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This paper demonstrates the first-of-its-kind additively manufactured microfluidics-based flexible RF sensor, combining microfluidics, inkjet-printing technology, and soft lithography, which could potentially enable the first “real-world” wearable “smart skin” applications. A low-cost, rapid, low-temperature, and zero-waste fabrication process is introduced, which can be used to realize complex microfluidic channel networks with virtually any type of sensing element embedded. For proof-of-concept purposes, a reusable and flexible microfluidics sensor was prototyped using this process, which only requires 0.6- \mu \text L fluid volume to produce a 44% frequency shift between an empty ( \epsilon r=1 ) and a water-filled channel ( \epsilon r=73 ), demonstrating a sensitivity that is higher than most previously reported microfluidics-based microwave sensors. Seven different fluids were used to measure the sensitivity of the prototype and an overall sensitivity of 24\%/ \log (\epsilon r) was observed. The “peel-and-replace” capability of the presented sensor not only facilitates the cleaning process for sensor reusability, but it also enables sensitivity tunability. For bent/conformed configurations, the sensor’s functionality is good even for a bending radius down to 7 mm, demonstrating its great flexibility. After bending multiple times, the sensor still exhibits a very good performance repeatability, which verifies its reusability feature. The introduced additively manufactured RF microfluidics-based sensor would be well suited for numerous wearable and conformal fluid sensing applications (e.g., bodily fluids analyzing and food monitoring), while it could also be utilized in a variety of microfluidics-reconfigurable microwave components. [ABSTRACT FROM AUTHOR]

This letter presents two high-gain, multidirector Yagi-Uda antennas for use within the 24.5-GHz ISM band, realized through a multilayer, purely additive inkjet printing fabrication process on a flexible substrate. Multilayer material deposition is used to realize these 3-D antenna structures, including a fully printed 120- μm-thick dielectric substrate for microstrip-to-slotline feeding conversion. The antennas are fabricated, measured, and compared to simulated results showing good agreement and highlighting the reliable predictability of the printing process. An endfire realized gain of 8 dBi is achieved within the 24.5-GHz ISM band, presenting the highest-gain inkjet-printed antenna at this end of the millimeter-wave regime. The results of this work further demonstrate the feasibility of utilizing inkjet printing for low-cost, vertically integrated antenna structures for on-chip and on-package integration throughout the emerging field of high-frequency wireless electronics. [ABSTRACT FROM PUBLISHER]

This communication presents a new reconfigurable origami bifilar helical antenna. This antenna can change its operating frequencies by changing its height. Also, analytical equations for the design of such antennas are derived based on an equivalent model of a standard helical antenna. An origami bifilar helical antenna is designed and its performance is verified using simulations and measurements. [ABSTRACT FROM PUBLISHER]

In this paper, a review of recent improvements on inkjet-printed microfluidic-based tunable/sensing RF systems is reported. The devices, such as Radio Frequency IDentification (RFID) passive wireless tags, coplanar patch antennas, bandstop filters, and loop antennas, are all fabricated by combining the inkjet printing technology on photographic paper for metallization and bonding layers, and laser etching for cavities and channels manufacturing. A novelty is also introduced for the loop antennas where the photographic paper is replaced with a polymer based substrate [i.e., (Poly(methyl-methacrylate))], to reduce the substrate losses for the RF part and solve the issue of paper hydrophylia. Along this paper an evolution toward higher working frequencies and higher detecting performance is shown, demonstrating a sensitivity up to 0.5\%/\varepsilon r with at most 6\,\mu \text L of liquid in the channel. [ABSTRACT FROM PUBLISHER]

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. [ABSTRACT FROM PUBLISHER]

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. [ABSTRACT FROM PUBLISHER]

This paper introduces the first-of-its-kind wireless passive sensing platform combining radio frequency identification (RFID), microfluidics, and inkjet printing technology that enables remote fluid analysis and requires as little as 3 \muL of fluid. The demonstrated variable microfluidic capacitors, resonators, and RFID tags are fabricated using a novel rapid, low-cost, and low-temperature additive inkjet process, making them disposable. However, even with their disposable nature, the RF microfluidic devices exhibit repeatability and long-term reusability for accurately detecting water, various alcohols, and % content of water/alcohol mixtures down to 1% water in ethanol. While the main discussion is on fluid sensing, the demonstrated components can also be used in fluid-tunable RF applications. [ABSTRACT FROM AUTHOR]

A complete characterization of the inkjet printing process using metallic nanoparticle inks on a paper substrate for microwave frequencies up to 12.5 GHz as well as its application to low-cost, high gain and wideband antenna design are demonstrated in this work. Laser and heat sintering of metallic nanoparticles are compared on paper substrate for the first time which demonstrate immense cost and time benefits of laser sintering. The antennas fabricated using the characterized process include a Vivaldi for the UWB band which exhibits a significantly higher gain of up to 8 dBi as compared to the currently published inkjet printed antennas, and a novel slow-wave log periodic dipole array which employs a new miniaturization technique to show 20% width reduction. [ABSTRACT FROM PUBLISHER]

For the first time, high quality factor (Q), meander inductors are demonstrated utilizing inkjet-printing on organic paper substrates. Quality factors of up to 25, which is an order of magnitude greater than previous works, and inductance values of up to 8 nH are achieved. The high self-resonance frequency (SRF) of 8 GHz makes it possible for the inductors to be used in the 900 MHz and 2.4 GHz RFID bands, and in 5 GHz Wifi band. Furthermore, a study into the performance and miniaturization effects of inkjet-printing ferromagnetic nanomaterial onto the inductors shows increases in inductance of up to 5%. Applications for inkjet printed inductors include all-printed flexible and wearable filters, resonators, and microwave matching networks. [ABSTRACT FROM PUBLISHER]

Vertically-integrated metal-insulator-metal (MIM) capacitors on silicon are demonstrated for the first time utilizing an entirely additive RF-specific inkjet-printing process. The inkjet-printed MIM capacitors demonstrate a high capacitance per unit area of up to 33 pF/mm^2 by utilizing novel dielectric inks, while achieving quality factors (Q) up to 25 and self-resonant frequencies (SRFs) above 1 GHz. Measurements of dielectric permittivity, leakage current, voltage breakdown, and fabrication repeatability are presented confirming the high-performance operation of the printed MIM capacitors. [ABSTRACT FROM PUBLISHER]

Flexible multi-layer inkjet printed capacitors that have a self resonant frequency above 3 GHz are demonstrated for the first time utilizing two custom formulated polymer-based dielectric inks. The formulation and characterization of both dielectric inks for optimal viscosity and film thickness are performed. The frequency dependent capacitance and quality factor (Q) are presented along with a study on the repeatability and measures to improve the quality factor of printed passives. [ABSTRACT FROM PUBLISHER]