Discover key insights in Med Tech: design medical robotics with care provider input, choose the right connectors for medical applications, retro electro (electricity or ethereal fire), and enhance ultrasound imaging with ultra-low noise power supplies.
We get technical
MedTech I Volume 12
The best medical robotics reflect care providers’ input Five considerations when specifying connectors for medical applications Electricity or ethereal fire considered How to improve ultrasound system image quality using ultra-low- noise supplies
we get technical
1
Editor’s note The MedTech industry is at the forefront of a technological revolution, combining advances in electronics, software, and materials science to transform healthcare delivery. From wearable devices that monitor vital signs in real time to advanced imaging systems and robotic-assisted surgeries, MedTech has emerged as a key driver of innovation in the healthcare sector. For engineers, this field offers unparalleled opportunities to contribute to life- changing applications that improve patient outcomes and streamline medical processes. At the heart of these innovations lies the integration of cutting-edge components, including microcontrollers, sensors, power management systems, and connectivity modules. As MedTech devices become smaller, smarter, and more connected, the challenges for engineers grow more complex. Regulatory compliance, ensuring device reliability, and meeting strict safety standards are just a few of the hurdles that must be navigated. For engineers working on MedTech projects, understanding these challenges and staying informed about the latest advancements in technology is crucial. DigiKey is committed to empowering engineers to succeed in this demanding yet rewarding field. As a trusted partner, DigiKey offers access to an extensive range of components, development tools, and resources tailored to the needs of the MedTech industry. Whether you are prototyping a new device or optimizing an existing design, DigiKey provides the tools and support to accelerate your innovation. This ebook is designed to provide engineers with the insights, knowledge, and inspiration needed to tackle the challenges of MedTech design. We will explore how to select and apply the right medical components, guidance for designing medical equipment alarms, and a close look at how medical robots are transforming the industry. Whether you are an experienced MedTech engineer or new to the field, this resource will guide you in navigating the complexities and seizing the opportunities of this transformative industry.
4 The best medical robotics reflect care providers’ input 8 How to select and apply the right components to protect medical devices, users, and patients 16 Five considerations when specifying connectors for medical applications 20 Select the right AC/DC power supply to meet unique medical requirements 28 Special feature: retroelectro Electricity or ethereal fire considered 36 How to use high accuracy digital temperature sensors in health monitoring wearables 42 IEC 60601-1-8 guidance for designing medical equipment alarms 46 Keep biomedical sensors firmly in place and reduce errors with medical securement tape 50 How to improve ultrasound system image quality using ultra- low-noise supplies 58 Tuning forks for medical applications
Together, let’s shape the future of healthcare.
we get technical
2
3
The best medical robotics reflect care providers’ input
facilities, robotics: ■ Improve the repeatability of delicate procedures – as in minimally invasive surgical (MIS) procedures and other robot- assisted surgery ■ Execute mundane tasks for periods longer than acceptable for medical staff – as in AGVs that shuttle bedding and other laundry around sprawling facilities ■ Assist in jobs that are unsafe for caretakers – as in patient lifts and robotic beds to help the immobile from bed to chair or vice versa
■ Complement automated systems employing data tracking. Watch the
online video presentation How to use RFID to Increase Patient Safety and Protect Revenue for more on this topic ■ Independently collect and deliver medications as well as lab specimens (leveraging secured patient data) Such advancements can extend the capabilities of nurses, physicians, and hospital cleaning along with maintenance staff. They also present opportunities to pre-program predictable and repeatable tasks as well as leverage information from various hospital systems – to continually improve patient care and support medical-research efforts. Surgical robotics continue to lead the increased automation of the medical field – for assisting surgeons as in the past and increasingly leveraging the benefits of artificial intelligence and machine learning. A report by Fortune Business Insights predicts the surgical-robot market will reach nearly $6.8B by 2026; it’s no wonder, as computer- assist systems are well-proven to help surgeons enhance patient outcomes with magnified images and precise end-effector movements not subject to fatigue, tremors, or distractions.
Other medical-robot design considerations The best medical-robotic designs are informed by experienced hospital personnel as well as other medical professionals and caretakers. This input and a thorough understanding of human anatomy can help robot designers deliver designs of sufficient accuracy and maneuverability, whether for goods transport, Figure 2: FSR 400-series single-zone force sensing resistors are robust polymer thick film devices that exhibit a decrease in resistance with an increase in applied force. Sensitivity is suitable for use in human-machine interfaces, medical systems, and robotics. Image source: Interlink Electronics
Written by Edward O’Brien
Figure 1: Medical robots take various forms. Some simply automate tasks that could be tedious or prone to increase the risk of human error. Image source: Getty Images
Popular interest in (and industrial adoption of) robotics has hastened since the COVID-19 pandemic and all the skilled-labor shortages it exposed. Now, robots are especially viable for medical applications of all types. Designs satisfying these uses take the form of professional- grade autonomous ground vehicles (AGVs), automated testing stations, and patient-support systems to compliment the most sophisticated surgery robotics in hospitals and other medical-treatment settings. Robotic designs to satisfy medical applications are also taking the form of household appliances designed to improve the quality of life for those who wish to maintain mobility and independence via age-in-place approaches despite medical issues. Though beyond the focus of this article, it’s worth noting that some robotics designs are adapting many of the technological advancements in home security (including video
for health-assist robotics that extend Internet of Things (IoT), home automation, and system interoperability. For example, some underlying IoT technologies are now being employed to help those aging in place to adhere to (sometimes complicated) medication schedules. Another bourgeoning type of medical robotics – that of exoskeletons – has come to represent the convergence of prosthetics, orthotics, and wearables to help the elderly as well as warehouse and other plant personnel aiming to avoid injury during strenuous manual tasks. Many of the technologies here borrow from innovations first pursued for military applications. Nearly all include IoT connectivity and sensor arrays for feedback.
Figure 3: Electronically commutated or brushless DC (BLDC) motors are used in some medical robots to help retrain and condition arm and hand movements in patients with arm-mobility impairments. That’s because such motors are particularly compact and efficient. Image: Portescap
Dynamic market poised for growth
systems) and HVAC energy monitoring for household use
In hospitals and other medical
we get technical
4
5
The best medical robotics reflect care providers’ input
executives should be involved in communicating those benefits to staff and the local community.
Figure 4: ND-series family extends the operating temperature from -20 to +85°C while pressure sensors feature a wide dynamic to serve the job of half a dozen sensors having a more traditional design. More specifically, these components include integrated electronics, advanced piezoresistive elements, an ADC, a DSP, and a digital interface to track pressures from
Conclusion In the U.S., the medical industry’s adoption of robotics has continued unabated for the last decade. Those investments will likely continue as an aging populous relies more heavily on the industry – even while hospital budgets nationwide face serious challenges. After all, robotics can offer long- term operational savings for many routine healthcare functions … not to mention the most advanced options for surgeries and other treatments that are maximally precise and minimally invasive. The caveats here are that adoption of robotics requires the clear mapping of hospital need and suitable robotics solutions; satisfying exceptionally stringent regulatory requirements; and sourcing from medical suppliers capable of long-term design support. At least for most larger hospital systems, robotics programs also require dedicated liaisons with automation expertise to coordinate continuous- improvement efforts. Ultimately, medical-robot offerings should also be thoroughly evaluated through the lenses of patient safety and comfort as well as procedure or treatment efficiency and effectiveness.
networks can let hospitals analyze data to assess robot programs’ effectiveness … which is especially useful where hospital systems aim to scale a given robotics program. Data for satisfying regulatory requirements Cohesive data-management systems can help multi-site hospital networks as well as standalone hospitals, clinics, and surgical centers more efficiently verify satisfaction of government and industry regulations. Sites employing medical robotics are more likely to have unified networks in place, or at least standard Figure 7: Medical-grade isolation transformers support the trouble-free operation of robotics and other equipment with continuous noise filtering and 100% isolation from input ac. UL 60601-1 medical- grade listing with hospital-grade plug and outlet receptacles render the transformers suitable for protecting electronic equipment in patient-care areas. Image: Tripp Lite
Training staff on medical- robot functions Healthcare organizations adopting medical robotics should ensure the technologies are well aligned with caretaker expertise; for all hospital staff who will interface with the new robotics, upfront and continuing
0.25 in. H2O to 5 psi for use in various designs – including automated eye-surgery equipment and autonomous
approaches to connect separate systems. The addition of robotic equipment for critical tasks also benefits from the way in which most healthcare facilities already have in place quick-response power and data backup systems. Of course, medical robotics require stringent physical security and cybersecurity. This often necessitates tightly restricted and monitored access to robotic actuators, controllers, networks, and data storage. Adherence to industry, supplier, and government
vehicles. Image: Superior Sensor Technology Inc.
caregiving, drug delivery, or surgery. Where medical robots rely on IoT data systems for real time information, their compatibility with existing hospital networks is key.
Medical-robot data considerations
training programs should be implemented. Here, standard
training standards can be lacking – so organizations should seek partners to recommend and craft training modules as needed. In addition to training on how to safely operate and maintain robotics (where applicable) such instruction should also include procedures for insurance documentation and billing – complemented by readily accessible manuals and digital refresher modules for hospital staff. Data to support connected operations Data visibility and AI can optimize control over equipment even while imparting deep insight into various roboticized procedures. Then equipment connectivity across
Before full-scale adoption, medical robotics should be evaluated for how they affect patient safety, treatment comfort, and outcomes. Results from previous implementations should be studied to quantify patient-recovery improvements and cost reductions. Medical-robotics programs should also be assessed for how they free existing hospital staff to put more of their focus on patient care – whether in person or remote. Where robotics prove to support hospital systems’ core missions related to quality care, patient satisfaction, and efficiency, hospital
Medical-robot supplier requirements
Medical-robotics engineers, software developers, and suppliers must have extensive knowledge of the best practices associated with the treatment or procedure being motorized or automated. Also required is a keen understanding of underlying business requirements and viable monetization approaches for the industry. Any systems associated with the retention of patient information require secure data management. That applies to both structured data (as held in databases) and unstructured data in text- retaining systems. Excellent network integration and analytics capabilities are core to justifying the extra data-management design efforts with predictive and adaptive system behavior.
regulations must be strictly satisfied and documented.
Figure 5: Components such as tension load cells ensure patient lifts are operating correctly and within design specifications. Image: Loadstar Sensors
Figure 6: USB-to-serial and network-to-serial products can provide the interfaces between medical robotics and equipment not initially designed for connectivity. Data connectivity solutions can also monitor environments that must be tightly controlled – and keep mobile robotics securely and reliably connected. Image: Digi
we get technical
6
7
Many of these issues apply to battery-powered units, not just those that are AC line powered. The function of many but not all protection devices is to suppress unacceptably large voltage transients. There are two major categories of transient suppressors: those that attenuate transients, thus preventing their propagation into the sensitive circuit; and those that divert transients away from sensitive loads and so limit the remaining voltage. It is critical to study device data sheets carefully for thermal and performance derating curves, as some are specified for transient protection of various durations bounded by defined voltage, current, and time limits rather than steady-state protection.
almost certainly be preferred or “standard” approaches, but there are also choices that must be judged, assessed, and made. Circuit protection options are many: choose wisely There are a variety of protection options. Each has a unique functionality and set of characteristics that makes it a suitable – or only – choice for implementing protection against specific classes of faults or unavoidable circuit characteristics. The main protection options are: ■ The traditional thermal fuse ■ Polymeric positive temperature coefficient (PPTC) devices ■ Metal oxide varistors (MOVs) ■ Multi-layer varistors (MLVs) ■ Transient voltage suppression (TVS) diodes ■ Diode arrays ■ Solid state relays (SSRs) ■ Temperature indicators ■ Gas discharge tubes (GDTs) The thermal fuse is simple in concept. It uses a conducting fusible link that is fabricated of carefully selected metals with precise dimensions. The flow of current beyond the design limit causes the link to heat up and melt, thus permanently breaking the current path. For standard fuses, the time to open circuit is on the order of several hundred milliseconds to several seconds, depending on the amount of overcurrent versus rated limit. In
various types of circuit and system protection components, using devices from Littelfuse, Inc. by way of example and examines the role and application of each. The role of protection in medical systems For most engineers the phrase “circuit protection” immediately brings to mind the classic thermal fuse, which has been in use for over 150 years. Its modern embodiment is largely due to the work of Edward V. Sundt, who in 1927 patented the first small, fast-acting protective fuse designed to prevent sensitive test meters from burning out (Reference 1). He then went on to found what eventually became Littelfuse, Inc. Since then, circuit protection options have expanded significantly in recognition of the many potential circuit failure modes. These can be: ■ Internal failures that may result in a cascade of damage to other components ■ Internal failures that may put the operator or patient at risk ■ Internal operational issues (voltage/current/thermal) that may stress other components and lead to their premature failure ■ Voltage/current transients and spikes which are an inherent and unavoidable part of the circuit’s functionality and must be carefully managed
How to select and apply the right components to protect medical devices, users, and patients
Among the many electrical parameters that must be
considered are clamp voltage, maximum current, breakdown voltage, reverse working maximum
to provide protection, and a typical system may need a dozen or more of these specialized protection devices. Protection devices are like insurance: while the latter may only be rarely or never needed, the cost of not having it far exceeds the cost of having it. This article looks at where protection is needed in such medical systems, including patient-facing signal/sensor I/O, power supply, communication ports, processing core, and user interfaces. It also discusses the
protection against multiple types of electrical issues that can harm the equipment, hospital staff, and patients. However, full circuit protection takes much more than just a thermal fuse, and implementing protection is not a matter of finding the single best device for a given design and application. Instead, it involves first understanding which circuits need protection and then determining the best mode of protection. In general, multiple passive components are needed
Written By Bill Schweber
or reverse stand-off voltage, peak pulse current, dynamic
resistance, and capacitance. It is also important to understand under what conditions each of these is defined and specified. Device size and number of channels or lines protected are also considerations. The choice of the best protection device to use in a given part of a circuit is a function of these factors, and there are often the inevitable trade-offs among the various parameters. There will
The use of non-laboratory, patient-contact diagnostic and life-sustaining medical equipment such as ventilators, defibrillators, ultrasound scanners, and electrocardiogram (EKG) units continues to increase. Reasons include an aging population, heightened care expectations among patients, and improvements in medical electronics technology which make such systems more practical. Such equipment needs
we get technical
8
9
How to select and apply the right components to protect medical devices, users, and patients
many designs, it is a final line of protection, as it acts decisively and irrevocably. Fuses are available for current values from under one ampere to hundreds of amperes or higher and can be designed to withstand hundreds or thousands of volts between their two terminals during fault-induced open-circuit conditions. A typical fuse is the Littelfuse 0215.250TXP , a 250 milliampere (mA), 250 volt AC (VAC) fuse in a 5 x 20 millimeter (mm) ceramic enclosure (Figure 1). Like most fuses, it is a cylindrical or cartridge-shaped housing that is not soldered into the circuit but instead goes into a fuse holder for ease of replacement. Fuses are also available in rectangular and “blade” housings as well as those that can be soldered; note that the soldering profile must be carefully observed to avoid damaging the fuse element. Despite their apparent simplicity, fuses have many variations, subtleties, and other factors that must be taken into account when selecting the appropriate one
back-to-back Zener diodes. Their symmetrical and sharp breakdown characteristics enable them to provide excellent transient suppression performance. When a high-voltage transient occurs, the varistor impedance decreases by many orders of magnitude from a near open circuit to a highly conductive level, clamping the transient voltage to a safe level in a few milliseconds (Figure 4). As a result of this clamping action, the potentially destructive energy of the transient pulse is absorbed by the varistor (Figure 5). MOVs are offered in a variety of packages such as the 390 volt, 1.75 kiloampere (kA) V07E250PL2T , which is a small disk with through-
Figure 2: The 2016L100/33DR 33 volt, 1.1 A PPTC device can be used in low voltage applications where resettable protection is needed; it reacts in under
Figure 4: The voltage- current (V-I) curve of the MOV shows its normal high resistance region as well as its very low impedance region, which occurs when the voltage increases beyond a design threshold.
0.5 s at an overcurrent of 8 A. Image source: Littelfuse, Inc.
for a circuit (References 2 and 3). Fuses are commonly used on input AC lines, output leads where a total short-circuit may occur, or internally where any overcurrent is a serious concern such that the current flow must be fully stopped, and the problem’s source determined and fixed before operation can resume. PPTC devices serve two main types of applications: safety regulation such as for a USB port, power supply, battery, or motor control; and risk prevention for an I/O port. During abnormal conditions such as overcurrent, overload, or overtemperature, the PPTC resistance will increase dramatically, which limits the power supply current in order to protect circuit components. Once a PPTC device trips into a high resistance state, a small amount of current continues to flow through the device. PPTC devices require a low joule heating “leakage” current or external heat source in order to maintain their tripped condition. After the fault condition is removed and the power is cycled, this heat source is
resistance status and the circuit is restored to a normal operating condition. Although PPTC devices are sometimes described as “resettable fuses” they are, in fact, not fuses but nonlinear thermistors that limit current. Because all PPTC devices go into a high resistance state under a fault condition, normal operation can still result in hazardous voltage being present in parts of the circuit. A good example of a PPTC is the Littelfuse 2016L100/33DR , a surface mount, 33 volt, 1.1 A PPTC device for low voltage (≤60 volts) applications where resettable protection is needed (Figure 2). It has a footprint of 4 x 5mm and will trip in under 0.5 seconds (s) at an overcurrent of 8 A. In a typical ventilator, the 2016L100/33DR might be used to protect the battery management system’s MOSFET from high currents due to external short circuits or provide overcurrent protection for USB chipsets (Figure 3). MOVs are voltage dependent, nonlinear devices that have an electrical behavior similar to
Image source: Littelfuse, Inc.
hole leads that measures just 7mm in diameter (Figure 6). They are often used on an input AC line to prevent damage due to AC line voltage transients (area 1 in Figure 3). Note that MOVs can be connected in parallel for improved peak current and energy handling capabilities, as well as in series to provide voltage
ratings higher than those normally available, or ratings between the standard offerings. MLVs are similar to MOVs and provide the same basic function but have different internal construction and thus somewhat different characteristics. MLVs are fabricated by wet stack printing layers of zinc oxide (ZnO) and metal inner electrodes, sintering, terminating, glassing, and finally plating. In general, for the same MOV voltage rating, smaller MLV parts have a higher clamp voltage at higher currents, while larger parts have a higher energy capability. The V12MLA0805LNH MLV, for example, was tested with multiple pulses at its peak current rating (3 A, 8/20 microseconds (µs)). At the end of the test – 10,000 pulses later – the device voltage characteristics are still well within specification (Figure 7). This device should be considered for transient protection in the ventilator power supply and
Figure 1: The Littelfuse 0215.250TXP is a 250 mA, 250 VAC fuse in a ceramic body with a 5mm diameter and a length of 20mm. Image source: Littelfuse, Inc.
Figure 3: In this ventilator block diagram, PPTC devices could be used in the battery management system as well as the USB port sections (areas 2 and 5). Image source: Littelfuse, Inc.
eliminated. The device can then return to a low
we get technical
10
11
How to select and apply the right components to protect medical devices, users, and patients
driving the unit’s paddles (Figure 11). Temperature indicators are specialized versions of temperature sensors such as thermistors. Although it may seem obvious that potentially hot areas such as power supplies or higher voltage sources need to be monitored for excess heating, even an I/O port such as USB-Type C can be handling significant current and thus overheat. This may be due to an internal failure or even a faulty load or shorted cable being plugged into it. To manage this potential problem, a device such as the SETP0805- 100-SE setP positive temperature coefficient (PTC) temperature indicator helps protect USB Type-C plugs from overheating. It has been designed to accommodate the unique specifications of this USB standard and is capable of helping to protect even the highest levels of USB Type-C power delivery. Available in an 0805 (2.0 x 1.2mm) package, it protects systems consuming 100 watts or higher, providing sensitive and reliable temperature indication as its resistance increases from a nominal 12 ohms (Ω) at 25⁰C to 35 kilohms (kΩ) at 100⁰C (typical values). GDTs may conjure up images in engineers’ minds of large, bulky tubes with visible sparks, but they are in reality very different. These tubes are placed between a line or
Figure 6: The V07E250PL2T MOV is a through-hole leaded, 7mm disk rated for operation to 390 volts and can handle transients up to 1,750 A. Image source: Littelfuse, Inc. sub-circuits or allow the high- side drivers of a half or H-bridge MOSFET configuration to “float” off ground. Another objective SSRs, also called optoisolators, allow one voltage to switch and control an independent, unrelated voltage with near-perfect galvanic isolation (no ohmic path) between input and output. They serve multiple broad objectives. One is functional: they can eliminate ground loops between separated +/18 kilovolts (kV) to +/-30 kV. Applications include protection of USB 2.0, USB 3.0, HDMI, eSATA, and display port interfaces, to cite a few possibilities. Note that the similarly named TVS diode array provides the same basic functionality but has higher capacitance and thus is better suited for lower speed interfaces. The SP3019-04HTG is an example of a such a diode array (Figure 10). It integrates four channels of ultra-low-capacitance (0.3 pF) asymmetrical ESD protection in a six-lead SOT23 package, and also features an extremely low typical leakage current of 10 nanoamperes (nA) at 5 volts. As with the TVS diode, typical applications are for protection of USB ports as well as the LCD/LED user interface display (again, areas 2 and 3 in Figure 9).
Figure 7: MLVs such as the V12MLA0805LNH can withstand repeated transient pulses without performance deterioration. Image source: Littelfuse, Inc.
Figure 5: The abrupt switch of the MOV from high impedance to low impedance when a transient voltage occurs clamps that voltage to an acceptable level. Image source: Littelfuse, Inc.
USB port (areas 1 and 5 in Figure 3). TVS diodes also protect sensitive electronics from
high-voltage transients and can respond to overvoltage events faster than most other types of circuit protection devices. They clamp and thus limit voltage to a certain level using a p-n junction that has a larger cross-sectional area than that of a normal diode, allowing the TVS diode to conduct large currents to ground without sustaining damage. TVS diodes are generally used to protect against electrical overstress such as those induced by lightning strikes, inductive load switching, and electrostatic discharge (ESD) associated with transmission or data lines and electronic circuits. Their response time is on the order of nanoseconds, which is advantageous for protecting relatively sensitive I/O interfaces in medical products, telecommunication and industrial equipment, computers, and consumer electronics. They have a defined clamping relationship between the transient voltage versus voltage across, and current
through the TVS, with specifics defined by the TVS model under consideration (Figure 8). The SMCJ33A is a unidirectional TVS diode with a 53 volt clamping voltage and 28 A peak current rating in a 5.6 x 6.6mm SMT package; a bidirectional version (B suffix) is also available for use when both positive and negative- going transients are anticipated. In a representative application such as a portable ultrasound scanner with a high voltage pulse generator to drive the piezoelectric transducers, TVS diodes could be used to protect the USB ports as well as the LCD/LED user interface display (areas 2 and 3 in Figure 9). Diode arrays use steering diodes centered around a large TVS diode (such as a Zener diode) to help
they serve is safety related and especially important for medical devices where their isolation provides an impassable barrier. This containment is needed where there are high internal voltages along with user or patient contact with instrumentation leads, knobs, probes, and enclosures. The CPC1017NTR is representative of a basic single-pole, normally open (1-Form-A) SSR. It is packaged in a diminutive 4mm2, four-lead housing while providing 1,500 volts RMS (VRMS) isolation
between input and output. It’s extremely efficient, requiring just 1 mA of LED current to operate, can switch 100 mA/60 volts, and provides arc-free switching without the need for external snubbing circuits. Further, it does not generate EMI/RFI and is immune to external radiated electromagnetic
fields – characteristics that are required in some medical
instrumentation and systems. In an application such as a defibrillator, designers can use it to electrically separate the low-voltage circuitry from the high voltages of the bridge
Figure 8: Shown is the general relationship for a TVS between voltage transients, voltage across the TVS, and current through the TVS,
with specific values determined by the
reduce the capacitance seen by I/O lines. These devices have a low off-state capacitance of 0.3 to 5 picofarads (pF) and are suitable for ESD levels from
selected TVS diode model. Image
source: Littelfuse, Inc.
we get technical
12
13
How to select and apply the right components to protect medical devices, users, and patients
Figure 13: GDTs do not have to look like the big spark-gap devices seen in movies; the GTCS23-750M-R01-2 is a 75 volt, 1 kA GDT
Standards guide the design
Medical devices must meet multiple safety standards, some of which apply to all consumer and commercial products, and some of which are for medical devices only. Many of these standards are international in scope. Among the many standards and regulatory mandates are: ■ IEC 60601-1-2, “Medical electrical equipment – Part 1-2: General requirements for basic safety and essential performance - Collateral Standard: Electromagnetic disturbances - Requirements and tests.” ■ IEC 60601-1-11, “Medical Electrical Equipment Part 1-11: General requirements for basic safety and essential performance – Collateral standard: Requirements for medical electrical equipment and medical electrical systems used in the home healthcare environment.” ■ IEC 62311-2, “Assessment of electronic and electrical equipment related to human exposure restrictions for electromagnetic fields (0Hz to 300GHz).”
in an SMT package that measures just 4.5mm in length and 3mm in diameter. Image source: Littelfuse, Inc.
with more general applicability. Each component brings a set of attributes that makes it a best fit – or at least a better one – in the different circuit and system locations requiring such protection. No single device will fit the multiple diverse system requirements and so designers will end up using multiple protection approaches. In most cases, the many decisions regarding which devices to use and how best to do so are inherently complicated and also subject to regulatory review. Designers should strongly consider asking for help from knowledgeable application engineers at the protection device vendor or their designated supplier (distributor). Their experience and expertise can reduce time to market, ensure a more thorough design, and ease the path to regulatory approval.
Figure 11: In a defibrillator, the SSR allows the low- voltage electronics to drive the high-voltage paddles while allowing the “floating” upper-side drivers of the H-bridge arrangement to remain isolated from system ground (area 5). Image source: Littelfuse, Inc.
Figure 9: In this portable ultrasound scanner block diagram, a TVS diode such as the SMCJ33A with a 53 volt clamping voltage can be used for protection against transients at USB ports as well as at the LCD/LED display (areas 2 and 3). Image source: Littelfuse, Inc.
■ IEC 62133-2, “Secondary cells and batteries containing alkaline or other non-acid electrolytes – Safety requirements for portable sealed secondary lithium cells, and for batteries made from them, for use in portable applications – Part 2: Lithium systems.” Being careful about circuit protection device selection and how they are used goes a long way toward meeting these safety mandates. Using accepted,
approved techniques and components can also speed up the approval process.
conductor to be protected – usually an AC power line or other “exposed” conductor and system ground – to provide a near-ideal mechanism for diverting higher overvoltages to ground. Under normal operating conditions, the gas inside the device acts like an insulator and the GDT does not conduct current. When an overvoltage condition (called the sparkover voltage) occurs, gas inside the tube breaks down and conducts current. When the overvoltage condition exceeds the parameters of the sparkover voltage rating, the GDT turns on and discharges, diverting the damaging energy. GDTs are available as two-pole devices for ungrounded lines and three-pole devices for grounded lines, both in small SMT
packages for ease of design-in and board assembly (Figure 12). GDTs are available for sparkover values rated as low as 75 volts and can handle hundreds and even thousands of amperes. For example, the GTCS23-750M-R01-2 is a two-pole GDT with a 75 volt sparkover and a 1kA current rating, housed in an SMT package measuring 4.5mm long and 3mm in diameter, allowing it to be placed almost anywhere to provide protection (Figure 13).
Conclusion
The requirements of where, why, what, and how to use circuit protection devices in general, and in medical units in particular, is a complicated design challenge. There are many suitable protection components, some specific to a given circuit function and others
Figure 12: GDTs are offered as (left) two-pole devices for ungrounded circuits and (right) as three-pole devices for grounded circuits (the GDT symbol is the “Z-like” graphic to the right of each schematic diagram). Image source: Littelfuse, Inc.
Figure 10: A diode array such as the SP3019-04HTG provides ESD protection for multiple high-speed I/O lines. Image source: Littelfuse, Inc.
we get technical
14
15
Five considerations when specifying connectors for medical applications
Five considerations when specifying connectors for medical applications
more elastic than brass and less susceptible to stresses that limit the cycle life of bronze contacts.
Figure 1: NRZ has a single eye (left) and transmits 1 bit of information per signal interval. PAM4 is a multilevel signal modulation format with three eyes (right) and has a throughput of 2 bits per interval. Image source: Samtec
IEC 60601, ISO 80369-1, and ISO 13485 There are numerous application- specific industry standards for various medical systems and devices. Three of the more general standards that need to be considered in all designs are: ■ ISO 80369-1: this focuses on the design methodology to reduce the risk of misconnections between medical devices, or between accessories for different applications ■ IEC 60601 focuses on the general requirements for basic safety and essential performance including electromagnetic interference (EMI) and electromagnetic compatibility (EMC) ■ ISO 13485 focuses on the quality systems needed for tracking the components and processes used in the manufacturing process. It is related to ISO-9001 Testing beyond industry standards Severe Environment Testing (SET) is a suite of tests developed by Samtec that extend beyond typical industry standards and specifications and includes: ■ 250 mating cycles with 100% humidity
Written by Jeff Shepard
Designers of medical devices and systems need connectors that will help them address increasing complexity and smaller form factors, while at the same time ensuring high levels of reliability and performance under various usage models. Some connectors are inaccessible within the system making reliability critical. Other connectors are regularly used by surgeons, physicians, nurses, or technicians, so ease of use, and a high number of mating cycles are also important. Depending on the application, connectors for medical devices and systems must comply with standards such as IEC 60601, ISO 80369-1, and ISO 13485, and may require severe environmental testing beyond typical industry standards and specifications. Along with a usable model and specific standards, designers need to consider technical tradeoffs between non-return-to-zero (NRZ), also called pulse amplitude modulation 2-level (PAM2), and pulse amplitude modulation 4-level (PAM4) connector technologies to arrive at the optimal cost and performance for a specific use case.
Designers have a broad range of connector types to consider when identifying the best solution. To assist in the process, this article begins by briefly reviewing five important factors to keep in mind
in high-speed links such as multi- gigabit communications.
terminations are being supplanted by surface mount terminations in a growing number of applications. Paste-in-hole connectors are mounted in holes that do not completely penetrate the pc board. To be used for surface- mount or paste-in-hole designs, the connector body material must be able to withstand solder reflow temperatures, and they need to have horizontal and vertical clearance around the leads to accommodate the required quantity of solder paste.
in applications where connectors need to be regularly mated and unmated. The lower the contact resistance, the less power that is lost through the connector. A low mating/unmating force can contribute to ease of use, as long as the contact resistance remains low enough to meet electrical requirements. Connectors have limited mating/unmating cycle specifications, ranging from tens of cycles to many thousands of cycles. The cycle life of the connector must be matched to the needs of the application. When connector contacts are mated, the contact is displaced, and the metal is flexed. The flexing is important and determines the force needed to mate and unmate the connector, and the contact resistance. Flexing also causes stresses in the contacts that results in both the mating/unmating force decreasing and the contact resistance increasing over time. Replacing the brass base metal commonly used in connector contacts with more expensive phosphor bronze will increase the cycle life. Phosphor bronze is
Mechanical considerations
Mechanical considerations when selecting connectors include contact pitch, mating type, termination style, and size (Figure 2). Pitch measures the center-to- center spacing of the contacts. It can be more than one number; the pitch between contacts in each row and the pitch between rows can be the same or different. Connectors on printed circuit boards (pc boards) can use horizontal, vertical, or right-angle mating. Retention force is another consideration that measures how easily the connector can be removed. Common termination styles include through-hole, surface- mount, paste-in-hole, and press fit. Through-hole contacts pass through a hole in the pc board and provide strong connections between the pc board layers. Surface-mount connectors mount on the surface of the pc board and don’t require holes to be drilled. They can have smaller pitch spacings compared with through- hole connectors. Though-hole
when specifying connectors for medical devices. It then
presents examples of connector options from Samtec and closes with an overview of application considerations when integrating connectors in high-speed systems.
NRZ versus PAM4
NRZ transmits 1 bit of information per signal interval. PAM4 is a multilevel signal modulation format with a throughput of 2 bits per interval. In the NRZ eye, the top represents “1” and the bottom represents “0”, while the PAM4 signal consists of three stacked eyes formed using four voltage levels; 00, 01, 10, and 11 (Figure 1). The height of the eyes is an important consideration. The greater eye height of the NRZ signal results in better signal quality. NRZ is simpler to implement, has lower reflections, a better signal-to-noise ratio (SNR), and is lower in cost compared with PAM4. However, PAM4 is inherently faster and used
Press fit terminations are solderless and lower in cost but require special tooling for
installation. They are pressed into a hole on the pc board and held in place by compressive forces. Less common termination styles include land grid arrays, ball grid arrays, wire wrapping, crimping, and screw terminations.
Ease of use
Contact resistance, mating cycles, and mating/unmating force contribute to connector ease of use
we get technical
16
17
Five considerations when specifying connectors for medical applications
■ Misalignment can be a significant problem on pc boards with multiple connectors. Closely follow the manufacturer’s recommended termination connection specifications and keep alignment pin hole diameter tolerances to ±0.002 inches (0.05mm) ■ EMI is not just a pc board problem. Board-to-board connectors can contribute to EMI concerns and need to be considered from the beginning as part of the overall design
Figure 2: A small selection of the variety of available contact pitches, terminations, and sizes. Image source: Samtec
Figure 4: SEARAY 1.27mm high- density open-pin field-press-fit arrays are available in vertical and right-angle (shown
High-density, high-speed connectors Applications that need high speed and high density can use Samtec’s SEARAY 1.27 mm open-pin field- press-fit arrays. These connectors have up to 500 contacts optimized for signal integrity and are available in vertical or right-angle mounting options (Figure 4). This system features up to 10 rows and 50 contacts per row to enable grounding and routing flexibility; a choice of 7mm, 8mm, 8.5mm, and 9.5mm stack heights; and can handle signals up to 28 gigabits per second (Gbits/s). For example, part number SEAFP-40-05.0-S-06 is a vertical mount design with 240 contacts and through-hole terminations. Connectors for PAM4 or NRZ Applications that need higher contact densities and more than 28Gbits/s speed can use the 56 Gbit/s SEARAY series. Their 0.8mm pitch delivers twice the contact density of connectors with 1.27
above) options. Image source: Samtec
to Samtec’s TFM and SFM series , members of the company’s Tiger Eye interconnect system. These connectors are designed for micro, rugged, high-reliability, high-cycle applications, and are available in three pitches; 0.80, 1.27, and 2.00 millimeters (mm). These connectors have heat-treated, beryllium copper (BeCu) multi- finger contacts optimized for high- cycle applications and are designed for rugged environments (Figure 3). For example, the model TFM-105- 01-S-D-A is a 10-position header with 1.27mm pitch contacts. The smooth contact mating surface does not stress the plating, providing lower contact resistance, longer plating life and longer cycle life. Solder can easily penetrate the micro slot on the tail providing greater solder joint strength. These connectors are polarized to guarantee proper mating, and optional friction locks improve connection security.
■ Intense shock and vibration based on low-level contact resistance (LLCR) and event detection ■ LLCR testing using 40 times the standard gravitational force (g) peak, 11 milliseconds (ms), half sine and 12g RMS, 5 – 2000 Hertz (Hz), 1 hour/axis ■ Event detection according to EIA-364-87, EIA-364-27 and EIA-364-28 using the same test procedure as the LLCR testing ■ 500 temperature cycles ■ Non-operating-class temperature testing where the connector is LLCR tested, exposed to -55 to 105°C for 100 cycles, then tested for LLCR again; exposed to -65 to 125°C for 100 cycles, and tested
mm pitches, are available with 7mm and 10mm stack heights, and can handle PAM4 or NRZ communications. Configurations are available with up to 12 rows of 60 contacts for a total of 720. These open-pin-field arrays provide maximum grounding and routing flexibility including differential signal pairs, single-ended signal transmission and power delivery (Figure 5). Part number SEAF8-20- 05.0-S-04-2-K features 80 gold- plated contacts and surface-mount terminations. These connectors are SET qualified.
in medical applications, there are numerous factors that designers need to consider related to signal integrity and EMI, a few of these considerations include: ■ Shorter is better. Shorter connectors deliver better signal quality. The shorter the connector, the shorter the time available for reflections and crosstalk to occur ■ The signal-to-ground ratio is important. In most instances, a ratio of 1:1 is optimal, but for connectors with large pin counts, a ratio of less than 1:1 may be needed for reliable high-speed, single-ended operation ■ Ground shielding of contact pairs is recommended for differential connectors carrying signals of 2.5Gbits/s or faster
Conclusion
Selecting connectors for medical systems is an important and complex activity. Connectors need to be optimized to meet the mechanical durability, reliability, and ease of use requirements, in addition to meeting the electrical specifications and supporting communications protocols such as NRZ and PAM4. Adhering to relevant industry standards is important, but testing beyond the industry norms, such as with the Samtec devices mentioned here, is often needed to ensure the high levels of performance expected from connectors in medical devices and systems.
High-speed connector application considerations
for LLCR again; the connector must maintain a change of ≤5 milliohms (mΩ) in LLCR to pass ■ Dielectric withstanding voltage at an altitude of 70,000 feet ■ Electrostatic discharge (ESD) testing is not usually performed on connectors but is included in SET Connectors that handle 10,000 mating cycles Designers that need up to 10,000 mating cycles can turn
When using high-speed connectors
Figure 3: Tiger Eye interconnects (left) are available in a variety of formats and sizes and provide a rugged contact system rated to 10,000+ mating cycles. The TFM-105-01-S-D-A (right) is a 10-position header with 1.27mm pitch contacts. Image source: Samtec
Figure 5: SEARAY high-density open-pin- field arrays provide maximum grounding and routing flexibility including differential signal pairs, single-ended signal transmission and power delivery. Image: Samtec
we get technical
18
19
Figure 1: The isolation transformer breaks the current path from neutral to Earth, so the current will not flow through the user even if the user’s device or system is accidentally connected to the exposed case. Image source: Quora
Improvements in battery technology along with advances in low-power circuitry have made portable, battery-powered systems a viable option for many designs, but in applications such as medical and home healthcare, battery-only, untethered operation is not feasible, practical, or even desirable. Instead, the equipment must operate directly from an AC line or have access to an AC outlet to ensure reliable operation when the batteries are low. For these cases, the AC/DC supply must provide the usual power supply performance with respect to
voltage and current output, static and dynamic regulation, as well as fault and other protection features. In addition, basic power supply performance is not the only concern for medical systems designers. Various regulatory standards exist – and have recently been upgraded – which add additional mandates for less-obvious performance issues such as galvanic isolation voltage, leakage current, and two means of patient protection (2×MOPP). These are in place to ensure that the equipment which the supply
is powering does not put the operator or patient at risk even if there is a failure in the supply or the equipment. The combination of performance, reliability, and standards requirements, as well as cost and time to market pressures, make designing a power supply from scratch a challenging proposition. Instead, designers need to sift carefully through an array of ready- made options for the optimum solution. This article looks at applications for AC/DC supplies in medical- instrument environments, reviewing the critical regulatory standards for these supplies. It then introduces example supplies from CUI Inc. and discusses their respective characteristics and how they can help solve the medical system power supply challenge.
Select the right AC/ DC power supply to meet unique medical requirements
Various regulatory standards exist – and have recently been upgraded – which add additional mandates for less-obvious performance issues such as galvanic isolation voltage, leakage current, and two means of patient protection (2×MOPP).
Written by Bill Schweber
we get technical
20
21
Page 1 Page 2-3 Page 4-5 Page 6-7 Page 8-9 Page 10-11 Page 12-13 Page 14-15 Page 16-17 Page 18-19 Page 20-21 Page 22-23 Page 24-25 Page 26-27 Page 28-29 Page 30-31 Page 32-33 Page 34-35 Page 36-37 Page 38-39 Page 40-41 Page 42-43 Page 44-45 Page 46-47 Page 48-49 Page 50-51 Page 52-53 Page 54-55 Page 56-57 Page 58-59 Page 60-61 Page 62Powered by FlippingBook