited to 40 kbps [3]. The other method is the electro-optical modulation, in which an electro-optical sensor is employed instead for detecting the signal transmitted within the human body [3,6,8], as shown in Fig. 2(b). The advantages of this method include 1) the extremely high input impedance of the electro-optical crystal (i.e. about 100 times higher than the electrical detection method), yielding significantly higher signal to noise ratios than obtained with the electrical detection method; 2) the ground electrode of the electro-optical sensor is electrically isolated from electronic circuits. Therefore, the influence of floating-ground potentials is eliminated [6]. As a result, both the noise and the signal distortions are decreased greatly, while a signal transmission rate of 10 Mbps can be achieved [3].

Fig. 2 Approaches for detecting the signal transmitted within the human body: (a) Electrical detection method. (b) Electro-optical modulation method.

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Previous researches of the electro-optical modulation method used in IBC mainly focused on the sensor based on a bulk electro-optical modulator [3,6,8], which have several unsolved issues: 1) The theoretical model of this kind of IBC has not been discussed, therefore, it is difficult to determine the corresponding parameters of the electro-optical sensor used in IBC to date; 2) Given that this kind of electro-optical sensor has a phase delay caused by natural binary refraction, which is critically sensitive with temperature, its communication quality is greatly impacted by ambient temperature; 3) the phase delay of this kind of electro-optical sensor depends on the aspect ratio of the electro-optical crystal, which results in a comparatively big size of the IBC receiver. Therefore, it will limit the application of IBC. In this paper, an IBC method based on Mach-Zehnder electro-optical sensor is proposed, which has the advantages described as following: 1) good temperature characteristic. The optical intensity modulation of the Mach-Zehnder sensor is not influenced by the phase delay caused by natural binary refraction, which decreases the impact of ambient temperature; 2) small size. Due to a Mach-Zehnder electro-optical modulator is produced by using an optical waveguide and photo etching technologies with micron or nanometer resolution [9–11], it can be miniatured down to 100-200µm [11].Moreover, it can also be integrated with a laser diode (LD) and a photo detector (PD). Therefore, the miniaturization of a Mach-Zehnder sensor can be achieved, which will results in a compact size sensor; 3) low power consumption. The half-wave voltage of a Mach-Zehnder type sensor (generally less than 6V) is far lower than that of a bulk type sensor (generally more than 200V), which results in the comparatively lower power consumption. Moreover, a bulk type sensor generally needs a wave plate and a polarizing beam splitter, which yield additional optical losses. Therefore, compared with a bulk type sensor, the power consumption of the Mach-Zehnder type sensor is comparatively lower [11].

In this paper, the modeling and characterization of Mach-Zehnder electro-optical modulator for IBC have been investigated for the first time. We present a mathematical model of the electrostatic coupling IBC based on the Mach-Zehnder electro-optical modulator. Next, important characteristics of this IBC form have been simulated, and the corresponding in-vivo measurements were carried out and compared to the simulations. Results show that the proposed method will help to achieve good temperature characteristics, small size and lower power consumption IBC system.

2. Modeling of IBC based on a Mach-Zehnder electro-optical modulator

The electrostatic coupling IBC based on a Mach-Zehnder electro-optical modulator is illustrated in Fig. 3 , in which the signal is coupled into the human body through the signal electrode at the transmitting terminal, which is also coupled into the earth ground through the ground electrode. At the receiving terminal, the signal transmitted through the human body is coupled into a Mach-Zehnder electro-optical modulator through the signal electrode. The functions of the Mach-Zehnder electro-optical modulator can be described as follows. The refractive index of the arm of the Mach-Zehnder modulator changes with the voltage of the received signal which is applied onit. As a result, when the laser light from the laser diode (LD) passes through the arms of the Mach-Zehnder modulator, the phase of the optical wave changes in one arm relative to the other. Subsequently, the Mach-Zehnder modulator sums the optical waves from each arm, and the phase change is converted to amplitude change, which results in optical intensity modulation. Finally, the change in optical amplitude is converted into the corresponding change in electric signals by a photo detector (PD). Moreover, because the ground electrode is insulated from the PD and the corresponding circuit of the receiver based on the Mach-Zehnder modulator, as shown in Fig. 3, signal detection with low noise and low signal distortion can be achieved in this IBC form.

Fig. 3 Model of the electrostatic coupling IBC based on Mach-Zehnder electro-optical modulator.

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2.1. Circuit model

The circuit model of the electrostatic coupling IBC based on a Mach-Zehnder electro-optical modulator, illustrated in Fig. 3, was developed and reported in Fig. 4 . Considering that the impedances of the signal return paths (Cg1, Cg2 and Cg3) are far greater than that of the body channel, the human body can be modeled as a perfect conductor [1]. Therefore, the human body is considered as a body node in the proposed circuit model. Meanwhile, compared with the modulator based on a bulk electro-optical crystal, which has one internal signal electrode and is generally modeled as a capacitance [3,6], the Mach-Zehnder electro-optical modulator has two internal signal electrodes corresponding to the two arms. The modulator itself can be modeled as two capacitances represented as Ce1and Ce2, respectively, in our circuit model. Additionally, some of the weak couplings (such as the coupling between the two ground electrodes) were ignored for simplifying the model of electrostatic coupling IBC, which may influence the precision of the model to some extent.

Fig. 4 The circuit model of the electrostatic coupling IBC based on a Mach-Zehnder electro-optical modulator.

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Based on the proposed circuit model and common practices, the relationship between the voltage (V_in)of the IBC transmitter and the measured voltage of the Mach-Zehnder modulator (V_e) can be shown to be given as

{\begin{array}{l} V_{e} = \frac{V_{i n} Z_{g 2} Z_{e}^{'}}{(R_{0} + Z_{s 1} + Z_{g 1} + Z_{g 2}) (Z_{s 2} + Z_{e}^{'} + Z_{g 3} + Z_{g 2}) - Z_{g 2}^{2}}, \\ \begin{matrix} Z_{g i} = \frac{1}{j 2 π f C_{g i}} \begin{matrix} (i = 1, 2, 3) \end{matrix}, \end{matrix} \\ Z_{e}^{'} = \frac{Z_{e 1} Z_{e 2}}{Z_{e 1} + Z_{e 1}} = \frac{1}{j 2 π f (C_{e 1} + C_{e 2})}, \\ Z_{s i} = R_{i} + \frac{1}{j 2 π f C_{s i}} \begin{matrix} (i = 1, 2) \end{matrix}, \end{array}

Where the “Z” parameters represent the impedances corresponding to the corresponding “C” parameters shown in Fig. 4. Therefore, the signal attenuation (G_H) caused by the human body can be represented as

G_{H} = 20 \log_{10}^{} (\frac{V_{e}}{V_{i n}}) = 20 \log_{10}^{} [\frac{Z_{g 2} Z_{e}^{'}}{(R_{0} + Z_{s 1} + Z_{g 1} + Z_{g 2}) (Z_{s 2} + Z_{e}^{'} + Z_{g 3} + Z_{g 2}) - Z_{g 2}^{2}}] .

2.2. Mathematical model

According to the circuit model shown in Fig. 4, the mathematical model of the electrostatic coupling IBC based on a Mach-Zehnder electro-optical modulator was next developed. In our investigation, in order to show the advantages of the IBC based on a Mach-Zehnder electro-optical modulator, the electro-optical modulation based on a bulk electro-optical crystal and the electro-optical modulation based on a Mach-Zehnder electro-optical modulator are discussed and compared. These two modulation methods are illustrated in Fig. 5 .

Fig. 5 The electro-optical modulator used in IBC. (a) Bulk electro-optical modulator.(b) Mach-Zehnder electro-optical modulator.

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2.2.1. Modulation based on a bulk electro-optical crystal

As shown in Fig. 5(a), in the transverse electro-optical modulation of the IBC based on a bulk electro-optical crystal [3], the direction of the signal electric field (i.e. along the z-direction) applied on the x-cut electro-optical crystal is generally perpendicular to the light propagation direction, which in this case is along the y-direction. If the polarized directions of the polarizer and analyzer are orthogonal, and the angle between the z-direction and the polarized direction of the polarizer is π/4, the relationship between the input optical power(Pin) and the output optical power(Pout)of the electro-optical crystal can be expressed as [12]

P_{o u t} = P_{i n} \sin^{2} (\frac{Δ φ}{2}) = P_{i n} \sin^{2} [\frac{π l}{λ} (n_{o} - n_{e}) + \frac{π l}{2 λ d} (n_{e}^{3} γ_{33} - n_{o}^{3} γ_{13}) V_{e}],

where △φ represents the phase delay of the output light relative to the input light, l and d are the length and height of the electro-optical crystal, respectively,γ₃₃ andγ₁₃ are the electro-optic coefficients of the electro-optical crystal, and V_e represents the voltage applied on the electro-optical crystal [12]. Finally, the change in light signal is converted into the corresponding electric voltage (Vout) by the photo detector, which is given as

V_{o u t} = \frac{S \cdot R_{k}}{10^{\frac{k}{10}}} P_{i n} \sin^{2} [\frac{π l}{λ} (n_{o} - n_{e}) + \frac{π l}{2 λ d} (n_{e}^{3} γ_{33} - n_{o}^{3} γ_{13}) V_{e}],

where k is the insertion loss of the modulator, and S and R_k represent the conversion eﬃciency and the transimpedance of the photo detector, respectively.

2.2.2. Modulation based on a Mach-Zehnder electro-optical modulator

As for the Mach-Zehnder electro-optical modulator shown in Fig. 5(b), if the electric field of the incident input light E_in equal Aexp(jωt), the electric fields in the two arms of the Mach-Zehnder electro-optical modulator can be described as E_a equal E_b equal (A/2)exp(jωt). Therefore, the electric field referring to the emergent light of the Mach-Zehnder modulator (E_out) can be expressed as [12]

\begin{array}{l} E_{o u t} = \frac{A}{2} \exp (j ω t) [\exp (j φ_{a}) + \exp (j φ_{b})] \\ \begin{matrix} = \end{matrix} A \exp {j [ω t + \frac{2 π l}{λ_{0}} (n_{e} - n_{o})]} \cdot \cos [\frac{Γ π L}{G λ_{0}} (n_{e}^{3} γ_{33} - n_{o}^{3} γ_{13}) V_{e} + φ_{0}], \end{array}

where φ_a and φ_b are the phases of the arm A and B, respectively, Γ is the overlap integral factor representing the interaction between the electric field applied on the electrodes and the light wave field, G is the distance between the signal electrode and the ground electrode of the Mach-Zehnder electro-optical modulator, and φ₀is the phase diﬀerence used for setting the operating point of the Mach-Zehnder electro-optical modulator. Subsequently, according to Eq. (6), the relationship between the (P_in) and (P_out) of the Mach-Zehnder electro-optical modulator can be expressed as

P_{o u t} = P_{i n} \cos^{2} [\frac{Γ π L}{G λ_{0}} (n_{e}^{3} γ_{33} - n_{o}^{3} γ_{13}) V_{e} + φ_{0}] .

Finally, the receiving voltage of the IBC receiver (V_out) based on the Mach-Zehnder electro-optical modulator can be expressed as [13]

V_{o u t} = 10^{- 10 / k} S \cdot R_{k} \cdot P_{o u t} .

Therefore, the theoretical value of the signal attenuation (G_EO1) caused by the Mach-Zehnder electro-optical modulation system, which includes the laser diode (LD), the Mach-Zehnder electro-optical modulator itself and the photo detector (PD),can be represented as

\begin{array}{l} G_{E O 1} = 20 \log_{10} (\frac{d V_{o u t}}{d V_{e}}) = 20 \log_{10} \frac{d}{d V_{e}} {10^{- k / 10} S \cdot R_{k} \cdot P_{i n} \cos^{2} [\frac{Γ π L}{G λ_{0}} (n_{e}^{3} γ_{33} - n_{o}^{3} γ_{13}) V_{e} + φ_{0}]} \\ = 20 \log_{10} {- 10^{- k / 10} S \cdot R_{k} \cdot P_{i n} \cdot \frac{Γ π L}{G λ_{0}} (n_{e}^{3} γ_{33} - n_{o}^{3} γ_{13}) \sin [\frac{2 Γ π L}{G λ_{0}} (n_{e}^{3} γ_{33} - n_{o}^{3} γ_{13}) V_{e} + φ_{0}]} . \end{array}

2.2.3. Influence factors

2.2.3.1. The frequency response of the Mach-Zehnder electro-optical modulation

The Mach-Zehnder electro-optical modulation as a function of the signal temporal frequency is an important factor that influences the frequency characteristic of the IBC system that is based on it. However, because the frequency response of the Mach-Zehnder electro-optical modulation system consisting of an LD, an electro-optical modulator, and a PDis determined by several factors such as input optical power, operating wavelength, the insertion loss and crystal type of the modulator and parameters of the PD, it is generally challenging to achieve an accurate mathematical model for the frequency response of the Mach-Zehnder electro-optical modulation. As a result, the proposed mathematical model for the signal attenuation (G_EO1) given in Eq. (8) that represents the Mach-Zehnder electro-optical modulation is typically taken to be a constant with signal frequency. In our investigation, the frequency response of the Mach-Zehnder electro-optical modulator was achieved by curve fitting of the measurements.

Our experimental setup for measuring the frequency response of the Mach-Zehnder electro-optical modulation was composed of a battery powered waveform generator (DSO8060, made by Qing Dao Hantek Electronic co., Ltd China), an LD, a Mach-Zehnder electro-optical modulator (10 Gb/sec intensity modulator, made by JDS Uniphase Corporation, USA), a PD and a digital oscilloscope(Agilent 54641A), in which the waveform generator served as an IBC transmitter, while the digital oscilloscope was used for measuring the output signal of the PD. Additionally, to avoid the influence of the AC power and the earth ground connected with the oscilloscope, a balun (a type of electrical transformer that converts balanced electrical signals relative to the earth ground to unbalanced signals, and the reverse) was used for separating the Mach-Zehnder electro-optical sensor from the digital oscilloscope [14] (see Fig. 6 ).

Fig. 6 Measured frequency response of the experimental setup together with curve fitting.

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Firstly, the frequency response function of the signal attenuation (G_EO2) associated with the Mach-Zehnder electro-optical modulation can be modeled using a piecewise fitting method as

G_{E O 2} = {\begin{matrix} - 25.22 e^{- {2.505}^{- 5} \cdot f} - 15.12 e^{- {2.878}^{- 6} \cdot f} & (10 k H z \leq f \leq 500 K H z), \\ - {1.639}^{- 15} f^{2} - {1.356}^{- 7} f - 3.415 & (500 K H z < f \leq 40 M H z) . \end{matrix}

Secondly, the frequency response function of the signal attenuation (G_balun) associated with the balun may be modeled, also based on curve fitting, as

G_{b a l u n} = - 1836 f^{- 0. 4761} + 0. 4708 .

2.2.3.2. Temperature

Temperature is an important influence factor of the IBC based on electro-optical modulation. Generally, the temperature effect on the electro-optical modulation mainly consists in a change in refractive index. As for a LiNbO₃crystal, which has been widely used in electro-optical modulation, the temperature effect on its refraction index (n_o, n_e) may be captured with the Sellmeier equations [15], given as

{\begin{cases} n_{o}^{2} = 4.913 + \frac{0.1173 + 1.64 \times 10^{- 8} T^{2}}{λ^{2} - {(0.212 + 2.7 \times 10^{- 8} T^{2})}^{2}} - 2.78 \times 10^{- 2} λ^{2}, \\ n_{e}^{2} = 4.5567 + 2.605 \times 10^{- 7} T^{2} + \frac{0.097 + 2.7 \times 10^{- 8} T^{2}}{λ^{2} - {(0.212 + 5.4 \times 10^{- 8} T^{2})}^{2}} - 2.24 \times 10^{- 2} λ^{2} . \end{cases}

Therefore, according to Eq. (4) that describes the relationship between V_out and V_e, the temperature characteristic of the electro-optical modulation based on a bulk electro-optical crystal can be determined using also Eq. (11). Similarly, the temperature characteristic of the Mach-Zehnder electro-optical modulator can also be described using Eq. (8) and (11).

2.2.4. The complete mathematical model

According to Eq. (2), (8), (9) and (10), the total signal attenuation (G_Total) that refers to the electrostatic coupling IBC based on the Mach-Zehnder electro-optical modulation can be represented as

G_{T o t a l} = G_{H} + G_{B a l u n} + G_{E O 1} + G_{E O 2} - K,

where G_H is the signal attenuation caused by the human body, G_Balun represents the signal attenuations caused by the balun at the receiving terminal, G_EO1 is the signal attenuation associated with the Mach-Zehnder electro-optical modulation when considered independent of signal frequency, G_EO2 is the signal attenuation caused by Mach-Zehnder electro-optical modulation achieved by the piecewise fitting based on measurements and is dependent of signal frequency, and K is the correction factor which is equal to the calculation value of G_EO1represented as Eq. (8).Based on the same parameters as our measurement setup and the same temperature, K = −0.41dB.

Finally, the complete mathematical model of the signal attenuation (G_Total) that refers to the electrostatic coupling IBC based on the Mach-Zehnder electro-optical modulation can be modeled and computed as

{\begin{array}{l} G_{T o t a l} = G_{H} + G_{B a l u n} + G_{E O 1} + G_{E O 2} - K, \\ G_{H} = 20 \log_{10} (\frac{Z_{g 2} Z_{e}^{'}}{(R_{0} + Z_{s 1} + Z_{g 1} + Z_{g 2}) (Z_{s 2} + Z_{e}^{'} + Z_{g 3} + Z_{g 2}) - Z_{g 2}^{2}}), \\ Z_{g i} = \frac{1}{j 2 π f C_{g i}} \begin{matrix} (i = 1, 2, 3), \end{matrix} \\ Z_{e}^{'} = \frac{1}{j 2 π f (C_{e 1} + C_{e 2})}, \\ Z_{s i} = R_{i} + \frac{1}{j 2 π f C_{s i}} \begin{matrix} (i = 1, 2) \end{matrix}, \\ G_{E O 1} = 20 \log_{10} {10^{- \frac{k}{10}} S \cdot R_{k} \cdot P_{i n} \cdot \frac{Γ π L}{G λ_{0}} (n_{e}^{3} γ_{33} - n_{o}^{3} γ_{13}) \sin [\frac{2 Γ π L}{G λ_{0}} (n_{e}^{3} γ_{33} - n_{o}^{3} γ_{13}) V_{e} + φ_{0}]}, \\ n_{o}^{2} = 4.913 + \frac{0.1173 + 1.64 \times 10^{- 8} T^{2}}{λ^{2} - {(0.212 + 2.7 \times 10^{- 8} T^{2})}^{2}} - 2.78 \times 10^{- 2} λ^{2}, \\ n_{e}^{2} = 4.5567 + 2.605 \times 10^{- 7} T^{2} + \frac{0.097 + 2.7 \times 10^{- 8} T^{2}}{λ^{2} - {(0.212 + 5.4 \times 10^{- 8} T^{2})}^{2}} - 2.24 \times 10^{- 2} λ^{2}, \\ G_{E O 2} = - \begin{matrix} 25.22 e^{- {2.505}^{- 5} \cdot f} - 15.12 e^{- {2.878}^{- 6} \cdot f} & (10 k H z \leq f \leq 500 k H z \end{matrix}), \\ G_{E O 2} = \begin{matrix} - {1.639}^{- 15} f^{2} - {1.356}^{- 7} f - 3.415 & (500 k H z < f \leq 40 M H z \end{matrix}), \\ G_{b a l u n} = - 1836 f^{- 0. 4761} + 0. 4708 . \end{array}

3. Experiments

3.1. Frequency response

To verify the frequency characteristic of the proposed model represented as Eq. (13), in-vivo measurements of the electrostatic coupling IBC based on the Mach-Zehnder electro-optical modulation were carried out by using the experimental setup mentioned in section 2.2.3.1. Our first experiment was concerning the signal transmission path from the left arm to the right arm, as shown in Fig. 7 , in which a signal is coupled into the left arm of the human body by using an electrostatic coupling electrode including a signal electrode and a ground electrode, while it is received using a same electrode on the right arm. Also, in-vivo measurements of signal transmission paths from the arm to the torso and from the arm to the leg were next carried out. Meanwhile, the frequency response of the electrostatic coupling IBC based on the Mach-Zehnder electro-optical modulation was simulated according to the model of Eq. (13).

Fig. 7 In-vivo measurements of the electrostatic coupling IBC based on the Mach-Zehnder electro-optical modulation

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The effectiveness of Eq. (13)in modeling overall signal attenuation that is equivalent to the electrostatic coupling IBC based on the Mach-Zehnder electro-optical modulation is shown in Fig. 8 , in which both in-vivo measurements of the frequency response and the corresponding simulated results are compared. Results show that in simulation and the corresponding measurement, the attenuation decreases gradually in the 200 kHz-2 MHz window, keeps relatively stable in the 2 MHz-10 MHz window, and increases gradually in the 10 MHz-40 MHz window, which indicate similar trend in these frequency regions.

Fig. 8 Comparison between in-vivo measurements and simulation results based on the proposed model given by Eq. (13).

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On the other hand, some potential advantages of the IBC based on the Mach-Zehnder electro-optical modulation can be found in other results. Figure 9 shows the in-vivo measurements of the frequency responses corresponding to the IBC based on the electrical sensor and the IBC based on Mach-Zehnder electro-optical modulation within the frequency range of 1MHz to 40 MHz. Results show that for the IBC based on the electrical sensor, all the signal attenuations corresponding to various paths (left arm-right arm, arm-torso and arm-leg) decrease from approximately 64.57dB to 47.16 dB in the range of1 MHz to 5 MHz, and have comparatively big variation (the maximum deviation is 15.96 dB) in the range of 5 MHz to 40 MHz. On the other hand, according to Fig. 9, the signal frequency has comparatively less effect on the signal attenuations in the case of the IBC based on the Mac-Zehnder electro-optical modulation. This phenomenon indicates that compared with the IBC based on an electrical sensor, the electrostatic coupling IBC based on Mach-Zehnder modulation has a comparatively steady frequency response, especially in the range of 2 MHz to 10 MHz (the maximum deviation of this range is only 0.82 dB).Therefore, if the signal frequency or the carrier frequency of IBC is set in this range, high quality of electrostatic coupling IBC will be expected.

Fig. 9 Measurements of the electrostatic coupling IBC with various signal transmission paths, including the frequency responses of the IBC based on the electrical sensor and that based on Mach-Zehnder electro-optical modulation.

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3.2. Temperature characteristic

In our investigation, the advantage of the IBC based on the Mach-Zehnder electro-optical modulation in terms of temperature characteristic was also verified in terms of temperature characteristic by the comparison between the temperature characteristic of this kind of IBC and that of the IBC based on a bulk electro-optical sensor.

According to Eq. (4) and (11), the signal attenuation of the IBC based on a bulk electro-optical sensor can be estimated as a function of temperature. Figure 10shows the simulation results of the bulk electro-optical sensor used in IBC in the temperature range of 283.15 K-305.15 K, which shows that the signal attenuation varies greatly. Moreover, it also can be seen from Fig. 10 that the variation is periodical, and the maximum variation is up to approximately 55 dB, which indicates that ambient temperature affects the communication quality greatly in the IBC based on bulk electro-optical sensor.

Fig. 10 Simulations of attenuation corresponding to different ambient temperatures (283.15 K-305.15 K) of the bulk electro-optical sensor used in IBC.

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Figure 11 shows the simulation results of the Mach-Zehnder electro-optical sensor used in IBC, the corresponding measurements and the errors between them, respectively. We can find that compared with Fig. 11, both the simulation results and the measurements shown in Fig. 11 have negligibly smaller variation. For instance, as the temperature increases from 283.15 K to 305.15 K, the increase in the simulation results is less than0.02 dB, while the measurements exhibit a periodic variation in the order of +/− 0.25 dB. Yet both are small, which indicates that the IBC based on Mach-Zehnder electro-optical modulation has good temperature characteristic.

Fig. 11 Measurements and simulation of attenuation corresponding to various ambient temperatures (283.15 K-305.15 K) of the Mach-Zehnder electro-optical sensor used in IBC.

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4. Conclusion

In this paper, the Mach-Zehnder electro-optical modulation method is first used in IBC, while the characteristics of the electrostatic coupling IBC based on Mach-Zehnder electro-optical modulation are investigated. We have shown that the frequency response of the IBC based on Mach-Zehnder electro-optical modulation was modeled and shown to agree with the corresponding measurements in the frequency of 200 kHz to40 MHz. Also, we demonstrated that, compared with the IBC based on an electrical sensor, the electrostatic coupling IBC based on Mach-Zehnder electro-optical modulation has a steady frequency response in the range of 2 MHz to 10 MHz. Therefore, the stability of electrostatic coupling IBC is increased. Finally, compared with the IBC based on a bulk electro-optical sensor, the IBC based on Mach-Zehnder modulation has good temperature characteristic, which decreases the impact of ambient temperature and finally increases the communication quality of electrostatic coupling IBC. Moreover, the proposed method can also help to decrease the size and power consumption of the IBC system compared with the method based on a bulk electro-optical sensor.

Acknowledgment

The work was supported by the National Natural Science Foundation of China (60801050), the Excellent Talent Fund of Beijing, China (2011) and the Scientific and Technological Innovation Project of Beijing Institute of Technology (3040012241002). Jannick Rolland was supported by the NYSTAR Foundation (C050070).

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Modeling and characterization of the electrostatic coupling intra-body communication based on Mach-Zehnder electro-optical modulation

Abstract

1. Introduction

2. Modeling of IBC based on a Mach-Zehnder electro-optical modulator

2.1. Circuit model

2.2. Mathematical model

2.2.1. Modulation based on a bulk electro-optical crystal

2.2.2. Modulation based on a Mach-Zehnder electro-optical modulator

2.2.3. Influence factors

2.2.3.1. The frequency response of the Mach-Zehnder electro-optical modulation

2.2.3.2. Temperature

2.2.4. The complete mathematical model

3. Experiments

3.1. Frequency response

3.2. Temperature characteristic

4. Conclusion

Acknowledgment

References and links

Cited By

Figures (11)

Equations (13)

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