Emerging biomedical ultrasound applications such as pulsed neurostimulation and shear-wave imaging demand single-pulse focused ultrasound waves with MPa-range acoustic pressures. Achieving high pressures typically involves driving transducers with high voltages, necessitating bulky power amplifiers. Recently, phased arrays have emerged to miniaturize these focused transducers. However, they often exhibit poor power efficiency and heat dissipation. To address this, we explore acoustic amplification through acoustic energy storage and release, where, with minimal voltage, high-amplitude ultrasound waves are produced. Prior work has shown the principle using bulky apparatus with limited applicability. In this work, we explore the theory and perform finite element modeling (FEM) to investigate this mechanism with miniaturized and micro-electro-mechanical systems (MEMS)-compatible materials and geometries.

The development of neurostimulation devices for visual and somatosensory prostheses is rapidly gaining momentum, where scaling the number of stimulation channels is crucial to improve treatment efficacy. To this end, optimizing power efficiency is critical, particularly in wirelessly powered systems. Although current-mode stimulation is generally preferred for safety reasons, it is often associated with significant power overhead losses in the output driver. This challenge becomes even more pronounced in multichannel configurations, where the required load voltage varies unpredictably across channels and over time. Compliance monitor circuits have been used to scale the output driver voltage supply, which in turn reduces losses and improves power efficiency. However, existing implementations lead to increased area and power overhead while lacking the ability to adapt rapidly to dynamic load conditions. This work presents a stimulator architecture that enables autonomous output supply scaling per channel, minimizing power dissipation across a wide range of currents and impedances without requiring explicit compliance monitoring. A two-channel prototype fabricated in 0:18 μm CMOS was validated with both linear loads and electrodes. The proposed strategy achieves outputdriver efficiencies above 80 % for stimulation currents of 30 k to 95 μA and load impedances from 30 k to 70 k, showing up to 4.3 times improvement compared to a fixed-voltage supply. Furthermore, the circuit shows rapid adaptation to changes in the required output voltage, enabling 100 μs stimulation pulses with a 1 μs inter-pulse delay. This feature allows time-division multiplexing across electrodes with varying load conditions, which could be further explored to increase the number of electrodes served per stimulation channel and thereby enhance scalability.

Wearable ultrasound devices for imaging and therapeutic applications demand low-power and low-area integrated circuits to interface with ultrasound transducers. In the case of ultrasound imaging front-ends, discrete time-gain compensation (TGC) simplifies gain control in ultrasound imaging (USI) ASICs, but higher gain-step resolution increases area and power dissipation, while high PSRR is needed to suppress switching noise from co-integrated HV digital circuits. This work presents a programmable-gain floating inverter low-noise amplifier (FIALNA) architecture in 28nm CMOS for low-power, wide-bandwidth USI. A thermometer-encoded variable reservoir capacitance enables fine TGC with five PVT-robust gain steps, achieving 53.6dB PSRR and an area of 0.0023mm2, an order of magnitude smaller than current PGA designs. The FIALNA dissipates 116μW and achieves 59μVrms input-referred noise, making it suitable for low-power wearable ultrasound devices.

Next generation wearable/implantable ultrasound imaging systems demand ultra-compact, power-efficient analog front-end circuits enabling high-resolution, high frame-rate multimodal imaging. Individual RF channel access allows for the use of state-of-the-art imaging methods such as synthetic aperture imaging, plane-wave compounding and adaptive beamforming, while remaining crucial for auto-calibration of sparse transducer arrays. Time-division multiplexing-based (TDM) architectures have been widely deployed to enable individual RF channel access, but impose severe trade-offs between power and silicon area for imaging quality and contrast. This work introduces a pseudo-random channel-shuffling TDM (PRCS-TDM) technique, emulating a non-uniform sampling-rate for each RF channel. Results show PRCS-TDM improves B-mode contrast-to-noise ratio (CNR) in anechoic regions up to a 2× increase compared to conventional TDM, achieving a 3.2 dB CNR increase for channel compression ratios greater than 8.

Ultrasound (US) technology has emerged as a powerful modality in both medical imaging and therapy, offering non-invasive, real-time, and high-resolution capabilities. Conventional dual-mode systems employ separate US transducers for imaging and therapy, each mechanically configured during fabrication for a fixed quality factor (Q-factor) through the presence of a backing layer or air-based backing layer, respectively. This approach increases system cost, physical footprint, power consumption, and integration complexity while preventing seamless real-time switching between modes. A novel electronically configurable Q-factor control circuit architecture for a single set of 2D phased-array piezoelectric transducers is proposed in this work. The proposed method employs an active damping compensation technique to electronically reduce the Q-factor during imaging mode while preserving the high-Q state for the therapeutic mode, eliminating the need for mechanical reconfiguration. System and circuit-level simulations in TSMC 180 nm BCD technology using a PZT-5A air-backed transducer BVD model demonstrate a reduction in the Q-factor from 78.3 to 8.08 with fewer than 1% variation across PVT corners. These results place the Q-factor achieved in the imaging mode within the optimal range for high-resolution ultrasound imaging, while maintaining high-Q performance for the therapeutic mode.

Power efficiency is critical for enabling the long-term use of implantable and wearable ultrasound (US) neuromodulation systems, where excessive power consumption leads to thermal dissipation and frequent battery replacement. Conventional therapeutic phased arrays typically generate equal pressures from all elements, not taking into account the directivity of each element, and thus the different source contributions to the focal spot, leading to power inefficiency. Although prior methods allow control of source pressure at the element level, such as driver supply control, duty cycle adjustment, or deterministic pulse skipping, they either require complex circuitry, introduce dynamic switching losses, or cause undesirable temporal fluctuations in focal pressure, respectively. To address these limitations, we introduce a novel driving scheme that explores pseud-random pulse skipping to control element-level source pressure and thus optimize power consumption in 2D phased array ultrasound transmitters. The pseudo-random pulse skipping approach allows for regulating the source pressure in each element while preserving a stable pressure at the focal spot, which is required for therapeutic applications. The driving scheme for a single element was implemented in an ASIC, and the result shows that by having different percentages of pulse skipping, we can also modulate the power consumption of the driving channel.

Accurate detection of physiological vibrations is vital for monitoring health and enabling sensory feedback in bioelectronics. Current technologies often suffer from low signal-to-noise ratios (SNR), bulkiness, and the need for external amplification. Here, we introduce piezoelectric internal ion-gated organic electrochemical transistors (Piezo-IGTs), which efficiently convert mechanical vibrations into amplified electrical signals. These devices integrate laminated P(VDF-TrFE) microfiber films as the gate atop the transistor channel, generating voltage upon deformation to modulate mobile ions in the conducting polymer. Fabricated via sequential deposition and lamination, Piezo-IGTs achieve high fill factors and efficient on-site amplification, improving SNR over standalone piezoelectric films. They operate near 0 V gate voltage, enabling low-power performance. We validate their functionality in mechanomyography, speech recognition, and mechanocardiography using microscale Piezo-IGTs. This self-contained, flexible architecture demonstrates promise for integration into implantable and wearable systems, offering real-time, high-fidelity acquisition of bio-mechanical signals in next-generation health monitoring and neuroprosthetic applications.

Developing an implantable/wearable 2D ultrasound phased array for ultrasound neuromodulation poses several challenges, including power requirements for driving the piezoelectric transducers to generate sufficient pressure at the focal spot. Therefore, minimizing power consumption is crucial to minimize excessive thermal dissipation and to ensure long-term usability without frequent charging or battery replacement. Prior work has improved efficiency based on transducer fabrication and circuit design optimizations. To further address this issue, we propose a new approach to minimize power consumption by tailoring the driving amplitude of each element in a 2D phased array based on their individual contribution to the focal spot pressure.

In the emerging research field of bioelectronic medicine, it has been indicated that neuromodulation of the vagus nerve (VN) has the potential to treat various conditions such as epilepsy, depression, and autoimmune diseases. In order to reduce side effects, as well as to increase the effectiveness of the delivered therapy, sub-fascicle stimulation specificity is required. In the electrical domain, increasing spatial selectivity can only be achieved using invasive and potentially damaging approaches like compressive forces or nerve penetration. To avoid these invasive methods while obtaining a high spatial selectivity, a 2-mm diameter extraneural cuff-shaped proof-of-concept design with integrated lead zirconate titanate (PZT) based ultrasound (US) transducers is proposed in this article. For the development of the proposed concept, wafer-level microfabrication techniques are employed. Moreover, acoustic measurements are performed on the device, in order to characterize the ultrasonic beam profiles of the integrated PZT-based US transducers. A focal spot size of around 200× 200 μ m is measured for the proposed cuff. Moreover, the curvature of the device leads to constructive interference of the US waves originating from multiple PZT-based US transducers, which in turn leads to an increase of 45% in focal pressure compared to the focal pressure of a single PZT-based US transducer. Integrating PZT-based US transducers in an extraneural cuff-shaped design has the potential to achieve high-precision US neuromodulation of the VN without requiring intraneural implantation.

Poor stimulus-response correlation, caused by acoustic reflections from conventional culture substrates, poses a significant challenge in cellular mechanistic studies of ultrasound neuromodulation. Existing specialized setups that mitigate this interference have limited recording capabilities. In this study, we propose an anti-reflective microengineered substrate (ARMS) that can be incorporated into a standard in vitro platform. The substrate's dimensions and material composition were optimized in simulation. The optimized simulated platform exhibited an 86.3% reduction in reflection amplitude on the substrate surface compared to the conventional glass substrate. Furthermore, the ARMS reduced stimulation signal distortion to a 19.2% deviation from the expected amplitude, a substantial improvement compared to the 76.4% deviation observed with glass.

This work presents the design and simulation of a PVT-robust x16 gain dynamic open-loop inverter-based Gm-ratio residue-amplifier for high-speed SAR-assisted pipeline ADCs. The amplifier is designed in a 28 nm standard bulk CMOS process with a regulated 0.9 V power supply and simulated across a -20°C to 85°C temperature range. It achieves a power dissipation of 1.67 mW at 1.3 GHz, corresponding to a power-speed ratio of 1.28 mW/GHz, with less than ±5% gain variation throughout all temperature corners in typical conditions.

Ultrasound (US) neuromodulation and ultrasonic power transfer to implanted devices demand novel ultrasound transmitters capable of steering focused ultrasound waves in 3D with high spatial resolution and US pressure, while having a miniaturized form factor. Meeting these requirements needs a 2D array of ultrasound transducers directly integrated with a high-frequency 2D phased-array ASIC. However, this imposes severe challenges on the design of the ASIC. In order to avoid the generation of grating lobes, the elements in the 2D phased-array should have a pitch of half of the ultrasound wavelength, which, as frequency increases, highly reduces the area available for the design of high-voltage beamforming channels. This article addresses these challenges by presenting the system-level optimization and implementation of a high-frequency 2D phased-array ASIC. The system-level study focuses on the optimization of the US transmitter toward high-frequency operation while minimizing power consumption. This study resulted in the implementation of two ASICs in TSMC 180 nm BCD technology: firstly, an individual beamforming channel was designed to demonstrate the tradeoffs between frequency, driving voltage, and beamforming capabilities. Finally, a 12-MHz pitch matched 12 × 12 phased-array ASIC working at 20-V amplitude and 3-bit phasing was designed and experimentally validated, to demonstrate high-frequency phased-array operation. The measurement results verify the phasing functionality of the ASIC with a maximum DNL of 0.35 LSB. The CMOS chip consumes 130 mW and 26.6 mW average power during the continuous pulsing and delivering 200-pulse bursts with a PRF of 1 kHz, respectively.