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Trimmer Capacitor Considerations in Practice

Trimmer Capacitor Considerations in Practice

Trimmer capacitors are adjustable components that are used for fine-tuning RF circuits during manufacturing or maintenance. They enable adjustable tuning for frequency values and rise and fall times, allowing for recalibration if necessary. Trimmer capacitors are critical for sensitive applications such as magnetic resonance imaging (MRI), where even minor instability can have a significant impact on image output.

During MRI scans, protons in a patient's body align themselves in the same direction when exposed to a magnetic field. When a computer-generated RF signal is applied to a proton, it is disrupted and then returns to its original state of alignment. As protons realign, they emit energy that can be measured to identify different types of molecules and their locations in the body. Trimmer capacitors are used to tune the TX and RX coils to Lamor Frequency, the frequency at which this energy is emitted. Thus, proper trimmer capacitor tuning is essential for accurate MRI imaging.

To meet the demanding requirements of MRI, it is critical to select the appropriate trimmer capacitor. Voltronics, a brand of Knowles Precision Devices (KPD), has developed a unique test setup to measure Q and RF voltage breakdown at MRI operational frequencies. KPD's portfolio includes precision trimmer capacitors made of air, glass, sapphire, and PTFE dielectrics that can be used from 1 MHz to over 2 GHz and at voltages up to 20,000 VDC. These capacitors are available in precision multi-turn and half-turn formats, making them suitable for any application level.

Q Factor

  • Influences power handling; higher Q lessens self-heating under RF conditions
  • Important in filter circuits; impacts insertion loss

K Value (dielectric constant)

  • Determines the capacitance density in conjunction with dielectric withstand voltage; higher the K Value, smaller the component can be

Dielectric Withstand Voltage

  • The maximum DC voltage the part can withstand without failure
Non-magnetic Properties
  • Essential for MRI components, especially body coil and surface coils
  • Close control of raw materials and processes required to ensure MRI accuracy and performance
Half-turn vs. Multi-turn Trimmers
  • Half turn trimmers have a lower Q, DWV, and precision; typically used in lower voltage and power environments where some tuning is required
  • Multi turn trimmers boast higher Q, DWV, and performance; provides precision where exact tuning is imperative 


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Our expert(s):

Dennis de la Roy Dennis de la Roy
Please contact Dennis with any questions or business opportunities relating to electronic Components of Heynen. We love to be involved in developing new solutions and bringing these to the Dutch market. Contact form dennis.delaroy@heynen.nl
+31 (0)485 55 09 37

Johan De Ceuster Johan De Ceuster
Please contact Johan with any questions or business opportunities relating to Electronic Components and RF. We love to be involved in developing new solutions and bringing these to the Belgian and Luxembourg market. Contact form johan.de.ceuster@heynen.be
+32 (0)11 60 09 10

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