Compact Low-Cost Wireless Ultrasonic System for Non-Destructive Testing and Wearables

Continuous ultrasound monitoring for non-destructive testing (NDT) and wearables requires systems that are miniature, energy efficient, and tightly integrated with low-profile sensor arrays for unobtrusive, multiday operation. Existing solutions struggle to balance size, power, and functionality. This paper presents a compact, low-cost, fully integrated wireless ultrasound patch for long-term single-channel pulse-echo monitoring. The system is derived from WULPUS, an open-source platform for wearable low-power ultrasound, and is optimized for size and bill-of-materials while supporting polymer-based capacitive micromachined ultrasonic transducers (polyCMUTs). PolyCMUTs enable thin (<1 mm) form factors, broad bandwidth, rapid prototyping, and low fabrication cost. The electronics, built entirely from off-the-shelf components, integrate a Bluetooth transceiver for connectivity, a microcontroller with a high-speed analog-to-digital converter, and an ultrasonic front end capable of 30 V unipolar excitation and a 30 V bias tailored to polyCMUT operation. A flexible interposer PCB allows direct wire bonding of the transducer and mates to a main PCB with a rechargeable 400 mAh cell sandwiched between boards; data can be streamed wirelessly to a host for real-time processing and visualization. The assembled device measures 28 mm × 26 mm × 12 mm, weighs 13.3 g, with estimated production costs approximately $25 USD. Active-mode power is <33 mW, supporting >40 h of continuous operation at a measurement rate of 50 Hz. Pulse-echo tests in deionized water demonstrated high signal strength, with receiver amplitudes up to 1.1 Vpp at 13.8 dB gain.