Navigation Links
A millimeter-scale, wirelessly powered cardiac device
Date:8/31/2012

A team of engineers at Stanford has demonstrated the feasibility of a super-small, implantable cardiac device that gets its power not from batteries, but from radio waves transmitted from outside the body. The implanted device is contained in a cube just eight-tenths of a millimeter in radius. It could fit on the head of pin.

The findings were published in the journal Applied Physics Letters. In their paper, the researchers demonstrated wireless power transfer to a millimeter-sized device implanted five centimeters inside the chest on the surface of the hearta depth once thought out of reach for wireless power transmission.

The paper's senior author was Ada Poon, a professor of electrical engineering at Stanford. Sanghoek Kim and John Ho, both doctoral candidates in Poon's lab, were first authors.

The engineers say the research is a major step toward a day when all implants are driven wirelessly. Beyond the heart, they believe such devices might include swallowable endoscopesso-called "pillcams" that travel the digestive tractpermanent pacemakers and precision brain stimulators; virtually any medical applications where device size and power matter.

A revolution in the body

Implantable medical devices in the human body have revolutionized medicine. Hundreds of thousands if not millions of pacemakers, cochlear implants and drug pumps are today helping people live relatively normal lives, but these devices are not without engineering challenges.

First off, they require power, which means batteries, and batteries are bulky. In a device like a pacemaker, the battery alone accounts for as much as half the volume of the device it drives. Second, batteries have finite lives. New surgery is needed when they wane.

"Wireless power solves both challenges," said Poon.

Last year, Poon made headlines when she demonstrated a wirelessly powered, self-propelled device capable of swimming through the bloodstream. To get there she needed to overturn some long-held assumptions about delivery of wireless power through the human body.

Her device works by a combination inductive and radiative transmission of power. Both are types of electromagnetic transfer in which a transmitter sends radio waves to a coil of wire inside the body. The radio waves produce an electrical current in the coil sufficient to operate a small device.

There is an indirect relationship between the frequency of the transmitted radio waves and the size of the receive antenna. That is, to deliver a desired level of power, lower frequency waves require bigger coils. Higher frequency waves can work with smaller coils.

"For implantable medical devices, therefore, the goal is a high-frequency transmitter and a small receiver, but there is one big hurdle," explained Kim.

Ignoring consensus

Existing mathematical models have held that high frequency radio waves do not penetrate far enough into human tissue, necessitating the use of low-frequency transmitters and large antennastoo large to be practical for implantable devices.

Ignoring the consensus, Poon proved the models wrong. Human tissue dissipates electric fields quickly, it is true, but radio waves can travel in a different wayas alternating waves of electric and magnetic fields. With the correct equations in hand, she discovered that high-frequency signals travel much deeper than anyone suspected.

"In fact, to achieve greater power efficiency, it is actually advantageous that human tissue is a very poor electrical conductor," said Kim. "If it were a good conductor, it would absorb energy, create heating and prevent sufficient power from reaching the implant."

According to their revised models, the researchers found that the maximum power transfer through human tissue occurs at about 1.7 billion cycles per second.

"In this high-frequency range, we can increase power transfer by about ten times over earlier devices," said Ho, who honed the mathematical models.

The discovery meant that the team could shrink the receive antenna by a factor of ten as well, to a scale that makes wireless implantable devices feasible. At that the optimal frequency, a millimeter-radius coil is capable of harvesting more than 50 microwatts of power, well in excess of the needs of a recently demonstrated eight-microwatt pacemaker.

Additional challenges

With the dimensional challenges solved, the team found themselves bound in by other engineering constraints. First, electronic medical devices must meet stringent health standards established by the IEEE, particularly with regard to tissue heating. Second, the team found that receive and transmit antennas had to be optimally oriented to achieve maximum efficiency. Differences in alignment of just a few degrees could produce troubling drops in power.

"This can't happen medical devices," said Poon. "As the human heart and body are in constant motion, solving this issue was critical to the success of our research."

The team responded by designing an innovative slotted transmit antenna structure. It resembles a swastika, but delivers consistent power efficiency regardless of orientation of the two antennas.

The new design serves additionally to focus the radio waves precisely at the point inside the body where the implanted device rests on the surface of the heart, increasing the electric field where it is needed most, but canceling it elsewhere. This helps reduce overall tissue heating to levels well within the IEEE standards. Poon has applied for a patent for the antenna structure.


'/>"/>
Contact: Andrew Myers
admyers@stanford.edu
650-736-2245
Stanford School of Engineering
Source:Eurekalert

Related biology news :

1. Heart-powered pacemaker could one day eliminate battery-replacement surgery
2. Research yields two firsts regarding protein crucial to human cardiac function
3. Sickle cell trait can cause sudden cardiac death in black athletes: Why is this controversial?
4. An economical, effective and biocompatible gene therapy strategy promotes cardiac repair
5. New method generates cardiac muscle patches from stem cells
6. Pilot Results Move GHX Closer to Delivery of Healthcare Industrys First Implantable Device Supply Chain Solution
7. Nowhere to hide: New device sees bacteria behind the eardrum
8. Tattoo-like devices for wireless pregnancy monitoring
9. NJIT professor awarded patent today for new desalination devices, more
10. Medical device, health professionals attend first national conference on value-driven engineering
11. Global Surgical Devices Market Growth Driven by Improving Standards of Living and Longer Life Expectancies, Research Shows
Post Your Comments:
*Name:
*Comment:
*Email:
(Date:4/14/2016)... 2016 BioCatch ™, the ... announced the appointment of Eyal Goldwerger as ... Goldwerger,s leadership appointment comes at a time of ... deployment of its platform at several of the world,s ... discerns unique cognitive and physiological factors, is a winner ...
(Date:3/31/2016)... March 31, 2016   ... or the "Company") LegacyXChange is excited to ... its soon to be launched online site for trading ... ) will also provide potential shareholders a sense ... technology to an industry that is notorious for fraud. ...
(Date:3/29/2016)... Florida , March 29, 2016 ... the "Company") LegacyXChange "LEGX" and SelectaDNA/CSI Protect are pleased ... in ink used in a variety of writing instruments, ... Buyers of originally created collectibles from athletes on LegacyXChange ... forensic analysis of the DNA. Bill ...
Breaking Biology News(10 mins):
(Date:6/23/2016)...  Blueprint Bio, a company dedicated to identifying, protecting ... has closed its Series A funding round, according to ... "We have received a commitment from Forentis Fund that ... meet our current goals," stated Matthew Nunez . ... complete validation on the current projects in our pipeline, ...
(Date:6/23/2016)... , June 23, 2016 On ... session at 4,833.32, down 0.22%; the Dow Jones Industrial Average ... 500 closed at 2,085.45, down 0.17%. Stock-Callers.com has initiated coverage ... INFI ), Nektar Therapeutics (NASDAQ: NKTR ), Aralez ... Inc. (NASDAQ: BIND ). Learn more about these ...
(Date:6/23/2016)... ... 23, 2016 , ... Regulatory Compliance Associates® Inc. (RCA), a ... webinar on Performing Quality Investigations: Getting to Root Cause. This ... charge. , Incomplete investigations are still a major concern to the Regulatory Authorities ...
(Date:6/23/2016)... FRANCISCO , June 22, 2016  Amgen (NASDAQ: ... sponsorship of the QB3@953 life sciences incubator ... human health. The shared laboratory space at QB3@953 was ... overcome a key obstacle for many early stage organizations ... part of the sponsorship, Amgen launched two "Amgen Golden ...
Breaking Biology Technology: