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Simulation Benefits For The Healthcare Industry - Electrical Medical Devices

Simulation for Healthcare | FEA CFD Electronics Consulting
August 8, 2017 By: Chris Mesibov

Today, there are a plethora of medical devices that must communicate wirelessly with devices outside the body.  These include devices that exchange data, and devices that need to wirelessly charge. Electromagnetic Interference (EMI) of multiple integrated and body-worn wireless tech needs to be studied so that these devices will work in harmony.  Some devices use common wireless bands such as Wi-Fi and Bluetooth, so designing efficient power electronics and antenna systems is critical to the success of these body area networks.

What are the challenges?

  • Multiplication of body hosted wireless devices from various vendors where interoperability is essential.
  • Interference between devices and body, where tissue RF absorption can mean unexpected signal attenuation.
  • Acceptable body absorption rates must be verified.

What are the solutions?

  • Modeling device and body interactions.
  • Simulating any potential interference with life-critical devices.
  • Studying extreme scenarios or corner cases.

Which leaves us with what impacts?

  • Facilitating the approval of new devices.
  • Protecting the population against excessive exposure to RF power.
  • Ensuring the safe multiplication of body hosted devices.

Simulation-Driven Electronic Product Development addresses:

  • Power
    • Static (Leakage) Power Reduction
    • Dynamic Power Reduction
    • Electrostatic Discharge Analysis
    • Wireless Power Charging
  • Antennas
    • EMI/EMC Compliance
    • Channel Modeling
    • Antenna Integration
    • Signal Integrity Analysis

Some medical devices are required to be implanted within the body. This poses challenges for supplying power to these devices and power dissipation within the human body.  If wireless charging is implemented, charging efficiency and tissue power absorption needs to be studied. Managing device power consumption is paramount, given that physically accessing the installed device is not going to be an option.

For example, simulations can be performed on coupling efficiency between the implanted device’s charging coil and the electromagnetic field of the charger. The human body model would host the embedded charging coil model, and the charger is placed in the intended proximity to the implant. The effect of the human body model power absorption can be readily determined. If the results indicate that the coupling is insufficient, the implanted charging coil model can be moved until the placement is optimized. At the same time, the results provide body absorption rate data to determine compliance with regulations.

Wearable devices typically use one or more antennas. They can be RF sensors, as in a smart watch, along with a Bluetooth antenna that talks to your cellphone. Putting these antennas close together and on complex shapes (your wrist) creates performance issues that you can only uncover through simulation.  Antennas, in conjunction with the device radios, must ensure the best balance between link efficiency, maximum transmitter power, tissue power absorption and interference with other antennas. In addition, signal integrity studies ensure data edge rates do not contribute to RFI/EMI/EMC.

The body absorbs RF power, thus designers need to consider the added attenuation in the communication link budget. Simulation using the human body model is a necessary step in evaluating this scenario. Multiple antennas for wearables, such as Bluetooth and WiFi, need to ensure that there is no spectral interference. Antenna placement should be simulated to ensure optimization with respect to body positioning. For example, Apple had to make design changes to iPhone antenna placement due to unexpected interactions between the phone and the environment. Simulation enabled Apple to optimize this placement.

A body worn/ implantable wireless device is susceptible to not only EMI issues, but also structural and thermal integrity problems. In my next post I will explore these issues and will also discuss the importance of simulation for devices that provide life-sustaining functions.