Select Magnetic Components for Medical Device Applications

Select Magnetic Components for Medical Device Applications

Implantable medical devices have gotten smaller and smaller over the years. Smaller devices can improve patient comfort and cause less damage to the body when implanted. At the same time, smaller instruments can reduce the invasiveness and complexity of surgery, making it easier for doctors to operate and easier for patients to accept. The magnetic components associated with these instruments are almost exclusively custom designed to fit specific applications in limited spaces. Because magnetic components are typically larger in size, raw materials and processing equipment are essential to achieving miniaturization goals.

Custom magnetics for implantable devices typically consist of bobbin transformers, toroid transformers, molded inductors, and antennas with unique performance and shape characteristics to maximize compliance with specified standards. To this end, various core materials and shapes are used in practice to optimize performance and meet the requirements of the application.

Most custom magnetic components used in implantable devices are the result of close collaboration between medical device manufacturers and magnetic component company engineers. It involves a discussion of how to balance size, price, and performance, with a focus on using the most cost-effective device in the available space. After the components are designed, very stringent manufacturing processes, controls and testing procedures are developed to ensure the highest quality and reliability of dimensional and magnetic properties.

Since only very small magnetic elements can be incorporated into implantable devices, special assembly techniques have been developed in practice, and most assembly work is done under a microscope to ensure that the electrical and mechanical connections are intact. Use high-tech inspection equipment, such as optical measuring equipment, to measure the critical dimensions required by these devices.

Due to the required tolerances and performance levels of these instruments, the functional and form factor options for different magnetic elements have greatly increased. Smaller form factor designs often require 3D CAD simulation for accurate component placement and prototyping. Some suppliers offer custom molds specially designed and manufactured to allow smaller carriers to be realized.

Dedicated air core, bobbin and toroidal coil winding equipment is widely used when manufacturing custom magnetic components. This device requires tight control of key electrical requirements such as leakage inductance, parasitic capacitance, DCR, inductance matching and dielectric breakdown voltage. Specially designed test stands and fixtures allow accurate 100% monitoring and testing of these parameters. Using these automated test benches allows for data analysis in the design to improve manufacturability.

The size and shape of magnetic components used in medical applications vary widely from application to application. For example, the 0402 small form factor inductors (0.040” x 0.020” x 0.020”) shown on the left below are used in telemetry/communication applications. These inductors can be wire bondable and are fabricated from a ceramic core material with 1 nH – 150nH inductance range.

Charging circuits in medical devices use larger magnetic components, as shown in the image above to the right. The maximum and minimum dimensions used are 0.550” x 0.750” x 0.470” and 0.275” x 0.600” x 0.400” respectively.

As shown above, the high frequency wire-bonded RF spiral inductor is available in two sizes: 0.030” x 0.030” x 0.020” and 0.050” x 0.050” x 0.020”. These inductors perform well in the RF band and are suitable for biasing, tuning and lumped element filters. They offer very high self-resonance and low dielectric constant. They have 125 mW of power, an operating temperature of −55 °C to +125 °C, and a derating temperature of 70 °C.

These inductors use proven MNOS capacitor technology to provide high Q, low DCR and the highest SRF in the industry. They are suitable for high frequency filters, impedance matching, and lumped element filters operating up to 20 GHz.

Post time: Jul-27-2022