Wearable Ultrasound Reaches Low-Power B-Mode Imaging

Wearable ultrasound sits between two conflicting requirements: continuous physiological monitoring needs small, battery-powered hardware, while clinically useful ultrasound imaging usually needs multi-channel acquisition, high-voltage transmit pulses, low-noise receive electronics, and enough bandwidth for array data. The authors position WULPUS PRO against that gap. Existing wearable ultra-low-power systems mostly support shallow A-mode sensing, while larger multi-mode ultrasound platforms are less suitable for true body-worn use.

WULPUS PRO is the paper’s answer: a 39 × 21 × 6 mm, 5 g acquisition front end that can operate as a programmable wearable ultrasound module rather than a fixed single-use sensor. The central claim is not that it matches cart-based imaging systems. It is that a compact, low-power board can now support 16-channel synthetic-aperture B-mode acquisition, both piezoelectric and CMUT transducers, and wireless host integration within a wearable power budget.

Core Contribution

The main contribution is an ultrasound acquisition platform that moves beyond single-channel or A-mode wearable sensing without giving up the constraints that make wearability plausible. The system integrates 30 V excitation, 16 time-multiplexed channels, a receive chain with up to 70 dB total gain, time-gain compensation, optional analog envelope extraction, and an 8-Msps ADC. The receive path is reported with 9.9 MHz bandwidth, 32 dB SNR, and roughly 1.4 MHz end-to-end bandwidth.

The paper’s more distinctive hardware point is transducer flexibility. WULPUS PRO supports conventional piezoelectric arrays and polymer-based capacitive micromachined ultrasonic transducers, which matters because skin-conformal CMUT arrays are a plausible route to long-duration monitoring. The authors report full compatibility with both transducer types and give the polymer CMUT implementation a high fractional transmit bandwidth of 94%.

Technical Approach

WULPUS PRO separates the ultrasound front end from the communication host. That design choice is practical: the same acquisition module can connect to BLE or Wi-Fi modules, letting the designer trade data rate, battery life, and application requirements without redesigning the ultrasound electronics. The conclusion emphasizes this host-agnostic role as part of the architecture rather than a side feature.

On the acquisition side, the board supports two operating modes. In RF-sampling mode, it can acquire deep-tissue echoes up to 2.2 MHz. In envelope-detection mode, an ultra-low-power envelope detector demodulates the RF signal before digitization, reducing sampling and data-throughput demands while supporting transducers up to about 8 MHz with 1.5 MHz envelope bandwidth. The authors report that this envelope detector consumes less than 2 mW in active mode, which is a meaningful figure because wireless transmission and battery capacity often dominate wearable system design.

For imaging, the paper uses low-channel-count synthetic-aperture B-mode reconstruction. The authors adapt an open-source beamforming framework to implement delay-and-sum with coherence-factor weighting, using plane-wave B-mode acquisition at 300 Hz PRF. The coherence weighting is included to emphasize spatially coherent echoes and suppress clutter or sidelobe artifacts, which is useful when the array has only 16 channels.

Results and Analysis

The evidence is strongest at the system-demonstration level. WULPUS PRO achieves B-mode imaging on a tissue-mimicking phantom, with approximately 0.7 mm axial resolution and about 2.3 mm lateral resolution at the center of the field of view using a 2.25 MHz transducer. The authors compare this with TinyProbe using delay-and-sum beamforming: TinyProbe gives a similar axial resolution of 0.8 mm and better lateral resolution of 1.6 mm. That comparison is useful because it prevents the result from being read as unqualified image-quality parity. WULPUS PRO’s lateral resolution is worse, but the paper argues that the signal quality is sufficient for useful B-mode imaging within a smaller, lower-channel wearable architecture.

Power is the other key result. The platform consumes less than 50 mW at 50 Hz PRF and less than 60 mW at 300 Hz PRF. With a compact 300 mAh, 6.4 g Li-Po cell, the authors project at least all-day BLE operation at 50 Hz PRF and multi-hour Wi-Fi operation at 300 Hz PRF, with the abstract giving 1–2 days for BLE and more than 3 hours for Wi-Fi streaming. Those are projections tied to external wireless modules rather than an integrated sealed wearable, but they make the power numbers concrete.

The CMUT result is promising but still early. The paper states that lower lateral resolution with the polymer CMUT array is mainly due to its smaller effective aperture, because only half the element pitch is acoustically active. That reduces active area per channel, lowers sensitivity, and increases reconstructed-image noise. The authors frame this as a trade-off: polyCMUTs bring small form factor, low weight, skin conformability, and low-cost production potential, but good lateral resolution at high SNR still wants a larger array aperture.

Limitations

The results support the claim that WULPUS PRO establishes a low-power, programmable wearable ultrasound front end with B-mode capability. They do not yet show a finished long-term clinical wearable. The imaging demonstrations are phantom-based, the wireless operation appears to rely on external BLE and Wi-Fi hosts, and the battery-life figures are projected from a 300 mAh cell. The authors also identify future work on custom arrays tuned to operating frequency, size requirements, and imaging constraints, plus evaluation of long-term reliability under direct and indirect DC bias conditions.