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The four AA batteries of the Qardio Smart Blood Pressure Monitor make up a large proportion of the device’s volume, but are required to power the electronics, pump, and Bluetooth signal.

Electrical medical device design: product design integration

Published: May 2024

Dave Shepherd

Dave Shepherd
Design Consultant

James McLusky

James McLusky
Director

Will Davies

Will Davies
Design Consultant

From blood glucose monitors to CT scanners, electromechanical medical products are becoming increasingly sophisticated and complex. Consequently, the performance, usability, and reliability of electrical medical device design demands a well-considered enclosure.

The enclosure’s purpose goes far beyond simply housing the electronics; it’s the human interface, enabling the operation of the device and protecting the user from harm. Additionally, the electronics will make anything up to 90% of the overall Bill of Material (BoM) cost. A successful electromechanical design will balance the various and often conflicting demands into an easy-to-use, compelling, and cost-effective solution.

Here at Shore, we have been developing award-winning electronic products for over 20 years, from user-focused diagnostic devices, point-of-care systems, and wearable technology, to connected drug delivery products and healthcare robotics. While the range of products is broad, many of the challenges and solutions are common.

As the first in a three-part series on the subject, we’ll take a closer look at some of these challenges and share our top 5 tips on electromechanical design for medical devices.

1. Detail the product architecture

As with all design development, in parallel to creating a compelling external form, it is essential to determine the optimal internal configuration. This is especially true with electrical products: by getting this right, the device will be smaller, more usable, and more efficient to manufacture.

Going beyond just defining the screen, connector, or button positions, the design team needs to define and manage all the interactions with and between the electronics; including how they are connected, retained, assembled, or serviced. Developing an efficient internal structure from the start with attention to PCB (Printed Circuit Board) layout, component placement, electromagnetic Interference (EMI) considerations, and regulatory safety requirements. This will pay huge dividends throughout the process and in the final product outcome.

Zoomed in image of the electronics within a medical devivce including multiple PCBs, touchscreen, power input, fibre optic cables, interconnects, motors and reader.

Compact product architecture of a point-of-care device; combining multiple PCBs, touchscreen, power input, fibre optic cables, interconnects, motors, and reader.

2. Optimise the PCB layout

PCB manufacture is an automated, controlled, reliable, and common process that is well understood. This can offer great opportunities to create the most efficient design, increasing reliability and reducing costs. Designing the PCB is a central point of collaboration between electrical and mechanical engineers. An appreciation and understanding of the needs of both disciplines goes a long way.

  • Collaborate: Designing the PCB is an iterative process between electrical and mechanical engineers. The mechanical engineering team should retain the final say on the space envelope of the PCB as they manage its place within the wider product.
  • Communicate: The mechanical engineers must communicate the space envelope for the PCB and understand the implications. Detailed 2D PCB drawings or 3D CAD are essential communication tools; showing mounting holes, connectors, battery contacts, displays, buttons, and any large or otherwise significant components allowing their locations to be agreed upon or moved as required.
  • Obstructions: Holes or mechanical features should be kept towards the edge of the board. While a feature may look small, it can quickly create significant choke points in the track layout.
  • Single-sided: As far as practical have all machine-placed components on one side of the PCB; this streamlines the process by eliminating the need to flip it during manufacturing.
  • Panelisation: PCBs are manufactured on panels; process costs are defined per panel. The more PCBs per panel, the more cost-effective they will be.
  • Location: To simplify supporting features and ensure a quick assembly process, position the PCB perpendicular to the enclosure’s moulding line of draw (if plastic).
  • Flexibility: Complex, compact devices often require multiple PCBs. Consider a Flexible Printed Circuit (FPC) or semi-rigid PCB to remove interconnections, reduce volume, and enable testing before final assembly.

A simplified PCB layout with mechanical fixings pushed to the edges allowing all machine-placed components to be in the centre of one side, increasing efficiency and decreasing costs.

3. Battery management

The fundamental chemistry of single-use alkaline or rechargeable lithium-ion batteries hasn’t changed significantly for decades. Devices can only last longer due to multiple incremental, power-saving enhancements within the electronics and the overall design.

  • Illumination: LED light uses a relatively large amount of power; carefully consider the number, duration, and type of LEDs to be used. Reducing the number and active duration of LEDs by design can significantly elongate the battery life.
  • Invest in displays: Traditional displays often use multiple LEDs for backlighting, and modern displays have also seen significant advancements in power efficiency. The cheapest display will often have the highest power consumption, potentially negating its value. Look for low-power options, ambient lighting controls, or alternatives like OLED displays which don’t require an LED backlight.
  • Advanced electronics: Integration of various components onto single System-on-Chip (SoC) solutions and Power Management Integrated Circuits (PMICs) along with optimised Firmware all work together to reduce the power consumption throughout the device.
  • Thermal management: Efficient thermal management is not only critical for preventing overheating but will also minimise performance and battery life degradation.
  • Battery directive: The EU Battery Directive 2006/66/EC now applies to medical devices. The main impact is the need to separate the battery at end of life. Considering this during the development, access can be created to easily remove or replace them.
  • Battery safety: There have been increasing incidents of small children swallowing lithium-ion ‘coin cell’ batteries, leading to electrical burns or even death. Safe access to the battery area should be considered, and designed with child-resistant measures.

The four replaceable AA batteries of this diagnostic device make up a large proportion of the internal volume.

4. Electromagnetic Interference (EMI)

Without protective measures, electronic devices will emit or be affected by electromagnetic interference which jeopardise proper function or user safety. To guard against this, all devices must comply with EMC (electromagnetic compatibility) regulations, such as IEC 61000. There are three common product design measures which work in combination:

  1. Shielding: The electronics may need to be shielded within a grounded metal enclosure, or Faraday cage. Typically, a metal box, mesh, or in extreme cases conductive paint.
  2. Grounding: This provides a reference point for electrical circuits and a path for unwanted electrical currents to dissipate safely. To be effective, a shield must be grounded relative to the device.
  3. Filtering: Specialist components that clean electrical signals, for example in cables, before exiting the grounded shield. These can require a larger-than-expected volume.

As the EMI solution develops, factors which need to be accounted for include:

  • Antennae: Used for wireless communication like Bluetooth or NFC (Near-Field Communications), these emit radio-frequency energy. These antennae should be outside the shielded area as their signal would be shielded.
  • Apertures: Holes in the shield will be required but need to be managed; air vents, antennae, cables, buttons, and connectors will all compromise the shield’s performance and need to be designed carefully.
  • Contingency: Additional measures may be needed to meet EMI regulations. These often only arise during testing late in the design process, causing challenges that are not easily resolved. Build contingency into the design early.

The two-part metal Faraday cage shield is clearly visible in the structure of this device.

5. Understand the standards

To advise the engineering team there are a range of regulatory standards, such as IEC 60601 for medical electrical equipment. Meeting these standards is a legal requirement that proves the device is safe to use and functions as intended. Understanding these needs will inform the considered design and material selection of the device. Common requirements include:

  • Electrical shock: Electrical insulation and defined electrical creepage & clearance distances must be observed to protect the user.
  • Mechanical hazard: Protection from sharp edges, moving parts that can crush, equipment that could fall, or expelled parts in the event of a fault.
  • Resistance to stress: The device should remain safe when subjected to mechanical stress, including static force and drop tests. Features like elastomeric bumpers can help absorb the impact.
  • Spread of fire: Should an internal fire occur it is the enclosure’s task to prevent its spread. Beyond just material selection, the design of apertures like ventilation holes should be considered.
  • Ingress protection (IP): Water and solid objects of various sizes from fingers to dust should be prevented from contacting the electronics. The housing serves as this barrier, and the required extent of protection depends on the potential risk.
An exploded view of an electronic device. It shows several components in a sequential arrangement, revealing the internal structure. There are visible circuit boards, screws, casings, and various other components. The casing parts are primarily black and red, and the overall design suggests a focus on mechanical and electronic assembly.

Impact, drop, flame, and ingress protection is provided by elastomeric bumpers on this robust device.

By understanding the factors discussed here and addressing them in close collaboration between electrical and mechanical engineers you can achieve an effective blend of functionality, performance, usability, cost, and compliance.

Shore’s interdisciplinary team brings together years of product development experience, including electronic integration expertise. This is applied to developing the next generation of high-performance medical devices.

If you’re looking for a design partner with electrical medical device design expertise, contact our Business Development Manager, Holly Milston, to arrange a discussion.

 

Part two coming soon!

Electrical medical device design: Robust, ingress-protected products.

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