The power demands of highly technical medical equipment and systems present challenges. If wired power is the preferred option, cables often get in the way. Systems based on induction or radio waves provide one remedy, but the cost of such systems often outweighs their benefits. A new method of “free” power transmission is setting new standards in terms of efficiency and space.

Devised by Triple Sensor Technologies GmbH in Jena, Germany, it bypasses the limitations of the familiar chemical and physical energy storage and transmission methods.

Transferring motion

The new patented process is based on the magnetic transfer of a rotary motion from a source to a receiver. In the receiver - the generator module - this rotary motion is then converted into electricity. Inventor and Triple Sensor CEO Holger Lausch highlights the particular advantages of the new solution: “The transmitter module is very compact, and can be easily worn on a belt for medical implants for example, says Lausch. “Its effective range is nevertheless about 50 cm. There are no emission losses as with radio waves, even under no load, as the transmitter only has to deliver more power when some has been tapped by the receiver. Moreover, the generator module is easy to locate for mobile probes.”

Currently available mobile receiver modules, measuring 10 × 12 mm (diam by length), allow up to 100 mW of power to be transmitted. To ensure the transmitter module design is as compact as possible, the manufacturer is working with miniature drive specialist Faulhaber GmbH, Schönaich, Germany. Adapted standard products provide the scaled power output in line with requirements and the compact, easy-to- program controller.

On the belt:efficiency off the rack

Since the universal application model demanded continuous duty and short-time power supply, Triple Sensor engineers chose wear-free EC motors by Faulhaber in 20 mm OD and with a length of 60 mm. In this design, the only mechanical parts that wear are the rotor bearings. Selected ball bearing materials and special lubricants allow for high speeds and service lives of several tens of thousands of hours.

The miniature drives deliver big performance, despite their compact size. They can be loaded well beyond their continuous torque limit for short periods on startup, which is a key advantage. This means the transfer module is able to supply power both continuously over long periods of time and on tap in short spells as required. As a result, swallowed capsules can be powered, as can dosage systems implanted in the body or hermetically sealed sensors in technical systems that only need to be powered on demand, such as for parameter polling.

To control the heart of the transfer module - the EC motor - developers chose compact motion controller measuring just 34 × 25 × 14 mm (W × H × D). Together with the Motion Manager operator control software, the parameters can be set quickly and cost-effectively for any specific application case.

Inner values

Of course, the applications of the ultra-miniature drives are not merely limited to the outer transfer module. Miniature drives are also well suited to use on the generator side, too. Depending on the task at hand, the power module also can be adapted to the power demand of various miniature motors for mobile operation.

The extensive product range offers the developers a broad basis for achieving precisely tailored solutions. It includes EC and DC motors, and offers diameters from 12 and 10 mm, through 6 mm variants, down to 1.9 mm. And flat penny motors or non-mechanical loads such as sensors can be supplied with mobile power. So the right non-contact powered drive is available for virtually any mechanical task, and minor adaptations can be easily made.

The compact design concept permits for the first time relatively far-reaching, efficient non-contact power transmission. It is based on standard components such as miniature motors and motion controllers. The transmitter and receiver modules are scalable to adapt to specific power requirements. This, too, lets the manufacturer profit from the wide range of miniature drives available.

HOW IT WORKS

The non-contact power supply described in this article employs an EC motor that powers a magnet in a special fixture inside the transfer module. Under no load, the drive merely has to compensate for the friction losses of the bearings; it consumes no additional energy. When a power module is then introduced into the virtually spherical transfer space, a small magnet there couples to the alternating field density of the source magnet.

This starts the small magnet itself rotating, generating a current in appropriately wound coils. This current is then available as useful load as long as the outer rotating field is exciting the generator. This secondary-side power draw naturally slows the outer magnetic field of the transfer module; the consumed energy has to be resupplied by the drive motor of the outer module in order to maintain the magnet's rotation speed. The use of a magnetic coupling enables the power to be transmitted through all non-magnetic materials.

Even biological tissue, plastic, nonferrous heavy metal, titanium or a magnetic stainless steel shells are no obstacle. Consequently, the process is suitable for many different medical and technical applications.