A CMOS SoC for Wireless Ultrasonic Power/Data Transfer and SHM Measurements on Structures

Abstract

This paper describes a highly-integrated CMOS system-on-chip (SoC) for active structural health monitoring (SHM). The chip integrates ultrasonic power and bidirectional half-duplex data transfer, a power management unit (PMU), and an ultrasound transceiver to enable wireless ultrasonically-coupled sensor SHM networks on structures. The PMU includes an active bias-flip rectifier with off-delay compensation, a high-efficiency dual-path DC-DC converter with inductor time-sharing, and five switched-capacitor DC-DC converters to generate multi-level spectrally band-limited pulses for guided-wave SHM. The chip was fabricated in a standard 180 nm process and has a die area of 2 × 2 mm 2 . Test results show power conversion efficiency (PCE) > 85% for the active rectifier, > 70% for the inductive DC-DC converter, and > 60% for the switched-capacitor DC-DC converters. Output pulses have a peak-to-sidelobe ratio (PSL) > 30 dB and worst-case out-of-band emissions < −30 dB, respectively. The SoC was integrated with a lowpower microcontroller and passive components to realize miniaturized (15 mm × 30 mm) wireless SHM nodes. A set of nodes was deployed on an SHM test-bed (carbon fiber reinforced polymer sheet) representing an airframe panel. Tests on this wireless network confirm both long-range ultrasound power/data transfer and the ability to detect structural damage.INDEX TERMS Energy harvesting, structural health monitoring (SHM), ultrasound power/data transfer.

Acoustic Backscatter Communication and Power Transfer for Batteryless Wireless Sensors

“…We see an approx-imately linear relationship between voltage and current, indicating that maximum power is extracted from the source if the MPPT threshold voltage is half the open-circuit voltage. This result confirms observations from [5,16]. The same experiment was repeated with different carrier frequencies, clearly showing that maximum extractable power strongly varies with frequency.…”

“…Alternatively, the receiver's Power Management Unit (PMU) can perform Maximum Power Point Tracking (MPPT), where the circuit automatically matches the resistance of the transducer but not the reactance. Furthermore, in some studies, the carrier frequency is automatically tuned to maximize received power, thereby avoiding strong impedance mismatches and improving transmitted power by more than 15 dB over a fixed carrier frequency [5].…”

“…As with wireless energy transfer, many studies use laboratory equipment as a proof of concept, leveraging high computational power computers for decoding and perfectly synchronized oscillators on the sender and receiver. An exception is Tang et al [5], who present a CMOS-integrated circuit.…”

“…While some of the work in Section 2.1 also includes communication from the sensor node back to the generator [5,16,18], none of them leveraged backscatter communication to enable even more energy-efficient sensor nodes. Our previous work showed the possibility of fast acoustic backscatter communication but did not employ wireless energy transfer to achieve completely batteryless sensor nodes.…”

“…However, conventional wireless communication is inapplicable in many scenarios due to electromagnetic shielding. Applications include structural health monitoring, where sensor nodes are embedded within a structure [4][5][6], underwater communication [7,8], fallback systems in nuclear power plants [9], and generally sensors within enclosed metal containers, e.g., pipelines, ship hulls, or cargo containers [10]. In contrast to electromagnetic waves, acoustic waves experience little attenuation in these scenarios and allow efficient transmission over longer distances.…”