Zheyu Wang

Embroidered Conductive Fibers on Polymer Composite for Conformal Antennas

We provide a novel class of conformal antennas based on embroidered conductive metal-polymer fibers (E-fiber) on polymer-ceramic composites. This new technology offers attractive mechanical and RF performance when compared to traditional flat and rigid circuits and antennas. The proposed E-fiber components are consisted of high strength and flexible polymer fiber cores and conductive metallic coatings. They were fabricated using automatic embroidery process, followed by assembly with polydimethylsiloxane and rare-earth titanate ceramic composites. Such composite substrates were tape-casted, and capable of providing tunable dielectric constant from 3 to 12 with a low tanδ <; 10-2 up to GHz frequencies. Basic RF prototypes, such as transmission lines (TL), patch antennas, and antenna arrays were fabricated for experimental evaluation. Measurement of the prototypes were conducted and compared to their copper counterparts. The RF characteristics of the E-fiber TLs exhibited an insertion loss of only 0.03 dB/cm higher than copper TLs up to 4 GHz . Also, the E-fiber patch antenna and antenna array exhibited 0.3 dB and 0.6 dB lower gains, respectively, than their copper counterparts. When applied onto a cylindrical surface, both the E-fiber patch antenna and antenna array only suffered 1 dB loss in realized gain, which is quite remarkable when compared with traditional antennas.

Textile Antennas and Sensors for Body-Worn Applications

This letter presents novel body-worn antennas and medical sensors based on embroidered conductive polymer fibers (e-fibers) on textiles. This technology offers attractive mechanical and RF performance when compared to traditionally flat and rigid antennas and circuits. The e-fibers are composed of high-strength and flexible polymer cores that incorporate conductive metallic coatings. They are readily embroidered onto regular textiles and can also be laminated on to polymer dielectric substrates. The RF characteristics of the e-fiber textiles were evaluated using microstrip transmission line (TL) structures. They exhibited an insertion loss of only 0.07 dB/cm at 1 GHz and 0.15 dB/cm at 2 GHz. Prototype body-worn multiband/wideband antennas and medical sensor were constructed to demonstrate their efficiency and comparable performance to that of copper. All designs were fabricated with high precision and resolution down to 0.5 mm.

Embroidered Multiband Body-Worn Antenna for GSM/PCS/WLAN Communications

A novel textile-based body-worn antenna covering the Global System for Mobile Communications/personal communications services/wireless local-area network frequency bands is presented. This antenna was made of densely embroidered metal-coated polymer fibers (e-fibers). These e-fibers are 15 μm thick and consist of high strength, flexible polymer cores with conductive silver coatings, providing mechanical flexibility and low loss at radio frequencies. When measured in free space, the textile antenna showed comparable performance to its copper counterpart, having ~ 2 dBi realized gain at all three bands. This textile antenna was simulated and measured on a full body phantom to determine the bodys influence on antenna performance, including frequency detuning and pattern shadowing. The measured radiation pattern of the body-worn antenna matched well with simulation at various on-body locations for the three bands. Field measurements were also carried out by mounting the antenna onto the shoulder of a jacket, and using it to replace the one of a cell phone. We found that the communication quality using the body-worn textile antenna was equivalent to the best location of the original cell-phone antenna. Therefore, this textile-based antenna provided for a more reliable body-worn communication when mounted on the bodys shoulder.

Flexible textile antennas for body-worn communication

This paper presents an embroidered body-worn antenna using conductive fibers (E-fibers). The antennas conductive surfaces were fabricated using precise and automated embroidering techniques to produce fully flexible and conformal antenna elements attached to regular fabrics and clothing. These E-fiber antennas offer desirable mechanical properties without undermining electrical performance for body-worn, on-clothing applications at radio frequencies (RF). In this study, we used an embroidered asymmetric meandered flare (AMF) dipole antenna to validate the textile antennas performance. Its excellent RF performance was found comparable to conventional printed antennas. Therefore, these new E-fiber antennas may be integrated into scarves, handbags, shirts, coats or hand bands for convenient carefree health monitoring and wideband communications.

Pulmonary Edema Monitoring Sensor With Integrated Body-Area Network for Remote Medical Sensing

A wearable health monitoring sensor integrated with a body-area network is presented for the diagnosis of pulmonary edema. This sensor is composed of 17 electrodes with 16 ports in-between and is intended to be placed on the human chest to detect lung irregularities by measuring the lungs average dielectric permittivity in a non-invasive way. Specifically, the sensors active port is fed by a 40 MHz RF signal and its passive ports measure the corresponding amplitudes of the scattering parameters (S-parameters). The dielectric constant of the lung is then post-processed and expressed as a weighted sum of the S-parameters measured from each port. An important aspect of the sensor is the use of multiple electrodes which mitigates the effect of the outer layers (skin, fat and muscle) on the lungs permittivity. This allows for the characterization of deeper tissue layers. To validate the sensor, tissue-emulating gels were employed to mimic in-vivo tissues. Measurements of the lungs permittivity in both healthy and pulmonary edema states are carried out to validate the sensors efficacy. Using the proposed post processing technique, the calculated permittivity of the lung from the measured S-parameters demonstrated error less than 11% compared to the direct measured value. Concurrently, a medical sensing body-area network (MS-BAN) is also employed to provide for remote data transfer. Measured results via the MS-BAN are well matched to those obtained by direct measurement. Thus, the MS-BAN enables the proposed sensor with continuous and robust remote sensing capability.

High-Strength, Metalized Fibers for Conformal Load Bearing Antenna Applications

We propose the use of high strength, metal-coated Kevlar yarns to weave flexible, conformal, and load-bearing antennas for an emerging class of applications emphasizing multiple functionality. In particular, here we present a unified, quantitative analysis of multiple properties of conductors as load-bearing materials in stress-, weight-, and shape-critical applications (e.g., in aerial vehicles), suggesting advantageous electrical conductor configurations to be metal-coated, multi-filament, high strength fibers. We then describe the fabrication of highly conductive metal coated Kevlar yarns, their mechanical and electrical properties, and the weaving of a flexible, stretchable, volumetric spiral antenna. The high frequency response of the antenna is found to match that of a traditionally made antenna comprised of electroplated copper on a rigid ceramic (Rogers TMM4) substrate. At low frequencies, the relatively lower conductivity of the metal-coated kevlar yarn leads to higher resistive losses compared to the traditional electroplated copper. We discuss strategies for mitigating such losses, and other means of improvement. More broadly, the results described here suggest a novel direction for multi-functional antenna design and applications, enabled by the superior mechanical characteristics of the composite conducting fibers, and the flexible, conformable, woven antenna architectures they help achieve.

Multilayer printing of embroidered RF circuits on polymer composites

This paper presents embroidered conductive fibers (E-fiber) on polymer composites for conformal and light-weight RF circuits and antennas. A polydimethylsiloxane, namely PDMS, is adapted. Our earlier studies showed that it had a remarkable RF performance with a tangent loss of less 0.02 at RF frequencies. In this paper, an embroidered E-fiber microstrip line sample was fabricated with conductive fibers on a polymer substrate, and its RF characteristics were measured. The S-parameters were compared with those of copper microstrip lines. Measurements indicated that the insertion loss of the E-fiber microstrip line was only 0.04dB/cm higher than that of the copper. A multilayer microstrip line using similar fabrication techniques was also printed and measurements were conducted. All results clearly demonstrate the feasibility of the proposed embroidered conductive fiber technique for flexible and conformal RF applications.

Embroidered flexible RF electronics

We introduce a novel class of flexible Radio Frequency (RF) electronics composed of conductive fibers on polymer or fabric substrates. The proposed fiber conductors and polymer substrates provide excellent RF characteristics, including mechanical flexibility and conformality. Key to the improved conductivity is the increased stitching density of the employed conductive fibers, reaching >;70 stitches per cm2. Prototype flexible antennas and circuits were fabricated and validated for their RF performance. These were realized by embroidering them on organza fabrics or by integrating them on thin polymer substrates. Their RF performance was found comparable to their conventional copper counterparts. Because of their excellent RF performance and high level of flexibility, these embroidered antennas should lead to a new class of devices expected to provide high data rate, low profile, and reliable operation for RF applications.

Embroidered e-fiber-polymer composites for conformal and load bearing antennas

Conformal, light-weight, load bearing antennas are critical for high data rate communication at low frequencies in connection with next generation Unmanned Aerial Vehicles (UAVs). As UAVs are small in size (as small as 4ft) and radio communication takes place at long wavelengths, the entire UAV airframe must serve as an antenna at those frequencies. Therefore, conformal and load bearing Radio Frequency (RF) apertures are very much needed for high data rate communication. Similarly, weight is of importance for solar powered UAVs as it adversely impacts operational duration. Therefore, antennas constructed of light-weight materials are vital to such solar powered UAVs. Similar requirements apply to body-worn antennas [1] and small ground vehicles. As individuals move and operate in harsh environments, it is important for body-worn antennas to be flexible and well conformed to the body for uninterrupted communication.

Wi-Fi energy harvesting system using body-worn antennas

This paper presents the design of a body-worn ambient RF energy harvesting system. The proposed system harvests freely available RF energy in an office environment using the 2.45-GHz WLAN band and converts it to usable DC power. To capture sufficient ambient RF energy, multiple body-worn embroidered textile antennas are conformally woven into a daily garment. A RF-to-DC rectifier circuit is also designed and optimized for operation at the WLAN band. Experimental tests are carried out to evaluate the average DC power that can be harvested in an office environment where significant wireless data traffic exists. These measurements will demonstrate the capability of the proposed body-worn energy harvester in supplying low-power electronics.