Search

Single modality wireless power transfer has limited depth for mm-sized implants across air/tissue or skull/tissue interfaces because they either suffer from a high loss in tissue (RF, optical) or high reflection at the medium interface [ultrasound (US)]. This article proposes an RF-US relay chip at the media interface avoiding the reflection at the boundary and enables efficient wireless powering to mm-sized deep implants across multiple media. The relay chip rectifies the incoming RF power through an 85.5% efficient RF inductive link (across air) using a multi-output regulating rectifier (MORR) with 81% power conversion efficiency (PCE) at 186 mW load and transmits using adiabatic power amplifiers (PAs) to the implant in order to minimize cascaded power loss. To adapt US focus to implant movement or placement, beamforming was implemented using six channels of US PAs with two-bit phase control (0°, 90°, 180°, and 270°) and three different amplitudes (6–29, 4.5, and 1.8 V) from the MORR. The adiabatic PA contributes a 30%–40% increase in efficiency over class-D and beamforming increases the efficiency by 251% at 2.5 cm over fixed focusing. The proof-of-concept powering system for a retinal implant, from an external PA on a pair of glasses to a hydrophone with 1.2 cm (air) + 2.9 cm (agar eyeball phantom in mineral oil) separation distance, had a power delivered to the load (PDL) of 946 $\mu \text{W}$. The 2.3 mm × 2 mm relay chip was fabricated in a 180 nm high-voltage (HV) BCD process. [ABSTRACT FROM AUTHOR]

Acoustic links for implantable medical devices (implants) have gained attention primarily because they provide a route to wireless deep-tissue systems. The miniaturization of the implants is a key research goal in these efforts, nominally because smaller implants result in less acute tissue damage. Implant size in most acoustic systems is limited by the piezoelectric bulk crystal used for power harvesting and data communication. Further miniaturization of the piezocrystal can degrade system power transfer efficiency and data transfer reliability. Here, we present a new method for packaging the implant piezocrystal; the method maximizes power transfer efficiency ($\eta $) from the acoustic power at the piezo surface to the power delivered to the electrical load and information transfer across the acoustic link. Our method relies on placing piezo-to-substrate anchors to the piezo regions where the vibrational displacement of the mode of interest is zero. To evaluate our method, we investigated packaged $1\times 1\times1$ mm3 piezocrystals assembled with different sized anchors. Our results show that reducing the anchor size decreases anchor loss and thus improves piezo quality factor (Q). We also demonstrate that this method improves system electromechanical coupling. A strongly coupled, high-Q piezo with properly sized and located anchors is demonstrated to achieve significantly higher $\eta$ and superior data transfer capability at resonance. Overall, this work provides an analysis and generic method for packaging the implant piezocrystal that enables the design of efficient acoustic power and data links, which provides a path toward the further miniaturization of ultrasonic implants to submillimeter scales. [ABSTRACT FROM AUTHOR]

Objective: Ultrasonic acoustic power transfer is an efficient mechanism for coupling energy to millimeter and sub-millimeter implants in the body. To date, published ultrasonically powered implants have been encapsulated with thin film polymers that are susceptible to well-documented failure modes in vivo, including water penetration and attack by the body. As with all medical implants, packaging with ceramic or metallic materials can reduce water vapor transmission and improve biostability to provide decadal device lifetime. In this paper, we evaluate methods of coupling ultrasonic energy to the interior of ceramic packages. Methods: The classic wave approach and modal expansion are used to obtain analytical expressions for ultrasonic transmission through two different package designs and these approaches are validated experimentally. A candidate package design is demonstrated using alumina packages and titanium lids, designed to be acoustically transparent at ultrasonic frequencies. Results: Bulk modes are shown to be more effective at coupling ultrasonic energy to a piezoelectric receiver than flexural modes. Using bulk modes, packaged motes have an overall link efficiency of roughly 10%, compared to 25% for unpackaged motes. Packaging does not have a significant effect on translational misalignment penalties, but does increase angular misalignment penalties. Passive amplitude-modulated backscatter communication is demonstrated. Conclusion: Thin lids enable the use of ultrasonically coupled devices even with package materials of very different acoustic impedance. Significance: This work provides an analysis and method for designing packages that enable ultrasonic coupling with implantable medical devices, which could facilitate clinical translation. [ABSTRACT FROM AUTHOR]

Contactless ultrasonic power transmission (UPT) through a metal barrier has become an exciting field of research, as metal barriers prevent the use of electromagnetic wireless power transfer due to Faraday shielding effects. In this paper, we demonstrate power transfer through a metal wall with the use of ultrasonic waves generated from a piezoelectric transducer. Accurate characterization and modeling of the transducer and investigation of the influence of the acoustic properties of the transmitting medium are instrumental for the performance prediction and optimal design of an ultrasonic power link. In this work, we applied the KLM model for the emitting and receiving transducers, with respect to the transmitting medium and model for both the emission and reception function. A practical UPT system was built by mechanically coupling and co-axially aligning two composite transducers on opposite sides of a transmitting medium wall. The optimal transmission performance of the ultrasonic power link through thickness-stretch vibrations of the wall together with two piezoelectric transducers working in TE mode was determined. Eventually, the operating frequency and ohmic loading condition for maximum power transmission were obtained for two different media, aluminium and polyoxymethylene (POM), with contrasting specific acoustic impedances. The results showed that the measured optimal electric loads and operating frequency for maximum power transfer agreed well with the theoretical predictions.

Ultrasonic power transfer (UPT) is a promising method for wireless power transfer technology for low-power medical applications. Most portable or wearable medical devices are battery-powered. Batteries cannot be used for a long time and require periodic charging or replacement. UPT is a candidate technology for solving this problem. In this work, a 40-KHz ultrasound transducer was used to design a new prototype for supplying power to a wearable heart rate sensor for medical application. The implemented system consists of a power unit and heart rate measurement unit. The power unit includes an ultrasonic transmitter and receiver, rectifier, boost converter and super-capacitors. The heart rate measurement unit comprises measurement and monitoring circuits. UPT-based transfer power and efficiency were achieved using 1-, 4- and 8-Farad (F) super-capacitors. At 4 F, the system achieved 69.4% transfer efficiency and 0.318 mW power at 4 cm. In addition, 97% heart rate measurement accuracy was achieved relative to the benchmark device. The heart rate measurements were validated with statistical analysis. Our results show that this work outperforms previous works in terms of transfer power and efficiency with a 4-cm gap between the ultrasound transmitter and receiver.

A first proof-of-concept mm-sized implantable device using ultrasonic power transfer and a hybrid bi-directional data communication link is presented. Ultrasonic power transfer enables miniaturization of the implant and operation deep inside the body, while still achieving safe and high power levels (100 \muW to a few mWs) required for most implant applications. The current implant prototype measures 4 mm\times 7.8 mm and is comprised of a piezoelectric receiver, an IC designed in 65 nm CMOS process and an off-chip antenna. The IC can support a maximum DC load of 100\muW for an incident acoustic intensity that is \sim 5% of the FDA diagnostic limit. This demonstrates the feasibility of providing further higher available DC power, potentially opening up new implant applications. The proposed hybrid bi-directional data link consists of ultrasonic downlink and RF uplink. Falling edge of the ultrasound input is detected as downlink data. The implant transmits an ultra-wideband (UWB) pulse sequence as uplink data, demonstrating capability of implementing an energy-efficient M-ary PPM transmitter in the future. [ABSTRACT FROM PUBLISHER]

Advances in miniature devices for biomedical applications are creating ever-increasing requirements for their continuous, long lasting, and reliable energy supply, particularly for implanted devices. As an alternative to batteries, energy harvesting and wireless power delivery are receiving increased attention. Although the former is generally only suited for lowpower diagnostic microdevices, the latter has greater potential to extend the functionality to include more energy demanding actuation such as drug release or mechanical adjustment of prosthetic devices. With this aim, we present an ultrasonic method of wireless power delivery for actuation, the novelty being that the actuation is powered by ultrasound directly, rather than via piezoelectric conversion. This paper describes a coupled mechanical system remotely excited by ultrasound at 200 kHz and providing conversion of acoustic energy into motion of a micromechanical mechanism using a receiving membrane coupled to a discrete oscillator. We address the problem of acoustic and mechanical impedance mismatch and simulate harmonic and frequency response of the system. The fabrication method is described, and the resulting devices are characterized, revealing hysteresis in their frequency response that is related to nonlinear behavior in the membrane-oscillator coupling. The experimental samples were successfully driven by an ultrasonic source, at various separations, and demonstrated maximum oscillator vibration amplitudes in the range of 9.6-9.9 μm. This provided a mechanical amplification with respect to the membrane in the range of 240-250. [ABSTRACT FROM AUTHOR]

Using a pre-designed, simple, and cost-effective acoustic hologram alongside a single ultrasonic transducer, as an acoustic source/transmitter, enables new capabilities in multi-focal focusing, acoustic patterning, and contactless ultrasonic power transfer (UPT), to selectively charge sensors/receivers. In this work, different multi-focal holograms are designed that cover single- to four-focus acoustic patterning for UPT purposes. The holograms are numerically designed to create multi-focal pressure patterns in a target plane where an array of receivers are placed. The incident sound wave from a transmitter, after passing through the hologram, is manipulated, hence, the output field is the desired pressure field, which excites the receivers located at the pre-determined focal points more significantly. Proof-of-concept experiments are also performed for a five-element receiver setup, using a two-focus hologram, to selectively power two specific receivers. The experiments indicate a significant electrical average power output enhancement ratio of 23.4 from the targeted receivers, compared to untargeted ones, which proves the functionality of the designed multi-focal holograms in arbitrarily patterning the contactless transfer of ultrasonic power. Using an acoustic hologram, we can significantly enhance the ultrasonic transfer of power from an actuator to targeted sensors (e.g., receivers 2 & 4) in the figure. [Display omitted] • The novelty of using multi-focal holograms for ultrasonic power transfer systems. • Using multi-focal holograms enhances the ultrasonic power transfer to sensors. • Using multi-focal holograms patterns the ultrasonic power transfer to sensors. [ABSTRACT FROM AUTHOR]

Contactless ultrasonic power transmission (UPT) through a metal barrier has become an exciting field of research, as metal barriers prevent the use of electromagnetic wireless power transfer due to Faraday shielding effects. In this paper, we demonstrate power transfer through a metal wall with the use of ultrasonic waves generated from a piezoelectric transducer. Accurate characterization and modeling of the transducer and investigation of the influence of the acoustic properties of the transmitting medium are instrumental for the performance prediction and optimal design of an ultrasonic power link. In this work, we applied the KLM model for the emitting and receiving transducers, with respect to the transmitting medium and model for both the emission and reception function. A practical UPT system was built by mechanically coupling and co-axially aligning two composite transducers on opposite sides of a transmitting medium wall. The optimal transmission performance of the ultrasonic power link through thickness-stretch vibrations of the wall together with two piezoelectric transducers working in TE mode was determined. Eventually, the operating frequency and ohmic loading condition for maximum power transmission were obtained for two different media, aluminium and polyoxymethylene (POM), with contrasting specific acoustic impedances. The results showed that the measured optimal electric loads and operating frequency for maximum power transfer agreed well with the theoretical predictions. [ABSTRACT FROM AUTHOR]

Ultrasonic power transfer (UPT) is a promising method for wireless power transfer technology for low-power medical applications. Most portable or wearable medical devices are battery-powered. Batteries cannot be used for a long time and require periodic charging or replacement. UPT is a candidate technology for solving this problem. In this work, a 40-KHz ultrasound transducer was used to design a new prototype for supplying power to a wearable heart rate sensor for medical application. The implemented system consists of a power unit and heart rate measurement unit. The power unit includes an ultrasonic transmitter and receiver, rectifier, boost converter and super-capacitors. The heart rate measurement unit comprises measurement and monitoring circuits. UPT-based transfer power and efficiency were achieved using 1-, 4- and 8-Farad (F) super-capacitors. At 4 F, the system achieved 69.4% transfer efficiency and 0.318 mW power at 4 cm. In addition, 97% heart rate measurement accuracy was achieved relative to the benchmark device. The heart rate measurements were validated with statistical analysis. Our results show that this work outperforms previous works in terms of transfer power and efficiency with a 4-cm gap between the ultrasound transmitter and receiver. [ABSTRACT FROM AUTHOR]

Multi-access networking with miniaturized wireless implantable devices can enable and advance closed-loop medical applications to deliver precise diagnosis and treatment. Using ultrasound (US) for wireless implant systems is an advantageous approach as US can beamform with high spatial resolution to efficiently power and address multiple implants in the network. To demonstrate these capabilities, we use wirelessly powered mm-sized implants with bidirectional communication links; uplink data communication measurements are performed using time, spatial, and frequency-division multiplexing schemes in tissue phantom. A 32-channel linear transmitter array and an external receiver are used as a base station to network with two implants that are placed 6.5 cm deep and spaced less than 1 cm apart. Successful wireless powering and uplink data communication around 100 kbps with a measured bit error rate below 10 -4 are demonstrated for all three networking schemes, validating the multi-access networking feasibility of US wireless implant systems.