Wireless power transfer for implantable medical devices that restore sight
Worldwide, there are more than 43 million blind persons.
That number has climbed by nearly 50% during the last 30 years. The majority of
blind persons are born with normal vision and gradually lose their sight as a
result of illnesses or accidents.
Frequently, the eyes or the connection between the eyes
and the brain are injured or lost, but the visual cortex in the brain is still
able to interpret electrical impulses. By using an implant to deliver the
proper electrical signals to the visual cortex, it is possible to partially
restore vision. Tom van Nunen, a Ph.D. researcher, has created a wireless
energy transfer system and created a prototype to link to the implant securely
and consistently.
The eyes gather optical data, which is then delivered
together with neuroelectric impulses to the visual cortex in the brain. What
people think they see is how they interpret this input. It is well known that
when their brain is triggered by electrical stimulation, even blind people can
detect some visual cues.
By establishing a connection between an external image
source, such as a camera, and electrodes implanted in the visual cortex, a
blind individual can experience a crude form of vision with these visual
stimuli.
The NESTOR
project, of which Van Nunens's research is part, aims to create such a visual
prosthesis. The brain implant the team is currently developing includes systems
for wireless data transfer, controlling the electrodes and wireless energy
transfer, among other things.
Wireless connection
In his Ph.D. studies, Van Nunen targeted at the
improvement of the wi-fi connection among the enter tool and the implant. A
wi-fi connection is tons extra comfortable, bendy and secure for the consumer
of the implant, however the query is: are they strong and effective enough?
Miniaturization is a non-stop improvement withinside the
international of scientific implants. Not most effective does this make current
packages smaller (~1 mm3), which has numerous blessings for the wearer of the
implant in phrases of comfort. It additionally reduces the scientific
complexity of putting the implants withinside the body. However, this makes the
implants too small to incorporate their personal electricity supply together
with batteries. Therefore, the implants want to be powered thru an wi-fi
connection.
In the case of an implant of some millimeters in size,
located at a intensity of some centimeters withinside the body, preceding
studies shows that the performance of wi-fi electricity switch is finest at GHz
frequencies. This operation regime is known as midfield wi-fi electricity
switch (MF-WPT), wherein electricity is transferred the use of propagating
waves, as opposed to induction.
Modeling optimal power transfer
Still, the predicted performance in wi-fi energy switch
to miniature implants stays as an alternative low. Using an opportunity method,
Van Nunen observed that maximizing obtained energy is a higher method than
maximizing performance to get the favored results. To decide the first-class
frequencies to use, he used analytical
fashions to calculate the electromagnetic fields.
In his thesis, he describes how he prolonged the
fashions to calculate the unique absorption rate (SAR-rate) of electromagnetic
radiation withinside the human body, the obtained energy, and general
dissipated energy withinside the tissue.
The records calculated with those fashions may be used
to decide the most transmit energy such that the SAR protection limits aren't
exceeded. It seems that each the best obtained energy and the best switch
performance are observed at 10 kHz, a far decrease frequency than recommended
through preceding research.
Biomedical phantoms
To validate his findings, the researcher used so-known
as biomedical phantoms, which mimic particular homes actual human tissue,
taking care to create substances whose dielectric homes are in an appropriate
variety and continue to be steady for an prolonged length of time.
Van Nunen gives numerous phantom recipes which can be
primarily based totally on simply to be had ingredients, along with water,
sugar and salt, and may be made with in a easy kitchen-like setup. What`s more,
the homes of the phantoms he offers continue to be nearly steady for at the
least ten days, making them very appropriate for his tests.
Self-made sensor
The phantoms he advanced and defined are homogeneous
substances. However, the human frame isn`t homogeneous. In a few instances it
is able to be vital to feature different information into the combinationture
to higher mimic the vicinity of an implant withinside the frame. The presence
of our cranium and tooth can also additionally as an example effect the manner
electromagnetic waves journey among the outside tool and the implant.
One method is to feature synthetic bones to the phantom,
for instance created with 3D-printing technology. Using a reasonably-priced
self-made sensor, Van Nunen become capable of degree the dielectric homes of
numerous commercially to be had 3D-printing filaments.
Some of those substances have dielectric homes which can
be near the ones of bone for positive frequency bands, and may for that reason
be utilized in biomedical experiments.
