Ultrasonic Wireless Power and Data Communication for Neural Stimulation

Wireless neural stimulation has gained wide interest, as it has potential in several clinical applications such as deep brain stimulation and neuromuscular stimulation. Most of the exiting wireless power and data transmission methods are using electromagnetic waves in the radio frequency range. However, the power transmission in this case often has limited penetration. In this study, we propose ultrasound as vehicles for both power and data transmission for wireless, implantable neural stimulation. The main advantage is that ultrasound in the MHz range can be focused at depth, thus providing an effective way for power transmission under FDA safety limits. In addition, the weak acoustic scattering in soft tissues also allows accurate data communication with the implanted device using ultrasound. To demonstrate the feasibility, we have designed and fabricated a prototype device, which consists of a PVDF transducer (1MHz center frequency and 6mm diameter) and a custom design IC that performs AC-DC conversion and decoding of the ultrasound signals for controlling the neural stimulator. power is measured and compared to the power consumption required by the stimulation circuit. Variations of amplitude-shift keying (ASK), frequency-shift keying (FSK) and phase-shift keying (PSK) are all tested and bit error rates (BERs) are calculated to assess performance of different coding schemes. A tissue mimicking phantom with speckle generating background and acoustic attenuation at 0.5dB/MHz/cm is used during measurements. At an acoustic power of 112 mW from the transmit transducer, 4.15 mW can be received and made available by the device, which only consumes a power of 1,8 mW for neural stimulation. A BER of 10(-6) at 25 kbps data rate is achieved. With the current device, it is possible to increase the transmission power to as high as 19.76 mW without exceeding the FDA safety limits (Ispta=720mW/cm2). A smaller transducer can also be used to reduce the size of the implantable device. Feasibility of ultrasonic wireless neural stimulation is clearly demonstrated.