Wireless Power and Data Transmission for Implanted Devices via Inductive Links: A Systematic Review
Implanted medical devices (IMDs) placed inside the body play a crucial role in monitoring and diagnosing diseases and disorders, even stimulating and improving the function of individual parts. The IMDs require a stable and continuous power source. Internal power sources, such as batteries or supercapacitors, need periodic replacement through invasive procedures. WPT is a secure and efficient technique for power and communication transmission in implanted devices, with minimum risk of infection.
The researchers present an analytical study of contemporary wireless power and data transmission techniques for IMDs. The application of wireless power transfer techniques has grown tremendously, from recharging power sources to powering a device. Wireless power transmissions (WPT) usually employ concepts like inductive, ultrasound, optical, capacitive, and electromagnetic links. The study systematically analyses current wireless power and data communication systems based on various key parameters and factors such as the link type, power carrier frequency, data transmission rates, modulation schemes, the distance between receiver and transmitter coils, power transfer efficiency, energy consumption per bit transmission, and receiver area.
Inductive power transmission (IPT) has a comparatively higher power transfer efficiency (PTE) and lower tissue wave absorption. It is a straightforward and safe power transmission technique for biomedical applications, such as brain and neural implants, cochlear implants, and spinal cord stimulators.
An electric current flowing through a coil generates a magnetic field. A part of the flux generated by the first coil gets absorbed by the second coil and induces an alternating current. This inductive power transmission is wireless and used in implantable devices.
The purpose of power transmission to IMDs is to provide the energy needed to send and receive data from or to the body or brain. The downlink communication sends commands from the external unit to IMD to stimulate the brain or body. Similarly, uplink data transfer sends the essential system-related or biological parameters back to the external monitoring unit. Many data modulation schemes are available to filter out noise and disturbances before and after transmission, thus reducing false readings.
Inductive power transmission techniques were categorized based on the number of inductive links and the geometric structures of the coils. Independent transmissions for power and data require simple configuration but have limited bandwidth. The simultaneous transmission of power and data offers a larger bandwidth but suffers from system complexity. Orthogonal and coplanar coils used in multiple inductive links eliminate crosstalk between the links. Data communication between IMDs and external units can be improved using radio frequency (RF) links.
IMDs offer an opportunity to acquire biological data, monitor and diagnose body and brain disorders and dysfunctions, and minimize the risk of surgical infections. Rapid developments in technology address the area constraint of implanted devices.
Emerging biomedical devices considerably improve the standard of living and longevity of patients. The WPT in these devices further reduces the requirement for invasive procedures and the risk of infection.
The methodological study and comparison of existing WPT schemes' strengths and limitations vis-à-vis specific purposes demonstrate the scope for future improvement and research.