Wavelength-Scaled Design and Validation of an Aluminum Horn Needle Hydrophone Attachment for Ex Vivo Transcranial Ultrasound Applications

Purpose Accurate measurement of ultrasound acoustic fields in biological tissues is essential for the characterization and calibration of therapeutic ultrasound devices, particularly in transcranial applications where high spatial resolution, broadband sensitivity, and controlled directivity are required. This paper presents a physically grounded framework for the design and validation of an acoustic horn needle attachment compatible with existing commercial ultrasound transducers, avoiding the need to develop fully custom hydrophone systems. Methods Numerical simulations were performed in COMSOL Multiphysics to investigate guided longitudinal wave propagation within the horn needle and to optimize key geometric parameters, including needle length and base transition geometry, using frequency-domain parametric studies over the 1–5 MHz range. Cylindrical, conical, and exponential horn geometries were evaluated in terms of geometry optimization, directivity and sensitivity. Experimental validation was carried out by mechanically coupling the optimized horn needle toa commercial piezoelectric transducer (Mitech, 1 MHz, 24 mm diameter) using epoxy adhesive bonding. Results The assembled system was characterized experimentally in water and in a cranial medical phantom. Measured receiver sensitivity ranged from − 53.34 to − 33.6 dB re 1 V/μPa over a bandwidth from 0.1 to 9 MHz. Sound transmission loss values between 63.4 and139.2 dB were obtained in the 0.5–5 MHz range at a depth of 15 mm within the brain-mimicking region, in agreement with values reported in the literature. Conclusion Overall, the results demonstrate that wavelength-scaled horn needle attachments can achieve performance comparable to custom hydrophones, providing a reproducible and versatile solution for broadband ultrasound field characterization.