**3. Antenna specifications for WCE**

Wireless capsule transmitting and receiving antennas belong to wireless communication unit. The transceiver in conjugation with an antenna was utilised. A bidirectional communication between the capsule and the external communication unit at recommended frequency for industrial, scientific and medical usage was established. Wireless capsule endoscopy transmitting antenna is for sending out the detected signal and receiving antenna receive the signal outside human body. The signal transmission efficiency of the antenna will directly decide the quality of the received real-images and rate of power consumption. Because a lossy dielectric material absorbs a number of waves and decreases the power of receiving signal, it presents strong negative effects on the microwave propagation (Johnson, & Guy, 1972). Therefore, some features to ideally possess are required. The WCE antenna should be less sensitive to human tissue influence. Enough bandwidth to transmit high resolution images and huge number of data is a requirement for antenna. Also, power saving and high data rate transmission can be obtained with enhancement of antenna efficiency.

In addition to the standard constraints in electronic design, a number of main challenges arise for systems that operate inside the human body. The size of the capsule endoscope system should be small because small-sized capsules are easier to swallow. Therefore, the foremost challenge is miniaturization to obtain an ingestible device (the volume should be smaller than endoscopy). The availability of small-scale devices can place severe constraints on a design, and the interconnection between them must be optimized. The size constraints lead to another challenge, noise. The coexistence of digital integrated circuits, switching converters for the power supply, and communication circuits in close vicinity of the analog signal conditioning could result in a high level of noise affecting the input signal. Therefore, capsule designers must take great care when selecting and placing components, to optimize the isolation of the front end.

The next vital challenge is to reduce power consumption. In particular, the generated wireless signal must not interfere with standard hospital equipment but still be sufficiently robust to overcome external interferences. On the basis of Friis's formula, the total loss between transmitter and receiver increases with the distance between the transmitting and the receiving antennas increasing. As the result of the dispersive properties of human body materials, the transmitting power absorbed by body varies according to the antenna's operating frequency. The radiated field intensity inside and outside the torso or gut area is determined for FCC regulated medical and Industrial Scientific Medical (ISM) bands,

second-generation capsule, PillCam COLON2, was cleared by the European Union. The capsule has the ability to adjust the frame rate in real time to maximize colon tissue coverage. To present, Olympus is working on the development of a new generation capsule endoscope, which features magnetic propulsion. Apart from the novel propulsion and guidance system, the capsule designers aim to provide a drug delivery system, a body fluid sampling system and also the ultrasound scan capability. RF System Lab Company announced the design of the new Sayaka capsule (RF System Lab, 2010), which acquires images at a rate of 30 frames per second and generate about 870,000 over an eight hour period of operation. Also, further

Wireless capsule transmitting and receiving antennas belong to wireless communication unit. The transceiver in conjugation with an antenna was utilised. A bidirectional communication between the capsule and the external communication unit at recommended frequency for industrial, scientific and medical usage was established. Wireless capsule endoscopy transmitting antenna is for sending out the detected signal and receiving antenna receive the signal outside human body. The signal transmission efficiency of the antenna will directly decide the quality of the received real-images and rate of power consumption. Because a lossy dielectric material absorbs a number of waves and decreases the power of receiving signal, it presents strong negative effects on the microwave propagation (Johnson, & Guy, 1972). Therefore, some features to ideally possess are required. The WCE antenna should be less sensitive to human tissue influence. Enough bandwidth to transmit high resolution images and huge number of data is a requirement for antenna. Also, power saving and high data rate transmission can be obtained with enhancement of antenna

In addition to the standard constraints in electronic design, a number of main challenges arise for systems that operate inside the human body. The size of the capsule endoscope system should be small because small-sized capsules are easier to swallow. Therefore, the foremost challenge is miniaturization to obtain an ingestible device (the volume should be smaller than endoscopy). The availability of small-scale devices can place severe constraints on a design, and the interconnection between them must be optimized. The size constraints lead to another challenge, noise. The coexistence of digital integrated circuits, switching converters for the power supply, and communication circuits in close vicinity of the analog signal conditioning could result in a high level of noise affecting the input signal. Therefore, capsule designers must take great care when selecting and placing components, to optimize

The next vital challenge is to reduce power consumption. In particular, the generated wireless signal must not interfere with standard hospital equipment but still be sufficiently robust to overcome external interferences. On the basis of Friis's formula, the total loss between transmitter and receiver increases with the distance between the transmitting and the receiving antennas increasing. As the result of the dispersive properties of human body materials, the transmitting power absorbed by body varies according to the antenna's operating frequency. The radiated field intensity inside and outside the torso or gut area is determined for FCC regulated medical and Industrial Scientific Medical (ISM) bands,

applications of magnetic fields are presented (Lenaertes & puers, 2006).

**3. Antenna specifications for WCE** 

efficiency.

the isolation of the front end.

including the 402MHz to 405MHz for Medical Implant Communications Service (MICS), 608MHz to 614 MHz for Wireless Medical Telemetry Service (WMTS), and the 902MHz-928MHz ISM frequency band. Moreover FCC has allocated new bands at higher frequencies such as 1395MHz–1400 MHz wireless medical telemetry services (WMTS) band. Carefully selection of target frequency is important during the antenna design.

The effective data rate was estimated to be about 500 Kbps (Rasouli et al. 2010). The transmit power must be low enough to minimize interference with users of the same band while being strong enough to ensure a reliable link with the receiver module. Lower frequencies are used for ultrasound (100 kHz to 5 MHz) and inductive coupling (125 kHz to 20 MHz). The human body is no place for operational obscurity, so the control software must enforce specific rules to ensure that all devices operate as expected. For that reason, key programs must be developed in a low-level (often assembly) language. The last challenge concern encapsulating the circuitry in appropriate biocompatible materials is to protect the patient from potentially harmful substances and to protect the device from the GI's hostile environment. The encapsulation of contactless sensors (image, temperature, and so on) is relatively simple compared to the packaging of chemical sensors that need direct access to the GI fluids. Obtaining FDA (Food and Drug Administration) approval for the US market or CE (European Conformity) marking in Europe involves additional requirements. Capsules must undergo extensive material-toxicity and reliability tests to ensure that ingesting them causes no harm. The maximal data rate of this transmitter is limited by the RC time constant of the Rdata resistor and the capacitance seen at the base. It is clear that formal frequency higher than 1/(Rdata\*Cbase), the modulation index decreases, because the injected base current is shorted in the base capacitance. Although the occupied bandwidth decreases, the S/N ratio decreases too, and robust demodulation becomes more difficult at faster modulation rates. From experiments, the limit was found to be at 2Mbps [22]. Considering the sensitivity of small receivers for biotelemetry, the designed antenna should have a gain that exceeds −20 dB (Chi et al. 2007; Zhou et al. 2009).

### **4. Special consideration of body characteristics for antenna design**

The antenna designed for biomedical telemetry is based on the study of the materials and the propagation characteristics in the body. Because of the different environment, the wave radio propagation becomes different in free space. The human body consists of many tissues with different permittivity and conductivity, which leads to different dielectric properties.

The same radio wave propagating through different media may exhibit different features. From an electromagnetic point of view, materials can be classified as conductive, semi conductive or dielectric media. The electromagnetic properties of materials are normally functions of the frequency, so are the propagation characteristic. Loss tangent defined as the ratio of the imaginary to the real parts of the permittivity, which is equation (Kraus & Fleisch, 1999).

$$
tan\delta = \frac{\sigma}{\alpha \varepsilon} \tag{1}
$$

With the specific classification are given in (Kraus & Fleisch, 1999), the body material is dielectric material. The loss tangent is just a term in the bracket. The attenuation constant is actually proportional to the frequency if the loss tangent is fixed; where the attenuation constant is

$$a = a\sqrt{\mu\epsilon} \left[\frac{1}{2} \left(\sqrt{1 + \frac{\sigma^2}{\varepsilon^2 \omega^2}} \cdot 1\right)\right]^{1/2} \cdot \tag{2}$$

The dominant feature of radio wave propagation in media is that the attenuation increases with the frequency. With the formula

$$
\gamma = \sqrt{j\alpha\mu(\sigma + j\alpha\epsilon)}\tag{3}
$$

$$E = E\_0 e^{j\alpha t - \mathcal{V}z} \Big|\_{\alpha} \tag{4}$$

$$
\Delta H = \frac{\dot{j}}{\alpha \mu} \nabla \times \mathbf{E} \,, \tag{5}
$$

It can find out that the power of E plane and H plane reduce with high dielectric constant and conductivity. The total power is consumed easily in human body. The efficiency of antenna becomes lower than free space. With the formula

$$w = \frac{1}{\sqrt{\mu \varepsilon}} \text{ and } \beta = \alpha \sqrt{\mu \varepsilon} \left[ \frac{1}{2} \left( \sqrt{1 + \frac{\sigma^2}{\varepsilon^2 \alpha^2}} + 1 \right) \right]^{1/2} = \frac{2\pi}{\lambda},\tag{6}$$

in a high dielectric material, the electrical length of the antenna is elongated. Compare dipole antenna in the air and in the body material, they have same physical length but electrical lengths are not same. Because of the high permittivity, the antenna in the body material has longer electrical length. The time-averaged power density of an EM wave is

$$S\_{av} = \frac{1}{2} \sqrt{\frac{\varepsilon}{\mu}} E\_0^{(2)}\,'\,. \tag{7}$$

which leads to high power density in human body. The intrinsic impedance of the material and is determined by ratio of the electric field to the magnetic field (Huang & Boyle, 2008).

$$
\eta = \sqrt{\frac{j\alpha\mu}{\sigma + j\alpha\varepsilon}}\,\,.\tag{8}
$$

Based on wave equation *2 2 E - γ E=0* , A and B in the wave propagating trigonometric form *E = xAcos(ωt - βz)+ yBsin(ωt - βz)* can be determined. With the relationship of A and B, it can confirm shape of polarization.

The multi-layered human body characteristic can be simplified as one equivalent layer with dielectric constant of 56 and the conductivity of 0.8 (Kim & Rahmat-Samii, 2004). So, with the change from free space to body materials, dielectric constant changes from 1 to 56 and conductivity changes from 0 to 0.8. What's more, to detect the transmitted signal independent of transmitter a position, the antenna is required the omni-directional radiation pattern (Kim & Rahmat-Samii, 2004; Chirwa et al., 2003). To investigate the characteristics of antennas for capsule endoscope, the human body is considered as an averaged homogeneous medium as described by the Federal Communications Commission (FCC) and measured using a human phantom (Kwak et al., 2005; Haga et al., 2009).
