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In this paper, radio signal propagation characteristics for ultra wideband (UWB) signal is discussed in a wireless body area network (WBAN) context. The studied system approach considers on-body communications, which, however, is affected also by the in-body parts. Multipath signal components could propagate both on-body and in-body. Depending on the sensor node installations and the tissue types and volumes in the vicinity of them, radio signals propagate in the environment differently. Thus, tissues, and especially highly conductive implants underneath the skin could also contribute to on-body propagation characteristics. The following discussion is based on the research carried out at University of Oulu, Finland.

Wireless Capsule Endoscopy (WCE) application is a challenging topic inciting a good designed receiving antenna, in order to improve the wireless communication with the capsule endoscope. In this context, the paper introduces a compact antenna operating at the low Ultra-Wide band (UWB) 3.75–4.25 GHz, defined in IEEE 802.15.6 standard for BAN (Body Area Networks) applications. The proposed UWB antenna is targeted to on-body use, to serve of receiving antenna, and has a total size of 30×25×1.6 mm3. In free space, the antenna has a directional radiation pattern with 9 dB measured gain at 4 GHz center frequency, and it covers the - 10 dB impedance bandwidth of 3.75–4.45 GHz range. Then, the antenna was placed at different distances next to a voxel model, to consider the human body effect on the antenna characteristics. Besides, measurements were carried out on a male person by taking into account two antenna positions, named “Parallel” and “perpendicular”, on the human body surface. The proposed antenna does not present any risk on the person safety. The maximum SAR value is estimated of 0.095 W/kg for the different positions, in compliance with IEEE C95.3 standard on 10 g average tissue. The on-body matching studies were followed by in-body investigations, by analyzing the power consumption by means of power-field probes, from skin to the Small Intestine (SI) layers in voxel model. All the conducted studies conclude that the antenna, in both positions, is a good receiving antenna suitable for Wireless Capsule Endoscopy communications.

Wireless capsule endoscopy systems utilize a combination of hardware and software devices to ensure the healthcare of a human being. In praise of involved antennas in the overall medical system design, UWB (Ultra-Wideband) range occupies highest ranks in the literature. The low-band of UWB is regarded as the best frequency range, within the approved standards, to realize the better transmission of captured medical images by the capsule inside the SI tract, in terms of high resolution and low-path loss. A variety of passive capsules have been designed and made available in the literature, while the accurate design of the corresponding on-body antenna is lagging. For this purpose, this paper provides an extended study of a recently published on-body antenna operating at 3.75—4.25 GHz band. The measured antenna realizes good directivity of 5.78 dBi and 9.50 dBi towards the body without and with the cavity, respectively. The direction of the proposed on-body antenna beam is targeted to be mounted on the body surface. On-body simulations were run with CST Microwave Studio by involving an abdominal multi-layer model, and followed by navel and back areas of the voxel model to predict the antenna behavior close to different lossy body environments. Later, the antenna structure was measured next to a real human abdomen. Simulation results reveal that the proposed antenna with or without the cavity enables enhanced in-body communication when mounted on the abdomen with less path loss. This is supported by the low power totaling 20 dB at the SI (Small Intestine) tract. Furthermore, on-body measurements confirm the good antenna performance. Consequently, the planar compact antenna is regarded as a good on-body candidate for wireless capsule endoscopy systems.

This paper analyses the impact of the human body on antenna radiation characteristics, with a focus on the polarization aspect. The effect of the body tissues on a wrist-worn ultra-wideband double loop antenna radiation characteristics is investigated at 3, 4 and 5 GHz, based on numerical full-wave simulations complemented with a voxel model of a hand. Results show a strong influence of the body on the gain and polarization characteristics; the radiation in the direction towards the body is suppressed by 20 dB or more, and the antenna polarization changes from a linear to an elliptical one. By simulating an off-body communications scenario with the user walking at a fixed distance from the off-body antenna, up to 6.5 dB lower received power is obtained by using the wearable antenna radiation pattern simulated with the hand phantom, compared to the case when the antenna in free space.

The paper presents a novel antenna operating at the lower UWB band (3.75–4.25 GHz), defined originally in IEEE 802.15.6 standard for Body Area Networks (BAN) applications. The proposed antenna is designed for biomedical application, wireless capsule endoscopy localization. In other words, the concerned application is dedicated to track a capsule, by means of an external device, swallowed by the patient to provide captured images of the Small Intestine (SI), essential part of the GastroIntestinal (GI) tract, and transfer them in real-time to the external device. In this context, antenna with and without cavity-backed structures, are presented and compared with the requirements for a receiving antenna in terms of directivity and bandwidth coverage in question. It was revealed that the cavity approach improved the antenna gain up to 8 dBi, at the 4 GHz center frequency, compared to 6 dBi without the cavity presence. Simulations were carried out using CST Microwave Studio, and the results were validated by measurements in proximity to human body. The antenna safety issue was assessed with CST SAR (Specific Absorption Rate) calculation, in compliance with IEEE/IEC 62704-1 standard. Results showed a maximum SAR of 0.112 W/kg and 0.005 W/kg at 4 mm and 30 mm antenna-skin distance, in the range of the SAR limit guidelines defined by safety standards. The cavity-backed antenna ability to penetrate the human tissues, to reach the small intestine layer was studied by means of CST voxel model and compared to a multi-layer model emulating the dielectric properties of the human tissues at 4 GHz. This analysis was conducted using power flow results and completed by the power field probes at the several tissue interfaces.

This paper presents a comprehensive study on the impact of the sternotomy wires on the characteristics of ultra wideband (UWB) radio propagation channel in the human chest area. The study is conducted using two simulation models: a planar layer model and a three-dimensional elliptical layer model. The study includes antennas designed for on-body and in-body communications. Furthermore, the measured data and propagation path calculations are presented to verify the simulation results. The main purpose is to show how the steel wires affect the on-body channel characteristics and in-body propagation within the tissues when the monitoring antennas are located in close vicinity of the human body. The study is conducted by evaluating: 1) channel characteristics in both frequency and time domains; 2) 2D power flow figures; and 3) Poynting vector values. Furthermore, the impact of the fat layer thickness on the visibility of sternotomy wires is studied. Moreover, the impact of sternotomy wires is studied for the case of the recently operated patient, for which the sternotomy wires are on the sternum bone surface, as well as for the case where the sternotomy wires are embedded into the sternum bone. It is found that sternotomy wires have a clear impact on the channel. The strength of the impact depends on the antenna types used by the monitoring devices, the thickness of the fat layer in the sternum area, and whether the sternotomy wires are on the sternum surface or whether they have already been embedded on the sternum as it happens with time.

A new antenna structure is presented in this paper. The antenna is operating at the Ultra-Wideband (UWB) band, 3.75—4.25 GHz, defined originally in Body Area Networks (BAN) part of IEEE 802.15.6 standard. The antenna size is 89 mm × 60 × 21 mm. The antenna is a directive with a measured gain of 8 dBi at 4 GHz center frequency. Since the proposed antenna is designed to meet the aspects of a receiving antenna for wireless capsule endoscopy localization, the antenna behavior in close proximity to a human body, in particular the small intestine area, is performed. For this end, initial on-body simulations were carried out by means of a tissue-layer model emulating the dielectric properties of the human body tissues at 4 GHz center frequency. This was followed by voxel model investigations. The human body impact on the antenna characteristics was analyzed firstly, followed by the examination of the power flow propagation inside the tissues. These analyses are consistent to evaluate the antenna ability to communicate with a capsule placed at the small intestine. Later, the antenna free-space propagation was assessed and validated by measurements. These results are followed by a measured on-body investigation conducted on male and female persons. Simulation results were obtained by CST Microwave Studio. Results were confirmed by measurements, conducted in an anechoic chamber at University of Oulu, Finland. The results were measured in frequency domain and later post-processed to a time domain. Consequently, measured results converge to the simulation ones. It is concluded that, the antenna could be used for Wireless Capsule Endoscopy communications with UWB signaling complying with IEEE 802.15.6 standard.

A recent reflector-backed antenna model is proposed in this paper for wireless capsule endoscopy localization. The antenna is designed to operate at the lowest 802.15.6 mandatory UWB (ultrawideband) channel, i.e., 4 GHz center frequency with 500 MHz bandwidth. The antenna achieves a good directivity and radiates well over the frequency band of interest. The proposed antenna was constructed within three successive steps. Initially, a planar omnidirectional antenna was designed of 3.15 dBi gain at 4 GHz. Since the antenna aims to operate as a receiving antenna, good directivity is preferred. Thus, an air-filled cavity was included backing the planar antenna to bolster the directivity toward the radiating element. The cavity-backed antenna has a measured gain of 6.4 dBi. The antenna was evaluated next to the homogenous and multilayer models. Then, the antenna design was optimized, by reducing its size, to a reflector-backed antenna structure reaching a maximum gain of 5.3 dBi, which is still promising for the regarded application. The body effect on the antenna matching was evaluated by means of multilayer and voxel models simulating the human body. This was followed by on-body measurements involving real subject. The depth of in-body propagation, from skin to small intestine, was studied using the multilayer and voxel models. Simulations were run using the CST Microwave Studio tool. While prototyping, free-space and on-body measurements took place at University of Oulu, Finland.

The paper introduces a novel antenna operating in the UWB band 3.75–4.25 GHz for BAN (Body Area Networks) applications. The proposed antenna has omni-directional and directional radiation patterns in absence and presence of a backed air-filled cavity, respectively. The antenna was simulated using CST Microwave Studio software, showing maximum realized gains of 2.6 and 7.37 dB with and without the cavity, respectively. The designed antenna is planned to have the role of a receiving antenna for wireless capsule localization purposes. Therefore, an initial on-body study was required and detailed in this paper giving the focus on the small-intestine area, since it is the vital human body part of interest for capsule tracking and monitoring. An on-body scenario is presented using two antenna structures and compared with the free-space results. SAR (Specific Absorption Rate) is also investigated in compliance with IEEE/IEC 42704-1 standard. These initial studies prove that the antenna can be regarded a good candidate for WCE (Wireless Capsule Endoscopy) localization.

This paper presents a comprehensive simulation and measurement data based study on the UWB on-body radio channel characteristics on the human abdomen area. The main target is to evaluate channel characteristics with several different antenna location options using a recently published ultra wideband (UWB) antenna designed for inbody communications, e.g. for capsule endoscope localization. For the simulations, we use two voxel models and two layer models. Measurement data consists of channel data for seven volunteers having different body size and body composition. The simulation and measurement data is compared and the reason for the differences is discussed. Furthermore, it is shown that the on-body channel characteristics vary significantly depending on the body size and shape of the volunteer if the antenna separation distance is large. With smaller antenna distances, the difference is minor.

This paper presents measurements on dynamic off-body radio channels in an ultra wideband frequency range for wireless body area network communications focusing on the human body shadowing effect. Measurements were conducted in an anechoic chamber at a bandwidth of 2–8 GHz by using a vector network analyzer. The investigation was performed at several discrete frequencies. Two planar prototype antennas were utilized (dipole and double loop). Six on-body antenna locations were applied and one off-body site. At first, ten frequencies were examined at two links, and the path loss values and standard deviations were determined. Second, all the links were considered at three discrete frequencies. The mean path losses varied between 47.6–69.4 dB, at human-pole distances on the average of 2m. The maximum recorded value was 101.7 dB. No clear difference was noted between the antennas. The usage of dipole and double loop as a link antenna pair has no remarkable effect compared to the case when all the antennas are similar.

This paper gives an insight of an on-body study using Low-UWB (lowest mandatory UWB band of IEEE 802.15.6 standard) directive antennas. Investigations are first carried out by simulations with male and female voxel models with different antenna body separation distances. The antenna performance is assessed in close proximity to a human body in terms of return loss, impedance matching, directivity, realized gain and efficiencies. The on-body matching results were confirmed by measurement with different real persons. Later, a free-space propagation study was conducted to assess the far-field antenna performance and to serve as a reference for on-body studies. Finally, an on-body propagation study is presented for different antenna positions with different separation distances from the body.

In this paper, the impact of the sternotomy wires and aortic valve implant on the ultra wideband (UWB) channel characteristics is studied. The evaluations are performed by calculations, measurement data analysis, and power flow simulations. The aim is to show that implants, which consist of steel, titanium, and other highly conductive materials, do have clear effect on the signal propagation even inside the tissues. This impact should be taken into account when using in-body or onbody communications devices, such as capsule endoscopes, etc.

This letter reports the shadowing effects of a human body on dynamic ultrawideband on-body radio links. A vector network analyzer is used to sweep the 3–5-GHz frequency band in an anechoic chamber. The sweep time is set fast enough to fulfill the channel coherence time requirements. This enables the data analysis to be performed in time domain by examining the corresponding channel impulse responses. Five on-body locations are examined: right wrist (RW), left wrist with an antenna on the palm (LWA) or back side of the hand, left arm, and left ankle (LA). Two antenna types are applied: dipole and double loop. The path loss (PL) lies between 35.9 and 85.8 dB depending on the case. The double loop has, on the average, higher PL than the dipole. The LWA-RW and RW-LA links have the lowest and highest PLs, respectively. The amplitudes of the first arriving paths follow the inverse Gaussian distribution. The level crossing rate (LCR) and the average fade duration (AFD) show weaker performance for the double loop antennas compared to the dipoles. In general, the LWA-LA is the poorest link with respect to the LCR and the AFD.

This article presents path loss models for creeping waves propagation around a human body at ultra-wideband frequency of 2–8 GHz. The results are based on measurements in an anechoic chamber using a vector network analyzer. Three antenna types are used: prototype dipole and double loop antennas together with the commercial Skycross antenna. The antennas are attached horizontally at the chest level and the waist level at in total 12 locations. Path loss values are defined from the first arriving paths of the channel impulse responses. Path loss models are developed for upper and lower horizontal body levels separately and for all available channels when also the cross channels between the levels are considered. The path loss exponents vary between 9.2–12.7 being clearly a higher result than previously reported. The double loop antenna has the lowest exponents and the commercial antenna the highest ones. No clear difference can be noted between the body and waist levels or when observing all channels. The scattering term of the path loss can be modeled with the generalized extreme value and generalized Pareto distributions.