Meridian Medical Systems Applies Microwave Office To Improve the Treatment of a Critical Heart Condition
The Design Challenge
Cardiac arrhythmia (when the heart beats too slowly, too fast, or irregularly) is typically treated with a procedure called cardiac ablation, which selectively destroys tissue to ensure that the "signal" controlling the heartbeat follows the proper path. A catheter is inserted into the patient's leg that runs upward and into the heart, where, through cryogenic cooling or electromagnetic or ultrasonic radiation, the target tissue is destroyed. None of these techniques, however, are able to provide real-time feedback about how much energy to apply while the doctor is performing the procedure. The temperature sensor in conventional catheters can measure only the value in the tip, which is typically cooled, so the value returned is not very precise. Without an accurate feedback mechanism, doctors tend to apply less-then-optimum energy levels to ensure the safety of the patient, which can reduce the procedure's effectiveness.
To solve this problem, MMS is developing a catheter that combines the ability to simultaneously deliver microwave radiation for tissue heating and a radiometer (essentially a remote sensing device) fabricated as a microwave monolithic integrated circuit (MMIC) to sense the temperature of the heart wall. The Dicke radiometer employed in the design obtains tissue temperature measurements noninvasively and operates by comparing an internal reference temperature with an actual radiometric measurement and using the difference to calculate body temperature. Early results show the technique to be extremely accurate. Although radiometers have been used for years in applications ranging from measuring atmospheric and terrestrial radiation from space to oceanographic remote-sensing, the radiometer designed by MMS incorporates several proprietary technologies that optimize its use for cardiac ablation.
How did Microwave Office software help deliver the solution?
Bob Allison, vice president and engineering manager at MMS, relied on AWR's Microwave Office electronic design automation (EDA) software along with a process design kit (PDK) developed jointly by AWR and TriQuint Semiconductor that accurately represents TriQuint's foundry process. Allison has used AWR tools since their earliest development, but his experience with EDA tools, as well as with virtually every other high-frequency design solution, dates back to the days of mainframe time-sharing. "I've found Microwave Office to be unique among these tools for its ability to make the design process comparatively simple," says Allison. "It's created by engineers who understand the difference between designing a microwave circuit and a digital one - and it shows in the software."
How did the combination of AWR and TriQuint contribute to your success?
The seamless integration of Microwave Office software and the TriQuint PDK enabled Allison to design the circuit, select the features from the PDK library, perform design rule checking, and send the result to TriQuint, all in a very short time. "The handoff to TriQuint was utterly painless," said Allison. "Designing and producing our radiometer MMIC with Microwave Office and the TriQuint design kit provided an immense productivity improvement. Measurements we've made on the devices we received from TriQuint agree extremely well with the Microwave Office simulation. In short, we got back exactly what we hoped for."
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