AMR Sensors: Tackling Position Sensing in Medical Device Applications

Position sensors can play a big role in the durability and longevity of medical device and healthcare systems. Such sensors measure position in practically any device with a lid, drawer, or door. Thus, they are used in an array of healthcare applications, from positioning hospital beds and measuring the position of cartridges in infusion pumps to positioning the drawers and doors of drug supply cabinets or carts. They can even be used to safeguard security doors and windows.

In such applications, position sensors need to provide enhanced reliability and high sensitivity to ensure patient or user safety. And in some cases, they need to offer reduced power and a small package to enable system portability or to fit into space-constrained designs.

A variety of different sensor types are available for measuring position in medical device applications. This article focuses on anisotropic magnetoresistive sensors, a new family of sensors that can replace the use of traditional technologies in positioning applications.

The Advantages of AMR Sensors

Over the last decade, reed switches and Hall effect sensors have been used in position sensor applications because alternative technologies were not readily available. Today, however, medical device and healthcare systems can benefit from new anisotropic magnetoresistive (AMR) sensor integrated circuits, which provide reliability, sensitivity, and durable sensing capability. In addition, their small package size and low power consumption make them suitable for use in many medical device applications. And because they are sensitive, these sensors can use smaller magnets, further reducing overall system costs while maintaining the same level of quality and reliability associated with reed switches and Hall effect sensors.

To reduce the size, increase the quality, and improve the durability of medical devices, medical design engineers looking for an alternative to reed switches can turn to such anisotropic magnetoresistive technologies as the Nanopower AMR sensors from Honeywell Sensing and Control. These sensors minimize the drawbacks associated with reed switches, such as susceptibility to breakage, limited lifetime, lower durability, and contact bounce. And they consume up to 10 times less supply current than Hall effect sensors and can significantly extend battery life. In addition, their sensitivity of 14 Gauss typical is twice that of highly sensitive Hall effect sensors, and their use of less magnetic material can increase design flexibility or cost savings in many medical device and healthcare applications.

Infusion Pumps

Thanks to their low power, small package, temperature stability, and solid-state technology, these technologies can be used in a variety of healthcare applications, including infusion pumps. Infusion pumps deliver medication to patients intravenously. When designers select a position sensor for infusion pumps, they must evaluate three critical factors: sensitivity, reliability, and size. In such applications, position sensors are used as a cartridge detection switch to detect when the cartridge is in the proper position. The reliability and sensitivity of the sensor ensures that the infusion pump is working correctly to deliver the right amount of medication.

AMR sensors’ high sensitivity enhances design flexibility by allowing the designer to place the sensor farther away from the magnet and still maintain reliability. This technology also enables the use of smaller or lower-strength magnets, reducing magnet costs. As the price of rare-earth magnets continues to increase, reducing magnet size or strength has become an important issue for system manufacturers.

Suitable for space-constrained designs, the AMR sensor ICs are housed in SOT-23 packages measuring 2.9 x 2.8 x 1.45 mm. Their small size, combined with low power, allows manufacturers to offer more-compact portable infusion pumps, improving patients’ quality of life. In addition, because they feature an average current of 360 and 310 nA typical, depending on the model, the sensors are suitable for battery-operated infusion pumps.

Conclusion

In medical device applications, AMR sensor ICs offer engineers a new means to solve such design challenges as reliability, durability, and board-space constraints. Because of their simple manufacturing process, design flexibility, easy integration into space-constrained circuit boards, and solid-state design, they can help to reduce the risk of equipment failure and lower overall system costs.

Joshua Edberg is the global product marketing manager for magnetic and optical sensors at Golden Valley, MN–based Honeywell Sensing and Control. In this role, he leads the implementation of the company’s product portfolio strategy, growth strategy, and new product development. He joined the company in 2006 and has held various strategic and product marketing positions. He received a bachelor’s degree in business economics from the University of California Santa Barbara and an MBA from the University of Southern California, Marshall School of Business. Reach him at [email protected].