Bernard Herrera

This paper reports on zero standby power human presence detectors based on an optimized micromechanical photoswitch (MP) with a metasurface-enhanced long wavelength infrared (LWIR) absorber, increased thermal sensitivity, reduced bias voltage, and a wide field-of-view. The reported device shows the capability of detecting a human body around 2.65 m and human hand around 1 m distance using low bias voltages without using any focal lenses. Existing wireless motion detectors based on pyroelectric IR sensors consume ∼100 μW power on standby continuously and produce frequent false alarms due to non-relevant objects (such as moving cars and falling leaves), which inevitably drains the battery in a relatively short period of time (typically less than a year). The demonstrated zero-power sensor here exploits the LWIR energy emitted from a human body for true presence detection without consuming any electrical power on standby. The first experimental demonstration of human body detection with vacuum packaged MP at a distance comparable to commercial motion detectors is enabled by the optimization of an MP in terms of thermomechanical performance (thermal sensitivity ∼1.5 nm/nW, stiffness ∼0.2 nN/nm, and threshold ∼10 nW) and IR absorption (η > 60% in λ = 6-14 μm, field-of-view ∼110 °). The new broadband LWIR metasurface absorbers improve the structural symmetry of MP by matching the material stacks of reflecting and absorbing heads. This improvement allows the MP to work with lower voltage bias thus, making it compatible with low-power electronics.

The present work reports on the novel usage of Scandium-doped Aluminum Nitride (AlScN) PMUT arrays for enhanced power transfer in implantable applications. Optimization considerations were explored for the PMUT array towards high performance. The transmission metric, compared to identical arrays based on Aluminum Nitride (AlN), showed a 25dB increase. Power transfer measurements also confirmed a considerable increase as compared to previous work based on AlN. Different matching strategies were explored to maximize the output power including inductor conjugate matching and matching utilizing resonators in series and parallel topologies. A full characterization of the transferred power versus incident acoustic intensity on the array revealed transmission of power levels of several milliwatts for intensities below the Food and Drug Administration’s (FDA) limit. The performance of the array, as compared with other implementations with a range of frequencies, dimensions and input acoustic intensities was bench-marked through the use of the conversion efficiency as the figure-of-merit. The practical applicability of the system, utilizing a realistic tissue phantom as the medium, was proven by interfacing with a commercially available boost converter to obtain a rectified voltage and power levels sufficient for powering and charging intra-body electronics.

Sc-doped aluminum nitride is emerging as a new piezoelectric material which can substitute undoped aluminum nitride (AlN) in radio-frequency MEMS applications, thanks to its demonstrated enhancement of the piezoelectric coefficients. Furthermore, the recent demonstration of the ferroelectric-switching capability of the material gives AlScN the possibility to integrate memory functionalities in RF components. However, its high-coercive field and high-leakage currents are limiting its applicability. Residual stress, growth on different substrates, and testing-temperature have already been demonstrated as possible knobs to flatten the energy barrier needed for switching, but no investigation has been reported yet on the whole impact on the dielectric and ferroelectric dynamic behavior of a single process parameter. In this context, we analyze the complete spectrum of variations induced by the applied substrate-RF, from deposition characteristics to dielectric and ferroelectric properties, proving its effect on all of the material attributes. In particular, we demonstrate the possibility of engineering the AlScN lattice cell to properly modify leakage, breakdown, and coercive fields, as well as polarization charge, without altering the crystallinity level, making substrate-RF an effective and efficient fabrication knob to ease the limitations the material is facing.

The present work reports on the novel usage of Scandium-doped Aluminum Nitride (AlScN) PMUT arrays for enhanced power transfer in implantable applications. As compared to identical arrays based on Aluminum Nitride (AlN), a 25dB increase in transmission was observed, and output power was increased by a factor of 50 as compared to previous work based on AlN arrays. After conjugate matching of the source impedance of the array, the output power showed a further 14x increase. Characterization of the transferred power versus incident acoustic intensity on the array enabled transmission of power levels of several milliwatts for intensities below the Food and Drug Administration's (FDA) limit. Finally, the array was interfaced to a commercially available boost converter to obtain rectified voltages of 1.8V and 1V in water and tissue phantom media, respectively, thus proving its practical applicability for powering and charging of intra-body electronics.

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.

The present work reports on the novel implementation of a miniaturized receiver for underwater networking merging a Piezoelectric Micromachined Ultrasonic Transducer (PMUT) array and signal conditioning circuitry in a single, packaged device. Tests in both a large water tank and a pool demonstrated that the system can attain large enough Signal-to-Noise Ratio (SNR) for communication at distances beyond two meters. An actual communication test, implementing an Orthogonal Frequency Division Multiplexing (OFDM) scheme, was used to characterize the performance of the link in terms of Bit Error Rate (BER) vs SNR. In comparison to previous work demonstrating high-data rate communication for intra-body links and acoustic duplexing, this implementation allows for significantly larger distances of transmission, while addressing the signal conditioning and submersible packaging needs for underwater conditions, thus enabling PMUT arrays for operating as complete underwater communication receivers. [2020-0185]

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 60 × 30 × 20 cm ³ .

This work proposes, for the first time, the use of Directly Modulated Ultrasonic Transducer (DMUT) array as an efficient way to drive individual sub-sections of Piezoelectric Micromachined Ultrasonic Transducers (pMUTs) arrays. The system allows to implement the phased-array technique and re-configure in quasi real-time the maximum radiation of the pMUT array through a commercially available micro-controller. The results in this work show an increase of the Sound Pressure Level (SPL) of 13dB when transmitting from a 10×5 pMUT array to a commercial hydrophone through the DMUT phased-array. The achievements are promising towards the improvement of intrabody and underwater communication networks.

Wirelessly networked systems of underwater devices are becoming the basis of many commercial, scientific, and military applications. In spite of increased attention in the last few years, underwater wireless networking technology still suffers from major limitations, including severe hardware dependence. In this paper, we introduce the SEANet Project, an NSF-funded effort that aims at developing a new generation of programmable platforms and a networking testbed to enable the vision of a programmable Internet of Underwater Things (IoUT). SEANet will be based on new software-defined platforms based on an open architecture to enable the flexibility to define, add, update, and swap new components in both hardware and software. SEANet is designed to support data rates at least one order of magnitude higher than existing commercial platforms over short and moderate range links. Moreover, the SEANet project will explore the design of new custom-designed ultra-wide band Microelectromechanical systems (MEMS) transducers that allow operating over much wider acoustic bandwidth (i.e., 0.01.-2 MHz) than possible with bulk piezoelectric transducers. We present a set of preliminary experiments showing that SEANet can outperform existing software-defined radio SDR-based acoustic modems based on a commercial off-the-shelf (COTS) SDR platforms. We also demonstrate the real-time reconfiguration capability of SEANet and preliminary performance of the MEMS transducers.