A study of a one-turn circular patch antenna array and the influence of the human body on the characteristics of the antenna

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nA Study of a One-turn Circular Patch Antenna Array and the Influence of the Human Body on the Characteristics of the Antenna Yang Li , Licheng Yang , Meng Gao , Xiaonan Zhao , Xin Zhang PII: DOI: Reference:

S1570-8705(19)30967-9 https://doi.org/10.1016/j.adhoc.2019.102059 ADHOC 102059

To appear in:

Ad Hoc Networks

Received date: Revised date: Accepted date:

6 November 2019 29 November 2019 6 December 2019

Please cite this article as: Yang Li , Licheng Yang , Meng Gao , Xiaonan Zhao , Xin Zhang , nA Study of a One-turn Circular Patch Antenna Array and the Influence of the Human Body on the Characteristics of the Antenna, Ad Hoc Networks (2019), doi: https://doi.org/10.1016/j.adhoc.2019.102059

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A Study of a One-turn Circular Patch Antenna Array and the Influence of the Human Body on the Characteristics of the Antenna Yang Li1,2, Licheng Yang1,2, Meng Gao1,2, Xiaonan Zhao1,2，and Xin Zhang1,2 1

Tianjin Key Laboratory of Wireless Mobile Communications and Power Transmission, Tianjin Normal University, Tianjin, 300387 China College of Electronic and Communication Engineering, Tianjin Normal University, Tianjin, 300387, China

2

Corresponding author: Yang Li (e-mail: [email protected]).

This work was supported by the Tianjin Higher Education Creative Team Funds Program; Tianjin Municipal Natural Science Foundation (No. 19JCQNJC01300; No. 18JCYBJC86400); Doctor Fund of Tianjin Normal University (No. 52XB1604).

ABSTRACT In this paper, an intelligent health monitoring system based on wireless body area network (WBAN) is considered, and a wearable one-turn circular patch antenna array designed for obese individuals is investigated. The purpose of this antenna array is to establish a good communication link between the human body and personal devices and to monitor the long-time health of these individuals. Thus, the far-field radiation pattern is considered an important indicator in the investigation and the omnidirectionality of a one-turn patch antenna array is pursued. In this research, first, the effect of the human body on a single patch antenna unit and a one-turn circular patch antenna array are explored. The arrangements of the patch antenna units in a one-turn antenna array are discussed. Then, an electromagnetic simulation is conducted mainly via the method of moment (MOM). The conclusions of the effect of the human body on a single antenna unit and antenna array are obtained. This study provides guidelines for the arrangement of wearable circular sensor antenna arrays. A method for the analysis of a cylinder antenna array is proposed as well. INDEX TERMS Wireless body area network, intelligent body health management, on-body wireless communication, wearable antenna array, circular antenna array, antenna arrangement

I.

INTRODUCTION

With an increasing demanding for long-term health monitoring and the development of wireless communication technology, the wireless body area network (WBAN) has been proposed for applications in intelligent health monitoring systems. Generally, a WBAN system contains three types of systems, namely, sensors, actuator and personal devices [1,2]. Through these three systems, we can monitor human health indicators, such as the heart rate, body temperature or blood pressure, and then process and store health data on personal devices, such as mobile phones [3]. Notably, the WBAN system uses wireless communication instead of traditional wired connection, which creates conditions for continuous or real-time health monitoring. Thus, we focus on the sensor antenna networks of the WBAN system which establish a good communication link between the human body and personal devices. There have been many studies regarding wireless body area network and sensor networks. In these researches, sensor networks are used to monitor a certain area, which are widely applied in the fields such as target detection [4,5], source localization [6,7] and direction estimation [8,9]. Q. Liang at University of Texas proposed a sparse sensor network constructed of a one-dimensional and multi-dimensional nested circular and cylindrical sensor network [10-12]. Therefore, in our opinion, it is appropriate to apply the sensor antenna networks to the field of intelligent

health monitoring. And the sensor antenna networks in this structure are more similar to the shape of human body. The One-turn Circular Patch Antenna array also can be wildly used in the network applications, such as ad hoc and wireless sensor network[13,14]. In this paper, the applications of wireless health sensor networks are mainly investigated. The wireless health sensor or wireless sensor network is regarded as the core of the intelligent health monitoring system. To ensure the effectiveness and reliability of the communication system and the stability of the users is the problem that wireless sensor networks need to solve. Because the sensor antenna transmits the information collected by health sensors. To improve the performance of the sensor antenna is critical. Thence we propose a kind of one-turn patch antenna array for wireless health sensors to achieve this goal. There are some researches on on-body antenna designs as well. A low-profile vertically polarized UWB antenna was pro- posed by Koohestan et al. [15]. And an attractive option for on-body communication antennas is the truncated conical dielectric resonator antenna(DRA) proposed by Almpanisetal et al. [16]. These on-body antennas with complex structures rise far above the surface of the body so that they are difficult to be integrated on the clothes. Therefore, the patch antenna with a simple mechanism and easy to integrate is used as a on-body wearable antenna in this research.

In our opinion, this circular antenna sensor network is especially designed for obese individuals. Because many obese individuals exhibit cylindrical shape and suffer from various chronic diseases, they have stronger needs for continuous health monitoring. And two different application scenarios of antenna sensor net-works are applied, such as monitoring of the vital signs of obese patients in the hospital or monitoring of the fitness indicators of obese individuals in their home. Mobile devices are playing increasingly important roles in our daily life. Some researches on the 5G-based sensor technologies and the green broadband communication system [17-19] are also focused. If the intelligent health monitoring system adopts 5G communication technology, users can directly use smartphones or other devices to receive health information from wireless sensors. In addition, 5 GHz is one of the central working frequencies of the 8011.ac WIFI standard. Health data can be directly transmitted to computers or other devices connected by wireless networks All health data are sent to the cloud for analysis and health warning. In this way, WBAN is combined closely with Internet of things technology and big data. Therefore, 5 GHz is chosen as the central operating frequencies of these antenna networks. In this research, a human body health monitoring system based on the WBAN is discussed. The purpose of this system is to monitor body area efficiently and persistently. Therefore, investigating the interaction between the human body and antenna unit or antenna array, especially at 5 GHz, is necessary. On this basis, the arrangements of patch antenna arrays are studied. The simulation results are carried out by the 3-D full-wave electromagnetic and computational life science simulation software FEKO, which is based on the method of moments (MOM). Our vision is to build a smart human health monitoring system that can monitor human health for a long time, which requires that the device does not restrict the user's normal activities. Due to the unpredictable position and movement of the user, the wireless sensor antenna worn by the user should have omnidirectional radiation to ensure the communication quality. Considering that most of the time a person's body is perpendicular to the ground and electromagnetic waves travel horizontally, the far-field gain pattern in the horizontal plane is a critical parameter of the patch antenna array. In this paper, the influence of human trunk on antenna and the impact of antenna elements arrangements on antenna array are studied. Two one-turn circular patch antenna arrays are proposed for different application scenarios. A method for the analysis of a cylinder antenna array is proposed as well. This manuscript is organized as follows. The numerical human trunk model and a single patch mode are introduced in Section 2. The effects of the human body on a single patch antenna unit are shown in Section 3. The influence of the human body on the one-turn circular patch antenna array and the characteristics of the on-turn circular patch antenna array are discussed in Section 4. Finally, the discoveries and results are summarized in Section 5. II. NUMERICAL HUMAN TRUNK MODEL AND A SINGLE

PATCH MODEL

As mentioned above, an intelligent health monitoring system designed for obese people is studied. Because the trunk shape of obese people is close to a cylinder, in this study, the trunk is simplified into a cylinder with a height of 500 mm and a radius of 180 mm. The human body tissue can be approximately equivalent to homogeneous muscle tissue [20,21]. Considering that the relative permittivity and the conductivity of the muscle tissue are variable at different frequencies, the linear interpolation method is used to calculate the dielectric constant at 4.7 GHz-5.3 GHz. The relative permittivity and the conductivity of the muscle are modeled as a function of frequency, as shown in Figure 1. And the relative permittivity and the conductivity data of muscle tissue at operating frequencies are proposed by [22]. FEKO software based on the MOM is used in this study. To improve the overall computational efficiency, the patch antenna and the trunk model are meshed with different accuracies. The patch antenna is subdivided into finer meshes. Each patch antenna is divided into 1126 units. The average length of tetrahedron is 1.809 mm. The human trunk model is subdivided into relatively fine meshes and is divided into 5356 units. The average length of each unit is set to 18.44 mm. According to the standard of WBAN (IEEE802.15.6), the dimension of a single antenna sensor is limited at approximately 1 cubic centimeter. Therefore, the microstrip patch antenna is suitable for a fundamental sensor antenna unit because of its small size and light weight. Furthermore, as a type of conformal antenna, a patch antenna can be easily attached to clothes to create a wearable antenna sensor network. And optimal design of circular patch antenna can be performed by convex or nonconvex optimization methods [23], [24]. Figure 2 shows the geometry of a single microstrip patch antenna unit. The patch antenna unit is composed of patch radiating element, substrate and GND board. The patch antenna unit adopts line excitation as a feeding model and a FR4 material (r= 3.5, tan = 0.017) as the substrate. Figure 3 shows the trunk model and the relative position between the trunk model and the antenna. The center of the trunk model coincides with the center of the coordinate axis. The patch antenna is placed vertically on the x-axis and is l away from the outer surface of the human body model. According to the following study, the value of l is set to 0 and 10 mm. The Gain of the single patch antenna can be evaluated as 𝑈(𝜃, 𝜑) 𝐺(𝜃, 𝜑) = 𝑃𝑖𝑛 /4𝜋 where 𝑈(𝜃, 𝜑) is the intensity of radiation from an antenna in one direction, Pin is input power.

52

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5

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3

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2 relative permittivity conductivity

1 0 0

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-6 -7 -8

|S11| [dB]

Conductivity σ [S/m]

Relative permittivity εr

0 -1

-9 -10 -11 -12 -13

1

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0 5.4

-15

l = 10 mm l=0 w/o human

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0

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Frequency [GHz] FIGURE 1. The relative permittivity and the conductivity of human muscle tissue. FIGURE 4. The reflection coefficient S11 of a single patch antenna in three cases: (1) l = 10 mm (2) l = 0 (3) without human.

z

z

patch

line excitation

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e y

z

y

x

y GND b

x

b

a

d c

l = 10 mm l=0 w/o human

substrate 0

a= 25 mm b= 6.1 mm c= 6.75 mm d= 12.5 mm e= 3 mm

Gain [dBi]

x

-10

-20

-30

a FIGURE 2. The geometry of a single patch antenna unit.

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φ [deg] FIGURE 5. The radiation pattern of a single patch antenna in three cases: (1) l = 10 mm (2) l = 0 (3) without human.

z

III. A SINGLE PATCH ANTENNA UNIT

h

x

y

l

patch antenna

d

h= 500 mm d= 360 mm l= 0,10 mm

human trunk model FIGURE 3. The trunk model and the relative position between the trunk model and the antenna.

The exploration of the influence of human body on a single patch antenna is the basis of this study. In this section, the influence of the human body on the impedance matching performance and the far-field performance of the patch antenna are discussed. It is considered that the patch antennas are either close to the human body or integrated into some clothes in practical applications. The distance between the antenna and the human model is set to 0 and 10 mm to simulate these two situations. The parameters of the antennas are compared with those of a single patch antenna without the influence of the human trunk. From the results of Figure 4, it is shown that in these three cases, the reflection coefficients of the patch antenna S11 are different. However, the trend of these three reflection coefficient curves is the same. The impedance matching performance is all good at nearly 5 GHz, which indicates that the human body affects the impedance matching effect of the antenna but does not change the resonant frequency of the antenna. From the point of view of practical application, the reflection coefficient of a single patch antenna S11

is -14 dB at 5 GHz without a human body. When the patch antenna is attached to the human body, the S11 increases to -10 dB at 5 GHz, resulting in a worsening of the impedance matching performance. When the patch is 10 mm away from the human body at 5 GHz, the reflection coefficient S11 will rapidly improve to -15 dB, which is slightly better than the case without the influence of the human body. Figure 5 shows the radiation pattern of a single patch antenna in these three cases. As shown in the figure, in the case of human body and without the human body, the maximum gain of the three cases approaches almost 5 dBi in the main lobe direction, and the single patch antenna obtains a maximum gain of 5.97 dBi when l = 10 mm. However, with the effect of the human body, the half-power bandwidth of the main lobe decreases. In the other directions, the human body rapidly affects the gain decrease. In summary, when designing a human health monitoring system, it is suggested that the influence of the human body on the operating frequency of the wearable antenna can be neglected, however, it is suggested that only the effect of human body on the impedance matching and radiation pattern of the wearable antenna are of concern. To obtain good impedance matching and radiation performance, a certain distance should exist between the human body and the wearable antenna. For example, in this study, the distance is set to 10 mm. For this reason, we propose to integrate patch antennas on a coat to obtain both wearable targets and good antenna performance. Furthermore, the relative permittivity of the human body is considerably high at 5 GHz, which leads to the loss of electromagnetic waves propagating in the human body. Hence, the gain of the antenna declines rapidly out of the main direction. Thus, to pursue the target of omnidirectional radiation, it is necessary to consider an antenna array composed of a certain number of antenna units instead of the radiation of a single antenna.

sition of the antenna unit. Comparing the models with and without the human trunks, under the condition that the human body's function is considered, it is found that the value of side lobe gain is increased, which is close to that of the main lobe. At the same time the lowest gain points are also increased, which causes an omnidirectional improvement in the antenna array in the far-field region. Figure 8 shows the radiation pattern of eight patch antennas with and without the influence of the human trunk model. It is shown that there are eight main lobes locating at  =0º, 45º, 90º, 135º, 180º, 225º, 270º and 315º, respectively, which are consistent with the position of the antenna unit. As the number of antennas increases from four to eight in one-turn, the maximum gain increases from 3 dBi to approximately 6 dBi, and the width of the main lobe becomes narrow. An increase in the lowest gain points causes an omnidirectional improvement in the antenna array in the far-field region. When the number of main lobes increase from eight to sixteen, the main lobes continued to become narrow and the omnidirectionality continued to improve. Figure 9 shows the radiation pattern of sixteen patch antennas in one-turn with and without the human trunk model. As shown in the figure, there are sixteen main lobes located at  = 0º, 22.5º, 45º, 67.5º, 90º, 112.5º, 135º, 157.5º, 180º, 202.5º, 225º, 247.5º, 270º, 292.5º, 315º and 337.5º, respectively, which are consistent with the position of the antenna unit. Compared to the case of eight antenna units in one turn,when the number of antenna units is increased to sixteen, z

z

z

x

x

y

y

x

y

IV. ONE-TURN CIRCULAR PATCH ANTENNA ARRAY

The effect of the human trunk on the patch antenna array and the arrangements of antenna units

To further study the influence of the human body on the antenna and for the sake of omnidirectionality, a one-turn circular antenna array is considered, and the distance between the antenna and human trunk model is set to 10 mm. Three different cases, four antennas in one-turn, eight antennas in one-turn and sixteen antennas in one-turn are discussed, as shown in Figure 6. The center of the trunk model coincides with the center of the coordinate axis. The one-turn circular patch antenna array is uniformly placed at the same distance apart on the XOY plane. In the case of four antenna units in one-turn, each antenna unit differs by 90º. In the case of eight antenna units in one-turn, each antenna unit differs by 45º. Each antenna unit differs by 22.5º in the case of sixteen patch antenna unit in one-turn. In these three cases, all patch antennas operate at 5 GHz. Figure 7 shows the radiation pattern of four patch antennas with and without the influence of the human trunk model. It is shown that there are four main lobes located at  = 0º, 90º, 180º and 270º, which are consistent with the po-

(c)

(b)

(a)

FIGURE 6. Three arrangements of one-turn circular patch antenna array: (a) four, (b) eight and (c) sixteen antennas in one-turn.

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FIGURE 7. The radiation pattern of four patch antennas in one-turn with

and without the influence of the human trunk model.

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In summary, because the human body reflects electromagnetic waves, the gain of the antenna array is boosted, especially at the lowest gain points, which render better omnidirectional performance in the far-field region than without the effect of human trunk. On this basis, the arrangements of the patch antenna unit in one-turn circular patch antenna array are discussed. The main lobes are formed in the direction of each antenna unit, and the number of main lobes coincides with the number of patch antenna units. Within a certain range of patch antenna unit numbers, in this study, there are less than eight, and the gain of the main lobe increases with an increase in the quantity of the single patch antenna units in a one-turn circular array. However, this increase is nonlinear and finite, which means that the maximum gain of a one-turn circular patch antenna array will not exceed the maximum gain of a single antenna. Furthermore, the bandwidth of the main lobes decreases with the gain of the main lobe. The gain of the main lobe is conserved with respect to its bandwidth. For the three cases in the study, as shown in Figure 10, the gain of main lobes in the case of the four antenna units in one-turn is lower than that in other two cases. The best gain performance can be obtained in the case of 16 antenna units in one turn, and the number of main lobes makes up for the narrow bandwidth of the main lobes. However, due to the large number of integrated antennas, it is inconvenient to wear this antenna array over a long time period. It is suggested that this antenna array should be used in fields, such as medical monitoring, that require high performance of antenna array and wearable systems that do not need to be worn for a long time. In the case of eight antennas, most of the gain of the lobes can reach 5 dBi, and the main lobe bandwidth is between the other two cases and is suitable for household use and the wearable systems that need to be worn for a long time. B.

FIGURE 9. The radiation pattern of sixteen patch antennas in one turn with and without the influence of the human trunk model.

the gain of the main lobes decreases slightly, and the side lobes are diminished greatly. This finding indicates that antenna units interfere with each other when numbers increase to sixteen. Under the condition that only the omnidirectionality in the far-field region is pursued, and at the same time the simplicity of the equipment is also required, it is recommended that a one-turn patch antenna array with 16 patch antennas meet the requirements. Considering that the gain of a single patch antenna used in this study is 5.97 dBi, the maximum gain of the one-turn antenna array is not improved compared with a single patch antenna. Furthermore, due to the limitation in the antenna size, in this study, 16 antenna units are the maximum number that can be integrated on a one-turn circular patch antenna array. Moreover, excessive wearable antennas integrated on clothing will reduce the user's wearing experience. Therefore, it is not realistic to continue to increase the number of antenna units. Therefore, we can conclude that the maximum gain of a one-turn circular patch antenna array will not exceed the maximum gain of a single antenna.

Discussion of the relative location between the patch antenna array and human trunk

In a previous discussion, an intelligent health monitoring system based on the wireless body area network (WBAN) are investigated. All results and conclusions are obtained when the antenna array is located at the middle of the human trunk model. To render the results and conclusions more general, it is critical to study the relationship between the antenna array performance and the relative position of the antenna array. For an intelligent health monitoring device, it is critical to find a suitable position that achieves the best performance of the patch antenna array. Figure 11 shows the relative position between the trunk model and the antenna array. The center of the trunk model coincides with the center of the coordinate axis. Each patch antenna unit in the antenna array is placed vertically on the x-axis and is 10 mm away from the outer surface of the human body model. Considering the symmetry of the human trunk model, it is only necessary to change the position of the antenna array in the positive direction of the z-axis. The distance between the antenna array and XOY plane is set as l. The value of l is set to 100 mm and 200 mm, to simulate situation of the antenna in the upper trunk and near the trunk

10

0

Gain [dBi]

edge, respectively, and to obtain more obvious results. The distance between the antenna array and XOY plane is set as l. The value of l is set to 100 mm and 200 mm, to simulate situation of the antenna in the upper trunk and near the trunk edge, respectively, and to obtain more obvious results. In the view of electromagnetism, 100mm is close to 2λ and 200 mm is close to 4λ. Figure 12 shows the radiation pattern for the cases of l=0 and l=100 mm. It is shown that in the case that one-turn circular patch antenna array is 100 mm away from the XOY plane, the numbers and positions of the lobes in the radiation pattern are almost the same as when the antenna array is placed on the XOY plane. The gain of patch antenna array is reduced by approximately 2 dBi at the interval of  = 12° to  =84°, and the gain is almost unchanged or slightly improved in other directions. On the whole, as the distance between patch antenna array and XOY plane is 100 mm, the gain is slightly increased，the lobe width is almost unchanged, and the lowest points of gain are improved.

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l=0mm l=100mm -20 0

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FIGURE 12. The radiation pattern of the different distances between the patch antenna array and XOY plane, l = 0 and l = 100 mm.

10 10

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Gain [dBi]

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φ [deg] FIGURE 10. The radiation pattern of the four, eight and sixteen patch antennas in one-turn.

z Location of patch antenna array x

l y

human trunk model FIGURE 11. The relative position between the patch antenna array and the human trunk model and the distance between the antenna array and XOY plane, l = 0, 100 mm and 200 mm.

FIGURE 13. The radiation pattern of different distances between the patch antenna array and XOY plane, l = 0 and l = 200 mm.

Figure 13 shows the radiation pattern of the cases of l = 0 and l = 200 mm. As shown in Figure 13, when l = 200 mm, the number of lobes and the position of the lobes are almost unchanged compared to the case in l = 0. The gain of the patch antenna array is improved largely as l = 200 mm, and the maximum gain points reach 8~9 dBi. In addition, the lowest gain points are increased as well. It can be concluded that a one-turn circular patch antenna array can obtain higher gain and better omnidirectionality when it is placed at the edge of the human trunk. In this discussion, it is found that the closer the antenna array is to the edge of the human body trunk, the smaller obstruction from the human body is, and the higher the gain is and better the omnidirectionality is. However, in reality, this is not the case. This study only discusses the impact of the human trunk on the patch antenna array, but in fact, the human body is an inseparable whole. Above the trunk are the neck and head, and below the trunk are the legs. First, the antenna array cannot be placed on the legs to avoid affecting the wearer‟s normal actions. When the antenna array is placed on the upper part of the trunk, even if the antenna array is placed at the edge of the human trunk, the antenna

array will still be affected by the head and neck, that is, the antenna cannot be placed at the edge of the human body, so the above discussion is difficult in practical applications. However, in realistic applications, it is recommended that the antenna should be placed on the upper part of the human body, such as the chest, for better antenna performance. At the same time, the conclusion that the one-turn circular patch antenna array cannot obtain a higher gain than a single antenna gain is still true.

C. The analysis of results and discovery In this study, a patch antenna is used as the radiation element of the one-turn circular patch antenna array. And in our previous research, a dipole is studied as the radiation element [25]. Comparing these two antennas, the patch antenna is more suitable for applications of on-body antenna arrays. Because the patch antenna has better orientation and higher gain in the main direction of radiation. And the conformal characteristic makes it easier to be applied into a wearable antenna. In the view of the human impact, more electromagnetic waves radiated by the dipole are reflected and absorbed by the human trunk because of its omnidirectionality. With the increase of the numbers of antenna units, the effect will be more obvious. Therefore, in the view of human health, using a patch antenna as the radiation element is more rational. A simple uniform cylinder is used as a numerical human trunk model in this research. In fact, the shape of the human trunk is more similar to an uneven elliptical cylinder. Using an even cylinder is aimed to simplify the analysis. And a numerical model closer to the actual shape of the human trunk will be used to arrive at more accurate conclusions in future research. Furthermore, considering that the limbs can also be approximated as cylinder, the results in this study are applicable for the arrangement of antennas around the limbs. Additionally, a concrete application will be discussed in future research, for example, a wristband for an intelligent health monitoring system. In the previous discussion, it was found that using a one-turn circular patch antenna array instead of a single patch antenna can obtain a better omnidirectionality performance. However, in this case, it is difficult to obtain a higher gain than when using a single patch antenna unit. The cylinder patch antenna array solves this problem, and a method for analyzing cylindrical antenna arrays is proposed. In this method, a cylinder patch antenna array is composed of several linear patch antenna arrays arranged along the z-axis. The antenna elements of the linear patch antenna array realize the superposition of the field intensity through an effective arrangement and achieve a higher gain. Then, the effect of the linear array can be equivalent to a single antenna unit, that is, each linear array is read as a special single antenna. Then, the cylindrical array formed by the linear array can be equivalent to a special one-turn circular antenna array. The characteristic of the special one-turn circular patch antenna array is consistent with the results obtained in this study. The research on cylindrical array will be further discussed in future research.

V. CONCLUSION

In this study, a wearable one-turn circular antenna array is studied for an intelligent health monitoring system based on the WBAN. A cylinder is used as an approximation for s numerical human trunk model. The effect of the human body on a single patch antenna and on a one-turn circular patch antenna array is investigated. Three cases of patch antenna units arranged in one-turn patch antenna arrays are discussed. The results are obtained using the electromagnetic simulation software FEKO. In the research, the effect of the human body on the antenna is carefully considered. The results show that the influence of the human body on the operating frequency of the wearable antenna unit can be neglected when only impedance matching is concerned. The effect of the human body is mainly reflected in the human body hindering the electromagnetic wave propagation and the human body reflecting the electromagnetic wave. Due to the obstruction of the human body to the electromagnetic waves, electromagnetic waves cannot propagate through the human body. The gain of antenna in other directions is quite low. Therefore, the antenna array must be used to boost the omnidirectionality of the device. At the same time, some electromagnetic waves are reflected by the human body, and the lowest gain point of the antenna array is improved, and a better omnidirectionality is obtained. For a uniform one-turn circular patch antenna array, the antenna array consists of a smaller number of antenna units, and in this study, there are less than eight. The maximum gain of the patch antenna array is actually lower than the gain of a patch single antenna unit. When the number of antenna units is increased from a small number to eight antenna units, the maximum gain of the antenna array increases. However, the maximum gain of the antenna array increases to the same value as the gain of a single antenna unit and cannot be improved, even if the number beyond eight. That is, by increasing the number of antenna units of the circular antenna array, a higher gain than a single antenna unit cannot be obtained. During the process of increasing the number of antenna units, the number of main lobes increases but the bandwidth becomes narrower. That is, the gain of the main lobe is conserved with respect to its bandwidth. The lowest point of the antenna gain continuously rises, and the omnidirectionality of the array antenna is improved. When pursuing a higher gain beyond a single patch antenna unit, it is recommended that the number of one-turn circular patch antenna arrays along the z-axis be increased to create a cylinder antenna array, and a method of cylinder antenna array analysis is proposed.

Conflict of Interest Statement 1.All authors of this manuscript have directly participated in planning, execution, and analysis of this study. 2. The contents of this manuscript have not been copyrighted or published previously.

3. The contents of this manuscript are not now under consideration for publication elsewhere. 4. The contents of this manuscript will not be copyrighted, submitted, or published elsewhere. 5. There are no directly related manuscripts or abstracts, published or unpublished, by any authors of this manuscript. 6. This work was supported by the Tianjin Higher Education Creative Team Funds Program; Tianjin Municipal Natural Science Foundation (No.19JCQNJC01300; No. 18JCYBJC86400); Doctor Fund of Tianjin Normal University (No. 52XB1604).

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[14]

[15]

[16]

ACKNOWLEDGMENTS

This work was supported by the Tianjin Higher Education Creative Team Funds Program; Tianjin Municipal Natural Science Foundation (No.19JCQNJC01300; No. 18JCYBJC86400); Doctor Fund of Tianjin Normal University (No. 52XB1604). The authors would like to thank Professor Qiang Chen at Tohoku University for allowing us to use the computer with the electromagnetic software installed in his lab.

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Biography

YANG LI received the B.E. and M.E. degrees from the College of Information Technology and Science, Nankai University, Tianjin, in 2008 and 2012, respectively, and the Ph.D. degree from the Department of Engineering, Tohoku University, Sendai, in 2017. He is currently with the College of Electronic and Communication Engineering, Tianjin Normal University. His research interests include antenna design, EM-wave propagation, and sensor networks.

Licheng Yang is currently pursuing the bachelor‟s degree with the College of Electronic and Communication Engineering, Tianjin Normal University, Tianjin, China. He is participating in the Excellent Students ‟ Training Project and the Future Engineer‟s Training Project. His current research interests include wireless communication, electromagnetic wave propagation, and sensor networks.

Meng Gao is currently pursuing the bachelor‟s degree with the College of Electronic and Communication Engineering, Tianjin Normal University, Tianjin, China. She is participating in the

Excellent Students‟ Training Project and the Future Engineer‟s Training Project. Her current research interests include wireless communication, electromagnetic wave propagation, and sensor networks.

Xiaonan Zhao received the Ph.D. degree from Tianjin University, Tianjin, China, in 2015. He is currently with the Tianjin Key Laboratory of Wireless Mobile Communications and Power Transmission, Tianjin Normal University (TJNU), Tianjin. His research interests include wireless communication channel measurement and modeling.

Xin Zhang received the Ph.D. degrees from Technology, City University of Hong Kong, in 2013. He is currently a Lecturer in the College of Electronic and Communication Engineering, Tianjin Normal University.His main research interests are swarm intelligence, communication network optimization, evolutionary computation, and machine learning. He has published more than 15 technical papers on these subjects, including more than eight international journal papers.