Transcutaneous Energy Transfer

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. Millar has patented, developed and tested, a TET technology and partners with device manufacturers to develop new implantable devices.

What is TET?

At present medical implantable devices which require more power than can be viably provided from a battery, rely on a connection and wire passing through the skin. This breach in the skin presents a serious risk for infection, limiting the use of life-saving devices to very sick patients where the relatively high risk is justified. The solution to this problem is Transcutaneous Energy Transfer (TET) in which power from a coil mounted outside the body flows to a coil located or implanted inside the body by using magnetic fields to transfer energy through or across the intact skin.

transcutaneous energy transfer (TET) devide manufacturers
  • Small implantable coil with a low component count providing enhanced tolerance and easy implantation in a variety of sites.
  • Delivery of up to 10W of power across 10 mm of skin with greater than 80% transfer efficiency.
  • Tolerance to a wide variety of coupling conditions provides for ease of implementation without the need for magnets or tissue adhesives.
  • Six patents under international examination awarded. Key patents have priority dates from 2003.
  • Animal tests confirm at all power transfer levels (up to 10W) tissue temperature does not exceed 40 °C and an absolute temperature increase of 4 °C. Histological analysis after prolonged power transfer confirms the absence of any alterations in tissue effects due to field or heating.

How It Works

Millar’s TET system has been designed to provide a balance between the practical size of the internal components and the performance of the system. The small size of our coils, low component count makes our system commercially viable as a TET system to be integrated with medical devices. 

Our TET system consists of two circular coils (one implanted, one external), an external controller box and a small internal battery.

Energy transfer using an inductive magnetic field is most efficient when the frequency of the magnetic field is at the resonant frequency of the two coils. Our novel approach injects energy into the coils when it's needed to regulate the power flow such that the implanted device receives the correct power – and under a wide tolerance of operating conditions. This technology has been researched and tested over the last 7 years and is currently used in animal monitoring devices which operate continuously.

Partnering With Us 

By partnering with Millar for TET-based technology, you’ll be able to leverage our Innovation and Research and Development teams in Houston and Auckland as well as our relationship with the University of Auckland. Our teams have extensive experience working with multi-disciplinary teams at medical device and life science companies. Through a collaborative process, we ensure the best ideas come forward and allow innovation to come to life.


  • Millar OEM team members have an extensive history in inductive power transfer technology  
  • Proven technology cited in over a dozen publications
  • Opportunity to leverage expertise from the Auckland Bioengineering Institute and the University of Auckland

Get Started

Learn More About TET Research


Download the poster to review the study, "Flexible Alignment Transcutaneous Energy Transfer Power Supply for Fully Implantable Left Ventricular Assist Devices," published by the team at the University of Auckland.


Download a list of relevant publications for TET technology and learn how the technology has been tested for different applications. 


Date: 23 May 2003

Granted Patent No.
NZ 526115
US 8093758 B2
JP 4614961
CA 2526544

Granted in US, NZ, China, Japan and Canada. Good coverage for controlling the power received by the implant (power pickup side) using cycle by cycle switching. Particularly relevant for providing pickup regulation to deal with a strong primary field or provide a safety mechanism if the radio link in not providing feedback. Also circumvents some other patents, not owned by Millar, relating to shorting control.

Date: May 23, 2003

Granted Patent Numbers: NZ 535012, NZ 526116, NZ 529869, US 8,050,068, JP 532160/2006, CN 200480018154.8

Granted in US, NZ, Japan and China. This is an important patent for powering single implantable devices. It covers our method of regulating power across the skin that compensates for variations in coil alignment through implementing a variable frequency primary resonant converter. It is based on implementing a variable capacitor (or inductor) at the primary side which alters the resonant frequency to match the load power needs and prevailing coupling conditions. Our publications reporting on providing 15W into sheep for 1 month was based on this technology.


Date: September 16, 2004

Granted Patent Numbers: GB 2433656, NZ 535390, US 9065284, AU2005285545

Granted in Great Britain, New Zealand and Australia. This is the key patent for small animal devices. Describes having multiple primary coils to power an implanted device of arbitrary orientation. US examiners have allowed US11/575,449 with the inclusion of frequency control in the primary circuit.


Date: August 3, 2005

Granted Patent Numbers: NZ 541629, US 8406017 B2, CN 101268604, GB 2442686, AU 2006276331

This patent describes a self-adjusting primary circuit used in the Millar products TR801/TR802/TR803 and TR875. The implementation is simple and low cost and might be helpful for high volume products.


Date: January 18, 2008

Granted Patent Numbers: NZ 565234, GB 2468990, US 9125242

This patent describes architectures that allow for redundancy and fail-soft operation. Includes multiple secondary coils and ability to switch components in and out to either regulate power, change from a high power to high-efficiency mode or allow for circuit self-recovery if a failure occurs. Most relevant for high power applications like heart pumps.


Date: October 1, 2012

US application number is US14/432,120. This patent describes novel ways of generating energy injection cycle patterns to provide fine level control over power flow and still allow fast response time to changes in alignment or load. This technology is extending the range of changes in alignment that our TET systems will accommodate and maintains a very low component count.