https://iopscience.iop.org/article/10.1088/0964-1726/25/12/123001/pdf

A review of acoustic power transfer for bio-medical implants

Radio Frequency Identification (RFID) sensors, integrating the features of Wireless Information and Power Transfer (WIPT), object identification and energy efficient sensing capabilities, have been considered a new paradigm of sensing and communication for the futuristic information systems. RFID sensor tags featuring contactless sensing, wireless information transfer, wireless powered, light weight, non-line-of-sight transmission, flexible and pasteable are a critical enabling technology for future Internet-of-Things (IoT) applications, such as manufacturing, logistics, healthcare, agriculture and food. They have attracted numerous research efforts due to their innovative potential in the various application fields. However, there has been a gap between the in-lab investigations and the practical IoT application scenarios, which has motivated this survey of this research to identify the promising enabling techniques and the underlying challenges. This study aims to provide an exhaustive review on the state-of-art RFID sensor technologies from the system implementation perspective by focusing on the fundamental RF energy harvesting theories, the recent technical progresses and commercial solutions, innovative applications and some RFID sensor based IoT solutions, identify the underlying technological challenges at the time being, and give the future research trends and promising application fields in the rich sensing applications of the forthcoming IoT era.

https://www.mdpi.com/1424-8220/19/18/4012/pdf

Radio Frequency Identification and Sensing Techniques and Their Applications-A Review of the State-of-the-Art.

We present Piezo-Acoustic Backscatter (PAB), the first technology that enables backscatter networking in underwater environments. PAB relies on the piezoelectric effect to enable underwater communication and sensing at near-zero power. Its architecture is inspired by radio backscatter which works well in air but cannot work well underwater due to the exponential attenuation of radio signals in water. PAB nodes harvest energy from underwater acoustic signals using piezoelectric interfaces and communicate by modulating the piezoelectric impedance. Our design introduces innovations that enable concurrent multiple access through circuit-based frequency tuning of backscatter modulation and a MAC that exploits the properties of PAB nodes to deliver higher network throughput and decode network collisions. We built a prototype of our design using custom-designed, mechanically fabricated transducers and an end-to-end battery-free hardware implementation. We tested our nodes in large experimental water tanks at the MIT Sea Grant. Our results demonstrate single-link throughputs up to 3 kbps and power-up ranges up to 10 m. Finally, we show how our design can be used to measure acidity, temperature, and pressure. Looking ahead, the system can be used in ocean exploration, marine life sensing, and underwater climate change monitoring.

https://dl.acm.org/doi/pdf/10.1145/3341302.3342091

Underwater backscatter networking

Wearable sensor electronics require a sustainable electrical power supply to operate. Energy harvesting techniques can be used to convert available nonelectrical energy sources into electrical energy. This paper presents WE-Harvest system, which is a new wearable energy harvesting system that combines piezoelectric and electromagnetic energy harvesters in one unit to generate a combined electrical energy source. Piezoelectric transducers are used to obtain sufficient regulated output voltages while electromagnetic is employed for its high power generation capability. Regular human body motions provide input vibrations for the proposed energy harvester unit. Several conditioning circuit topologies are proposed to efficiently extract energy from the two sources. The experimental results demonstrate that the combined topology enhances the power generation efficiency as well as enables stable output DC voltages. The dependence of energy harvester output on the load and input frequency has also been investigated.

A wearable energy harvester unit using piezoelectric–electromagnetic hybrid technique

Wireless power transmission (WPT) is a critical technology that provides an alternative for wireless power and communication with implantable medical devices (IMDs). This article provides a study concentrating on popular WPT techniques for IMDs including inductive coupling, microwave, ultrasound, and hybrid wireless power transmission (HWPT) systems. Moreover, an overview of the major works is analyzed with a comparison of the symmetric and asymmetric design elements, operating frequency, distance, efficiency, and harvested power. In general, with respect to the operating frequency, it is concluded that the ultrasound-based and inductive-based WPTs have a low operating frequency of less than 50 MHz, whereas the microwave-based WPT works at a higher frequency. Moreover, it can be seen that most of the implanted receiver’s dimension is less than 30 mm for all the WPT-based methods. Furthermore, the HWPT system has a larger receiver size compared to the other methods used. In terms of efficiency, the maximum power transfer efficiency is conducted via inductive-based WPT at 95%, compared to the achievable frequencies of 78%, 50%, and 17% for microwave-based, ultrasound-based, and hybrid WPT, respectively. In general, the inductive coupling tactic is mostly employed for transmission of energy to neuro-stimulators, and the ultrasonic method is used for deep-seated implants.

/pdf/wireless-power-transfer-approaches-for-medical-implants-a-1otgwfy743.pdf

Wireless Power Transfer Approaches for Medical Implants: A Review

This paper presents a novel CMOS hybrid rectifier that can simultaneously and efficiently scavenge energy from a low-amplitude radio-frequency (RF) signal and a low-frequency, low-energy signal from a piezoelectric (PZT) transducer. The piezoelectric signal is used for biasing a complimentary, cross-coupled rectifier (CCCR) chain to an operating point such that the RF signal energy can be efficiently harvested, even if its amplitude is well below the threshold voltage (V
 TH
) of the rectifier transistors. The device sizes for the proposed design have been optimized to achieve the maximum DC output voltage and the proposed design is shown to effectively eliminate dead-zones in the rectifier response. The measurement results show that a 6-stage hybrid rectifier (HR) can generate up to 1 V DC output voltage at a load current of 3 μA when a 300 mV peak-to-peak, 13.56 MHz RF signal is applied in conjunction with a 10 KHz, 2 V piezoelectric signal. Using measured results from prototypes fabricated in a 90 nm CMOS process, the proposed HR is shown to yield a significant improvement in power conversion efficiency (PCE) for low levels of input power when compared to a conventional CCCR that has been implemented on the same die.

Hybrid CMOS Rectifier Based on Synergistic RF-Piezoelectric Energy Scavenging

While radio-frequency based remote powering and back-telemetry is popular for many of the surface implants, like neural prosthesis or under-the-skin implanted batteries, it is not suitable for implants located deep inside the tissue. In this paper, we investigate the feasibility of using a commercial off-the-shelf (COTS), diagnostic ultrasound technology for delivering energy to a sub-cm2 sized device implanted at depths more than 10cm away from the tissue surface. Using a COTS 3.5MHz ultrasound scanner we show how the B-mode interrogation protocol can be used to deliver energy to an encapsulated PZT transducer and how the B-mode video sequence can be parsed to retrieve the data from the transducer. In this paper we also discuss the limits of energy transfer at different implantation depths and we also discuss the energy requirements at the implant to achieve robust data transfer.

/pdf/feasibility-of-b-mode-diagnostic-ultrasonic-energy-transfer-5d3jd4dbw5.pdf

Feasibility of B-mode diagnostic ultrasonic energy transfer and telemetry to a cm 2 sized deep-tissue implant

Due to the current epidemic levels of sport-related concussions (SRC) in the U.S., there is a pressing need for technologies that can facilitate long-term and continuous monitoring of head impacts. Existing helmet-sensor technology is inconsistent, inaccurate, and is not economically or logistically practical for large-scale human studies. In this paper, we present the design of a miniature, battery-less, self-powered sensor that can be embedded inside sport helmets and can continuously monitor and store different spatial and temporal statistics of the helmet impacts. At the core of the proposed sensor is a novel time-dilation circuit that allows measurement of a wide-range of impact energies. In this paper an array of linear piezo-floating-gate (PFG) injectors has been used for self-powered sensing and storage of linear and rotational head-impact statistics. The stored statistics are then retrieved using a plug-and-play reader and has been used for offline data analysis. We report simulation and measurement results validating the functionality of the time-dilation circuit for different levels of impact energies. Also, using prototypes of linear PFG integrated circuits fabricated in a 0.5 $\mu{\rm m}$ CMOS process, we demonstrate the functionality of the proposed helmet-sensors using controlled drop tests.

Self-Powered Monitoring of Repeated Head Impacts Using Time-Dilation Energy Measurement Circuit

Many packaging and structural materials are made of conductive materials such as metal or carbon-fiber composites, which limits the use of embedded radio frequency-based telemetry systems for sensing. In this paper, we present the design of a complete passive ultrasonic energy harvesting and back-telemetry system that exploits near-field acoustic coupling to wirelessly transfer energy and data across conductive barriers. The use of near-field operation makes the telemetry robust to multipath reflections that occur at barrier discontinuities and robust to crosstalk when multiple sensors are simultaneously interrogated. Underlying the proposed architecture is a system-on-chip (SoC) that integrates different ultrasonic energy harvesting and telemetry modules. The operation of the system has been verified using SoC prototypes fabricated in a 0.5- $\mu \text{m}$ CMOS process which have been integrated with a piezoelectric transducer attached to an aerospace-grade aluminum substrate. Measured results show that the proposed near-field ultrasonic telemetry system can effectively operate across a 2-mm-thick metallic barrier at a frequency of 13.56 MHz with the SoC consuming 22.3 $\mu \text{W}$ of power.

Design of a CMOS System-on-Chip for Passive, Near-Field Ultrasonic Energy Harvesting and Back-Telemetry

A key challenge in structural health monitoring (SHM) sensors embedded inside civil structures is that elec- tronics need to operate continuously such that mechanical events of interest can be detected and appropriately analyzed. Continuous operation however requires a continuous source of energy which cannot be guaranteed using conventional energy scavenging techniques. The paper describes a hybrid energy scavenging SHM sensor which experiences zero down-time in monitoring mechanical events of interest. At the core of the proposed sensor is an analog floating-gate storage technology that can be precisely programmed at nano-watt and pico- watt power levels. This facilitates self-powered, non-volatile data logging of the mechanical events of interest by scavenging energy directly from the mechanical events itself. Remote retrieval of the stored data is achieved using a commercial off-the-shelf Gen-2 radio-frequency identification (RFID) reader which periodically reads an electronic product code (EPC) that encapsulates the sensor data. The Gen-2 interface also facilitates in simultaneous remote access to multiple sensors and also facilitates in determining the range and orientation of the sensor. The architecture of the sensor is based on a token-ring topology which enables sensor channels to be dynamically added or deleted through software control.

Tao Feng

Papers

Hybrid CMOS Rectifier Based on Synergistic RF-Piezoelectric Energy Scavenging

Feasibility of B-mode diagnostic ultrasonic energy transfer and telemetry to a cm 2 sized deep-tissue implant

Self-Powered Monitoring of Repeated Head Impacts Using Time-Dilation Energy Measurement Circuit

Design of a CMOS System-on-Chip for Passive, Near-Field Ultrasonic Energy Harvesting and Back-Telemetry

Gen-2 RFID compatible, zero down-time, programmable mechanical strain-monitors and mechanical impact detectors