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.

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.

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.

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.

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.

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.

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.

Piezoelectric Micromachined Ultrasonic Transducers (PMUT) and Capacitive Micromachined Ultrasonic Transducers (CMUT) have seen great developments in recent years, both in terms of performance and scope of applications within the biomedical ultrasound domain. This paper presents a review of the state-of-the-art of PMUT and CMUT technologies, focusing on their principle of operation, microfabrication techniques and use in different biomedical imaging and therapeutic applications. The advantages and drawbacks of PMUT and CMUT technologies in comparison with conventional bulk transducers are highlighted, the trade-offs among PMUTs and CMUTs are discussed, and their relevance in the current landscape of medical diagnostics and therapeutic uses is outlined, thus providing a clear overview of these promising technologies for the present and the next generation biomedical ultrasound applications.

Emerging ultrasound (US) biomedical applications, from battery-powered US imaging to US neuromodulation, demand wearable form factor and power-efficient US transmitters. Fulfilling these specifications demands a high-frequency and power-efficient 2D US phased-array transmitter directly integrated with the ASIC. In such systems, pulsers are the most power-hungry block owing to delivering high-voltage pulses to the US transducers. This paper presents a power-efficient high-voltage pulser to drive a 2D phased-array of piezoelectric transducers. The proposed pulser employs two storage capacitors per channel to save the charge of the US transducer and reuse it in the next phase. Moreover, utilizing a stack of two low-voltage CMOS transistors enables delivering 15-MHz pulses with an amplitude of 10 V to the piezoelectric transducers. The proposed pulser is designed and simulated in 180 nm CMOS technology. The simulation results demonstrate that the proposed pulser reduces the power consumption by 40.9% compared to the conventional class D pulser.

Electrical stimulation is proven to be an effective way of neuromodulation in bioelectronic medicine (e.g. cochlear implants, deep brain stimulators, etc.), delivering localized treatment by the means of electrical pulses. To increase the stimulation efficiency and neural-type selectivity, there is an increasing interest to employ non-rectangular stimulation waveforms [1-4]. Even though delivering and storing digital data at the stimulator provides the highest flexibility for generating stimulation waveforms, state-of-the-art approaches suffer either from poor resolution or the requirement of high data bandwidth for wirelessly powered implants [2]. Using Analog waveform generators is an alternative approach at the cost of extra implementation complexity for each type of waveform [3]. To fulfill the same goals as employing arbitrary waveforms for stimulation, we propose to shape the typical rectangular waveform using a programmable first-order low-pass filter, mimicking the natural filtering characteristic of the neural membrane. Using bio-realistic modeling, we show that such a pre-filtered waveform requires less or equal energy for the activation of neurons when compared with other energy-efficient waveforms (e.g. Gaussian). Notably, this comes at the low cost of only one extra programmable parameter (i.e., the filter’s corner frequency), on top of the typical duration and amplitude parameters. The basic concept of this work is driven by the fact that the natural low-pass characteristic of the neuron’s membrane limits the energy transfer efficiency from the stimulator to the cell. Thus, it is proposed to pre-filter the high-frequency components of the stimulus [4]. The method is validated for a Hodgkin-Huxley (HH) axon-cable model using NEURON v8.0 software. The required activation energy is simulated for rectangular, Gaussian, half-sine, triangular, ramp-up, and ramp-down waveforms, all with pulse durations of 10-1000µs, and low-pass filtered with cut-off frequencies of 0.5-50kHz. Simulations show a 51.5% reduction in the required activation energy for the shortest rectangular pulse (i.e., 10-μs pulse width) after filtering at 5kHz. It is also shown that the minimum required activation energy can be decreased by 11.04%, 9.49%, 8.28%, 1.81%, 0.17%, and 0% when an appropriate pre-filter is applied to the rectangular, ramp-down, ramp-up, half-sine, triangular, and Gaussian waveforms, respectively. Finally, a perspective usage of this method to improve the selectivity of electrical stimulation is drawn.

Developing neuroprosthetic bioelectronic devices requires wirelessly-powered implantable stimulator systems with hundreds to thousands of output channels. Power efficiency optimization is crucial for scaling up the number of output channels. Current-mode electrical stimulation is favored for safety but is power-inefficient in conventional designs, particularly in multichannel stimulators. An adaptive voltage supply can improve power efficiency, but implementing channel-specific voltage supplies in large-scale systems is challenging. Conventional power management suffers from losses and low efficiency due to multiple conversion stages. This work proposes a multichannel current-mode stimulator with a parallel, adaptive ac/dc power management strategy using single-stage phase-controlled converters to prevent cascaded losses. This allows for generating channel-specific supply voltages within a small area for high power efficiency and high-density electrical stimulation. The proposed circuit was designed and simulated using TSMC 180 nm technology and demonstrates an improvement in the power efficiency of up to 45% with respect to a conventional power-management strategy using a fixed supply voltage.

Responsive neuromodulation is increasingly being used to treat patients with neuropsychiatric diseases. Yet, inefficient bridges between traditional and new materials and technological innovations impede advancements in neurostimulation tools. Signaling in the brain is accomplished predominantly by ion flux rather than the movement of electrons. However, the status quo for the acquisition of neural signals is using materials, such as noble metals, that can only interact with electrons. As a result, ions accumulate at the biotic/abiotic interface, creating a double-layer capacitance that increases impedance and negatively impacts the efficiency of neural interrogation. Alternative materials, such as conducting polymers, allow ion penetration in the matrix, creating a volumetric capacitor (two orders of magnitude larger than an area-dependent capacitor) that lowers the impedance and increases the spatiotemporal resolution of the recording/stimulation. On the other hand, the increased development and integration capabilities of CMOS-based back-end electronics have enabled the creation of increasingly powerful and energy-efficient microchips. These include stimulation and recording systems-on-a-chip (SoCs) with up to tens of thousands of channels, fully integrated circuitry for stimulation, signal conditioning, digitation, wireless power and data telemetry, and on-chip signal processing. Here, we aim to compile information on the best component for each building block and try to strengthen the vision that bridges the gap among various materials and technologies in an effort to advance neurostimulation tools and promote a solution-centric way of considering their complex problems.

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.

Bulk piezoelectric ultrasound transducers on integrated circuits offer unique properties for therapeutic applications of ultrasound neuromodulation. However, current implementations of such transducers are not optimized for the high transmit efficiency required to stimulate neurons. This is mainly due to the challenge of implementing a metal layer on top of the piezoelectric film using microfabrication techniques. Here, we propose a micromachined capping structure providing an electrical connection on top of the piezoelectric film with minimal acoustic losses. The structure can potentially be used as a common ground connection in phased-array ultrasound transducers.

2D phased array ultrasonic transducers realized through the combination of bulk piezoelectric ceramics and complementary metal-oxide-semiconductor (CMOS) integrated circuits (IC) are enabling a new range of wearable ultrasound therapeutic applications. Traditional therapeutic ultrasound transducers have an air backing layer to maximize transmitted acoustic intensity. Yet, the pairing of piezoelectric transducers and silicon substrates commonly used in CMOS is still poorly understood. We integrated lead zirconate titanate (PZT) film on silicon membranes of various thicknesses to understand the im-pact of the silicon backing on the performance of bulk piezoe-lectric ultrasound transducers. The transducers with thinner sil-icon membranes exhibited higher acoustic intensity (up to 1.95 times while taking into account frequency shift), which is con-sistent with the simulation in finite element modeling. Transduc-ers with silicon substrate also demonstrated a consistent shift to a higher resonance frequency.

Power efficiency in electrical stimulator circuits is crucial for developing large-scale multichannel applications like bidirectional brain-computer interfaces and neuroprosthetic devices. Many state-of-the-art papers have suggested that some non-rectangular pulse shapes are more energy-efficient for exciting neural excitation than the conventional rectangular shape. However, additional losses in the stimulator circuit, which arise from employing such pulses, were not considered. In this work, we analyze the total energy efficiency of a stimulation system featuring non-rectangular stimuli, taking into account the losses in the stimulator circuit. To this end, activation current thresholds for different pulse shapes and durations in cortical neurons are modeled, and the energy required to generate the pulses from a constant voltage supply is calculated. The proposed calculation reveals an energy increase of 14%–51% for non-rectangular pulses compared to the conventional rectangular stimuli, instead of the decrease claimed in previous literature. This result indicates that a rectangular stimulation pulse is more power-efficient than the tested alternative shapes in large-scale multichannel electrical stimulation systems.

Deep brain stimulation is currently the only technique used in the clinical setting to modulate the neural activity of deep brain nuclei. Recently, low-intensity transcranial focused ultrasound (LIFU) has been shown to reversibly modulate brain activity through a transcranial pathway. Transcranial LIFU requires a low-frequency ultrasound of around 0.5 MHz due to skull attenuation, thus providing poor axial and lateral resolution. This paper proposes a new conceptual device that would use a stent to place a high-frequency ultrasound array within the brain vasculature to achieve high axial and lateral spatial resolution. The first part of this work identified the most commonly treated deep brain nuclei and examined the human brain vasculature for stent placement. Next, a finite element analysis was carried out using a piezoelectric array that follows the blood vessels curvature, and its ability to focus ultrasound waves in clinically relevant brain nuclei was evaluated. The analytical solution provided promising results for deep brain stimulation via a stent with ultrasound transducers for high spatial resolution neuromodulation.