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Introduction:
Optical sensor technology is ushering in a new era in healthcare, particularly in biomedical applications and military healthcare. The Centers for Disease Control and Prevention (CDC) reports alarming statistics on high blood pressure and heart diseases, highlighting the critical need for continuous health monitoring. Optical sensors, with their ability to non-invasively measure various physiological parameters, are becoming instrumental in diagnosing and treating a range of health conditions. This article explores the transformative impact of optical sensors in remote patient monitoring, wearable health monitoring, and military healthcare, showcasing how these advancements are reshaping the landscape of medical technology.
According to the Centers for Disease Control and Prevention (CDC), approximately 70 million people in the United States had high blood pressure. Further, nearly 600,000 deaths occur every year in the US due to various heart diseases. Continuous health monitoring is essential for recuperating patients and patients with chronic health conditions. It can be used in judging whether an individual is in a physiological state suitable for his duties, and it is also useful for people of all age groups who have possible health problems or have opted for a healthy lifestyle.
Chronic diseases can be effectively controlled if they are diagnosed at their early stages and they are regularly monitored with proper medication cares and guides. For example, detection of cardiac arrhythmias from continuous electrocardiogram (ECG) recordings is an important approach that physicians use to adjust medication for post myocardial infarction patients. Common chronic neurological disorders, such as epilepsy and Alzheimer’s disease, can be identified from electroencephalogram (EEG) recordings.
The changes in brain function may occur several hours before any clinical manifestation in patients with progressive brain ischemia, or in patients suffering from vasospasms after a subarachnoid hemorrhage. These events are important parts of a patient’s health history, and the detection and recording of these events play a key role in the risk stratification process used by physicians to plan treatments. Therefore, continuous real time monitoring is a valuable tool that can help both diagnosis and treatment planning.
Many accidents, which have frequently happened on aircraft, high-speed passenger trains, long-range highway express buses and so on, were caused by the operational errors of the pilots or drivers. Most of the operational errors were due to the high mental stress or drive dozing of the pilots or drivers, and some of them were diagnosed as sleep apnea syndrome (SAS). Diseases such as SAS and sudden infant death syndrome (SIDS) mostly happen while an individual is in sleep or in an unconscious condition. These diseases are generally difficult to detect by physicians without a continuous monitoring of the change in a person’s vital signs. Therefore, close and continuous monitoring is needed, which can assist healthcare providers to identify whether a patient is in a healthy condition.
Remote patient monitoring (RPM)
Remote patient monitoring (RPM) is an emerging area of telemedicine, which includes devices and technology that enable healthcare providers to remotely diagnose, treat, and advise patients. RPM systems usually monitor a patient’s vital signs, which could include ECG, EEG, respiration rate, blood pressure and temperature, depending upon the condition to be monitored. Such a system can obviate the need for repeated visits to the hospital. Moreover, the continuously monitoring of human physiology by such a system can provide valuable data to prognosticate the onset of critical health problems.
The increasing need to reduce hospital costs and the launch of new products are expected to drive the demand for activity monitors. Digitized and continuous monitoring of biohealth signals is a key element for mobile health care, where a patient or a potential patient may receive an alert on changes to his or her health condition or seek medical advice from health care providers while remotely located from a hospital.
Body area network (BAN)
The concept of body area network (BAN) is defined as a network of independent wireless nodes that span the personal space of a user. As an ultimate objective of BAN, the independent sensors for physiological signals, such as ECG, EOG, EMG, pulse rate, blood oxygen saturation, temperature and respiration, will send data through their wireless transmitters, to a single receiving station which may be a Smartphone, a personal digital assistant (PDA), a personal computer (PC), or a custom receiver unit.
The data, tagged with the current GPS location and the time, are also sent to a remote server through the 3G network. In case of an emergency, a message with recorded data and current location and time can be sent to the emergency response team. Further, the collected data is sent to a backend cloud infrastructure for data storage, data dissemination, and abnormality detection using machine learning techniques.
Optical Sensors
Optical sensors, measuring vital signs like ECG, EEG, respiration rate, blood pressure, and temperature, contribute to RPM systems. These systems not only reduce the need for frequent hospital visits but also provide valuable data for prognosticating critical health problems.
An optical sensor converts light rays into an electronic signal. The purpose of an optical sensor is to measure a physical quantity of light and, depending on the type of sensor, then translates it into a form that is readable by an integrated measuring device. Optical Sensors are used for contact-less detection, counting or positioning of parts. Optical sensors can be either internal or external. External sensors gather and transmit a required quantity of light, while internal sensors are most often used to measure the bends and other small changes in direction. The measurands possible by different optical sensors are Temperature, Velocity Liquid level, Pressure, Displacement (position), Vibrations, Chemical species, Force radiation, pH- value, Strain, Acoustic field and Electric field
Photonic sensors, including fiber optic sensors, have been the subject of intensive research over the last two decades for use in civil and military environments for detection of a wide variety of biological, chemical and nuclear agents. They have wide applications including for smart barcodes, new sensing systems in the fight against crime and terrorism, advanced manufacturing and production techniques, environmental monitoring and in new medical diagnostic devices.
There are different kinds of optical sensors. Photoconductive devices used to measure the resistance by converting a change of incident light into a change of resistance. The photovoltaic cell (solar cell) converts an amount of incident light into an output voltage. The Photodiodes convert an amount of incident light into an output current. Phototransistors are a type of bipolar transistor where the base-collector junction is exposed to light. This results in the same behavior of a photodiode, but with an internal gain.
The operating principle is the transmitting and receiving of light in an optical sensor, the object to be detected reflects or interrupts a light beam sent out by an emitting diode. Depending on the type of device, the interruption or reflection of the light beam is evaluated. This makes it possible to detect objects independently of the material they are constructed from (wood, metal, plastic or other). Special devices even allow for a detection of transparent objects or those with different colors or variations in contrast. Different types of optical sensors are show in Figure.
Through-Beam Sensors
The system consists of two separate components the transmitter and the receiver are placed opposite to each other. The transmitter projects a light beam onto the receiver. An interruption of the light beam is interpreted as a switch signal by the receiver. It is irrelevant where the Large operating distances can be achieved and the recognition is independent of the object’s surface structure, color or reflectivity. To guarantee a high operational dependability it must be assured that the object is sufficiently large to interrupt the light beam completely. interruption occurs.
Retro-Reflective Sensors
Transmitter and receiver are both in the same house, through a reflector the emitted light beam is directed back to the receiver. An interruption of the light beam initiates a switching operation. Where the interruption occurs is of no importance. Retro-reflective sensors enable large operating distances with switching points, which are exactly reproducible requiring little mounting effort. All objects interrupting the light beam are accurately detected independently of their surface structure or color.
Diffuse Reflection Sensors
Both transmitter and receiver are in one housing. The transmitted light is reflected by the object to be detected. The diffused light intensity at the receiver serves as the switching condition. Regardless of the sensitivity setting the rear part always reflects better than the front part. This leads to the consequence to erroneous switching operations.
There are many types of light sources. The sun and light from burning torch flames were the first light sources used to study optics. As a matter of fact, light coming from certain (exited) matter (e.g., iodine, chlorine, and mercury ions) still provides the reference points in the optical spectrum. One of the key components in optical communication is the monochromatic light source. In optical communications, light sources must be monochromatic, compact, and long lasting.
The development of optical sensing technology not only contributes to the scientific research community as a versatile tool, but also offers substantial commercial value for smart city and Internet of Things (IOT) applications due to its energy efficiency, lightweight, small size and suitability for remote sensing. Reinforcing its significance, the Scientific American identified plasmonic sensing as one of the top 10 emerging technologies of 2018.
Smart bands are portable devices used to monitor a person’s real-time fitness, heart rate, sleep statistics, and calorie control, as well as provide other health insights. These bands are equipped with miniaturized electronic devices, such as microchips and sensors, which gather data, record activities, and offer and transform information on a real-time basis.
Mobile wearable health monitoring systems represent a new generation of healthcare by providing real-time unobtrusive health monitoring through the on-body sensors. Besides monitoring physiological parameters, a wearable health monitoring system can also be designed for monitoring body motions. The monitoring of human movement is important for the clinical applications of fall detection, fall risk assessment, and energy expenditure. The importance of these applications is considerable in light of the global demographic trends and the resultant rise in the occurrence of injurious falls and the decrease of physical activity.
These sensors, coupled with advancements in smartphones and cloud computing, provide a platform for real-time health data relay to cloud servers, facilitating data storage, dissemination, and abnormality detection through machine learning techniques.
Nanosensors offer the unique advantage of small size and high sensitivity that makes them ideally suited for everyday use as they bear no conspicuous presence. Additionally, a Smartphone can be used to relay health and activity monitoring data from these user worn devices to a cloud resident server. Advances in medical nanotechnology coupled with rapid development in Smartphones and cloud computing offer significant advantages over existing systems.
Nanosensors offer the unique advantage of small size and high sensitivity that makes them ideally suited for everyday use as they bear no conspicuous presence. Additionally, a Smartphone can be used to relay health and activity monitoring data from these user worn devices to a cloud resident server.
In military healthcare, optical sensor technology is playing a crucial role in the development of advanced medical devices. The Air Force Office of Scientific Research is funding projects aimed at creating wearable sensors, point-of-care imaging devices, and other optical technologies to diagnose and treat injuries on the battlefield. The incorporation of multidimensional optical sensors is particularly highlighted, showcasing their potential to accurately measure hemodynamics, blood pressure, and other vital parameters, thus providing soldiers with advanced healthcare capabilities in challenging environments.
Conclusion:
As optical sensor technology continues to advance, its applications in biomedical and military healthcare are proving transformative. From continuous monitoring of chronic conditions to enabling remote patient care and revolutionizing military healthcare on the battlefield, optical sensors are at the forefront of innovation. The integration of these sensors into wearable devices and the development of multidimensional optical sensors exemplify the versatile and impactful nature of this technology. With ongoing research and development, optical sensor technology is poised to revolutionize healthcare, offering personalized, efficient, and accessible solutions for monitoring and managing health.
Novel framework for tracking developments in optical sensors
Plasmonics and photonics have been drawing attention in both academia and industry due to their use in an extensive range of applications, one of which includes optical sensing. Various optical sensing mechanisms and sensor structures have been proposed and demonstrated in the past few decades. Almost every new sensing mechanism or sensor configuration would be explored regularly to test its sensing ability. However, information on the gap between the experimental realisation and theoretical limits, difference between metal-based plasmonic sensors and dielectric-based photonic sensors, and discrimination between propagating eigenwave and localised eigenmode structures was not readily available.
Researchers from the Singapore University of Technology and Design (SUTD), Singapore, Agency for Science, Technology and Research (A*STAR), Singapore, and Austrian Institute of Technology, Austria conducted extensive literature research, systematically summarised and compared the sensing abilities of these optical refractive index sensors according to their sensitivities and figure of merits. A 3D technology map was then established to define the standard and development trend for optical refractive index sensors using plasmonic and photonic structures.
In particular, the following four common types of label-free optical refractive index sensors using plasmonic and photonic structures were reviewed:
1) Metal-based propagating plasmonic eigenwave sensors, such as prism-coupled surface plasmon polariton sensor;
2) Metal-based localised plasmonic eigenmode sensor, such as metallic nanoparticle-based localised surface plasmon resonance sensors;
3) Dielectric-based propagating photonic eigenwave sensors, such as fiber interferometers;
4) Dielectric-based localised photonic eigenmode sensors, such as photonic crystal cavities.
Additionally, more advanced hybrid refractive index sensors such as Fano resonance sensors and 2D materials integrated plasmonic and photonic sensors were included in the review. “This technology map, just like a searchlight, clearly indicates the sensing ability, merits and shortcomings of different categories of optical refractive index sensors for researchers in the field,” said first-author Yi Xu, PhD student from SUTD and Institute of High Performance Computing (IHPC), A*STAR.
Any new developed optical refractive index sensors can be added to this technology map to compare their sensing abilities with prior works. The continuous addition of new plasmonic and photonic refractive index sensors will enrich the technology map, thus providing a benchmark for this rapid development of optical refractive index sensors.
“Bearing this technology map in mind and thoroughly understanding the merits, limitations, mechanisms and development trends of different categories of RI sensors, together, we can advance the field more effectively,” said co-corresponding author and PhD co-advisor, Dr. Lin Wu, IHPC, A*STAR.
With the technology map, various optical refractive index sensors could be better selected according to different applications. “We believe such a comprehensive review on optical refractive index sensors with plasmonic and photonic structures will attract much attention in the research communities, which will help engineers to use the right sensors for the design of sub-systems in smart city and IOT,” said SUTD Professor Ricky Ang, co-corresponding author and PhD advisor.
Applications of Optical Sensors
Application of these optical sensors ranges from computers to motion detectors. For optical sensors to work effectively, they must be the correct type for the application, so that they maintain their sensitivity to the property they measure. Optical sensors are integral parts of many common devices, including computers, copy machines (xerox) and light fixtures that turn on automatically in the dark. And some of the common applications include alarm systems, synchros for photographic flashes and systems that can detect the presence of objects.
Biomedical Applications
Optical sensors have robust applications in the biomedical field. Some of the examples Breath analysis using tunable diode laser, Optical heart-rate monitors an optical heart-rate monitor measures your heart rate using light. A LED shines through the skin, and an optical sensor examines the light that reflected back. Since blood absorbs more light, fluctuations in light level can be translated into heart rate. This process is called as photoplethysmography.
Wearable health monitoring using optical sensors
The purpose of a biosensor is the detection of biologically-relevant targets such as proteins, DNA, pathogens, cells, bacteria, pollutants, hormones and enzymes. In most cases, their presence and/or concentration in samples such as blood, urine, saliva, sweat or tears can be an early indicator of disease, so that the sensor can be used as a valuable diagnostic tool.
The collected biohealth signals may carry even more profound implications by serving as a basis for medical “big data” that could identify unknown linkages between diseases and certain patterns of a given biohealth signal in a new medical era brought about by artificial intelligence. Photoplethysmogram (PPG) and peripheral oxygen saturation (SpO2) signals are a good example of such biohealth signals that can benefit from continuous monitoring; they not only provide key information related to a person’s vital state but also are expected to have potential links with other symptoms or physical conditions.
Both signals can be measured simultaneously with a medical device called a “pulse oximeter,” which generally consists of light sources in two different wavelengths and a photodetector that produces electrical signals modulated by the wavelength-dependent absorption of photons by oxygenated and nonoxygenated hemoglobin (HbO2 and Hb) in blood vessels.
Silica‐fiber‐based sensors have the advantage of being small, electrically isolated, immune to electromagnetic fields, and easily incorporated into networks. However, only few of them were used for monitoring physiological signals directly, due to their limited sensitivity, comfort, and safety.
Researchers have proposed simple architecture for sensitive and wearable photonic sensors, which are capable of strain and pressure detection for healthcare applications is reported. The proposed sensor consists of a hybrid plasmonic microfiber knot resonator embedded in a polydimethylsiloxane membrane
Microsoft Patents Multidimensional Heart Rate Sensor that Delivers Accurate Data on Wearables
Neowin reports on a new patent filing by Microsoft, which says the tech giant has filed a patent for a multidimensional optical sensor which could detect heart rate, pulse wave velocity, blood and tissue oxygenation, and even blood pressure. “A rather interesting new wearables-related technology has been patented by the Redmond firm – a device containing a multi-dimensional optical sensor to generate and output data regarding hemodynamics of users. Notably, the device is stated to be incorporable with wearables,” Neowin said in the report.
According to Neowin, Microsoft believes that one-dimensional optical sensors found in currently available wearable devices may not accurately measure health data and are quite limiting. For example, the sensor may report inaccurate data while the person is walking. Moreover, these sensors fail to deliver accurate data on other fitness-related matters which are essential to the wearer’s health, the report said.
For the reasons, the advanced sensor proposed by Microsoft aims to not only address the inaccuracies in measurement, but also measure new hemodynamics – the dynamics of blood flow. The sensor will be able to detect and then display include arterial heart rate, arterial blood oxygenation, pulse waveform, tissue pulse, arterial stiffness, rate, tissue oxygenation, and many more. The design is reportedly more accurate than existing optical sensors found in wearables, and also less invasive than clinical measuring tools. The sensor could be incorporated into various wearable devices including devices such as smartwatches and fitness trackers or devices worn on arm and leg. One of the patent images shows a sensor built into a pair of glasses, over the wearer’s temple, reports MobiHealthNews.
Optical sensor Technology Covers Soldiers on Battlefield
Military personnel have sophisticated technology at their fingertips in combat, and thanks to a federally funded research program, they may soon also have optical technologies ranging from wearable sensors to point-of-care imaging devices to help diagnose and treat their wounds. The Air Force Office of Scientific Research (AFOSR) recently announced $6.8 million in continued funding to the Beckman Laser Institute at the University of California, Irvine (UCI) to continue in the creation of medical technologies for this purpose.
Called “Advanced Optical Technologies for Defense Trauma and Critical Care,” the program incorporates eight different projects aimed at evaluation and treatment, with another targeted for traumatic brain injury. These projects include the development of wearable sensors for monitoring of physiological information; adaptation of flow-enhanced pulse oximetry for monitoring patients; creation of a compact blood-coagulation analyzer; an enhanced surgical camera to identify burns and wounds; invention of an optical coherence tomography tool to diagnose airway damage; validation of a hand-held, point-of-care wound imaging device; and development of an in vitro assay system for mechanisms of traumatic brain and spinal cord injuries.
Michael Berns, UCI’s Arnold and Mabel Beckman chair in laser biomedicine and distinguished professor of surgery, biomedical engineering, and developmental and cell biology, said the program received its first grant in 1986 and since then has come to benefit all branches of the military. Berns serves as the principal investigator for the grant at the Beckman Laser Institute, which is projected to continue through March 2023.
“There are seven or eight distinct projects, each run buy a faculty member (or two), and each focused on a particular photonic application/technology,” he said. “Interestingly, the program started out in the 1980s with an equal emphasis on basic research and applied technology. But over the years it became clear that there was no real medical application, so the focus of the program changed to be more on a combination of research on laser interaction with tissue/cells and the development of biophotonic diagnostic and therapeutic modalities.”
The Military Medical Photonics Program (MMPP) is a photonics and light-based program focused on meeting military medical needs with diagnostic, imaging, and therapeutic solutions based on optical science and technology. The AFOSR currently oversees the program, ranging from biological medical sciences to physics, chemistry, and engineering, with imaging researchers expected to work alongside others in fields such as acoustics, electronics, micromechanics, and nanotechnology.
The MMPP is currently funded at about $10 million annually and involves research groups at the Wellman Center for Photomedicine at the Massachusetts General Hospital-Harvard and UCI’s Beckman Laser Institute, with other research activities occurring at Stanford University and the Army Institute for Surgical Research. William Roach and Patrick Bradshaw, MMPP program managers, pointed to developments such as fractional laser scar treatment currently in use; retinal prosthesis undergoing clinical trials in the U.S.; photochemical tissue bonding for peripheral nerve repair awaiting joint funding; and low-level light therapy brain dysfunction and wound healing for which there is growing commercial interest.
Roach, Bradshaw, and Berns confirmed that a number of startup companies have sprung up to commercialize these innovations. Modulim, for example, has a product called Clarifi, for assessment of blood microcirculation and will soon be used in connection with diabetic ulcers. OCT Medical Imaging Inc. also has a device undergoing Food and Drug Administration approval for intravascular imaging.
The Worldwide Market for Optical Pulse Sensors (2019-2024): Smart Bands Expected to Hold Significant Market Share
Accoeding to the “The Worldwide Market for Optical Pulse Sensors (2019-2024)” report by Research And Markets.com, the Optical Pulse Sensors market is expected to witness a CAGR of 9.3%, over the forecast period (2019-2024).
The demand for diagnostic wearable medical devices is expected to be augmented by factors, such as the increase in the incidences of chronic diseases among people of all ages, prevalence of heart and respiratory disorders, and rise in premature births. The increasing need for continuous diagnosis and growing awareness among the general population will drive the market. New advances in technology, the US FDA approval for new products, and subsequent product launches are driving the market of the optical pulse sensors.
The capability of the sensors to improve accuracy, and increase functionality and efficiency of several applications, along with the growth in the use of wearable, will produce significant demand for optical pulse sensors.
The rise in the use of diagnostic wearable medical devices for regular personal health monitoring is expected to drive the global optical pulse sensor market. Advances in some diagnostic wearable medical devices have led to an increased number of individuals to use these devices. The integration of IT in most diagnostic wearable medical devices is on the rise, and the automated generation of medical records in digital format [electronic health record (EHR)] has driven the demand for advanced devices.
Wearable devices and analytical software revolutionized sports and fitness training, by engaging in performance improvement and injury prevention. Companies in the market are implementing strategic initiatives to meet the growing demand in the market.
The optical pulse sensors market is moderately competitive and consists of several major players. In terms of market share, few of the major players currently dominate the market. However, with the growth in technological innovation across the wearables segment, most of the companies are increasing their market presence by securing new contracts thereby tapping into new markets.
References and Resources also include:
https://www.elprocus.com/optical-sensors-types-basics-and-applications/
https://www.photonics.com/Articles/Optical_Technology_Covers_Soldiers_on_Battlefield/a65900
