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The advent of wearable and Internet of Things (IoT)‐connected technologies has enabled and brought to light the potential for a cornucopia of new health‐applied wearable devices. Given a dense implementation of RFID devices for medical and biomonitoring applications owing to the advent of the IoT, a proper way to simultaneously interrogate and gather useful information from an array of sensors is required. An attractive means to achieve this is through the employment of RADAR principles, specifically frequency‐modulated continuous wave. The use of additive manufacturing technologies–such as the commonly encountered inkjet‐printing technology or the popular forms of 3D printing approaches–enables, through their versatility, a surprising wealth of solutions to the limitations of the state‐of‐the‐art health wearables. This chapter presents new strategies enabling the powering of printed wearable systems using both legacy radio‐frequency wireless networks and upcoming 5G millimeter‐wave implementations.

A first-of-its-kind design methodology to realize thermally actuated origami-inspired multilayer Miura frequency selective surfaces (MLM-FSSs) using a polyester-based substrate is presented in this article that can change its frequency response according to the variation in its ambient temperature. In order to maintain the optimum interlayer distance between the two-layer Miura-FSS structures, a specialized low-loss origami-inspired spacer layer is introduced that preserves its desired overall frequency response during different folding configurations. It also features an unprecedented high mechanical strength, making it suitable for a wide range of terrestrial, outer-space, and biomedical applications. The frequency response and its relationship to kinematics of the proposed structure are also presented in detail, which gives a unique insight into the operation principles of such structures. The proposed structure features twice the bandwidth as compared to single-layer Miura-FSS, an excellent angle of incidence rejection, and is the first demonstration of a fully inkjet-printed MLM-FSS that is realized completely by a rigid heat-sensitive substrate as opposed to traditional cellulose-based Miura-FSSs that lack self-actuation mechanism as well as rigidity, which is a key attribute of most practical thick origami structures.

In this article, the particular importance of nanotechnology-enabled materials associated with additive manufacturing techniques for the realization of radio-frequency (RF) components and modules for Internet of Things (IoT) and millimeter-wave (mm-wave) applications is discussed.

This paper presents a novel 4D printed tunable frequency selective surface (FSS) utilizing a multi-layer mirror-stacked “Miura-ori” structure that can be applied in numerous mm-Wave, IoT, RFID, WSN, 5G, and smart city applications. The prototype was fabricated with fully additive hybrid (3D and inkjet) printing processes to realize a flexible two-layer substrate with conductive traces on both top and bottom. The proposed multi-layer/multi-material manufacturing process features very significant strength improvement over paper-based origami structures, while enabling the realization of increasingly complex “morphing” designs that would be otherwise difficult to fabricate using traditional paper-based substrates. The proof-of-concept prototype demonstrates great frequency tunability, angle of incidence (AoI) rejection, and significantly improved insertion loss performance over simpler single-layer Miura-based designs as well as an operability up to much higher mm-wave frequencies up to at least 28 GHz.

This paper presents a first-of-its-kind fully 3D-printed mm-wave reflectarray with one-shot deployability. It consists of an array of kirigami-inspired flat-foldable dielectric-based unit cells featuring an unprecedented reduction in volume as compared to its conventional counterparts. The prototype is fabricated with high-resolution stereolithography 3D printing together with flexible photosensitive resin. The outcome of this work demonstrates a low-cost, high-performance dielectric reflectarray design that can be folded to 1/3 of the full-scale volume which can be used for outer-space, 5G and various other terrestrial applications.

Significance Conventional reconfigurable electrical and radio frequency (RF) structures commonly used in applications involving real-time reconfigurability in response to fast varying operational scenarios require specialized substrates or complex electrical circuits. Origami-based RF reconfigurable components and modules offer a solution featuring unique properties. First, they enable reconfigurability over continuous-state ranges (as opposed to discrete states). Second, they do not require specialized mechanical support for multilayer frequency-selective surface structures. Moreover, deployable origami-based RF structures can achieve large surface reconfigurability ratios from folded to unfolded states. Finally, these structures allow for independent control of multiple figures of merit: bandwidth, frequency of operation, and angle of incidence., The tremendous increase in the number of components in typical electrical and communication modules requires low-cost, flexible and multifunctional sensing, energy harvesting, and communication modules that can readily reconfigure, depending on changes in their environment. Current subtractive manufacturing-based reconfigurable systems offer limited flexibility (limited finite number of discrete reconfiguration states) and have high fabrication cost and time requirements. Thus, this paper introduces an approach to solve the problem by combining additive manufacturing and origami principles to realize tunable electrical components that can be reconfigured over continuous-state ranges from folded (compact) to unfolded (large surface) configurations. Special “bridge-like” structures are introduced along the traces that increase their flexibility, thereby avoiding breakage during folding. These techniques allow creating truly flexible conductive traces that can maintain high conductivity even for large bending angles, further enhancing the states of reconfigurability. To demonstrate the idea, a Miura-Ori pattern is used to fabricate spatial filters—frequency-selective surfaces (FSSs) with dipole resonant elements placed along the fold lines. The electrical length of the dipole elements in these structures changes when the Miura-Ori is folded, which facilitates tunable frequency response for the proposed shape-reconfigurable FSS structure. Higher-order spatial filters are realized by creating multilayer Miura-FSS configurations, which further increase the overall bandwidth of the structure. Such multilayer Miura-FSS structures feature the unprecedented capability of on-the-fly reconfigurability to different specifications (multiple bands, broadband/narrowband bandwidth, wide angle of incidence rejection), requiring neither specialized substrates nor highly complex electronics, holding frames, or fabrication processes.

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 first-of-its-kind fully inkjet-printed tunable hybrid n-ripple Miura (n-RiM) frequency selective surface (FSS) is presented that combines the advantages of n-RiM FSS structures (i.e. ultra wideband frequency & bandwidth tunability) and traditional Miura-FSS (i.e. ability to form multilayer FSS structures without mechanical support). They also feature high angle of incidence rejection, making them suitable for wide range of terrestrial and outer-space wireless communication applications.

A first-of-its-kind design methodology to realize origami-inspired multi-layer frequency selective surfaces (FSS) with a thermally actuated smart shape-shifting spacer layer is presented. The spacer not only features low dielectric losses but can also change its shape to maintain optimum inter-layer distances as the Miura-FSS structure is folded to preserve desired frequency response. It also introduces unprecedented high mechanical strength making it suitable for wide range of applications. The proposed structure features twice as broad bandwidth as compared to single layer Miura-FSS and an excellent angle of incidence rejection.

This work outlines the first-of-its-kind integration of 3D and inkjet printing additive manufacturing processes for the realization of tunable origami structures. The outcome of this process demonstrated a tremendous structural strength improvement over paper-based origami structures, also featuring very good potential for more complicated origami-inspired designs. A mm-wave 4D tunable Miura-shaped frequency selective surface (FSS) is demonstrated using this process. This FSS shows both frequency and bandwidth tunability, and has excellent angle of incidence rejection.

A first-of-its-kind fully inkjet-printed electronically tunable active flexible frequency selective surface (FSS) using varactors with integrated on-package solar cells is presented in this paper. Each varactor is biased by a dedicated on-package inkjet-printed solar cell using a low-temperature fabrication process. The solar cell changes its output voltage with variation in light intensities that eventually leads to a change in capacitance of the varactor and overall frequency response of the FSS. The proposed design eliminates the use of labor intensive biasing network, bulky power supply and micro-controllers to tune the FSS frequency response. These structures presents an autonomous, ultra low cost on-package RF shielding mechanism for next-generation of system-on-chip packaging applications that can be tuned on-demand at different frequency bands by simple variation of incident light intensities. Thus making them useful for a wide range of terrestrial, outer-space and EMI shielding applications.

A state-of-the-art inkjet-printed tunable origami frequency selective surface (FSS) on cellulose paper is presented that can change its resonant frequency as well as its bandwidth by mechanically folding the structure. Special “bridge-like” structures are introduced alongside the conductive traces to increase their flexibility, thereby avoiding breakage during the folding or bending process. The structure also features a wide angle of incidence rejection capability that facilitates it usage to a wide range of applications ranging from smart skins, tunable radome design and reduction in radar cross section of antennas.

A state-of-the-art methodology for the realization of fully inkjet-printed tunable frequency selective surfaces using ripple-Miura (an origami) structure is presented. The dipoles are inkjet-printed along multiple foldlines of the ripple-Miura structure which facilitates systematic reduction in inter-element distance and an unprecedented transformation of the dipole elements into a ripple-shaped structure with folding. This results in substantial reduction in electrical length of the dipoles to realize wide range of resonant frequency and bandwidth tunability. The design also features an excellent anale of incidence rejection.

This paper presents a novel approach to realize 3D-printed flexible reconfigurable antennas, along with a proof-of-concept tunable bow-tie antenna inspired from Chinese origami fan. Stereolithography (SLA) printing, a low-cost high-performance additive manufacturing technique, is utilize to enable the easy fabrication of origami structure prototypes and the structure is metallized using a liquid metal alloy (LMA) to facilitate folding without breakages. The proposed bow-tie antenna features a frequency tuning range from 896 MHz to 992 MHz and bandwidth reconfigurability. This reconfigurable antenna can be applied to various dynamically changing scenarios such as wireless communications, collapsible/portable radars, wearable applications.

This work outlines the design, simulation, and fabrication of a millimeter-wave (mm-wave) frequency selective surface (FSS) integrated directly onto a 3D-printed die encapsulation. The cross-shaped slot FSS is designed to function as a bandpass filter centered at 77 GHz for on-package tunability. Stereolithography (SLA) 3D printing is used to fabricate encapsulations for silicon dies attached to a metallic QFN leadframe. Surface profilometry is used to assess the roughness of the SLA-printed surfaces, yielding roughness 25× lower than standard fused deposition modeling (FDM) 3D printing techniques. Finally, inkjet printing is used in a post-process fashion to fabricate the package-integrated FSS directly onto a 3D-printed die encapsulation as a proof-of-concept demonstration.

The first-of-its-kind origami antenna “tree” model is introduced in this paper, enabling the integration of multiple 3D antennas with a minimal interference and an on-demand reconfigurability of frequency, polarization and radiation pattern to optimize performance in dynamically changing environments. EGaIn, a liquid metal alloy(LMA) is used to switch between antennas and to enable flexible implementations. An origami structure, the zipper tube, coupled with Voronoi topology implementations is utilized as the scaffolding structure facilitating the mechanical tuning of the radiation pattern while minimizing storage requirements. The “tree” was fabricated by 3D printing, enabling on-demand fast-prototyping and low-cost manufacturing. A proof-of-concept two-antennas “tree” (zigzag/helical antenna) was presented, featuring a dual-band (3GHz/5GHz) operability and different polarizations (linear/circular) along with varying radiation patterns with “tree” compression. The “tree” can be applied to various dynamically changing scenaria such as wireless communications, collapsible/portable radars, satellite communications, while it can also realize numerous other reconfigurable RF components, such as filters, reflectors and shielding structures.

A state-of-the-art fully Inkjet-printed tunable frequency selective surface on cellulose paper is presented, which uses a Miura origami structure for an on-demand linear variation in inter-element distance and the effective length of the resonant dipole elements, resulting in an observable shift in the operational frequency of the structure. The dipole elements are placed on the foldlines along with special “bridge-like” structures to realize first-of-its-kind truly flexible conductive traces over sharp bends. Simulation and measurement results show that the Miura-FSS can be tuned to a wide range of frequencies and features a large angle of incidence rejection.

This publication provides an overview of additive manufacturing techniques including Inkjet, 3D and 4D printing methods. The strengths, opportunities and advantages of this array of manufacturing techniques are evaluated at different scales. We discuss first the applicability of additive manufacturing techniques at the device scale including the development of origami inspired tunable RF structures as well as the development of skin-like conformal, flexible systems for wireless/IoT, Smartag and smart city applications. We then discuss application at the package scale with on package printed antennas and functional packaging applications. Following this, there is a discussion of additive manufacturing techniques in applications at the die scale such as 3D printed interconnects. The paper is concluded with an outlook on future advancements at the component scale with the potential for fully printed passive components.

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.

This paper demonstrates a new approach to build 3D reconfigurable antennas at an extremely low cost and the first 3D printed reconfigurable helical antenna based on microfluidics and liquid metal alloy (LMA). With the fused deposition modeling (FDM) 3D printing technique, 3D microfluidic channel can be fabricated in a short production cycle cost-effectively. EGaIn, a non-toxic LMA, is filled into a 3D printed helix channel and form the helical antenna. As the gain of the antenna is determined by the number of turns of the helix which is controlled by the volume of LMA, the gain of the antenna can be tuned when needed. A more than 4 dB gain increase around 5 GHz is measured with the prototype when the number of turns of helix increases from 2 to 8 (0.2 mL LMA volume change), which demonstrates the reconfigurability of the proposed helical antenna.

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 SIW's, 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

This publication considers the use of a variety of additive manufacturing techniques in the development of wireless modules and sensors. The opportunities and advantages of these manufacturing techniques are explored from an application point of view. We discuss first the origami (4D-printed) structures which take advantage of the ability to alter the shape of the inkjet-printed conductive traces on the paper substrate to produce a reconfigurable behavior. Next, focus is shifted towards the use of additive manufacturing technology to develop skin-like flexible electrical system for wireless sensing applications. We then discuss the development of a fully flexible energy autonomous body area network for autonomous sensing applications, the system is fabricated using 3D and inkjet printing techniques. Finally, an integration of inkjet and 3D printing for the realization of efficient mm-wave 3D interconnects up to 60GHz is discussed.

This paper reviews the fabrication and design of two different types of energy harvesting systems, that utilize ambient energy to power up connected wireless modules. A 3D/inkjet-printed origami-style (morphing) cube with orthogonally-placed patch antennas is presented which enhances the nodes diversity reception capabilities. The cube changes its shape upon heating upto 60°C. In contrast, the presented near-field energy harvester utilizes the ambient RF energy of a handheld two-way radio to convert the RF signal with an efficiency of 82.5%. For proof-of-concept purposes, an E-field energy harvesting receiver is fabricated on a flexible LCP substrate with inkjet printing technology featuring an open-circuit voltage of 17.87V for an output power of 43.2 mW for the E-field energy harvester placed 7 cm away from a 1W Walkie-Talkie transmitter.

A novel planar printed stub-loaded square helical (PSLSH) antenna is presented for 2.4GHz WLAN applications. Unlike conventional stub loaded helical (SLH) antennas, the input impedance of the proposed antenna is real. Therefore, a simple quarter-wave transformer can be used to match this antenna. Simulation results show that the antenna has a maximum gain of 10 dBi, a front-to-back ratio of 12dbi, a 70° half-power beam width and a good axial ratio. The volume of PSLSH antenna is 75% less than conventional axial mode helical antennas and 17% less than SLH antennas. Furthermore, the usable bandwidth of PSLSH antenna (46%) is significantly higher compared to SLH antenna (10%).