Lanlin Zhang

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.

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.

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.

Experimental Validation of Frozen Modes Guided on Printed Coupled Transmission Lines

Previous work has theoretically demonstrated that nonreciprocal slow-wave modes, namely, “frozen modes,” can be supported on a pair of coupled transmission lines printed on a magnetic substrate. Small antennas have also been designed by exploiting these modes. However, to date, we have yet to demonstrate and observe their existence experimentally. To this end, we construct two printed prototypes comprised of several unit-cells and employ the “T-matrix method” to determine the dispersion properties by measuring the S-parameters of these finite periodic prototypes. The printed unit-cell is designed to exhibit a unique stationary inflection point in the dispersion diagram corresponding to a frozen mode with almost zero group velocity. Through careful measurements and calculations, the frozen mode is observed to propagate at a significantly slower speed (286 times slower) than the speed of light. Importantly, this extraction method can be applied to any other periodic layout to obtain related dispersion properties.

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.

GSM and Wi-Fi textile antenna for high data rate communications

This paper presents the performance of body-worn GSM and Wi-Fi textile antennas fabricated using embroidered conductive fibers (E-fibers). The textile antennas were fabricated onto regular fabrics using automated embroidering, coupled with high density stitching. These textile antennas offer desirable conformality and flexibility, without undermining electrical performance for body-worn high data rate communications at radio frequencies (RF). RF performance was measured both freestanding and on the human body. For the latter, the textile antennas were sewn onto a jacket and connected to GSM and Wi-Fi communication modules to evaluate their performance. These novel E-fiber textile antennas can be integrated into daily garments (shirts, coats, scarves, etc) for convenient wideband and high data rate communications.

Embroidered textile circuits for microwave devices

A novel class of embroidered electrical textiles suitable for flexible circuits and radio frequency (RF) devices is introduced. These textiles were functionalized using electrically conductive fibers (E-fibers). The E-fibers consist of uniform metal coatings on high-strength polymer core, delivering excellent mechanical and electrical performance. These E-fibers were automatically and precisely embroidered onto textiles to form a conductive surface. High stitching density and multi-strand E-fibers were critical to achieving high conductivity for the embroidered surface. In the past, we reported on the performance of E-fiber antennas. Here, we examine the performance of RF and antenna matching circuits.