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We present the first microacoustic metamaterial filters (MMFs). The bandpass of the reported MMFs is not generated by coupling, electrically or mechanically, various acoustic resonances; instead, it originates from the passbands and stopbands of a chain of three acoustic metamaterial (AM) structures. These structures form an AM transmission line (AMTL) and two AM reflectors (AMRs), respectively. Two single metal strips serve as input and output transducers with a wideband frequency response. Since MMFs do not rely on resonators, they do not require high-resolution trimming or mass-loading steps to accurately tune the resonance frequency difference between various microacoustic resonant devices. These steps often involve finely controlling the thickness of a device layer, with resolutions that can be as low as a few Angstroms when building GHz filters. The acoustic bandwidth of MMFs is mostly determined by geometrical and mechanical parameters of their AM structures. MMFs necessitate external circuit components for impedance matching, in contrast to the existing microacoustic filters that often employ circuit components only to eliminate ripples within their passband. We have designed and constructed the first MMFs from a 400-nm-thick scandium-doped aluminum nitride (AlScN) film using a 30% scandium-doping concentration. These devices operate in the radio frequency (RF) range. We validated these devices' performance through finite-element modeling (FEM) simulations and through measurements of a set of fabricated devices. When matched with ideal circuit components, the built MMFs exhibit filter responses with a center frequency in the ultrahigh-frequency range, a fractional bandwidth (FBW) of ~2.54%, a loss of ~4.9 dB, an in-band group delay between 70 ± 25 ns, and a temperature coefficient of frequency (TCF) of ~22.2 ppm/° C.
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Optical frequency combs, featuring evenly spaced spectral lines, have been extensively studied and applied to metrology, signal processing, and sensing. Recently, frequency comb generation has been also extended to MHz frequencies by harnessing nonlinearities in microelectromechanical membranes. However, the generation of frequency combs at radio frequencies (RF) has been less explored, together with their potential application in wireless technologies. In this work, we demonstrate an RF system able to wirelessly and passively generate frequency combs. This circuit, which we name quasi-harmonic tag (qHT), offers a battery-free solution for far-field ranging of unmanned vehicles (UVs) in GPS-denied settings, and it enables a strong immunity to multipath interference, providing better accuracy than other RF approaches to far-field ranging. Here, we discuss the principle of operation, design, implementation, and performance of qHTs used to remotely measure the azimuthal distance of a UV flying in an uncontrolled electromagnetic environment. We show that qHTs can wirelessly generate frequency combs with µWatt-levels of incident power by leveraging the nonlinear interaction between an RF parametric oscillator and a high quality factor piezoelectric microacoustic resonator. Our technique for frequency comb generation opens new avenues for a wide range of RF applications beyond ranging, including timing, computing and sensing.
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We report on a new class of Ising machines (IMs) that rely on coupled parametric frequency dividers (PFDs) as macroscopic artificial spins. Unlike the IM counterparts based on subharmonic-injection locking (SHIL), PFD IMs do not require strong injected continuous-wave signals or applied dc voltages. Therefore, they show a significantly lower power consumption per spin compared to SHIL-based IMs, making it feasible to accurately solve large-scale combinatorial optimization problems that are hard or even impossible to solve by using the current von Neumann computing architectures. Furthermore, using high quality factor resonators in the PFD design makes PFD IMs able to exhibit a nanowatt-level power per spin. Also, it remarkably allows a speedup of the phase synchronization among the PFDs, resulting in shorter time to solution and lower energy to solution despite the resonators' longer relaxation time. As a proof of concept, a 4-node PFD IM has been demonstrated. This IM correctly solves a set of Max-Cut problems while consuming just 600 nanowatts per spin. This power consumption is 2 orders of magnitude lower than the power per spin of state-of-the-art SHIL-based IMs operating at the same frequency.
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This work describes the implementation of acoustic metamaterials (AMs) made of a forest of rods at the sides of a suspended aluminum scandium nitride (AlScN) contour-mode resonator (CMR) to increase its power handling without causing degradations of its electromechanical performance. The increase in usable anchoring perimeter with respect to conventional CMR designs, enabled by the adoption of two AM-based lateral anchors, permits to achieve improved heat conduction from the resonator's active region to the substrate. Furthermore, thanks to such AM-based lateral anchors' unique acoustic dispersion features, the attained increase of anchored perimeter does not cause any degradations of the CMR's electromechanical performance, even leading to a ~15% improvement in the measured quality factor. Finally, we experimentally show that using our AM-based lateral anchors leads to a more linear CMR's electrical response, which is enabled by a 32% reduction of its Duffing nonlinear coefficient with respect to the corresponding value attained by a conventional CMR design that uses fully etched lateral sides.
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Massive deployments of wireless sensor nodes (WSNs) that continuously detect physical, biological or chemical parameters are needed to truly benefit from the unprecedented possibilities opened by the Internet-of-Things (IoT). Just recently, new sensors with higher sensitivities have been demonstrated by leveraging advanced on-chip designs and microfabrication processes. Yet, WSNs using such sensors require energy to transmit the sensed information. Consequently, they either contain batteries that need to be periodically replaced or energy harvesting circuits whose low efficiencies prevent a frequent and continuous sensing and impact the maximum range of communication. Here, we report a new chip-less and battery-less tag-based WSN that fundamentally breaks any previous paradigm. This WSN, formed by off-the-shelf lumped components on a printed substrate, can sense and transmit information without any need of supplied or harvested DC power, while enabling full-duplex transceiver designs for interrogating nodes rendering them immune to their own self-interference. Also, even though the reported WSN does not require any advanced and expensive manufacturing, its unique parametric dynamical behavior enables extraordinary sensitivities and dynamic ranges that can even surpass those achieved by on-chip sensors. The operation and performance of the first implementation of this new WSN are reported. This device operates in the Ultra-High-Frequency range and is capable to passively and continuously detect temperature changes remotely from an interrogating node.
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This article proposes the first acoustic discovery architecture (ADA) for intrabody networks (INs). The main objective of ADA is to discover and interrogate, in real-time (RT), all the implanted medical devices (IMDs) that are part of an IN. This permits noninvasive RT diagnosis for patients with multiple IMDs. ADA will allow medical doctors to have vital information, on-the-go, for treating patients and to constantly monitor them. The architecture was implemented in a network simulator emulating a real-life IN, based on preliminary experimental results. ADA is in charge of scanning the body volume, by exploiting the beam-forming and beam-steering capability of piezoelectric micromachined ultrasonic transducers (pMUTs) arrays, and efficiently interrogating all the reached devices for their status. As a result, a full IN map can be reconstructed together with all the vital signs of a patient. ADA shows very good RT capabilities, with a full scanning time from 1500 down to 100 ms and energy consumption from 2.6 down to 0.2 mJ, depending on the scanning accuracy, for a body torso volume of [Formula: see text].
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The present work details a novel approach to increase the transmitting sensitivity of piezoelectric micromachined ultrasonic transducer arrays and performing the direct modulation of digital information on the same device. The direct modulation system can reach 3× higher signal-to-noise ratio level and 3× higher communication range (from 6.2 cm boosted to 18.6 cm) when compared to more traditional continuous wave drive at the same energy consumption levels. When compared for the same transmission performance, the direct modulation consumes 80% less energy compared to the continues wave. The increased performance is achieved with a switching circuit that allows to generate a short high-AC voltage on the ultrasonic array, by using an LC tank and a bipolar junction transistor, starting with a low-DC voltage, making it CMOS-compatible. Since the modulation signal can directly be formed by the transmitted bits (on/off keying encoding) this also serve as the modulation for the data itself, hence direct modulation. The working principle of the circuit is described, optimization is performed relative to several circuital parameters and a high-performance experimental application is demonstrated.
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We report on the design and operation of a novel class of nonreciprocal acoustic filters operating in the radio frequency (RF) range. These devices use the spectral characteristics of commercial acoustic filters placed in angular momentum biased networks to achieve large nonreciprocity, low insertion loss (I.L.), and wideband operation. Owing to the high rejection exhibited by acoustic filters, these novel devices can achieve an unprecedented suppression of undesired intermodulation products, thus approaching the spectral purity attained by conventional linear-time-invariant (LTI) filtering components. In addition, a new analytical model suitable to capture the behavior of any angular-momentum-biased nonreciprocal device is presented. This model allows us to identify the main characteristics of the transfer function (poles and zeroes) relative to this new class of nonreciprocal filters, thus enabling new synthesis capabilities through standard numerical methods. Ultimately, the performance of a built 1.1-GHz nonreciprocal acoustic filter prototype is reported. This device relies on a modulation implemented through switched capacitors and shows I.L., isolation, and half-power bandwidth values of 4.5 dB, 28 dB, and 20 MHz, respectively, achieved through the use of a 40-MHz modulation frequency. Moreover, by showing an intermodulation distortion lower than -34 dBc, it approaches the operation of LTI circuits.
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This work describes a new method to enhance the electromechanical coupling coefficient ( kt2 ) of 2-D mode resonators (2DMRs). This approach exploits the multimodal excitation of different Lamb waves to achieve a quasi-uniform vertical displacement distribution in the electrode regions of 2DMRs. To do so, the 2DMRs reported in this work rely on the use of metal frame structures placed at the edges of each metal strip forming the electrode gratings. To demonstrate the effectiveness of this new technique in enhancing kt2 , we report the design and simulated performance through the finite-element methods of a 2.5-GHz 2DMR using metal frames. Our analysis proves that this device can simultaneously exhibit high kt2 in excess of 6.4% and wide lithographic frequency tunability in excess of 10%, thus approaching the reported performance of aluminum nitride (AlN) film bulk acoustic resonators (FBARs) operating within the same frequency range.
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This paper reports on a novel simulation method combining the speed of analytical evaluation with the accuracy of finite-element analysis (FEA). This method is known as the rapid analytical-FEA technique (RAFT). The ability of the RAFT to accurately predict frequency response orders of magnitude faster than conventional simulation methods while providing deeper insights into device design not possible with other types of analysis is detailed. Simulation results from the RAFT across wide bandwidths are compared to measured results of resonators fabricated with various materials, frequencies, and topologies with good agreement. These include resonators targeting beam extension, disk flexure, and Lamé beam modes. An example scaling analysis is presented and other applications enabled are discussed as well. The supplemental material includes example code for implementation in ANSYS, although any commonly employed FEA package may be used.
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State-of-the-art sensors use active electronics to detect and discriminate light, sound, vibration and other signals. They consume power constantly, even when there is no relevant data to be detected, which limits their lifetime and results in high costs of deployment and maintenance for unattended sensor networks. Here we propose a device concept that fundamentally breaks this paradigm-the sensors remain dormant with near-zero power consumption until awakened by a specific physical signature associated with an event of interest. In particular, we demonstrate infrared digitizing sensors that consist of plasmonically enhanced micromechanical photoswitches (PMPs) that selectively harvest the impinging electromagnetic energy in design-defined spectral bands of interest, and use it to create mechanically a conducting channel between two electrical contacts, without the need for any additional power source. Our zero-power digitizing sensor prototypes produce a digitized output bit (that is, a large and sharp off-to-on state transition with an on/off conductance ratio >1012 and subthreshold slope >9â dec nW-1) when exposed to infrared radiation in a specific narrow spectral band (â¼900â nm bandwidth in the mid-infrared) with the intensity above a power threshold of only â¼500â nW, which is not achievable with any existing photoswitch technologies.
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Through the use of a laser Doppler vibrometer, it is shown that a 31% variation in quality factor can occur due to the effect of undercutting of the device layers outside of the anchors of a 220-MHz aluminum nitride contour-mode resonator. This undercutting is a result of the isotropic etch process used to release the device from the substrate. This paper shows that the variation in Q is a function of the release distance, L , between the active region of the resonator and the edge of this released region. This paper also determined a design modification that eliminated this issue and achieved a Q of 3048, which is independent of L .
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We present the first parametric oscillator based on the use of a 226.7 MHz aluminum nitride contour-mode resonator. This topology enables an improvement in the phase noise of 16 dB at 1 kHz offset with respect to a conventional feedback-loop oscillator based on the same device. The recorded phase noise is -106 dBc/Hz at 1 kHz offset.