Ultrathin wearable ultrasound patch with anti-matching for carotid artery monitoring

Carotid ultrasound provides structural, motion-related, and flow-related information for cardiovascular assessment. However, conventional handheld examinations are limited by short acquisition windows and the need for stable probe positioning. Wearable carotid ultrasound may enable long-term and hands-free monitoring, but achieving a thin transducer profile while maintaining adequate imaging performance remains challenging. Here, we present an ultrathin anti-matching-layer ultrasound patch (UTAM-UP) for carotid-region monitoring. A double anti-matching-layer (AML) stack was designed using a transmission-line model. Under the dual quarter-wavelength condition, a closed-form rear-side impedance-transformation relation was derived to guide AML material and thickness selection, and the complete stack was evaluated using a Krimholtz-Leedom-Matthaei (KLM) model. The fabricated 128-element patch integrates a locally rigid linear array and a flexible printed-circuit interconnect without a conventional absorptive backing. The active acoustic stack was 0.73 mm thick, while the fully assembled device had a maximum thickness of 1.14 mm. The mean center frequency and -6 dB fractional bandwidth were 6.91 MHz and 61.0%, respectively. Phantom imaging achieved axial and lateral resolutions of 0.359 and 0.455 mm, respectively. In vivo experiments demonstrated hands-free B-mode and M-mode acquisition, with M-mode-derived beat-to-beat intervals evaluated against simultaneously recorded electrocardiogram (ECG) as an independent temporal reference.