Capacitive-coupling-based information transmission system for implantable devices: investigation of transmission mechanism

Development of a battery-free ultrasonically powered functional electrical stimulator for movement restoration after paralyzing spinal cord injury

BACKGROUND

Functional electrical stimulation (FES) is used to restore movements in paretic limbs after severe paralyses resulting from neurological injuries such as spinal cord injury (SCI). Most chronic FES systems utilize an implantable electrical stimulator to deliver a small electric current to the targeted muscle or nerve to stimulate muscle contractions. These implanted stimulators are generally bulky, mainly due to the size of the batteries. Furthermore, these battery-powered stimulators are required to be explanted every few years for battery replacement which may result in surgical failures or infections. Hence, a wireless power transfer technique is desirable to power these implantable stimulators.

METHODS

Conventional wireless power transduction faces significant challenges for safe and efficient energy transfer through the skin and deep into the body. Inductive and electromagnetic power transduction is generally used for very short distances and may also interfere with other medical measurements such as X-ray and MRI. To address these issues, we have developed a wireless, ultrasonically powered, implantable piezoelectric stimulator. The stimulator is encapsulated with biocompatible materials.

RESULTS

The stimulator is capable of harvesting a maximum of 5.95 mW electric power at an 8-mm depth under the skin from an ultrasound beam with about 380 mW/cm2 of acoustic intensity. The stimulator was implanted in several paraplegic rats with SCI. Our implanted stimulator successfully induced several hindlimb muscle contractions and restored leg movement.

CONCLUSIONS

A battery-free miniature (10 mm diameter × 4 mm thickness) implantable stimulator, developed in the current study is capable of directly stimulating paretic muscles through external ultrasound signals. The required cost to develop the stimulator is relatively low as all the components are off the shelf.

Implantable Device Positioning based on Magnetic Field Detection using Genetic Algorithm in Body Area Biosensor Networks

Background:

Minimally invasive medical care by the aid of Information Communication Technology (ICT) has attracted considerable attention. Sensor nodes including implantable devices within the bio-sensor network or Body Area Network (BAN) have been utilized to reduce the burden on patients. To control the operation of devices properly or collect vital data effectively, it is important to obtain accurate information on their position.

Methods:

This paper provides an effective positioning method based on the detection of magnetic fields generated from implantable devices using the Genetic Algorithm (GA). After providing the principle of the proposed method, some laboratory test measurement results are given to confirm its effectiveness.

Results:

Magnetic field detection using multiple magnetic field sensors was achieved. From the results of multiple point measurements on the three-dimensional components of the magnetic field strength, the position of the target was obtained with a smaller error. Laboratory test measurement results are in good agreement with the theoretical values.

Conclusion:

The proposed positioning method is an effective and an economical approach. It is also effective for detecting moving devices such as a capsule endoscope in a human body. With the aid of the GA, high-speed detection is obtained with a low calculation costs. The compressed sensing method reduces the number of measurement points.

Investigation of implantable signal transmission characteristics based on visible data of the human leg

Background

Signal transmission characteristics between implanted medical devices and external equipment has been a common key issue, as has the problem of supplying energy to the devices. It can be used to enable signal transmission from implanted devices that the human body’s conductive properties. Using signal transmission by galvanic coupling is one of the most effective signal transmission methods.

Methods

The signal transmission characteristics by galvanic coupling of implantable devices using a frequency range of 10 kHz to 1 MHz was analyzed in this article. A finite element (FEM) model and a phantom model established by visible human leg data were used to investigate the signal transmission characteristics of implant-to-surface, with implantable receiver electrodes at different locations.

Results

The results showed that the FEM model and the phantom model had similar implantable signal transmission characteristics, with an increase of frequency, signal attenuation basically remained unchanged. The gain in signal attenuation in the fixed attenuation values fluctuated no more than 5 dB and signal attenuation values rose as the channel length increased.

Conclusions

Our results of signal transmission characteristics of surface-to-implant will provide a theoretical basis for implantable transceiver design, and for realization of a recharging method for implanted medical devices.