Evolution of Medical Sensor Design
As the connected medical industry continues to grow, sensor technology design evolves to meet the demanding needs. Explore these five considerations for non-contact medical applications and review key trends.
As new developments in personal devices and medical equipment are established, sensor technology continues to evolve to meet the demanding needs of the growing connected medical industry. With trends such as Internet of Things (IoT) and enhancements in data analytics and artificial intelligence, sensors are becoming more crucial to collect accurate data. To collect this critical data, invasive and non-invasive sensor technology can be used. Invasive sensors are designed for applications such as arterial blood pressure monitoring during surgical procedures and temperature measurement through micro-thermocouples in catheter assemblies. These sensors require specialized compatibility and packaging, typically in a miniature disposable package. Non-invasive and non-contact sensor technologies have a broader use-case and have both mechanical and electrical design considerations to support the growth in medical devices and equipment. In this article, we will explore these sensor design considerations for non-contact medical applications and review key trends to keep in mind.
One of the first essential concepts to consider is the survivability, or ruggedness, of these devices. The sensing elements that measure properties such as temperature, vibration, and position are relatively small and delicate. For example, a thermopile sensor is comprised of a precise array of miniature thermistors to measure the temperature within its field of view. These sensors are packaged in a way to protect the sensing element from external environments. This becomes crucial in applications such as ventilation equipment, where a thermopile is designed to measure surface temperature and mass airflow sensors measure the airflow temperature to compensate for condition changes and provide a baseline temperature measurement for other sensors on board. Encapsulated in a stainless-steel housing, the sensing element is hermetically sealed to protect against external conditions such as humidity and other harsh factors.
Similarly, sensors can be packaged within an assembly through non-contact measurement for position sensing. The demand for Anisotropic Magneto-Resistive (AMR) position sensors has increased with its ability to be packaged and sealed within a device while measuring a magnetic scale external to the assembly. Prosthetic joints are an interesting example. Within this application, AMR sensors can measure rotation of a joint such as a knee or ankle to compensate for movement and create a more natural gait pattern. Since the sensor is packaged within the knee assembly, it protects it from the environmental conditions such as water, impact, and general wear. Therefore, it allows independent rotational movement between the sensor and moving limb without physical contact.
Packaging sensors and electronics in sealed assemblies addresses sterilization concerns, as well. Sterilization in medical applications can be accomplished in a variety of ways including the use of steam or exposure to ethylene oxide. With a sensor encapsulated within a device, it is protected against extreme temperatures or moisture at the component level. Non-contact sensors used for motion control has the ability to be installed in assemblies with the sensor submerged in non-conductive hydraulic oil. This further allows the sensor to be embedded within the assembly without external components exposed. Wearable devices can also exposed to elements in daily life including sweat and chlorinated water. While both elements seem harmless, electronic devices and sensors could experience corrosion issues and electrical shorts if not properly protected. To protect against these conditions, specialty coatings can be applied to sensing devices while still allowing for accurate detection and measurement.
Another major trend to consider in the sensors industry is miniaturization, an effort to limit a sensor’s required ‘real estate’ within a product. In 2018, TE Connectivity designed and conducted a survey for engineers on a variety of topics related to IoT design. Responses were received from 180 engineers with a stated interest in consumer, industrial, and automotive IoT. The survey explored IoT applications and design methods and then identified common challenges that exist across this space. On the topic of miniaturization, eighty-five percent of survey participants overwhelmingly agreed that this should be an area of focus. At the same time, fifteen percent believe sensor miniaturization has already gone as far as needed. The miniaturization of sensors is not unique to the medical market but it is increasing in importance.
With the increase in wearable, connected devices, the ability to create lightweight, compact designs becomes necessary. Even though watches, chest-mounted heart rate monitors, and jewelry are monitoring health factors with varying accuracy, they are providing more information than was available in the past. As the consumer focus on healthy living grows, the drive to have more precise data increases sensor demand and the need to fit more sensors into the same size package.
Beyond healthy living wearables, miniature sensors can be built into electronic robotic prosthetics. The force and control of fingers is a meticulous skill requiring precise measurements. When considering force measurement, the difference between holding a grape and crushing it can be significant; therefore, it demands accurate data for the fingers to perform seemingly simple tasks. Applying magnetic sensors to the finger joints at the point of rotation and strain gages allow for the precise contactless control and movement needed.
TE Connectivity (TE) designed a survey for engineers on a variety of topics related to IoT design. We got responses from 180 engineers ... primarily senior engineers with a stated interest in consumer, industrial, and automotive IoT. Our survey explored IoT applications and design methods and then identified common challenges that exist across this space.
The Internet of Things is changing everything — everywhere. Yet the path and scope of those changes seem very unsettled — particularly for design engineers who have to fully understand and embrace the changes and how to best leverage them in new designs.
With this in mind, TE Connectivity (TE) designed a survey for engineers on a variety of topics related to IoT design. We got responses from 180 engineers ... primarily senior engineers with a stated interest in consumer, industrial, and automotive IoT. Our survey explored IoT applications and design methods and then identified common challenges that exist across this space.
So where do we stand just now, and is it just hype?
We think our survey assesses the opportunities and separates the hype from the reality. Here’s what we learned.
First, 5G will continue to expand the proliferation of IoT.
5G networked devices can be just about anything. With the ability to connect to thousands of devices at once at exceptionally fast speeds and low end-to-end latency, engineers anticipate 5G will have a significant impact on IOT applications. Nearly 60 percent of respondents believe the advent of 5G will mean getting data faster and that, in turn, will result in new applications of all kinds for IoT.
Second, engineers see several areas that they expect to dramatically shape IoT.
Here’s what we learned.
- 29% said the ability to capture different kinds of data was critical.
- 26% said gathering more data faster from applications was significant.
- 25% cited lower current consumption in IOT devices that would enable networks to reduce power consumption overall and therefore also diminish strain on data transmission.
- 19% mentioned the importance of smaller, miniaturized components.
Third, engineers think IoT requirements are not being fully met in a number of areas, and ranked these areas as most important:
- Hardware endurance: 57%
- Measurement accuracy tied with measurement stability: 52%
- Sensor intelligence: 46%
- Processing speed: 31%
- Cloud analytics: 16%
These last two areas – processing speed and cloud —were considered less vital.
Fourth, we found that miniaturization is universally seen as key to IoT development.
- 85% of survey participants overwhelmingly agreed, and 47% thought this was very true.
- Another 38% felt it was somewhat significant to the continued proliferation of the IoT.
- At the same time, 15% believe sensor miniaturization has already gone as far as is needed.
Fifth, we talked about how IoT is expected to evolve into what experts predict will be a pervasive network that connects virtually every aspect of our lives.
Survey participants see three common major challenges when designing for IoT.
The first two challenges were finding the right hardware and connectivity. Nearly half of respondents — some 49% mentioned these two challenges. We don’t think that is surprising given that today there are multiple wired and wireless options to connect IoT devices. All of these connectivity standards and technologies serve valuable purposes yet taking on all of those standards from Wi-Fi to Bluetooth to Ethernet is a significant undertaking.
The third challenge was security — 44% mentioned this. Others mentioned developing the right software at 43% and cloud computing issues, trailing at 14%.
Sixth, when we asked how many engineers have really started their IoT solution design — we discovered that most seem to start at the same point.
The vast majority of engineers are beginning with hardware choices — 78% — while only 22% started by specifying software.
At TE Connectivity, we think all of these findings are exceedingly relevant today. We believe we are in the midst of what we call the fourth industrial revolution — the convergence of physical things with the Internet of Things. It’s why we think this data and our analysis is so important.
From the data, it is clear that IoT is here to stay, it’s growing, and will impact design engineers moving forward. TE Connectivity has extensive experience with engineers worldwide. We expect the growth of connected things within the next five to ten years to be very significant — and we plan to play a key role with our products. Let’s work together on the IoT opportunity.
Reach out to us today.
Digital Signal Processing
Greater accuracy is a key objective in choosing a sensor for medical applications which makes digital sensors a more desirable option due to their more precise and robust outputs. For example, digital thermopile temperature sensors can deliver high accuracy ±1°C readings of temperature ranges from 0° to 100°C. When customized to accommodate a wider range of applications for intensely harsh environments, these sensors can deliver high accuracy of ±4.5°C at 300°C. While analog products are often less expensive, digital sensors, by virtue of their design and configuration, do not require the purchase of additional electrical components including low offset/low noise amplifiers and associated filters. Certain sensor technologies, when packaged with digital outputs, can offer multiple output signals from the same device, thus eliminating the overall platform and real estate of the circuit board.
In the same survey referenced above, twenty-five percent cited the need for lower current consumption in IoT devices. If achieved, this would enable networks to reduce power consumption overall which would result in diminishing the strain on data transmission. Sensors can be designed for more consumer-based medical devices by adopting digital signal processing. This would allow for lower current consumption, the capability to ‘sleep’ while not in use and operate with lower supply voltages which would enable the use of smaller batteries on board.
Digital Signals and Scalability
Digital signal processing plays a role in scalability, as well, which is another fundamental consideration. Traditional analog output signals require some level of conversion for modern electronics to read and process the data. However, on-board digital signal processing reduces the calibration time during system or device manufacture which leads to greater accuracy. Since the sensor manufacturer’s calibration equipment is designed to test and qualify the sensor, it requires less investment by the OEM to duplicate the system requirements to manage the signal processing from analog to digital. In addition, sensor manufacturers can customize mechanical tooling, sensor programming, and calibration to customer requirements to enable plug and play designs.
SMT Technology and Scalability
According to the American Hospital Association, over 5,000 US registered hospitals experienced over 35 million admissions in 2017. While the medical industry in the US is pivoting to reduce hospital visits, admissions, and admission times, the demand to support the patient and the need for monitoring equipment remains consistent. Therefore, designing sensors for scalable, automated production has become a more desired option in the medical space to keep up with demand.
Surface mount technology for sensors enables design engineers to embed the sensor within the electronics of the assembly. Photo optic sensors offer traditional lead-frame designs which are hand soldered into assemblies and are now packaged for SMT designs. The reflow solderable packaging allows engineers to design sensors into assemblies that are embedded through pick and place machines, increasing overall quality while reducing manufacturing time and cost. With the flexibility to be mounted vertically or horizontally, AMR sensors are designed for SMT packages, as well. Depending on the design of the system, this can play an important role to ensure the sensor can fit within the system and give more flexibility on the magnet placement.