Simulation of low-frequency sonophoretic piezoelectric transducer applied over human skin

Sonophoresis is the process that involves the passage of drug molecules through the skin under ultrasonic stimulation. Drugs with a molecular weight greater than 500 daltons require some kind of stimulus to catalyze their penetration into the skin. Low-frequency sonophoresis, i.e., applying low-frequency (20–100 kHz) ultrasonic waves, is one of the active methods of stimulation used in transdermal drug delivery. The aim of this research is to explore the possibility of achieving high enough acoustic pressures inside human skin using a single-element piezoelectric transducer required to realize the transdermal delivery of drugs with a high molecular weight. Therefore, this paper presents a design and simulation of a single-element transducer to find voltage versus sound pressure levels (SPLs), as well as frequency response curves for low-frequency sonophoresis on human skin. A piezoelectric transducer composed of PZT-5H placed over human skin was simulated by combining the pressure acoustic module, solid mechanics, and electrostatic modules of the simulation tool. The presented simulation applies sinusoidal excitation to a PZT-5H-based transducer. The peak voltage and the frequency of the input are varied to study the resulting variations in acoustic pressure and SPL inside the human skin. Measurements of acoustic pressure are taken 0.1 mm deep into the human skin. The peak acoustic pressure increases linearly from 0.072 Pa to 0.72 Pa as the peak applied voltage increases from 1 mV to 10 mV. The peak acoustic pressure increases exponentially from 0.2 mPa to 5 mPa as the frequency varies from 20 kHz to 100 kHz for a constant peak voltage of 1 mV. The SPL achieved at 880 kHz is 186 dB, which is suitable for drug delivery in some areas of medicine, such as ophthalmology.