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1. A Power Budget Analysis for an Implantable UWB Transceiver for Brain Neuromodulation Application

   https://doi.org/10.23919/USNC-URSI52669.2022.9887429  

   Reza, Sakib ; Mahbub, Ifana ( July 2022 , 2022 IEEE USNC-URSI Radio Science Meeting (Joint with AP-S Symposium))

   The next evolutionary step in biological signal monitoring will be enabled by wireless communication. Low power and cost-efficient wireless transceivers are currently being employed for implantable medical devices (IMDs), in addition to military and civilian applications such as monitoring, surveillance, and home automation. The major goal of this paper is to do a thorough and realistic link budget analysis for an implantable wireless transceiver operating in the 3–5 GHz ultrawideband frequency with a link distance of 2 m (which includes 10 mm of brain tissue layer and 1.99 m of air medium), data rate of 100 Mbps with On-Off keying (OOK) modulation, and a minimum receiver sensitivity of −58.01 dBm. The proposed power budget analysis is particularly well suited for distributed brain implant applications as it models the path loss including the tissue layer without compromising the spectrum regulation imposed by the Federal Communications Commission (FCC) for UWB communication. 

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2. Biphasic quasistatic brain communication for energy-efficient wireless neural implants

   https://doi.org/10.1038/s41928-023-01000-3  

   Chatterjee, Baibhab ; Nath, Mayukh ; Kumar_K, Gaurav ; Xiao, Shulan ; Jayant, Krishna ; Sen, Shreyas ( September 2023 , Nature Electronics)

   Wearable devices typically use electromagnetic fields for wireless information exchange. For implanted devices, electromagnetic signals suffer from a high amount of absorption in tissue, and alternative modes of transmission (ultrasound, optical and magneto-electric) cause large transduction losses due to energy conversion. To mitigate this challenge, we report biphasic quasistatic brain communication for wireless neural implants. The approach is based on electro-quasistatic signalling that avoids transduction losses and leads to an end-to-end channel loss of only around 60 dB at a distance of 55 mm. It utilizes dipole-coupling-based signal transfer through the brain tissue via differential excitation in the transmitter (implant) and differential signal pickup at the receiver (external hub). It also employs a series capacitor before the signal electrode to block d.c. current flow through the tissue and maintain ion balance. Since the electrical signal transfer through the brain is electro-quasistatic up to the several tens of megahertz, it provides a scalable (up to 10 Mbps), low-loss and energy-efficient uplink from the implant to an external wearable. The transmit power consumption is only 0.52 μW at 1 Mbps (with 1% duty cycling)—within the range of possible energy harvesting in the downlink from a wearable hub to an implant. 

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3. Batteryless, Wireless, and Secure SoC for Implantable Strain Sensing

   https://doi.org/10.1109/OJSSCS.2022.3230000  

   Abdelhamid, Mohamed R. ; Ha, Unsoo ; Banerjee, Utsav ; Adib, Fadel ; Chandrakasan, Anantha P. ( December 2022 , IEEE Open Journal of the Solid-State Circuits Society)

   The past few years have witnessed a growing interest in wireless and batteryless implants, due to their potential in long-term biomedical monitoring of in-body conditions such as internal organ movements, bladder pressure, and gastrointestinal health. Early proposals for batteryless implants relied on inductive near-field coupling and ultrasound harvesting, which require direct contact between the external power source and the human body. To overcome this near-field challenge, recent research has investigated the use of RF backscatter in wireless micro-implants because of its ability to communicate with wireless receivers that are placed at a distance outside the body (∼0.5 m), allowing a more seamless user experience. Unfortunately, existing far-field backscatter designs remain limited in their functionality: they cannot perform biometric sensing or secure data transmission; they also suffer from degraded harvesting efficiency and backscatter range due to the impact of variations in the surrounding tissues. In this paper, we present the design of a batteryless, wireless and secure system-on-chip (SoC) implant for in-body strain sensing. The SoC relies on four features: 1) employing a reconfigurable in-body rectenna which can operate across tissues adapting its backscatter bandwidth and center frequency; 2) designing an energy efficient 1.37 mmHg strain sensing front-end with an efficiency of 5.9 mmHg·nJ/conversion; 3) incorporating an AES-GCM security engine to ensure the authenticity and confidentiality of sensed data while sharing the ADC with the sensor interface for an area efficient random number generation; 4) implementing an over-the-air closed-loop wireless programming scheme to reprogram the RF front-end to adapt for surrounding tissues and the sensor front-end to achieve faster settling times below 2 s. 

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4. Wireless, Batteryless, and Secure Implantable System-on-a-Chip for 1.37mmHg Strain Sensing with Bandwidth Reconfigurability for Cross-Tissue Adaptation

   https://doi.org/10.1109/CICC53496.2022.9772815  

   Abdelhamid, M. R. ; Ha, U. ; Banerjee, U. ; Adib, F. ; Chandrakasan, A. ( April 2022 , 2022 IEEE Custom Integrated Circuits Conference (CICC))

   There is a growing interest in wireless and batteryless implants for long-term sensing of organ movements, core pressure, glucose levels, or other biometrics [1]. Most research on such implants has focused on ultrasonic [2] and nearfield inductive [3-4] methods for power and communication, which require direct contact or close proximity (<1-5cm) to the human body. Recently, RF backscatter has emerged as a promising alternative due to its ability to communicate with far-field (> 10cm) wireless devices at ultra-low-power [5]. While multiple proposals have demonstrated far-field RF backscatter in deep tissues, these proposals have been limited to tag identification and could neither perform biometric sensing nor secure the wireless communication links, which is critical for ensuring the confidentiality of the sensed biometrics and for responding to commands only from authorized users [6]. Moreover, such far-field RF implants are susceptible to tissue variations which impact their resonance and hence their efficiency in RF backscatter and energy harvesting. 

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5. Magnetoelectric Transducer Designs for Use as Wireless Power Receivers in Wearable and Implantable Applications

   https://doi.org/10.3390/ma12030512  

   Rupp, Tyrel ; Truong, Binh Duc ; Williams, Shane ; Roundy, Shad ( February 2019 , Materials)

   As the size of biomedical implants and wearable devices becomes smaller, the need for methods to deliver power at higher power densities is growing. The most common method to wirelessly deliver power, inductively coupled coils, suffers from poor power density for very small-sized receiving coils. An alternative strategy is to transmit power wirelessly to magnetoelectric (ME) or mechano-magnetoelectric (MME) receivers, which can operate efficiently at much smaller sizes for a given frequency. This work studies the effectiveness of ME and MME transducers as wireless power receivers for biomedical implants of very small (<2 mm3) size. The comparative study clearly demonstrates that under existing safety standards, the ME architecture is able to generate a significantly higher power density than the MME architecture. Analytical models for both types of transducers are developed and validated using centimeter scale devices. The Institute of Electrical and Electronics Engineers (IEEE) and the International Commission on Non-Ionizing Radiation Protection (ICNIRP) standards were applied to the lumped elements models which were then used to optimize device dimensions within a 2 mm3 volume. An optimized ME device can produce 21.3 mW/mm3 and 31.3 W/mm3 under the IEEE and ICNIRP standards, respectively, which are extremely attractive for a wide range of biomedical implants and wearable devices. 

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