Contact vs. Contactless Transmission: Why Capacitive Contactless Data Transmission Is So Important For CT Slip Rings

In CT scanners, precise and quick data transfer between stationary and rotating parts is crucial. As the image resolution and speed increase, the contact slip rings struggle to make capacitive contactless transmission, which is necessary for low maintenance and high-performance CT imaging. It helps to eliminate noise and wear so that clean signals are transmitted.

Contact (Brush‑based) Slip Rings: What and Why?

Structure And Mechanism

Contact slip rings consist of a simple design that is known for its effectiveness. The metal brushes are responsible for maintaining contact with conductive rings. When the ring rotates, the brush moves along its surface, allowing the transmission of electric power or signal through a rotating interface.

This design ensures that power and signal transmission take place through direct electrical contact. It is used widely in industries where moderate speed and reliable electrical transfer and rotation are required.

Advantages of Contacting

The advantages of contacting are as follows:

● Contact slip rings can handle high current and voltage, which makes them suitable for power transmission. CT systems commonly use contact-based rings for power transfer.

● It is a proven method that is highly reliable under stable conditions and is usually considered for its robust and simple industrial applications. 

Disadvantages in CT Applications

The disadvantages of CT applications are as follows:

● Due to constant friction between the ring and brush, wear and tear are caused, which produces debris and requires timely maintenance.

● Brush degradation leads to electrical noise, which increases the signal loss and causes disruptions in medical CT systems.

● Some designs support a speed of up to 300rpm. Most of the contact slip rings impose mechanical limits on high speed and continuous rotation, which makes them suitable for next-generation CT systems.

Contactless Slip Rings: Overview

What Are They?

Contactless slip rings transmit signals and power without any physical contact. These comprise:

● Inductive slip rings that use magnetic fields for transferring power.

● RF slip rings that use radio frequency for data transmission.

● Capacitive slip rings that depend on high-frequency electric field coupling.

Among all of these rings, capacitive slip rings are best suited for high-speed data transfer that offers high signal integrity and low latency with minimal interference.

How Capacitive Transmission Works

Capacitive slip rings operate using two electrode plates, one of which is on the stator and one on the rotor. These plates have a small dielectric gap, and high-frequency signals are transmitted across that gap through an electric field without any physical contact.

It results in no brush wear and no friction as there are no moving contact surfaces, and it is ideal for high data rates and continuous rotation.

Why Capacitive Contactless Is Ideal For CT Slip Rings

High Data Rates & Low Error

Capacitive slip rings allow for a reliable and quick transmission that is necessary for CT imaging. Many commercial systems tend to support data rates of 5 Gbit/s, while others support 10 Gbit/s per track.

Ultra‑low Latency & Real‑time Support

The latency is as low as <1µs, capacitive transmission supports real-time protocols like Profinet and EtherCAT, which is important for accurate image reconstruction and responsive control.

Support For Continuous & High‑speed Rotation

CT gantries rotate at 300 rpm; they have no inherent speed limitations that enable the uninterrupted data flow with stability during high-speed scans.

Modular, Customizable Form Factors

Modern capacitive slip rings are designed with expandable diameters, and among them, some even exceed 1300 mm free inner diameter for integrating in CT ring systems. They even support protocol multiplexing and multiple data tracks, which makes them adaptable to evolving CT scanner designs.

Comparison Table: Contact vs Contactless (Capacitive) In CT Slip Rings

CT‑Specific Use Cases Enabled by Capacitive Slip Rings

Continuous Gantry Rotation Enabling Advanced Clinical Modes

The introduction of slip ring CT has revolutionized scanning by allowing continuous gantry rotation, which helps to support clinical models with advancements like helical CR, perfusion studies, cardiac images, CT fluoroscopy, and gated lung scans.

Capacitive contactless transmission makes these modes reliable and scalable, offering high speed and real-time data flow that is needed for modern systems.

High‑Volume Image Data Transfer

The volumetric CT scanners create vast image datasets per rotation. Capacitive slip rings support high bandwidth with uninterrupted transmission, ensuring low latency and low artefact image acquisition. It is important for diagnostic accuracy in radiology.

Reliability in Medical Environment

In clinical environments, reliability isn't a choice. Capacitive slip rings work with brushes and eliminate particle contamination, which can lead to degradation of the image quality. Such a sealed and frictionless design also reduces unplanned downtime.

Technical Specifications

● Data transmission from 800 Mbit/s up to 120 Gbit/s with scalable modular 10 Gb/s channels.

● Mechanical gap comprises a tolerance from 2 mm to 3.5 mm based on the system design.

● Latency is < 1µs, meant for real-time imaging.

● HTL/TTL quadrature outputs with an angular resolution of 0.1°

● Low bit rate error at 10⁻¹² supporting signal fidelity of medical grade.

● It is designed for 10 years of consistent use.

● It can support a rotation speed up to 300 rpm.

● Dimensions can be customized to around 1800 mm in diameter.

Practical Considerations & Engineering Tips

Engineering for Gap and Alignment

Capacitive slip rings need careful attention to the rotor-stator gap, which is kept around 2 to 4mm to ensure optimal signal integrity. Advanced designs of modules like NBG units can handle the gaps of up to 3.5 to 4 mm.

They offer mechanical flexibility by keeping the performance stable. Assessing alignment at the time of installation is crucial to avoid signal degradation.

Signal Interfaces & Integration

To ensure seamless integration in CT systems, capacitive modules consist of standardized interfaces like RJ45, which support industrial real-time protocols like Ethernet, EtherCAT, etc.

This allows plug-and-play compatibility with the existing networked imaging platforms and reduces the efforts involved in custom engineering.

Redundancy & Stacking

If you require higher bandwidth or fail-safe operation, capacitive systems are stackable and modular. Combining multiple segments helps to scale up throughout and incorporate redundancy to ensure uninterrupted performance at the time of critical scans.

Hybrid Systems

Although data transmission is handled without any contact, most of the CT systems use hybrid slip rings that incorporate contact-based tracks for the delivery of high current power along with contactless data channels. It ensures the best results in the form of stable power transfer and free data communication that allows full system functionality.

Conclusion

Capacitive contactless slip rings offer low latency, high speed, and maintenance-free performance, which is important for modern CT imaging. They offer scalable, clean, and reliable transmission, which makes them a good choice for continuous rotation and long-term system efficiency in medical setups.