Jimmy Hester

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.

Ambient RF Energy Harvesting From a Two-Way Talk Radio for Flexible Wearable Wireless Sensor Devices Utilizing Inkjet Printing Technologies

A complete design and additive fabrication process of flexible wearable radio-frequency (RF) energy harvesters for off-the-shelf 2 W two-way talk radios utilizing inkjet printing technology is discussed in this paper. As a result of numerous output dc power measurements of fabricated proof-of-concept prototypes, a maximum output power of 146.9 mW and 43.2 mW was achieved with an H-field and E-field harvester, respectively. Also, the effect of misalignment between receiver and hand-held radio on harvesting performance is discussed in detail. To verify their potential in real-world wearable autonomous RF modules, the operation of E- and H-field energy harvesters was verified by utilizing an LED and a microcontroller communication module under on-body and on-bottle conditions, and the effect of the energy harvesters on the performance of the harvested communication systems was inspected through received power measurements in an anechoic chamber.

Inkjet-Printed Flexible mm-Wave Van-Atta Reflectarrays: A Solution for Ultralong-Range Dense Multitag and Multisensing Chipless RFID Implementations for IoT Smart Skins

In this effort, the authors implement the first ultralong-range chipless sensing sticker, by providing more than an order of magnitude increase in reading range, compared with the state of the art. The theoretical advantages of the use of millimeter-wave frequencies for high-performance chipless radio-frequency identification (RFID) sensor implementations are first argued before both a new fully inkjet-printed flexible device, based on the Van-Atta reflectarray structure, as well as a new chipless RFID polarimetric interrogation, and time-frequency data-processing approach is then presented and implemented, for operation in the Ka-band. The array, fully inkjet printed on Kapton HN polyimide, was demonstrated as being robust to variations of interrogation angle (between ±70° from normal), as well as to bending. With its demonstrated range, in excess of 30 m, and its proven adequacy for dense multitag and multisensing implementations in indoor environments, the structure may set the foundation for the emergence of flexible printable low-cost sensing smart skins for the Internet of Things.

A Novel Solar and Electromagnetic Energy Harvesting System With a 3-D Printed Package for Energy Efficient Internet-of-Things Wireless Sensors

This paper discusses the design of a novel dual (solar + electromagnetic) energy harvesting powered communication system, which operates at 2.4 GHz ISM band, enabling the autonomous operation of a low power consumption power management circuit for a wireless sensor, while featuring a very good “cold start” capability. The proposed harvester consists of a dual port rectangular slot antenna, a 3-D printed package, a solar cell, an RF-dc converter, a power management unit (PMU), a microcontroller unit, and an RF transceiver. Each designed component was characterized through simulation and measurements. As a result, the antenna exhibited a performance satisfying the design goals in the frequency range of 2.4–2.5 GHz. Similarly, the designed miniaturized RF-dc conversion circuit generated a sufficient voltage and power to support the autonomous operation of the bq25504 PMU for RF input power levels as low as −12.6 and −15.6 dBm at the “cold start” and “hot start” condition, respectively. The experimental testing of the PMU utilizing the proposed hybrid energy harvester confirmed the reduction of the capacitor charging time by 40% and the reduction of the minimum required RF input power level by 50% compared with the one required for the individual RF and solar harvester under the room light irradiation condition of 334 lx.

Additively Manufactured RF Components and Modules: Toward Empowering the Birth of Cost-Efficient Dense and Ubiquitous IoT Implementations

In this review, the particular importance and associated opportunities of additively manufactured radiofrequency (RF) components and modules for Internet of Things (IoT) and millimeter-wave ubiquitous sensing applications is thoroughly discussed. First, the current advances and capabilities of additive manufacturing (AM) tools are presented. Then, completely printed chipless radio-frequency identification (RFID) systems, and their current capabilities and limitations are reported. The focus is then shifted toward more complex backscattering energy autonomous RF structures. For each of the essential components of these structures, that encompass energy harvesting and storage, backscattering front ends, passive components, interconnects, packaging, shape-chaging (4-D printed) topologies and sensing elements, current trends are described and representative stateof- the-art examples reported. Finally, the results of this analysis are used to argue for the unique appeal of AM RF components and systems toward empowering a technological revolution of costefficient dense and ubiquitous IoT implementations.

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.

Inkjet-printed Van-Atta reflectarray sensors: A new paradigm for long-range chipless low cost ubiquitous Smart Skin sensors of the Internet of Things

In this effort, the authors improve upon most of the limitations of state-of-the-art chipless sensing technologies, by introducing a novel, and demonstrably robust, platform and reading scheme for long-range, wireless sensing. This platform was built upon a fully-inkjet printed and flexible 30GHz square patch antenna Van-Atta reflect-array, which provides high RCS over a broad range of interrogation angles, with only a 10 dB decrease in RCS at ±70 degrees from boresight. Furthermore, the signal reflected by the structure is cross-polarized with respect to that of the impinging wave, providing high polarimetric detectability. For this first application, the device was fully inkjet-printed on a polyimide (Kapton) substrate, whose humidity-dependent permittivity was taken advantage of, associated with an appropriate high performance signal processing scheme, in order to provide the first long-range capable, fully-printed chipless flexible sensor to date.

A bio-enabled maximally mild layer-by-layer Kapton surface modification approach for the fabrication of all-inkjet-printed flexible electronic devices

A bio-enabled, environmentally-friendly, and maximally mild layer-by-layer approach has been developed to surface modify inherently hydrophobic Kapton HN substrates to allow for great printability of both water- and organic solvent-based inks thus facilitating the full-inkjet-printing of flexible electronic devices. Different from the traditional Kapton surface modification approaches which are structure-compromising and use harsh conditions to target, and oxidize and/or remove part of, the surface polyimide of Kapton, the present Kapton surface modification approach targeted the surface electric charges borne by its additive particles, and was not only the first to utilize environmentally-friendly clinical biomolecules to build up a thin film of protamine-heparin complex on Kapton, but also the first to be conducted under minimally destructive and maximally mild conditions. Besides, for electrically charged ink particles, the present surface modification method can enhance the uniformity of the inkjet-printed films by reducing the “coffee ring effect”. As a proof-of-concept demonstration, reduced graphene oxide-based gas sensors, which were flexible, ultra-lightweight, and miniature-sized, were fully-inkjet-printed on surface modified Kapton HN films and tested for their sensitivity to dimethyl methylphosphonate (a nerve agent simulant). Such fabricated sensors survived a Scotch-tape peel test and were found insensitive to repeated bending to a small 0.5 cm radius.

Inkjet-printed substrate integrated waveguides (SIW) with “drill-less” vias on paper substrates

In this paper, an inkjet-printed substrate integrated waveguide (SIW) on commercially available cellulose paper is implemented for the first time. Unlike traditional inkjet-printed SIWs, it does not require any etching process to form the conductive side walls and utilizes the porosity of the paper to get through-substrate conduction. The frequency response of the waveguide along with its performance under bending is discussed in this paper, verifying that such a structure would be particularly suitable for Quality of Life and Internet of Things applications.

RFID-Based Wireless Passive Sensors Utilizing Cork Materials

This paper presents the design of low-cost, conformal UHF antennas and RFID tags on two types of cork substrates: natural cork and agglomerate cork. Such RFID tags find an application in wine bottle and barrel identification, and in addition, they are suitable for numerous antenna-based sensing applications. This paper includes the high-frequency characterization of the selected cork substrates considering the anisotropic behavior of such materials. In addition, the variation of their permittivity values as a function of the humidity is also verified. As a proof-of-concept demonstration, three conformal RFID tags have been implemented on cork, and their performance has been evaluated using both a commercial Alien ALR8800 reader and an in-house measurement setup. The reading of all tags has been checked, and a satisfactory performance has been verified, with reading ranges spanning from 0.3 to 6 m. In addition, this paper discusses how inkjet printing can be applied to cork surfaces, and an RFID tag printed on cork is used as a humidity sensor. Its performance is tested under different humidity conditions, and a good range in excess of 3 m has been achieved, allied to a good sensitivity obtained with a shift of >5 dB in threshold power of the tag for different humid conditions.