Wireless signals keep devices connected in virtually any environment. However, confined areas can pose challenges for many closely located users and their wireless devices. This is especially true when some of these devices (e.g., remote analyzers, monitors, and pacemakers) are part of the recovery process in hospitals and healthcare clinics. Therefore, it is imperative that effective wireless medical devices be designed and manufactured for use in dense signal environments where they operate at full performance levels even when surrounded by many wireless signals. They must also be designed to not cause interference with other nearby wireless devices.
The need to protect patient data adds to this complexity. With so many electronic devices in hospitals, patient data must be transmitted and received in both wired and wireless forms without loss to support successful medical outcomes. Fortunately, an integrated design and manufacturing approach can develop effective solutions for a wide range of medical device problems, even when used in hospitals filled with wireless users and their devices.
Operating Medical Devices in Signal-Intense Environments
Crowded radio frequency (RF) signal environments — such as hospitals with many patients, medical staff, and their wireless devices — cause competition for available RF spectrum. Medical wireless devices typically operate within the frequency spectrum reserved for international use and in industrial-scientific-medical (ISM) frequency bands (such as 2.4 to 2.5 GHz and 5.725 to 5.875 GHz). Wireless local area networks (WLANs) based on Wi-Fi wireless technology usually occupy the 2.4 to 2.5 GHz frequency region. To ease signal crowding, medical device developers have been invited to take advantage of ISM frequency bands in the millimeter-wave range, such as 24.00 to 24.25 GHz and 61.0 to 61.5 GHz, although the higher frequencies come with higher costs for components.
Medical device developers may not be overly familiar with the requirements for developing devices that operate at these less-utilized frequencies. For example, a medical electronic device developed for an ISM frequency band may require added electromagnetic interference (EMI) shielding and filtering to withstand higher power signal sources close in frequency. To avoid signal interference and invite wireless coexistence, medical device developers are encouraged to operate with the lowest possible RF signal power, although receivers working with low-level signals can risk having those signals masked by higher power signals near in frequency.
Medical Device Testing in Crowded Signal Environments
New electronic products are not typically tested in the presence of multiple signals. However, medical electronic products must be characterized in test environments that are as close as possible to actual operating conditions for the electronic product, such as in a signal-crowded hospital. A wireless medical device may underperform or not function properly in crowded signal environments unless designed and constructed with the filtering and shielding required to suppress interference from other sources and prevent the generation of interference from their own active components.
Fortunately, medical electronic product developers who have teamed with Benchmark on the design, manufacturing, and testing of medical devices have learned that Benchmark’s enclosed test chambers can closely duplicate actual hospital operating environments. The results of such testing can reveal a great deal about a medical electronic product and how to properly prepare it for a crowded signal environment such as a hospital.
Government organizations within the United States — such as the Food and Drug Administration (FDA) and the Federal Communications Commission (FCC) — define testing for wireless medical devices, including risk management and coexistence in proximity to other wireless devices such as cellular telephones and WLANs. The FDA regulates manufacturers of medical electronic products through medical device provisions of federal law and Electronic Product Radiation Control (EPRC).
The FDA’s Center for Devices and Radiological Health (CDRH) works with medical device manufacturers to meet electromagnetic compatibility (EMC) requirements. The CDRH tests a medical device under development for conducted and radiated electromagnetic (EM) levels as well as a device’s susceptibility to electrostatic discharge (ESD). A device under test (DUT) must be tested as a source of EMI and for electromagnetic compatibility (EMC), as well as its capability of operating alongside other wireless devices. The FDA classifies medical electronic products as Class I, II, or III categories of low-, medium-, and high-risk devices, respectively, with testing and regulations established for each category.
Standards for EMI and EMC have been established by the American National Standards Institute (ANSI), the International Electrotechnical Commission/International Organization for Standardization (IEC/ISO), and the Association for the Advancement of Medical Instrumentation (AAMI). In addition, the Health Insurance Portability and Accountability Act (HIPAA) establishes requirements for the safety and security of a user’s healthcare information and personal data when transferred by a wireless medical device.
For a new medical electronic device to achieve clinical benefits, it must work without fail under sometimes hostile conditions, including when surrounded by RF signals. Wireless technology can keep a doctor informed of a patient’s progress, provided it operates reliably under all conditions, whether in a handheld tool or a massive electronic system. With a more than 40-year legacy working with the medical community, Benchmark’s engineers intimately understand the importance of integrating design, manufacturing, and test to ensure reliability in a wireless medical product. In developing a wireless medical device, the FDA poses a five-step approach:
- Selecting a wireless technology
- Establishing quality of service (QoS)
- Determining wireless coexistence
- Ensuring security
- Evaluating EMC
Electronic design is a critical step in selecting wireless technology — such as Wi-Fi or radio-frequency identification (RFID) — and ensuring wireless coexistence of a medical electronic device in a crowded signal environment. Although electronic devices with reduced size, weight, and power (SWaP) are important for all industries, printed circuit board (PCB) layouts with minimally spaced active components can be challenging for environments with many closely operating wireless devices. But the use of EM, circuit, and system-level software simulators, the behavior of individual circuits and subsystems together can be reliably predicted prior to assembly to avoid problems (e.g., improperly tuned circuits operating outside of a designed ISM frequency channel).
Smooth Transition from NPI to Validation Testing
Working as a medical electronics design partner, Benchmark explores numerous PCB layout iterations using simulators such as the Advanced Design System (ADS) to identify potential problems before fabricating the first PCBs. Since both EMI and EMC are concerns in crowded signal environments, simulations examine not only the impacts of changing circuit layouts and placements of components but such factors as circuit linewidths and linewidth tolerances, and even the permittivity or dielectric constant (Dk) of the PCB material. When working with a customer as a medical electronics partner, years of medical design and manufacturing experience at Benchmark support a smooth transition from new product ideas to prototypes ready for validation testing.
But electronic design is often just one step in the development of a wireless medical device — mechanical design can be just as critical. As an example, a customer challenged Benchmark’s engineers with the redesign and update of a successful but obsolete medical electronics system. Not only did it require the addition of RF telemetry capability and Bluetooth wireless technology, but it also needed to achieve EMI/EMC compliance in approximately 50 percent of the size and weight of the legacy system. Innovative mechanical design contributed to exceeding all those goals, with the next-generation system achieving approval from both the FDA and European Union (EU) thanks to miniaturized packaging, cable rerouting, and careful component selection.
Ensure Your Medical Device Performance in Signal-Intense Environments with Benchmark
Benchmark’s ongoing commitment to ensuring the optimal performance of our customers’ medical devices has been a cornerstone of our legacy for over 40 years. Our dedicated teams of seasoned industrial designers and engineers collaborate closely with medical device developers to create solutions that guarantee seamless operation, even in the most challenging conditions, such as bustling hospital settings.
With Benchmark’s global presence and expertise in both RF systems and medical devices, we help to ensure your medical device's performance in signal-intense environments. Don’t let signal interference be a barrier to your success. Partner with Benchmark and discover the future of reliable, high-performance medical devices.