Frequently Asked Questions

MEMS stands for “MicroElectroMechanical System”.  “Micro” means these devices measure less than a millimeter in any direction. They are “systems” in that they employ both electrical and mechanical forces in a single unit.

MEMS pressure sensors make use of piezoelectricity. Pressure applied to certain materials produces an electrical voltage, which can be measured.

Millar pressure transducers are the “gold standard” for accurate measurement of pressure in humans and research animals. Throughout Millar’s history, the company has developed progressively smaller sensors both to minimize interference with physiological parameters and to access smaller venues. Miniaturization to the level of MEMS devices opens up new opportunities for acquisition of pressure information in greater detail and from formerly inaccessible areas.

Transcutaneous (across skin) energy transfer (TET) systems allow powering of an implantable device by wirelessly transferring power across the skin eliminating the need for a percutaneous driveline. TET systems that operate by inductive power transfer generally consists of two coils of electrical wires. Externally, a power source supplies an AC current to an external coil which generates an oscillating magnetic field. This oscillating magnetic field extends a certain distance in all directions and is capable of penetrating non-metallic materials such as air, or human skin and fat. When the second coil (implanted) is brought into the range of the magnetic field (the coils are now ‘coupled’), the magnetic field is used to generate an electrical current, which is then converted to DC power to be used to power devices. 

When the external coil is not directly on top of the internal coil and on the same plane, the coils are said to be misaligned. This can happen easily as a result of patient movement, postural changes, tissue swelling or oedema, and changes in fat tissue surrounding the implanted coil. The implication is that if the coils are sufficiently misaligned, the implanted coil may be out of the range of the magnetic field generated by the external coil, and thus power transfer stops. Therefore, the amount of tolerance to misalignment is an important feature of a TET system.

Misalignment issues can be minimized by choosing an area to place the implanted coil that is less susceptible to postural changes or changes in tissue fat, as well as improving the tolerance of a system to misalignment. 

Millar’s TET system has a high tolerance for misalignment due to its dynamic operating frequency to follow the changes in the resonant frequency of the coils.  It is important to note that the resonant frequency of the coils does not remain constant but varies with the changes in load and the alignment between the two coils.    

Other TET systems use a fixed frequency (close to the resonant frequency of the system) regardless of the shifting nature of the resonant frequency with variations in coil alignment. This means that when the coils are misaligned and the resonant frequency of the system changes, other systems no longer operates on resonant frequency and the range of the oscillating magnetic field becomes smaller. A smaller oscillating magnetic field means that the implanted coil becomes out of range at shorter distances away from the external coil and there is less tolerance to movement before power transfer stops. These coils will often need to be secured in place with tissue adhesive or magnets to ensure proper alignment, at the expensive of comfort and convenience of the patient. 

The novelty of our system is that the frequency at which the system operates is dynamic and changes when the alignment of the coils change such that such that the system always operates on resonant frequency. The larger range of the magnetic field generated by the external coil when operating on resonant frequency allows up to 20mm of a movement of the external coil from the implanted coil. The high tolerance of our system to coil misalignment means the system is easy to use and can be implemented without the need for adhesive or magnets to secure the coils in place.