Wireless Infusion System with Liquid Flow Rate Self-Measuring Module

Xiang Zheng Tu

   

A large volume infusion can be done using gravity driving method. In this method, a spit need inserts into an infusion bottle containing a drug liquid. The spit need has two side channels, one channel connecting the bottle to atmosphere and the other connecting the bottle to the infusion line. In operation, air enters into the bottle and drives the liquid into the infusion line. The driving force is provided by the height of the liquid of the bottle. Although this method is manual and labor intensive, it offers some significant advantages. First, the use of gravity for a driving force is energy efficient. Second, the force is low, so the dangers of large volume infusions can be avoided. Third, the gravity infusions are allowed to use a low cost and readily available pressure cuff. Forth, a gravity administration is not capable of infusing much air into the infusion tube line, because the driving force goes to zero as the liquid empties. 

In order to keep the advantages of the gravity driving method and reduce its labor independence, a liquid flow rate self measuring module has been developed by POSIFA.

The module comprises a house with an inlet and an outlet tubes, a print circuit board, a thermal flow sensor, an amplifier, a microcontroller, a wireless communication IC, and a lithium battery. When air flows through the house the thermal flow sensor will measure the flow rate of the air and produce a corresponding electronic signal. After conditioning and processing, the signal will be further send to a wireless infusion monitor.

The thermal flow sensor is fabricated using MEMS technology based on silicon micromachining processes. It is well known that silicon and other materials adapted for MEMS are bio-compatibility. Many MEMS devices are implantable for medical applications. For example, MEMS implantable pressure sensors have been used for continuous monitoring in Glaucoma patients. MEMS accelerometers have been used in defibrillators and pacemakers. An implantable drug delivery system based on MEMS technology also has been designed as a platform for treatment in ambulatory emergency care.  Generally, the thermal flow sensor based liquid flow rate self measuring module can be not used only for gravity driving infusion, but also for pump driving infusion. It means that the thermal flow sensor is allowed to measure drug liquid flow rate without worry about cross contamination.

As shown in the above picture, a bottle filled with a drug liquid is hung up and inserted with a split needle. The module is installed on the air suction side of the split needle. The liquid flow out side of the split needle is connected to an infusion line. When the liquid flows into the infusion line, a similar volume air will flow into the bottle. According the laws of physics, the flow rate of the liquid is equal to the flow rate of the air. So the module has a liquid flow rate self-measuring function.

In the picture, the wireless infusion monitor locates at the central region of an infusion room. It receives the signals from all modules arranged in the room and then displays graphically them. Through the monitor, a nurse in charge of the infusion room can see the liquid volume, battery level and all the other infusion parameters online and can be instantly notified for clinical issues. Physicians can supervise the infusion progress and therapy related events like the requested and given bolus. The physicians also can view the patient’s infusion history, make decision on the evolution of the therapy, and change protocol online. Indeed with the module everything can be done in real time through the web.

Smart Phone Compatible Thermal Conductivity

Carbon Dioxide and Humidity Sensors

              

                        

A smart phone sensor has built-in more and more sensors to gather all kinds of data on who we are, what we are doing, and the world around us. Any sensors used in smart phones should be miniaturization, low power consumption, fast response, high accuracy, high reliability, and low cost. Micromachined thermal conductivity sensors provided by POSIFA can meet all these requirements. It has been used for hydrogen, vacuum, and methane measurement, and exhibited very high performance.

The device is fabricated with CMOS compatible micromachining processes. The sensor structure consists of a hot plate suspending over a cavity. A platinum resistor is located on the hot plate, which acts as both a heater and a temperature sensor. The sensor chip is installed in a metal casing using a high thermal conductivity epoxy adhesive. A metal mesh disposed on the metal casing provides gas exchange with the surrounding atmosphere. A photo graph of the encapsulated sensor can be seen in the above figure.

A thermal conductivity sensor measurement circuit is shown in the following figure. The circuit consists of two thermal conductivity sensors: a measurement sensor and a reference sensor, in which the measurement sensor is used for measuring the mixture gas containing air, carbon dioxide, and water vapor (humidity), and the reference sensor is sealed and used for canceling the signal generated by the pure air and the temperature of the surrounding atmosphere. The heaters of the sensors are heated by two DAC respectively, which are provided by a precision analog microcontroller such as ADuC7019/20 or the like. The differential voltage of the two sensor output is amplified by a chopper stabilized zero-drift operational amplifier, such as TP5554-TR. When zeroing, the measurement sensor is immersed in a reference air, the output of the two sensors will be the same and the output of the amplifier will be zero. When the measurement sensor is immersed in the mixture air containing carbon dioxide and water vapor, the output of the amplifier will correlate to the concentrations of the carbon dioxide and water vapor.

     

The working principle of the thermal conductivity sensor is easy to understand. It senses change of the thermal conductivity of a mixture air consisting of air, carbon dioxide, and water vapor, and compares it to the thermal conductivity of reference pure air. Since both carbon dioxide and water vapor have a thermal conductivity less than the thermal conductivity of a pure air, the thermal conductivity of the mixture air will be low containing carbon dioxide and a detectable signal will be produced.

According to Wassiljewa equation and empirical measurements, at fixed temperature t₁, a linear equation can be used for calibration and calculation of the concentration of each composition gas of a mixture air, which can shown as the follows:

y(t₁) = a(t₁)_air+a(t₁)_carN_car+a(t₁)_waterN_water.           (1)

In this equation (1), y is the output of the sensor response; a(t₁)_air is a bias term, N_car and N_water are the carbon dioxide and water vapor concentrations, and a(t₁)_car and a(t₁)_water are the coefficients sensitive to carbon dioxide and water vapor concentrations. The output is expressed in the unit of volt, and so are the coefficients, a(t₁)_car and a(t₁)_water, while the concentrations N_car and N_water are expressed as molar fractions. The equation (1) has two degrees of freedom, so N_car + N_water + N_air = 1, where N_air is the air concentration.

The coefficients a(t₁)_air, a(t₁)_car, a(t₁)_water can be obtained by measurement of several precision calibration sample mixtures. The data collected by the sensors can be processed using partial least squares (PLS). It has been shown that PLS can produce proper coefficient.

It should be noticed that N_car and N_water are two independent variables. It is impossible to find two variables by solving a single linear equation. Another similar linear equation (2) at fixed temperature t₂ needs to be built as follows:

y(t₂) = a(t₂)_air+a(t₂)_carN_car+a(t₂)_waterN_water.        (2)

In this equation the coefficients a(t₂)_air, a(t₂)_car, a(t₂)_water are different from the above similar coefficients, while N_car and N_water are the same. Based on the measured data collected by the thermal conductivity sensors, both N_car and N_water can be calculated by solving the equation (1) and equation (2).

Thermal Flow Sensors and Thermal Conductivity Sensors for Fuel Cell Applications

Xiangzheng Tu

A fuel cell generates electricity by the chemical reaction of hydrogen and oxygen. It is different from a battery in that it requires a continuous source of hydrogen and oxygen to sustain the chemical reaction, whereas in a buttery the chemicals to be reacted for generating electricity are stored in the buttery. The fuel cell can produce electricity continuously for as long as these inputs are supplied.

Fuel cell cars have been on the road for many years. The first commercial fuel cell cars are being sold in California by Toyota. Fuel cells are being developed and tested in buses, boats, motorcycles and bicycles, among other kinds of vehicles. Fuel cells have many more applications including portable generators, battery replacements, residential back power, and so on.

As shown in the above picture, the heart of the fuel cell is the polymer electrolyte membrane. It is sandwiched by the anode layer and the cathode layer. At the anode layer, the input hydrogen is converted into the hydrogen ions and the electrons. The hydrogen ions are transferred to the cathode through the conductor and the electrons are transferred through the outer circuit. At the cathode the transferred hydrogen ions together with the transferred electrons and the oxygen of the input air react to produce the water vapor. The water vapor is carried away by the unused input air.

It can be seen that in order to regulate the chemical reaction of the fuel cell the amount of the reacted hydrogen, the reacted oxygen and the produced water vapor should be measured in real-time. The fuel cell converts chemical energy into electrical energy and also, as a by-product of this process, into heat energy. This makes capacitive and resistive humidity sensors no useful for measuring the water vapor. Fortunately, POSIFA Microsystems provide thermal conductivity humidity sensors with greater resolution at higher temperature. It measures the absolute humidity by quantifying the difference in thermal conductivity of the input air and the output air containing water vapor. The accuracy of the sensors can reach at least +3 g/m3; this converts to about ±5% RH at 40°C and ±0.5% RH at 100°C. It is worth to note that the unused hydrogen also contains water vapor, which moves through the polymer electrolyte membrane from cathode to anode by diffusion. Similarly, the absolute humidity in the unused hydrogen can be measure by quantifying the difference in thermal conductivity of the input hydrogen and the unused hydrogen containing water vapor.

The thermal flow sensors provided by POSIFA Microsystems have been used for fuel cells successfully. The sensor consists of a heater and two symmetric thermopiles positioned on a porous silicon membrane. The heater is made of polysilicon, whereas the thermopiles are made from a combination of polysilicon and aluminum. The sensor is operated by a constant power circuit which provides constant power to the heater during the measurement. Power consumption and response time of the sensor are 30mW and 5ms, respectively. The noise of the sensor is very low and has the same amount of the noise as the equivalent resistor of the thermopile.

Flow rate and humidity are critical parameters associated with the performance of fuel cells. The product of the chemical reaction that proceeds in a fuel cell is water, which lowers the working efficiency of the cell and affects the fuel flow rate. With POSIFA thermal conductivity sensors any water vapor flooding in the fuel cell can be diagnosed easily and correctly. When the chemical reaction is not balanced well a microcontroller can modify the hydrogen flow rate and air flow rate automatically, which is based on the data collected by the thermal flow sensors. It should be no doubt that POSIFA flow sensors and POSIFA thermal conductivity sensors is a powerful combine for promoting fuel cell applications in fuel cars, fuel boats, fuel smart phones, etc.

Wireless Drinking Water Flow Sensor Systems

A wireless drinking water flow sensor system has been developed by POSIFA Microsystems, as shown in the above picture. This system can be installed in the lid of a water bottle and measures the flow rate and the water volume taken by a user.

The working principle of the system is very simple. Suppose that a bottle is filled with water, it is at a pressure as atmosphere. When you suck water from the bottle, the pressure is lower. Once the pressure in the bottle is lower than atmosphere, air is forced into the bottle. Then the pressure in the bottle is back to atmosphere. Such cycle can be carried out until the water in the bottle has gone completely. Based on this principle, the system can be used to measure the water flow rate and the water volume from a water bottle taken by users.

In combine with any drinking water application software such as iDrated, Waterlogged, Daily Water, Eight Glass a day, and OasisPlaces, this system can work with your smart phone for tracking your water intake easier than ever. With such system a drinking water schedule can be designed to help you reach drinking water goals and control the volume of water you are drinking on a daily basis. It also allows for schedule reminders and offers a basic statistical analysis of the amount of what you have consumed over the course of a day.

The wireless drinking water flow sensor system includes an integrated thermal flow sensor, a preamplifier, a microcontroller, a RF transmitter, a RF receiver, and a lithium battery. The system performs flow measurement, A/D conversion, digital processing, and scaling. The flow single measured by the system is transmitted to your smart phone via the RF transmitter. The incorporated drinking water application software processes the flow signal received by the smart phone and converts it into video Information displaying on the screen of your smart phone.

An outstanding advantage of the system is that the measured water taken by a user can be precisely expressed in liters/second or in liters instead of in glasses. Glass is not a standard volume unit. A drinking glass actually could be range from 8-16 ounces. People may drink a part of water in a glass which is difficult to count in glasses correctly. If drinking water application software is equipped with the system all these confusions can be eliminated forever.

As well known, water is our body's principal chemical component and makes up about 60 percent of our body weight. Every cell in our body depends on water. Water flushes toxins out of vital organs, carries nutrients to our cells, and provides a moist environment for ear, nose and throat tissues. Lack of water can lead to dehydration, a condition that occurs when we don't have enough water in our body to carry out normal functions. Even mild dehydration can drain our energy and make us feel tired.

Drinking water is absolutely essential. How do you make drinking water part of your daily routine? No worries, the wireless drinking water flow sensor system has been created for you. It can help you to find drinking enough water according your drinking water schedule. You will get endless benefits. Among them are: helping with weight loss; natural wrinkle-buster; stopping headaches and dizziness; clearing your skin; fighting your infections; keeping you regular, making you exercise better; improving your concentration; boosting your energy; supporting your heart; and so on.

Wireless Spirometers Based on Integrated Thermal Flow Sensors

Reference to the above figure, in combination with a smart phone a spirometer is used to generate a flow-volume loop for a man who is required to measure his forced vital capacity.

As shown in the graph on the screen of the smart phone, a normal flow-volume loop begins on the x-axis (volume axis): at the start of the test both flow and volume are equal to zero. After the starting point the curve rapidly mounts to a peak: peak (expiratory) flow.

After the forced expiratory volume in one second (PEF) the curve descends as more air is expired. A normal, non-pathological F/V loop will descend in a straight or a convex line from top of PEF to bottom of forced vital capacity (FVC). The forced inspiration that follows the forced expiration has roughly the same morphology, but the peak inspiratory flow (PIF) is not as distinct as PEF.

The flow-volume loop can take on many distinguishable shapes that correspond to a certain type of pathology. Using the flow-volume loop displayed by the smart phone, the following pathologies can be easily and correctly diagnosed.

• normal spirometry,
• pathological spirometry,
• obstructive lung disease,
• restrictive lung disease,
• mixed lung disease,
• obstruction of the large airways,
• exercise induced asthma.

The spirometer in the above figure utilizes an integrated thermal flow sensor provided by POSIFA Microsystems, which is a famous MEMS company located in Silicon Valley in the United States. The integrated thermal flow sensors exhibit short response time (1ms), low power consumption (30mw), and high accuracy (0.5%). It represents an attractive solution for portable spirometers in home-care applications.

The spirometer further consists of a CC2650 ultra-low power wireless MCU, which can provide a wireless connectivity solution supporting multiple standards to enable faster internet designs. With this device the spirometer can be managed being small, inexpensive and up to years of battery life.

The smart phone is not only to visualize a flow-volume loop based on the data send by the spirometer, but also con­nect the spirometer to the cloud. The cloud is a great place to back things up, because the spirometer has lim­ited stor­age and unre­li­able flash mem­ory. Plus, the spirometer could get lost, dam­aged, or stolen. The cloud is great for data pro­cess­ing because pro­cess­ing in the cloud reduces the load on the micro­proces­sor. This saves power and might reduce the per­for­mance require­ments of the micro­proces­sor. Furthermore, data that is already in the cloud can be shared quickly and eas­ily by many users.

The flow-volume loop is a remarkably versatile and informative measurement, which can identify a range of diseases including chronic obstructive pulmonary disease (COPD). COLD is a type of obstructive lung disease characterized by chronically poor airflow. It typically worsens over time. The main symptoms include shortness of breath, cough, and sputum production. Most people with chronic bronchitis have COPD. Used together with other clinical features, the flow-volume loop can substantially improve assessment of the patient and their long-term management.

Worldwide, COPD affects 329 million people or nearly 5% of the population.^[6] In 2013, it resulted in 2.9 million deaths up from 2.4 million deaths in 1990. The number of deaths is projected to increase due to higher smoking rates and an aging population in many countries.^[8] It resulted in an estimated economic cost of $2.1 trillion in 2010.

Walking Distance Measurement Systems

POSIFA Microsystems developed walking distance measurement systems as shown above. These systems can measure the distance for many walking ways to take including:

• Walk with your spouse, child, or friend
• Walk the dog
• Use the stairs instead of the elevator
• Park farther from the store
• Better yet, walk to the store
• Get up to change the channel
• Window shop
• Plan a walking meeting
• Walk over to visit a neighbor
• Walk around the garden or do a little weeding 

There are countless physical activities out there, but walking is a good form of exercise for many people. Knowing walking distance will help people develop an exercise program that's effective for losing weight, increasing aerobic fitness, and improving heart health.

Many efforts have been made to measure the distance traveled by humans for a long time. There are several ways to measure the distance moved by walking or running in daily life, some of which already use commercial products, but none of them is ideal and perfect.

As well know, one way is based on radio frequency, such as GPS, or may use optical-based systems, such as video tracking. Such systems are not available indoors and degrade significantly in deep city canyons.

As an alternative, the measurement can be made by self-contained tracking systems. Such systems use commercially available MEMS inertial sensors and magnetic sensors. However, the performance of MEMS accelerometers and angular rate sensors is limited by random noise and calibration error. When they are used in a position tracking systems, it becomes the source of unbounded growth in position error.

A new walking distance measurement system is developed by POSUFA Microsystems, which is based on their MEMS thermal flow sensors. Human walking exhibits variability from step to step. As above listed walking ways, all most each step may be different in walking direction or in step length. It is impossible to do correct and precise measurement using available distance measurement systems. Only the POSIFA systems can do that because it measures the distance simply by adding all step length together. 

Each human walking step consists of stance phase, swing phase, and stance phase again. In any stance phases the foot traveling velocity is zero. In the swing phase the foot traveling velocity increases from zero to maximum and then decreases from maximum to zero like a pendulum curve. The thermal flow sensor can be managed to measure any instantaneous velocity of a particular foot traveling step. Then the instantaneous velocity is integrated over the traveling time of the particular step to produce the length of the particular step. All the lengths of each traveling steps can be accumulated to provide the distance of this human walking event.

In such systems, the thermal flow sensor only measures the instantaneous velocity.  The measurement signals are sent to a smart phone using Wi-Fi communication. The Smart phones are useful in this application because they are portable and have sufficient computational power to compute and analyze the measurement signals to provide the walking distance and other information people are interested. 

Thermal Flow Sensors for Man-Potable Vehicles Applications

Thermal Flow Sensors for Man-Potable Vehicles Applications

Man-portable air vehicles (UAVs) or micro air vehicles (MAVs) can be used in

many dangerous civil and military missions without any risk to human life, and they also have many potential industrial applications such as plant supervision, power line and construction site inspection, pollution and weather monitoring, forest fire and disaster control, etc.

All these vehicles operate exclusively within the atmospheric boundary layer,

which typically extends up to 5 km above ground level depending on surface heating, climatic conditions, and terrain. The flow in the atmospheric boundary layer is dominated by horizontal transport of atmospheric properties. As air travels over buildings and various obstacles, there will be a local increase in wind speed. It has been shown that mean wind speeds above a certain threshold can make the air speed vary substantially. When a steady 4.6 m/s magnitude wind is presented it is inability of an MAV to reach its pre-programmed waypoints. This degradation in performance puts the aircraft at risk and often leaves the MAV unable to complete its mission.

In order to improve the performance of the air vehicles a powerful onboard

sensing system is required. This sensing system can detect individual air speeds in a turbulent boundary layer. Once detected, the turbulent influence can be suppressed or eliminated by an action of micro electromechanical devices.

As shown in figure 1, POSIFA thermal flow sensors are ideal for the onboard

sensing system. These thermal flow sensors have the benefits of miniature size, low power dissipation and fast response time, which is essential for detecting turbulent flow. The miniature size allows for their installation in small spaces without significantly interfering with the flow and consequently altering its behaviour.                   

These thermal flow sensors can be used for detecting the surface velocity

distribution over critical locations of the wing area, such as the points of flow transition, reversal, or separation.

POSIFA thermal flow sensors can be used to determine three flight parameters: air

speed, angle of attack and angle of sideslip. As shown in figure 2, so as to do so an array of thermal flow sensors is installed over critical locations of the wing area, such as the points of flow transition, reversal, or separation. The signal of each thermal flow sensor is send to a microcontroller through wireless communication. The microcontroller will act the micro electromechanical device for suppressing or eliminating the turbulent influence.

 Figure 1. An assembled printed circuit board with a POSIFA thermal flow sensor and a lot of diced POSIFA thermal flow sensor chips surrounding the PCB.

These thermal flow sensors can be used for detecting the surface velocity

distribution over critical locations of the wing area, such as the points of flow transition, reversal, or separation.

POSIFA thermal flow sensors can be used to determine three flight parameters: air

speed, angle of attack and angle of sideslip. As shown in figure 2, in order to do so an array of thermal flow sensors is installed over critical locations of the wing area, such as the points of flow transition, reversal, or separation. The signal of each thermal flow sensor is send to a microcontroller through wireless communication. The microcontroller will act the micro electromechanical device for suppressing or eliminating the turbulent influence.

Figure 2. An Unmanned air vehicle equipped with a POSIFA thermal flow sensor array controlled by a microcontroller.