Taoran Le

Inkjet Catalyst Printing and Electroless Copper Deposition for Low-Cost Patterned Microwave Passive Devices on Paper

A scalable, low-cost process for fabricating copper-based microwave components on flexible, paper-based substrates is demonstrated. An inkjet printer is used to deposit a catalyst-bearing solution (tailored for such printing) in a desired pattern on commercially-available, recyclable, non-toxic (Teslin®) paper. The catalystbearing paper is then immersed in an aqueous copper-bearing solution to allow for electroless deposition of a compact and conformal layer of copper in the inkjet-derived pattern. Meander monopole antennas comprised of such electroless-deposited copper patterns on paper exhibited comparable performance as for antennas synthesized via inkjet printing of a commercially-available silver nanoparticle ink. However, the solution-based patterning and electroless copper deposition process avoids nozzle-clogging problems and costs associated with noble metal particle-based inks. This process yields compact conductive copper layers without appreciable oxidation and without the need for an elevated temperature, post-deposition thermal treatment commonly required for noble metal particle-based ink processes. This low-cost copper patterning process is readily scalable on virtually any substrate and may be used to generate a variety of copper-based microwave devices on flexible, paper-based substrates.

Additively Manufactured Nanotechnology and Origami-Enabled Flexible Microwave Electronics

Inkjet printing on flexible paper and additive manufacturing technologies (AMT) are introduced for the sustainable ultra-low-cost fabrication of flexible radio frequency (RF)/microwave electronics and sensors. This paper covers examples of state-of-the-art integrated wireless sensor modules on paper or flexible polymers and shows numerous inkjet-printed passives, sensors, origami, and microfluidics topologies. It also demonstrates additively manufactured antennas that could potentially set the foundation for the truly convergent wireless sensor ad-hoc networks of the future with enhanced cognitive intelligence and “zero-power” operability through ambient energy harvesting and wireless power transfer. The paper also discusses the major challenges for the realization of inkjet-printed/3-D printed high-complexity flexible modules as well as future directions in the area of environmentally-friendly “Green”) RF electronics and “Smart-House” conformal sensors.

Inkjet-printed graphene-based wireless gas sensor modules

In this paper we demonstrate the use of graphene as the basis for design and development of low-cost, self-powered, battery-less, wireless sensor solutions utilizing thin films produced from environmentally friendly, water-based, inkjet printed graphene oxide (GO) ink. The in-house developed novel sensor material demonstrates good response to ammonia gas (NH3), yielding a 6% normalized resistance change within 15 minutes of exposure to a concentration of 500 ppm. In addition, excellent recovery time is achieved using the RGO thin films, with over 30% of material recovery observed within 5 minutes without exposure to high temperature or any UV treatments. Finally, we present in this work important distinctive characteristics in the behavior of the RGO sensor when exposed to different types of gases, including the hard-to-detect CO gas, that can be exploited in order to further enhance the applicability of the material. The introduction of mass producible, stable, environmentally friendly, inkjet-printable GO on organic paper/kapton substrates lays the foundation for the development of a wide range of new low-cost, high performance graphene-based devices, such as inkjet-printed diodes, capacitors and transistors.

Infill-Dependent 3-D-Printed Material Based on NinjaFlex Filament for Antenna Applications

This letter presents one of the first examples of the exploitation of 3-D printing in the fabrication of microwave components and antennas. Additive manufacturing represents an enabling technology for a wide range of electronic devices, thanks to its inherent features of fast prototyping, the reasonable accuracy, fully 3-D topologies, and the low fabrication cost. A novel 3-D printable flexible filament, based on NinjaFlex, has been adopted for manufacturing the substrate of a 3-D printed patch antenna. NinjaFlex is a recently introduced material with extraordinary features in terms of mechanical strain, flexibility, and printability. Initially, the electrical properties of this material are investigated at 2.4 GHz using the ring resonator technique. The capability of selectively changing the dielectric constant by modifying the printed material density by fine-tuning printing infill percentage is verified experimentally. Subsequently, a square patch antenna is prototyped through 3-D printing and measured to validate the manufacturing technology. Finally, exploiting mechanical flexibility properties of NinjaFlex, the antenna is tested under different bending conditions.

RFID-Based Sensors for Zero-Power Autonomous Wireless Sensor Networks

Radio frequency identification (RFID) technology has enabled a new class of low cost, wireless zero-power sensors, which open up applications in highly pervasive and distributed RFID-enabled sensing, which were previously not feasible with wired or battery powered wireless sensor nodes. This paper provides a review of RFID sensing techniques utilizing chip-based and chipless RFID principles, and presents a variety of implementations of RFID-based sensors, which can be used to detect strain, temperature, water quality, touch, and gas.

Only Skin Deep: Inkjet-Printed Zero-Power Sensors for Large-Scale RFID-Integrated Smart Skins

The ability to monitor and sense environmental conditions in real time over large areas is a difficult and expensive task, especially when it comes to monitoring in harsh environments. Whether it is monitoring suspension bridges that experience immense forces from storms and earthquakes for structural integrity, detecting noxious gases in manufacturing facilities, or making sure the vegetables on the supermarket shelf are still fresh and being kept at the correct temperature and humidity level, these sensors and sensor networks have the ability to greatly improve cognitive intelligence and knowledge of the environment around us, that is, as long as they come at the right price. Current methods for deploying large-scale sensor networks involve miles of cabling that source power and collect data, or battery operated wireless sensors, which pose a serious environmental risk with the disposal of billions of batteries every year. While these methods are necessary in some situations where real-time data or harsh environments prohibit manual monitoring of critical environment parameters, the cost, installation difficulty, and maintenance rarely justify their use over manual inspections and monitoring. This is where the concept of smart skins comes in. Smart skins are cognitive, intelligent skins that sense, wirelessly communicate, and, in the future, will be able to modify environmental parameters using simple passive RFID technology. These skins can be applied everywhere be it a shelf lining in a grocery store or the outside of a Boeing 787, all while maintaining an unobtrusive and lightweight form factor similar to the application of a decal sticker. Smart skins are zero-power devices meaning they scavenge their own energy using ambient electromagnetic, solar, thermal, mechanical, or RFID/Radar-based interrogation techniques. In short, smart skins could prove to be the ultimate sensing tool that could potentially allow for the mass implementation of perpetual wireless networks even in extremely rugged environments. The system overview of a conventional smart skin is shown in Figure 1, which shows a skin consisting of several types of sensors that can be uniquely identified in a sensing matrix, and an interrogation network that is used to poll/interrogate the sensors and relay the data back to a processing hub. This allows realtime knowledge of various sensed parameters, such as the stress gradients due to trucks passing over bridges, or of the propagation rate of a gas leak or fire within a building. The smart skin concept can also be extended to that of body-wearable skins for continuous monitoring and reporting of critical biosignals utilizing novel liquid antenna principles. Biocompatibility and wearability requirements further push the need for autonomous, self-powering sensors.

Wireless sensing with smart skins

The ever-increasing need for perpetual ubiquitous cognition of our environment prompts the integration of numerous unobtrusive, extremely low-cost and passively powered wireless sensors into our surroundings. Smart skins, i.e. thin layers of modified materials on top of surfaces that surround our every-day lives, constitute ideal such sensor candidates for the ubiquitous awareness vision. In this paper we are presenting three different types of highly sensitive smart skin sensors for identity and genuineness authentication and seal proof, large metallic structural strain and crack detection and chemical gas sensing of ammonia and nitrogen dioxide. These low-profile smart skin prototypes share not only all the aforementioned desired characteristics but also exhibit high levels of accuracy and reliability in a flexible and rugged design.

A novel strain sensor based on 3D printing technology and 3D antenna design

The additive manufacturing technique of 3D printing has become increasingly popular for time-consuming and complex designs. Due to the special mechanical properties of commercial NinjaFlex filament [1] and in-house-made electrically conductive adhesives (ECAs) [2], there is great potential for the 3D printed RF applications, such as strain sensors and flexible, wearable RF devices. This paper presents the flexible 3D printed strain sensor, as a 3D dipole antenna of ECA stretchable conductor on 3D printed Ninjaflex filament.

Graphene enhanced wireless sensors

In this paper we demonstrate the design and development of a family of low-cost, self-powered, wireless sensor solutions utilizing both analog and digital principles. The sensors will utilize Graphene-based thin films integrated directly into the structure. For an immediately deployable digital sensing solution compatible with current commercial technologies we will utilize the Intel WISP platform, which can be read with current COTS products. Our thin films are produced from water-based, inkjet printed graphene oxide (GO) on paper/Kapton, developed using both conventional thermal and laser reduction techniques. In addition to reporting the first ever integration of inkjet-printed water soluble GO inks into low cost, flexible RF electronics, we also bring gas sensing capabilities to RFID tags relying on purely wireless digital transmission. The introduction of low cost, mass producible, eco-friendly, reduced graphene oxide (RGO) films on paper substrates lays the foundation for the development of a wide range of new low-cost, high performance Graphene-based electronic devices.

A novel, facile, layer-by-layer substrate surface modification for the fabrication of all-inkjet-printed flexible electronic devices on Kapton

A facile, environmentally-friendly, low-cost, and scalable deposition process has been developed and automated to apply polyelectrolyte multilayers (PEMs) on flexible Kapton HN substrates. Two weak polyelectrolytes, poly(acrylic acid) and polyethylenimine, were deposited in an alternating, layer-by-layer fashion under controlled pH and ionic strength. Compared to strong polyelectrolytes, weak electrolytes can control the properties of the PEMs more systmatically and simply. To our knowledge, this work on surface modification of Kapton is not only the first to use only weak polyelectrolytes, but is also the first to take advantage of the surface properties of calcium-bearing additive particles present in Kapton HN. The resulting surface-modified Kapton HN substrate allowed for the inkjet printing of water-based graphene oxide (GO) inks and organic solvent-based inks with good adhesion and with desired printability. While the deposition of a single PEM layer on a Kapton substrate significantly reduced the water contact angle and allowed for the inkjet-printing of GO inks, the deposition of additional PEM layers was required to maintain the adhesion during post-printing chemical treatments. As a conceptual demonstration of the general applicability of this PEM surface modification approach, a flexible, robust, single-layered gas sensor prototype was fully inkjet printed with both water- and ethanol-based inks and tested for its sensitivity to diethyl ethylphosphonate (DEEP), a simulant for G-series nerve agents. The electrical conductivity and morphology of the sensor were found to be insensitive to repeated bending around a 1 cm radius.