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This paper introduces a novel additive-manufacturing technique to obtain high-resolution selective-ink-deposition on complex 3-D objects, packages, and modules for 5G applications. The technique consists of embossing the desired pattern directly on the 3-D printed dielectric surface and then applying ink with a suitable tool. This approach is tested in combination with stereolithography 3-D printing technology to obtain selectively metallized 3-D circuits. In particular, the “clear” resin from FormLab is utilized for the 3-D printed dielectric, while the metallization is performed with silver nanoparticle ink from Suntronic. As a preliminary study, test samples containing lines with different widths are manufactured, demonstrating a pitch down to $135~\mu \text {m}$ and satisfactory sheet resistance of $0.011~\Omega /\text {sq.}$ (the electromagnetic characterization of the dielectric resin is reported in the Appendix). Then, two broadband multiport RF structures are developed to show the versatility of the proposed technology. First, an ultrawideband 3-D crossover, operating in the range 100 MHz–5 GHz, is conceived to test the suitability of the proposed technology to perform selective metallization on curved semienclosed areas. Then, the technology is applied to a multiple-input–multiple-output (MIMO) antenna system, based on four proximity-fed annular slot antennas, arranged on the lateral sides of a cube and decoupled by introducing a cross-shaped structure in the interior of the cube. This circuit offers a broad range of metallization challenges, as it features embossed and engraved parts, high-resolution patterns (line widths down to 0.7 mm) and sharp edges. Each slot radiates unidirectionally with the same polarization and uses the cube and its internal cross-shaped structure as a resonant cavity. The antenna system is designed to operate in the band 3.4–3.8 GHz, which is one of the sub-6-GHz 5G bands in Europe, and it is thought for hotspot and access-point applications. The final antenna topology is composed of only two blocks, weighs 21.29 g, and occupies a volume of $44.4\times 45.8\times 45.8\,\,\text {mm}^{3}$ , featuring an envelope correlation coefficient (ECC) lower than 0.005 and a total active reflection coefficient (TARC) lower than −6 dB in all the bands of interests. [ABSTRACT FROM AUTHOR]

Controlled measurements by a low-cost single-pixel microwave radiometer operating at 12.65 GHz were carried out to assess the detection and counting capability for targets warmer than the surroundings. The adopted reference test targets were pre-warmed water and oil; and a hand, both naked and wearing a glove. The results showed the reliability of microwave radiometry for counting operations under controlled conditions, and its effectiveness at detecting even warm targets masked by unheated dielectric layers. An electromagnetic model describing the scenario sensed by the radiometer antenna is proposed, and comparison with the experimental observations shows a good agreement. The measurements prove that reliable counting is enabled by an antenna temperature increment, for each target sample added, of around 1 K. Starting from this value, an analysis of the antenna filling factor was performed to provide an instrument useful for evaluating real applicability in many practical situations. This study also allows the direct people counting problem to be addressed, providing preliminary operational indications, reference numbers and experimental validation. [ABSTRACT FROM AUTHOR]

This paper aims to demonstrate that novel additive manufacturing (AM) technologies like metal adhesive laminate and multilayer inkjet printing can be effectively exploited to fabricate high-performing radio-frequency passive components on flexible substrates. Both processes are substrate independent and therefore suitable for manufacturing circuits on several unconventional materials, such as photo-paper. In addition, their complementary features can be combined to develop a novel hybrid process. Proof-of-concept AM prototypes of passive components, such as capacitors and inductors, exhibiting quality factors over 70, never achieved before on paper, and self-resonant frequencies beyond 4 GHz are described. The maximum inductance and capacitance per unit area are 1.4 nH/mm2 and 6.5 pF/mm2, respectively. Moreover, an AM RF mixer with a conversion loss below 10 dB is demonstrated still on paper substrate. The mixer, fabricated with the copper adhesive laminate method, operates at 1 GHz and exploits a lumped balun transformer connected to two packaged diodes in series. [ABSTRACT FROM PUBLISHER]

This paper proposes a review of several circuits for communication and wireless sensing applications implemented on cellulose-based materials. These circuits have been developed during the last years exploiting the adhesive copper laminate method. Such a technique relies on a copper adhesive tape that is shaped by a photo-lithographic process and then transferred to the hosting substrate (i.e., paper) by means of a sacrificial layer. The presented circuits span from UHF oscillators to a mixer working at 24 GHz and constitute an almost complete set of building blocks that can be applied to a huge variety communication apparatuses. Each circuit is validated experimentally showing performance comparable with the state-of-the-art. This paper demonstrates that circuits on cellulose are capable of operating at record frequencies and that ultra- low cost, green i.e., recyclable and biodegradable) materials can be a viable solution to realize high frequency hardware for the upcoming Internet of Things (IoT) era. [ABSTRACT FROM AUTHOR]

Energy harvesting is well established as one of the prominent enabling technologies [along with radio-frequency identification (RFID), wireless power transfer, and green electronics] for the pervasive development of Internet of Things (IoT). This paper focuses on a particular, yet broad, class of systems that falls in the IoT category of large area electronics (LAE). This class is represented by “smart surfaces.” The paper, after an introductory overview about how smart surfaces are collocated in the IoT and LAE scenario, first deals with technologies and architectures involved, namely, materials, antennas, RFID systems, and chipless structures; then, some exemplifying solutions are illustrated to show the present development of these concurrent technologies in this area and to stimulate further solutions. Conclusions and future trends are then drawn. [ABSTRACT FROM AUTHOR]

This paper presents a novel passive Schottky-diode frequency doubler equipped with an on-off keying (OOK) modulation port to be used in harmonic transponders for both identification and sensing applications. The amplitude modulation of the second-harmonic output signal is achieved by driving a low-frequency MOSFET, which modifies the dc impedance termination of the doubler. Since the modulation signal is applied to the gate port of the transistor, no static current is drained. A proof-of-concept prototype was manufactured and tested, operating at 1.04 GHz. An on/off ratio of 23 dB was observed in the conversion loss of the doubler for an available input power of −10 dBm. The modulation port of the circuit was excited with a square wave ( f m up to 15 MHz), and the measured sidebands in the spectrum featured a good agreement with the theory. Then, the doubler was connected to a harmonic antenna system and tested in a wireless experiment for f m up to 1 MHz, showing an excellent performance. Finally, an experiment was conducted where the output signal of the doubler was modulated by a reed switch used to measure the rotational speed of an electrical motor. This work opens the door to a new class of frequency doublers, suitable for ultra low-power harmonic transponders for identification and sensing applications. [ABSTRACT FROM AUTHOR]

This letter presents the design of a Schottky diode frequency doubler suitable for harmonic RFID tags. A microwave frequency doubler is implemented in a cellulose-based (paper) substrate, i.e., an ultra-low cost, recyclable and biodegradable material. The circuit exploits a distributed microstrip structure that is fabricated using a copper adhesive laminate to have low conductor losses. The measurements show a conversion loss of 13.4 dB at the output frequency of 2.08 GHz. This is achieved with an available input power of -10 dBm only. Finally a harmonic RFID experiment proves a reading range of 50 cm, obtained by transmitting 0 dBm and receiving a second harmonic of -60 dBm, i.e., well above the sensitivity of a typical microwave receiver. [ABSTRACT FROM PUBLISHER]

A review of technological solutions for RFID sensing and their current or envisioned applications is presented. The fundamentals of the wireless sensing technology are summarized in the first part of the work, and the benefits of adopting RFID sensors for replacing standard sensor-equipped Wi-Fi nodes are discussed. Emphasis is put on the absence of batteries and the lower cost of RFID sensors with respect to other sensor solutions available on the market. RFID sensors are critically compared by separating them into chipped and chipless configurations. Both categories are further analyzed with reference to their working mechanism (electronic, electromagnetic, and acoustic). RFID sensing through chip-equipped tags is now a mature technological solution, which is continuously increasing its presence on the market and in several applicative scenarios. On the other hand, chipless RFID sensing represents a relatively new concept, which could become a disruptive solution in the market, but further research in this field is necessary for customizing its employment in specific scenarios. The benefits and limitations of several tag configurations are shown and discussed. A summary of the most suitable applicative scenarios for RFID sensors are finally illustrated. Finally, a look at some sensing solutions available on the market are described and compared. [ABSTRACT FROM AUTHOR]