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The authors present a semipassive Rotman lens-based reconfigurable intelligent surface at 28 GHz for beyond-5G applications. One proof-of-concept prototype is inkjet-printed on a thin Rogers substrate using a masking technique followed by etching. The system is characterized by its autonomous mode switching, power consumption, radar cross section (RCS) against angle, and mid-range performance. This millimeter-wave identification (mmID) tag system detects radio frequency (RF) signals with a half-wave rectifier and retransmits signals in selective directions with a 270-kHz amplitude shift keying modulation. This proposed system consumes $65~\mu $ W in the detection mode and $143~\mu $ W in the communication mode, suggesting the potential to be further developed into a fully passive and energy-autonomous system for long-range applications in complex environments. To switch between detection and communication modes, the rectifier oscillates between 6.1 and 9.7 mV, which means that the Rotman lens-based RIS-assisted mmID tag system can operate up to 75 m away for communication mode and 89 m for the detection mode.

This article presents the first shape-changing phased array operating at 28 GHz as an alternative to traditional planar phased arrays. By combining electrical beamsteering with mechanical shape change, this design achieves high degrees of freedom, resulting in near-limitless radiation pattern reconfigurability and overcoming the tradeoff between gain and angular coverage. Utilizing the eggbox origami structure, a 4-D multifaceted foldable phased array is developed, and a modular tile-based (unit-cell) approach is employed to enable TX/RX selective activation and scalability to massive MIMO. This results in near 360° continuous beam steering in the azimuth plane with reconfigurable multibeam or quasi-isotropic radiation patterns. Additive manufacturing processes are employed to realize the first shape-changing phased array at a miniaturized millimeter scale. The eggbox phased array features highly integrated on-structure beamformer ICs and a flexible feeding network utilizing a uniquely designed foldable interconnect. As the first additively manufactured mm-wave hinge interconnects, the presented “arch” interconnect exhibits near-constant insertion loss of 0.02 dB/mm across various folding angles and cycles. In addition, a microservo-based actuation mechanism is designed to precisely control the origami folding action. Measurements demonstrate the phased array’s pattern reconfigurability, and its effectiveness is further validated in an orthogonal frequency division multiplexing (OFDM)-based communication testbed setup. Furthermore, this article provides a holistic multidisciplinary framework guiding the development of a new era of mm-wave shape-changing phased arrays, encompassing considerations in hardware realization, actuation, and 3-D beam shaping/calibration. Given its multitude of novel features, the eggbox phased array can enable a plethora of applications, ranging from multimode in-band full-duplex applications to multifunction multibeam use cases, extreme interference mitigation, and space-constrained deployments.

The development of flexible phased array systems has drawn significant interest due to their adaptive beam steerability and deployable structures to support various platforms virtually on every conformal surface. Additively manufactured tile-based phased array offers a lightweight, flexible, and massively scalable solution with reduced cost and fabrication time. The main challenge for such conformal phased array systems is to maintain array performance under various deformations, which requires calibration of the amplitude and/or phase distribution of the antenna elements. To address this challenge, a computer vision-enabled on-the-fly adaptive shape calibration and phase correction method is proposed. The authors introduce the usage of smartphones, with integrated 3-D depth cameras and infrared (IR) sensors, and a novel computer vision algorithm to detect the bend angles between neighboring subarray tiles. A $2 \times $ additively manufactured tile-based flexible phased array is utilized as a proof-of-concept (POC) prototype to demonstrate the calibration approach. The proposed algorithm achieves a very good <1° angular prediction accuracy and demonstrates successful calibration of the phased array under 15°, 30°, and 45° bend angles under both symmetrical and asymmetrical configurations with improvements of gain as much as 7 dB. The calibrated bent phased arrays can also achieve a maximum steering range of 110°. This approach presents a highly accurate and cost-effective calibration process that can enable massive fabrication and implementation of tile-based flexible phased arrays for next-generation 5G/mmWave wearable and conformal smart skin, Internet of Things (IoT), Industry 4.0, and massive multiple-input multiple-output (MIMO) applications.

In this study, we introduce a novel antenna design method for superdirective antennas that combines low complexity with high radiation efficiency, while being impedance-matched to $50~\Omega $ . We applied this approach to design, fabricate, and measure a superdirective antenna array (SDA) with a high realized antenna gain (i.e., 6.3 dBi) and radiation efficiency (i.e., 99.3%), consisting of two strip dipole elements operating at a frequency of 3.5 GHz. The fabricated antenna has an electrical size of 1.55, underscoring its compactness in addition to its high gain. Our approach is distinguished by its ability to achieve high directivity and radiation efficiency, along with impedance-matching to $50~\Omega $ , through meticulous adjustments of the strip dimensions (i.e., length and width) and the phase difference between elements. This method eliminates the need for external impedance-matching networks, amplifiers, attenuators, parasitic elements, or loads, marking a significant advancement in the development of practical superdirective antenna designs.

This article presents the first and most comprehensive design, fabrication, and reliability evaluation of the electrical and mechanical performance of fully inkjet-printed 3-D “ramp” interconnects. Inkjet-printed interconnects feature superior RF performance and better mechanical reliability for heterogeneous integration for 5G mmWave flexible electronics packaging. The packaged systems are required to survive various flexing conditions over a large number of cyclic bending for conformal applications. In this work, ramp interconnects are designed with excellent and reliable performance for flexible packaging over the 20–40-GHz frequency band. A test vehicle of a monolithic microwave integrated circuit (MMIC) attenuator die placed in the middle of two microstrip lines is used, where ramp interconnects are fabricated by inkjet printing SU8 dielectric ink to form ramp base and inkjet printing silver nanoparticle (SNP) ink for conductive interconnects to build the connection between the die and microstrip lines. The fabricated sample exhibits a superior $S_{21}$ performance with less than 1.16-dB insertion loss per interconnect throughout the whole operation range from 20 to 40 GHz. Monotonic bending tests are conducted over mandrels of various radii ranging from 50 to 10 mm, and the designed ramp interconnects are able to maintain robust transmission with a minimum variation of less than 0.15-dB insertion loss per interconnect. Moreover, the fabricated samples are able to survive over 20 000 times of cyclic bending tests over the mandrel of 10-mm radius, with less than 0.2-dB additional loss from each interconnect. The proposed design takes advantage of a low-cost, on-demand additive manufacturing method by selectively depositing SU8 ink layer by layer with varying dimensions to enable rugged ramp structures for curved mounting platforms. The results reported in this article could enable rapid production of high-performance and reliable flexible system-on-package (SoP) and multichip module (MCM) designs and build the foundation of next-generation 5G mmWave flexible hybrid electronics (FHE) technologies for various applications.

Emerging additive manufacturing (AM) technologies, specifically additively manufactured electronics (AME), 4-D printing, and origami, are reshaping the design capabilities and functionalities of contemporary electronic devices. Cutting-edge 3-D/4-D printing technologies facilitate the prototyping and realization of complex electronic functions that are challenging to conventional methods. This article provides a comprehensive overview of the evolving techniques in AME, 4-D printing, and origami, employing multimaterials (conductive and dielectric materials) and shape-memory materials (SMMs) to fabricate functional electronic components and devices. Additionally, the overview delves into the state-of-the-art AME and 4-D-printed electronic components across diverse fields, including biomedical electronics, space engineering, and the advancements in the next-generation wireless communications and sensing.

This article describes sensors and radio frequency (RF) components manufactured by applying selective-metallization processes (metal foil tape, liquid metal filling, electro and electroless plating, and surface embossing) to 3-D-printed and flexible dielectric substrates. All these technologies can be implemented at room temperature, thus enabling the adoption of unconventional materials and biopolymers with low glass transition temperatures. In this article, we also describe how the above technologies are used to manufacture wireless transponders for tracking and sensing applications. Several examples of RF components are reported, including antennas, beamforming networks, Doppler radars, and wireless passive transponders based on backscatter radio. Innovative circuit design approaches (such as the via-less approach) are presented and their impact on circuit manufacturing and recyclability is discussed.