Microwaves Energize Medical Applications

July 14, 2011
Despite a steep learning curve posed by FDA approvals and unique application environments, a growing number of RF and microwave firms are finding success serving medical markets.
1. RF technology can be used in medical applications ranging from external heat treatment and electro-surgical tools to minimally invasive endoscopic cancer treatment. Here, the BLF578 LDMOS power transistor enables RF ablation to be used on the heart.

Bringing new medical products to market has always posed challenges, owing to requirements for FDA approval in the US and similar regulatory demands in many other countries. With more medical devices now employing wireless data transfer, however, this process has gotten a bit more complicated. Requirements like non-interference, standards compliance, frequencies occupied, and more also have to be met. Despite a seemingly ever-lengthening approval process, however, more microwave and RF companies are now finding opportunities in medical markets. While many have been entrenched for years in applications like magnetic resonance imaging (MRI), an increasing number of firms are enabling and supporting applications like imaging, testing, scanning, and rehabilitation.

According to Larry Hawkins, Core Marketing for Americas for Analog Devices' RF Group, "Many in the industrial and medical segments are trying to replace what was traditionally done using wires with a wireless link. Generally, these wireless links are in the industrial, scientific, and medical (ISM) bands, run off batteries, and are low data rate. They are looking for low-cost, integrated solutions that they can build a network around. Power levels will change based on distance needed to transmit, but cannot exceed federal regulations for the band in which they are operating. Modulation standards will change based on frequency and tradeoffs between using a proprietary network or an industry standard (i.e., IEEE 802.15.4)."

In fact, IEEE 802.15.4 radios form the basis for the sensor-networking technology, Wireless HART. This protocol addresses the growing need for process measurements. Users gain a simple, reliable, secure, and cost-effective method to deliver new measurement values to control systems without having to run more wires. Essentially, it adds wireless capability to the original HART technology, which provides field communications for intelligent process instrumentation.

Among other standards taking hold in the medical segment is Bluetooth Low Energy (BLE). According to Cambridge Consultants, one of its biggest advantages is battery life. For example, a remote-control running on a typical BLE cell that is used 50 times a daywith its television listening continuouslywill have a battery life of roughly 11 years. Price also is a factor, as BLE chips are going for about $1 each.

Outside of the growth of wireless networking in the medical arena, some cutting-edge applications are being spawned by RF power. As stated by Mark Murphy, Director of Marketing for RF Power at NXP Semiconductors, "We see RF power being increasingly developed as an energy source in medical equipment used in treatments such as RF ablation. The same technique can also be used to treat some heart disorders and also some beauty treatments." In terms of the healthcare market at large, Murphy notes, "Typical frequencies used for these applications range from 500 MHz to 40 GHz, depending on the type of treatment. Typical power levels can vary from 0 to +50 dBm." An example of a part used for ablation is a 1300-W NXP RF amplifier operating at 2.45 GHz (Fig. 1).

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In addition to RF power, a growing opportunity exists for sensors. They are being used to gain accurate information in a less invasive manner. At last month's Sensors Expo in Chicago, IL, for example, Plessey Semiconductors debuted its Electric Potential Integrated Circuit (EPIC) sensor technology (Fig. 2). The EPIC sensor measures changes in an electric field much like a magnetometer detects changes in a magnetic field. As a result, it does not require physical or resistive contact to make measurements. The sensor is expected to enable the creation of new products. For example, medical scanners could simply be held close to a patient's chest to obtain a detailed electrocardiograph (ECG) reading.

2. This high-input impedance sensor acts as a stable, sensitive, contactless digital voltmeter to measure changes in the body's electric field down to millivolts.

The first EPIC product, called the PS25150, is a high-impedance, solid-state ECG sensor for applications like non-critical patient monitoring and emergency-response diagnostics. It can be used as a dry-contact ECG sensor without requiring potentially dangerous, low-impedance circuits across the heart. Because EPIC detects the voltage change in muscles and nerves without electrical contact, there is no need to have electrodes on or in the body to detect current changes.

Another sensor making news is Novelda's NVA6000 Impulse Radar Transceiver, which recently won the 2011 Frost & Sullivan Europe New Product Innovation Award in Radar Sensors. Because it is based on the Continuous Time Binary Valued (CTBV) design platform, this CMOS transceiver does not involve the use of synchronous clock-based digital designs (Fig. 3). Thanks to its use of extremely short microwave pulses, it is well suited for high-resolution ranging. Its high sensitivity enables it to detect very weak signalseven amidst considerable noise. The transceiver targets sensor applications including health monitoring (such as stress and pulse monitoring) and medical diagnosis (including heartbeat monitoring and three-dimensional RF imaging).

Speaking of imaging, PXI has garnered a lot of attention for the benefits of a modular approach in many test and measurement applications. Yet it also offers advantages in medical imaging. "Time to market is of critical importance for medical instruments," explains John Hottenroth, Product Manager for National Instruments. "Yet medical-imaging instrument developers are required to integrate the latest technology to build systems with excellent analog performance, complex processing and visualization, and high data throughput resulting from higher-speed ADCs and increasing channel counts. Not surprisingly, these challenges are very similar to those faced by RF system designers. While time-to-market pressures combined with the integration of new technologies can create design challenges, reconfigurable field-programmable-gate-array (FPGA) technologies coupled with flexible integration platforms can help develop prototype systems more quicklywhile delivering new innovations to the market. Developers are combining modular FPGA hardware, higher-level design tools, and industry-standard platforms to create highly flexible, scalable, and customizable systems."

As an example, Hottenroth points to researchers at Japan's Kitasato University, who recently demonstrated the world's first real-time, 3D optical-coherence-tomography (OCT) imaging system. That system is capable of displaying images at 12 volumes per second. For the system design, the researchers chose the NI PXI platform, which provided the following: high-throughput data transfers over PCI Express; accurate timing and synchronization of multiple modules; a wide variety of input/output (I/O) options; and the ability to create "peer-to-peer data streams" that connect multiple FPGA modules over direct memory access (DMA) without ever needing to involve the host. The system housed 22 FPGA modules, which combined data from 320 channels (each acquiring data at 10 MSamples/s), as well as performing noise subtraction, windowing, and Fast Fourier Transform (FFT) processing.

3. This transceiver is based on the Continuous Time Binary Valued platform, which allows it to avoid the use of synchronous clock-based digital designs.

In terms of medical "pictures," ultrasound imaging may be one of today's best known imaging technologies for its depiction of fetuses. Interestingly, ultrasonic testing is equally at home performing an MRI or checking pipes for weaknesses and leaks. To serve this area, a careful selection of frequency, resolution, and sensitivity is needed to match a transducer to the requirements of an application. According to John Fortune, Director of Sales and Marketing at Valpey Fisher, "Although the ultrasound frequencies start at 20 kHz, most ultrasonic transducers start at 200 kHz. At Valpey Fisher, we build transducers from quartz (piezoelectric) blanks for industrial testing. Taking advantage of the short wavelengths, transducers in this industry are often used for flaw detection, where the abnormalities are microscopic (e.g., micro-cracks in steel supports) or hidden from view (e.g., inside a packaged semiconductor). Along with sensitivity and resolution, transducer size, frequency, beam angle, and operating environment (open air or fluid immersion) are all tradeoffs made in determining the type of ultrasonic transducer that is right for an application."

No matter how they are usedfor imaging a patient or infrastructureultrasonic testers typically rely on wireless frequencies to relay image data back to a control unit and computer. Yet challenges exist for transceivers in both medical and industrial applications that operate at the ISM frequency bands. By their nature, for example, they serve only one of a number of applications using the same bands. As ADI's Hawkins notes, "This requires the use of integrated transceivers that have good blocking specification (e.g., they work even when there are many other people transmitting close to their frequency)."

For medical applications, the need to get FDA approval for all medical equipment adds to the complexity of product development. Although many microwave and RF firms are not as familiar with this approval process, they are committed to making sure that the device manufacturerstheir customersmeet all FDA requirements. Clearly, the medical and industrial markets are just starting to "go wireless." They are figuring out the best route as they go, and it is up to the many RF and microwave firms that partner with them to help them do it successfully.

About the Author

Nancy Friedrich | Editor-in-Chief

Nancy Friedrich began her career in technical publishing in 1998. After a stint with sister publication Electronic Design as Chief Copy Editor, Nancy worked as Managing Editor of Embedded Systems Development. She then became a Technology Editor at Wireless Systems Design, an offshoot of Microwaves & RF. Nancy has called the microwave space “home” since 2005.

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