Integrating RF & IoT technologies into the design of smart PPE wearables to improve workplace safety
The management of workplace health and safety risks in the Covid-19 era has highlighted the importance of Personal Protection Equipment (PPE) for workers across industries including healthcare. Designers are now integrating technology, and often wireless solutions into equipment to create smart PPE. However, RF devices worn close to the body pose challenges, which Nick Wood, Sales & Marketing Director at RF circuit miniaturisation, system-in-package & antenna-in-package expert, Insight SiP reviews here…
Smart PPE couples traditional PPE (reinforced clothing, helmets, safety shoes, ear plugs and protective eyewear) with integrated electronics (sensors, microprocessors and RF devices) to deliver enhanced safety and improved productivity. The European Agency for Safety & Health at Work (EU-OSHA) says that: “Smart PPE promises a higher level of protection and more comfort through the use of enhanced materials or electronics components”.
IoT & Industry 4.0 technologies drive smart PPE development
The technologies that underpin Industry 4.0 including low-powered IoT sensors, sophisticated wireless connectivity, Artificial Intelligence (AI), machine learning, cloud computing and edge computing can be applied to handle Covid-19 and the new workplace constraints that it imposes, or otherwise improve workplace safety. Smart PPE can be embedded in wearables in multiple forms: you could have a sensor equipped with a light, a buzzer and/or a vibration alert you to the fact that you are too close to a colleague via a tag integrated into protective clothing, a hard hat or a wristband, for example.
Through wireless connectivity, the tag could be used by management for the geo-positioning and geo-fencing for employees and industrial equipment at rest or in motion. Industry 4.0 technology can be applied to wearables to monitor employee body temperatures and alert the wearer to excessive temperatures which might require intervention such as drinking more liquids or resting in a cooler place to recover. Of course, these types of application need to be carefully managed to comply with personal data protection regulation, such as GDPR in Europe.
Smart PPE wearable use cases
- Face masks – Northwestern University in the USA, is developing smart PPE face masks for healthcare workers which monitor the wearer’s health and determine if they are correctly worn.
- Gas masks – 3M Scott Fire & Safety has developed the firefighting industry’s first in-mask, hands-free thermal imaging solution, helping firemen locate people trapped in fires and rescue them more quickly.
- Connected shoes – Intellinium designed smart PPE shoes with a ‘smart man-down’ feature which detects a fallen or motionless wearer, enabling an automatic alert.
- Body heat sensor system – Kenzen has developed a smart PPE patch which monitors physiological signs to prevent injury through excessive heat and generates an alert when a safety intervention is needed.
- Smart hard hats – LA-based WorkerSense has embedded microchips into construction workers' hard hats that track their social distancing and send alerts when they get closer than 2m to each other.
Designers are now integrating IoT & Industry 4.0 technologies, including RF &wireless solutions, into equipment to create smart PPE wearables.
RF design considerations for smart PPE wearables
Body worn RF devices present unique challenges, as the body will absorb and interfere with RF transmission. Challenging trade-offs therefore arise between optimal performance and comfort/practicality for everyday use.
Use case analysis
To determine the boundaries of the problem, you first must define the use case:
- What will your smart PPE wearable communicate with and when?
- What throughput/data rate is required
- Is near continuous connection required, or in case of interrupt is ‘store and forward’” acceptable, or simple break in data continuity?
Such an exercise needs to define the worst case in terms of smart PPE wearable positioning, the device it connects to and possible obstructions - body of the wearer and other elements of the environment.
RF absorption
Many wearable devices use Bluetooth to communicate but might also include a GPS receiver and/or long-range radios such as cellular or LoRA. These different technologies have different data rate/range/RF absorption characteristics.
For example, Bluetooth’s 2.4 Ghz frequency is easily absorbed by the human body. A device held one side of the body will be attenuated by 60 to 80 dB relative to a device on the other side, which can be compared with a typical link budget between high quality BLE devices of around 94dB.
Physical design Issues
The next stage is to review the physical design of the device. The key issues from a radio perspective are:
- Materials used in the housing
- Battery placement
- Placement of the radio component and PCB within the device
- Antenna choice/design
Housing materials
The ideal is RF transparent material such as polymeric (for instance, ABS, Perspex); conductive metal is a negative choice.
Battery
The battery should be metal cased and beside the PCB containing the RF component with the antenna separated as far as possible.
PCB placement
The PCB placement is critical as the body is a strong absorber of RF radiation, especially at 2.4 GHz. Achieving the maximum distance between the body and the RF component (specifically the antenna) is crucial.
A separation of ¼ λ – which at 2.4GHz equates to ~ 3cm would be optimum. This might not be possible in but nevertheless our extensive simulations showed that at 2mm spacing from the body the antenna gain away from the body is close to -2 dBi, increasing to 0dBi at 3 to 4 mm.
Antenna choice
For smart PPE wearables, antennas need to be small and convenient to wear, which may not align with technical objectives. The simplest choice for antennas is to use a certified Standard RF module with integrated antenna, minimising design effort and risk and removing the need for lengthy and expensive certification efforts such as CE, FCC and Bluetooth SiG.
The other two options are to connect an antenna part to the RF circuit or design a custom antenna. A custom antenna design could be optimised for the design of the specific smart PPE but requires advanced RF expertise.
Antenna directivity
Most small wearables require an omni-directional antenna with a gain as close to 0dBi as possible. Highly directive antennas will lead to reduced performance when antennas are not aligned.
There are standard miniature solutions available, small enough for most wearables. The problem is then the placement of the RF component, ideally retaining a ‘keep out’ zone around the antenna portion. In a space constrained wearable there may be a trade-off between size and performance.
Ground plane
Any small antenna will work best with a metal plane called a “ground plane” that has at least one dimension close to a quarter wavelength. For a 2.4Ghz device (BLE or WiFi) this is a manageable 3cm, but a more challenging 9cm in the 868Mhz ISM band (LoRa or Sigfox). Our simulations show that antenna gain and hence link budget decreases with decreasing “ground plane” dimension.
Summary
We have presented an overview of the challenges in designing an RF wearable. Tackling everything “from the ground up” should be left to the highly experienced. For most using pre-existing modules will be a better choice. Following simple design principles from the start reduces the risk and improves the chances of bringing your smart PPE to market on time.
