Advanced wireless solutions
for charging implantable devices

Holst Centre has built a unique toolset for wireless communication and powering of implantable devices and smart pills. Both implants and pills can be close to the skin surface or deeper in the body. With this toolset medical device companies can develop customized solutions in a relatively short period of time. 

At Holst Centre we believe that new technologies can change the life of chronic patients with implants. We recently launched an ultra small radio chip: 30 times smaller than state-of-the-art systems performing the same functionality. This chip can be used to set up a wireless link with smart pills, small implantables and insertables, to exchange data. Our chip is also designed to make recharging much easier and user-friendlier, or to even make devices that don’t require any battery. Therefore, it leverages with the lower-power system design as reported by Holst Centre in the past.

With a battery-less implant the patient would wear an external device like a patch or belt with a battery, a radio chip and an antenna that sends wireless signals to power the implanted device for a short period of time to do the necessary sensing and stimulation. The implant can afterwards be depowered when the therapy allows for that.

Which wireless technology to choose?

Holst Centre has a lot of expertise in all kinds of wireless communication technologies. We believe that every application has different requirements when it comes to wireless communications with an implant: for exchanging sensor data and actuation instructions, for reprogramming, etc. For the wireless charging, we are investigating inductive coupling, RF signals and ultrasound technologies.

• Inductive wireless powering is the most used technique for powering implants because the magnetic permeability of the body is almost equal to the one of air. Because of that, the path losses in the human tissues are close to insignificant. Another important advantage is the relatively large power density safety limit, up to 100mW/mm². In addition, since energy is not transferred via wave propagation, no energy is lost because of reflections by the skin and between tissues with different properties. However, inductive powering suffers from strong sensitivity to misalignment between the power-transmitting coil outside the body and the implanted receiving coil. This limits its adoption to cases in which the location of the implant is known in advance.
  
  

• Wireless RF powering using mid-field or far-field radio frequency electromagnetic waves on the other hand is less sensitive to misalignment. However, radio frequency power transmission suffers from significant path losses in human tissue. Additionally, safety power-limits are 1000 times lower. Also, since the energy transfer happens via wave propagation, significant reflection occurs already at the interface between air and skin. Finally, since the body is not a homogeneous medium, multi-path reflections will occur also inside the body, reducing further the effectiveness of this technique.
  
  

• Wireless power transfer can also occur via mechanical means, via ultrasound pressure waves. Given that the body is mostly composed of water, the propagation of sound waves is very effective and path losses are low while the safety power limits are reasonable. The main challenge with ultrasound power transfer is the reflection coefficient between air and skin, which is as high as 99.9%. In order to mitigate this loss, good acoustic coupling must be ensured in the whole path from transmitter to receiver. This implies the use of acoustic gels and the implant must remain in close contact with the tissue in order to receive power. Even then, good acoustic coupling cannot be guaranteed throughout the body, for example due to the presence of bone tissue. So again, every application has different requirements and a different optimal technological solution.

Custom designed solutions

Thanks to our expertise in IC design, system design and integration, it is possible to make very compact radio solutions that support different radio technologies for wireless communication and charging. For every specific application, a customized solution may work. These capabilities can be extremely interesting for medical device companies to innovate in the field of implantables, insertables and ingestibles.

We have an extensive toolset ready to mix and match our knowledge and our technological building blocks to make a dedicated solution for each specific application. Our long track record in the development of wearable solutions (including regulatory approved medical devices both in the US FDA and Japan’s PMDA) strengthens the system-level proposition, being able to offer both implants and external wearable solutions to power them. The possibilities are enormous, and, together with medical device companies with much more experience on the application-end, we can make true innovations happen. In the design process, Holst Centre is the best partner in selecting, developing and optimizing the best technology for the specific application.