Inexpensive acoustoelectric hydrophone for measuring high intensity ultrasound fields

We describe an inexpensive alternative to conventional hydrophones used to map an ultrasonic beam pattern. Instead of relying on piezo materials to detect pressure, these hydrophones depend on a bias current flowing through a conductive material. According to the well-described acoustoelectric (AE) effect, as a pressure wave interacts with a current field, a voltage is generated. We exploit this principal to design and test a variety of disposable hydrophones composed of common laboratory supplies. Designs varied primarily by the shape and material of their conductive layer, such as graphite or saline gel. The hydrophone was used to map the beam pattern of a 540-khz annular transducer and compared with a conventional fiber optic hydrophone. The detected AE signal was amplified, high-pass filtered and captured using a fast 12-bit acquisition board. The hydrophone in the form of a bowtie and composed of a thin layer of graphite on a paper substrate accurately reproduced the beam pattern and spectrum of the ultrasound transducer with decent sensitivity less than 50 kPa. The detected AE signal at 2 MPa was proportional to the applied bias current (2.90 μV/mA). The axial and lateral resolutions (5.2 and 4.1 mm, respectively) were both within 200 μm of the values obtained from a less sensitive fiber optic hydrophone. The disposable AE hydrophone may be an attractive alternative for clinical applications that require close monitoring of high intensity acoustic fields.