Higher harmonics dynamic focalization in single-element ring transducers using biaxial driving

Area of Science:

• Ultrasound Technology
• Biomedical Engineering
• Acoustic Physics

Background:

• Biaxial driving is an innovative technique for steering ultrasound fields using single-element piezoceramic transducers.
• Ring transducers, due to their axisymmetric geometry, are well-suited for biaxial driving to manipulate beam focus with two signals.

Purpose of the Study:

• To investigate the application of biaxial driving to a single-element PZT ring transducer for altering focal spot size and position.
• To evaluate the effects of different harmonic excitations (1st, 3rd, and 5th) on the transducer's focal characteristics.

Main Methods:

• A single-element PZT ring transducer (500 kHz) with biaxial driving capabilities was utilized.
• The transducer's focal properties were analyzed using harmonic excitations at 482 kHz (1st), 1.362 MHz (3rd), and 2.62 MHz (5th).
• Simulation and experimental measurements were conducted to assess focal area size and position based on driving signal phase and power differences.

Main Results:

• Biaxial driving successfully modified both the size and position of the focal spot.
• The focal area was reduced by up to 89% (from 31.6 mm² to 3.4 mm²) at the first harmonic.
• Dynamic displacement of the focal spot center was achieved, ranging from 3.0 mm to 9.3 mm from the transducer surface, depending on the harmonic used.

Conclusions:

• Biaxial driving offers precise control over the focal characteristics of PZT ring transducers.
• The ability to dynamically adjust focal spot size and position is highly advantageous for preclinical focused ultrasound applications.
• Potential applications include enhanced drug delivery and neuromodulation studies in small animal models.