Custom optical sensors play an important role in the advancement and growth of the medical device market.Custom sensors today enable devices that improve patient care worldwide with their performance, connectivity and portability.
In the age of the Internet of Things (IoT), and given the stringent semiconductor standards of the medical industry, the importance of optical sensors as a basic building block for a complete solution in this market continues to grow. Medical devices must consistently meet a level of performance and reliability that many other systems or industries cannot match, sometimes under extremely critical and complex conditions. Whether at a patient's home, in an emergency vehicle, in an operating room, in remote or harsh environments, or even just "non-stop" in a large hospital.
Because each application is unique, ordinary standard sensors often do not produce the desired result given the many facets of medical applications. Standard sensors carry the risk of false or inconsistent readings due to, for example, excessive or low sensitivity. Developing the optimal sensor solution with the appropriate sensitivity range, optical performance, and required footprint is critical to ensure accurate performance.
These custom optical sensing solutions are matched with compatible LEDs, sensors, packages, and factory configurations or tests to achieve the desired results for a turnkey solution. Adding cables, connectors, passive circuit components, and custom PCBs complements and often increases the flexibility and reliability of the desired solution.
However, the options for creating an optimized sensor solution are quite diverse. They range from simple procurement of paired discrete transmitter and sensor components to higher-level custom assemblies.
The discrete sensor is the fundamental element of a sensing solution, but it still requires careful selection of associated components. Matching an appropriate LED to the sensing element illustrates the challenge: Multiple sensor options include basic phototransistors, photodiodes, and even smart detectors that complement the sensing element itself. Features such as temperature compensation, automatic gain control, or autonomous decision making can be added with this type of smart sensor. Ultimately, the right sensor depends on the specific application requirements as well as performance requirements such as wavelength, sensitivity, device footprint and more.
A discrete emitter is also usually part of the design. LEDs are most commonly used, although vertical cavity surface emitting lasers (VCSELs) are also becoming more common, depending on parameters such as wavelength, optical output power, optical output angle and forward voltage. Emitter-sensor coupling is part of the consideration and is also affected by wavelength, power levels, and sensitivity to mechanical alignment.
The housing of the sensor solution is the next step in the design hierarchy, with application requirements driving a wide range of optical and mechanical housing options. Designers must be aware of the mechanical tolerances associated with each design, along with considerations such as sensor-to-emitter distance, aperture size, through-hole, surface area, and mounting angle. It is also important to recognize that discrete components and package design contribute to overall system performance.
The custom design of the optical sensing solution must be developed to meet a spectrum of design needs and performance requirements, ranging from variability in mounting location and sensing distance to the type of media being sensed and environmental conditions.
Because optical sensors are often mounted far from the system's primary PCB or microcontroller, connectivity is critical for input performance and communications. In these cases, cable length and connector types are important factors in designing a robust solution.
Medical applications often have optical sensor requirements that go beyond simple detector and emitter design techniques. Multiple sensors and/or emitters, other passive and active components (such as a voltage regulator), or other mechanical components may require placement on a common PCB. Additional wiring and connections with multiple discrete components would also be required. Higher-level assemblies can take many different forms, determined by application requirements for function, performance, and size.
With some 23 billion IoT devices installed in 2018 alone, finding a standard solution for a given optical sensor application is a major challenge. It takes optical, electrical and mechanical engineering expertise to develop a solution that will work consistently and reliably over time and under varying operating conditions.
In medical technology in particular, the demand for customized, optoelectronic sensor solutions is high - and growing. The complexity of integrating compatible light emitters and sensors, balancing the trade-offs between optical performance and sensitivity, and balancing stacking tolerances and overall costs can only be achieved through a customized solution. Reliable performance - even in low-volume, high-product-mix applications - creates high competitive value and strong profitability in a market characterized by growth and global demand for ever-new connected health applications.