Over the years, implantable medical devices have become smaller and smaller. Smaller devices can improve patient comfort and cause less damage to the human body during implantation. At the same time, smaller instruments can reduce the invasiveness and complexity of the operation, which is not only convenient for doctors to operate, but also easier for patients to accept. Almost all the magnetic components associated with these devices are custom-designed to adapt to specific applications in limited spaces. Because magnetic components are usually large in size, raw materials and processing equipment are indispensable to achieve the goal of miniaturization.
Custom magnetic components used in implantable devices are usually composed of a skeleton transformer, a toroidal coil transformer, a molded pressure sensor, and an antenna with unique performance and shape characteristics to maximize compliance with the specified standards. For this reason, various magnetic core materials and shapes are used in practice to optimize performance and meet application requirements.
Most custom magnetic components used in implantable devices are the result of close collaboration between medical device manufacturers and magnetic component company engineers. Which involves the discussion of how to balance size, price and performance, focusing on the use of the most cost-effective devices in the available space. After the components are designed, very strict manufacturing processes, control measures and test procedures must be developed to ensure the highest quality and reliability of size and magnetic properties.
Since only very small magnetic components can be incorporated into implantable devices, special assembly techniques have been developed in practice, and most of the 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 level requirements of these devices, the selection of functions and shapes of different magnetic components has been greatly increased. Smaller form factors often require 3D CAD simulation for accurate component layout and prototyping. Some suppliers provide specially designed and manufactured custom molds to allow the realization of smaller carriers.
When manufacturing customized magnetic components, special air-core coils, bobbin and toroidal coil winding equipment are widely used. This equipment requires strict control of key electrical requirements, such as leakage inductance, parasitic capacitance, DCR, inductance matching, and dielectric breakdown voltage. Specially designed test benches and fixtures allow accurate 100% monitoring and testing of these parameters. The use of these automated test benches allows data analysis in the design to improve manufacturability.
The size and shape of magnetic components used in medical applications vary greatly from application to application. For example, the small 0402 inductors (0.040" x 0.020" x 0.020") shown in the left picture below are used for telemetry/communication applications. These inductors can be wire bondable and made of ceramic core materials with 1 nH-150nH inductance range.
The charging circuit in medical equipment uses larger magnetic components, as shown in the right figure above. 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 in the figure above, there are two size options for high frequency wire bonding RF spiral inductors: 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 provide extremely high self-resonance and low dielectric constant. They have a power of 125 mW, an operating temperature of −55 °C to +125 °C, and a derating temperature of 70 °C.
These inductors use mature and reliable MNOS capacitor technology to provide high Q, low DCR and the industry's highest SRF. They are suitable for high frequency filters, impedance matching and lumped element filters with a maximum operating frequency of up to 20 GHz.
