The Right Connections Help Medical Equipment Designers Satisfy Demanding Applications
- Monday, 01 October 2012
The need to minimize healthcare costs is creating greater demand for medical electronics equipment that, among other things, improves and expands patient diagnostics inside and outside healthcare facilities. For example, portable medical instruments such as glucose meters, blood pressure monitors, and oxygen meters can be designed with communication capabilities to provide continuous information to caregivers almost anywhere. Small handheld devices can also improve various diagnostic procedures in medical offices. While such devices hold the promise of improved care at lower cost, they require advanced technologies that allow greater miniaturization to improve portability and functionality while providing safe usage.
Many of the same considerations apply to medical instruments used in fixed locations or with limited mobility. Larger, more complex instrumentation, such as robotics used in surgery, can benefit from advanced electronic interconnections that make production more efficient and the final product more compact and user friendly. In these applications, larger connectors may be acceptable or even desirable when more wires and other interconnections are needed to control complex computerized functions, while making connections simpler and more reliable.
FDA Approval Issues
Taking a new medical device of any kind through all the steps for FDA approval is a time-consuming process. Therefore, R&D engineers must take all practical steps to shorten the product development cycle and time to market. The latest electronic connector and interface technologies can help achieve these goals. Some ways modern connectors and interfaces can help are:
• Shrinking connector sizes for a given
set of functions
• Adding functions to connectors that once required separate circuit components
• Allowing hybrid connectors that carry pow er, communications, control signals, etc.
• Improving safety through better latching methods and electromagnetic interference (EMI) shielding
Data Communication Interfaces
The use of data communications is a feature common to many medical devices as they are linked to healthcare providers wirelessly or by cabled LAN networks. Electronic connectors are essential elements in these connections and must work flawlessly without contributing noise or distortion to the signals.
Often, despite careful system design, EMI and noise can find its way into data lines. Another danger is damage from electrostatic discharge (ESD), which is the transfer of a static high voltage charge from a human body into the electronic system. Often, separate suppression devices are added to data communications interface circuitry for protection, but this adds considerable cost and bulk in the form of components and assembly labor.
Today, subminiature D-sub connectors, the most common digital I/O interface, are available with built-in filtering that minimize these dangers to sensitive medical instruments. They can be purchased with inductive ferrite filtering in the printed circuit board (PCB) material that holds the connector pins, as seen in Figure 1, left. This cost-effective low-level filtering has minimal insertion loss while reducing EMI emissions that might otherwise be close to the specified limit.
Another approach to D-sub filtering is a patented four-layer PCB material with surface mount chip capacitors, as seen in Figure 1, right. As a result of the filtering performance of the capacitors and the screening effect of the PCB, this provides complete protection from any introduction or radiation of noise through the I/O port. In addition, ringing and crosstalk are virtually eliminated.
Filtered D-sub connectors are available in a range of configurations that include standard and custom pin-outs, various housing and hood styles, cable and bulkhead mountings, surface mount types, straight and right angle pins for PCB reflow soldering, etc. Builtin filtering eliminates or reduces the need for separate suppression devices, resulting in smaller, less costly data communications circuit designs. In addition, this style of built-in filtering fits within standard D-sub shells, which allows designers to add filtering late in the design stage if an EMI or ESD glitch is discovered, and may avoid the need to modify a circuit board to suppress these problems.
Another way to shrink medical electronics is with molded interface device (MID) technology. MID, combined with other electronic packaging technologies, such as flexible PCBs and a variety of semiconductor chip mounting techniques, can be used to create medical devices with higher-level functionality and miniaturization.
MIDs are injection molded plastic elements carrying electrical circuits. Their electrical connections can be routed “around corners,” and components can be mounted in various spatial directions. MID incorporates such technologies as active compounds (typically metal complexes) in the plastic moldings, two-shot molding processes, laser direct structuring (LDS), and laser subtractive structuring (LSS) to create connection interfaces and conductor paths. This allows highly miniaturized circuit assemblies with a great deal of complexity, manufactured to precise specifications.