Design of Tunable Ultrasonic Receivers for Efficient Powering of Implantable Medical Devices With Reconfigurable Power Loads

Chang, Ting Chia; Weber, Martina; Wang, Max L.; Charthad, Jayant; Khuri‐Yakub, Butrus T.; Arbabian, Amin

doi:10.1109/tuffc.2016.2606655

Cited by 47 publications

(54 citation statements)

References 35 publications

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“…However, the use of lead-based piezoelectrics in implantables is undesirable due to the cytotoxicity of lead. Barium titanate (BaTiO 3 ) is a promising candidate to replace lead-based piezoceramics as it has a higher electromechanical coupling coefficient than other lead-free piezoceramics such as LiNbO 3 and AlN [55]. Switching to BaTiO 3 would be 70% as efficient as PZT (Fig.…”

Section: Alternative Lead-free Piezoelectric Materials Are Compatimentioning

confidence: 99%

Design of Ceramic Packages for Acoustically Coupled Implantable Medical Devices

Shen

Maharbiz

2019

Preprint

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Objective: Ultrasonic acoustic power transfer is an efficient mechanism for coupling energy to millimeter and submillimeter 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 acoustic energy to the interior of ceramic packages. Methods: The classic wave approach and modal expansion are used to obtain analytical expressions for acoustic 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. Results: Bulk modes are shown to be more effective at coupling acoustic 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 amplitudemodulated backscatter communication is demonstrated. Conclusion: Thin lids enable the use of acoustically coupled devices even with package materials of very different acoustic impedance. Significance: This work provides an analysis and method for designing packages that enable acoustic coupling with implantable medical devices, which could facilitate clinical translation. Fig. 1. System overview for acoustically coupled implantable medical devices (IMDs) utilizing ultrasonic backscatter communication. Information from many different energy domains can be encoded in the amplitude of the backscatter (green/blue waves). For these devices to be clinically useful, packaging must be designed that both protects the devices and also allows for acoustic coupling.

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Section: Alternative Lead-free Piezoelectric Materials Are Compatimentioning

confidence: 99%

Design of Ceramic Packages for Acoustically Coupled Implantable Medical Devices

Shen

Maharbiz

2019

Preprint

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“…Major unavoidable challenges arise from miniaturization including degraded bandwidth, lower directivity, and limited processing capability stemming from packaging and power constraints. 4,9 These challenges have prevented ultrasonic IMDs from reaching the speeds necessary for more complex functionality.…”

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confidence: 99%

“…At these dimensions, the transducers can be modeled using length expander bar mode operation. 9 Bulk lead zirconate titanate 4 (PZT4) is diced to 1.08 × 1.08 × 1.44 mm 3 dimensions to resonate near 1 MHz and provide ~2 kΩ radiation resistance at resonance, achieving a good tradeoff between transmit and receive efficiency. 9 Fig.…”

mentioning

confidence: 99%

“…9 Bulk lead zirconate titanate 4 (PZT4) is diced to 1.08 × 1.08 × 1.44 mm 3 dimensions to resonate near 1 MHz and provide ~2 kΩ radiation resistance at resonance, achieving a good tradeoff between transmit and receive efficiency. 9 Fig. 1(b) shows the cross-section of the identical printed circuit boards (PCBs) designed for the receiver and transmitter.…”

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confidence: 99%

“…The transducers are positioned over large, sealed vias in the PCB to provide air-backing and increase their sensitivity. 9,15 The boards are placed in a tank filled with mineral oil, which is used to mimic the acoustic impedance of the body, albeit with lower attenuation, while minimizing electrical parasitics. A linear stage is used to move the receiver relative to the transmitter.…”

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Exploiting spatial degrees of freedom for high data rate ultrasound communication with implantable devices

Wang

Arbabian

2017

Applied Physics Letters

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We propose and demonstrate an ultrasonic communication link using spatial degrees of freedom to increase data rates for deeply implantable medical devices. Low attenuation and millimeter wavelengths make ultrasound an ideal communication medium for miniaturized low-power implants. While small spectral bandwidth has drastically limited achievable data rates in conventional ultrasonic implants, large spatial bandwidth can be exploited by using multiple transducers in a multiple-input/multiple-output system to provide spatial multiplexing gain without additional power, larger bandwidth, or complicated packaging. We experimentally verify the communication link in mineral oil with a transmitter and receiver 5 cm apart, each housing two custom-designed mm-sized piezoelectric transducers operating at the same frequency. Two streams of data modulated with quadrature phase-shift keying at 125 kbps are simultaneously transmitted and received on both channels, effectively doubling the data rate to 250 kbps with a measured bit error rate below 10 -4 . We also evaluate the performance and robustness of the channel separation network by testing the communication link after introducing position offsets. These results demonstrate the potential of spatial multiplexing to enable more complex implant applications requiring higher data rates.Advances in miniaturized, wireless, and deeply implantable medical devices (IMDs) can enable coordinated closed-loop diagnostics and treatments for applications like neuromodulation and drug delivery. 1 As their capabilities become more complex and numerous, robust and low-power communication becomes increasingly important. Research into wireless networks in the body have largely focused on radio frequency (RF) communications. 2 However, a major challenge for the propagation of electromagnetic (EM) waves in the body is power absorption in tissue. The absorbed power is dissipated as heat leading to both health concerns and significant path loss. 3 More recently, there has been increased interest in using ultrasonic waves for intra-body communication and power transfer. 2,4 At low MHz frequencies, reduced scattering due to relative homogeneity in tissue density and compressibility as well as low attenuation of about 1 dB·cm -1 ·MHz -1 in soft tissue allow ultrasonic waves to safely propagate much farther in tissue than EM waves. 1 The orders of magnitude slower propagation velocity of acoustic waves in the body (~1500 m/s) also results in millimeter wavelengths around a MHz, allowing for simpler circuits, beamforming capabilities, and smaller transducers. 1 On the other hand, the lower operating frequency and fundamentally smaller bandwidth drastically limit the achievable data rate and available modulation schemes. Required data rates can vary considerably depending on the application. For example, glucose monitoring may need kbps speeds while imaging/video may require Mbps speeds. 2 Recent studies have proposed and demonstrated different protocols with varying data rates for intra-body ultrasou...

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Ultrasound‐Powered Implants: A Critical Review of Piezoelectric Material Selection and Applications

Turner

Senevirathne

Kilgour

et al. 2021

Adv Healthcare Materials

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Ultrasound‐powered implants (UPIs) represent cutting edge power sources for implantable medical devices (IMDs), as their powering strategy allows for extended functional lifetime, decreased size, increased implant depth, and improved biocompatibility. IMDs are limited by their reliance on batteries. While batteries proved a stable power supply, batteries feature relatively large sizes, limited life spans, and toxic material compositions. Accordingly, energy harvesting and wireless power transfer (WPT) strategies are attracting increasing attention by researchers as alternative reliable power sources. Piezoelectric energy scavenging has shown promise for low power applications. However, energy scavenging devices need be located near sources of movement, and the power stream may suffer from occasional interruptions. WPT overcomes such challenges by more stable, on‐demand power to IMDs. Among the various forms of WPT, ultrasound powering offers distinct advantages such as low tissue‐mediated attenuation, a higher approved safe dose (720 mW cm−2), and improved efficiency at smaller device sizes. This study presents and discusses the state‐of‐the‐art in UPIs by reviewing piezoelectric materials and harvesting devices including lead‐based inorganic, lead‐free inorganic, and organic polymers. A comparative discussion is also presented of the functional material properties, architecture, and performance metrics, together with an overview of the applications where UPIs are being deployed.

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Design of Tunable Ultrasonic Receivers for Efficient Powering of Implantable Medical Devices With Reconfigurable Power Loads

Cited by 47 publications

References 35 publications

Design of Ceramic Packages for Acoustically Coupled Implantable Medical Devices

Design of Ceramic Packages for Acoustically Coupled Implantable Medical Devices

Exploiting spatial degrees of freedom for high data rate ultrasound communication with implantable devices

Ultrasound‐Powered Implants: A Critical Review of Piezoelectric Material Selection and Applications

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