Bubble sensors are used to detect the presence of

bubble Bubble, Bubbles or The Bubble may refer to: Common uses * Bubble (physics), a globule of one substance in another, usually gas in a liquid ** Soap bubble * Economic bubble, a situation where asset prices are much higher than underlying fundame ...

s in fluid-filled tubes. They play a vital role in many fields, including

medical technology Health technology is defined by the World Health Organization as the "application of organized knowledge and skills in the form of devices, medicines, vaccines, procedures, and systems developed to solve a health problem and improve quality of liv ...

process control Industrial process control (IPC) or simply process control is a system used in modern manufacturing which uses the principles of control theory and physical industrial control systems to monitor, control and optimize continuous Industrial processe ...

pharmaceutical Medication (also called medicament, medicine, pharmaceutical drug, medicinal product, medicinal drug or simply drug) is a drug used to diagnose, cure, treat, or prevent disease. Drug therapy ( pharmacotherapy) is an important part of the ...

s, and the

petroleum industry The petroleum industry, also known as the oil industry, includes the global processes of hydrocarbon exploration, exploration, extraction of petroleum, extraction, oil refinery, refining, Petroleum transport, transportation (often by oil tankers ...

. The most common type of sensors used are

ultrasonic Ultrasound is sound with frequencies greater than 20 kilohertz. This frequency is the approximate upper audible limit of human hearing in healthy young adults. The physical principles of acoustic waves apply to any frequency range, includi ...

capacitor In electrical engineering, a capacitor is a device that stores electrical energy by accumulating electric charges on two closely spaced surfaces that are insulated from each other. The capacitor was originally known as the condenser, a term st ...

based.

Ultrasonic sensors

Ultrasonic sensors use two techniques to detect bubbles, one method involves transmitting sound waves from a transducer through the fluid to a second transducer that detects the waves. A second method involves pulse-echo, sound waves are transmitted to the fluid, reflected and received by the same transmitter that sent it. In both of these methods bubbles will have an effect on the velocity, attenuation and the scattering of the sound, thus they are easily detected.

Capacitive sensors

Due to their ease of fabrication and minimization capability,

Capacitive sensor In electrical engineering, capacitive sensing (sometimes capacitance sensing) is a technology, based on capacitive coupling, that can detect and measure anything that is conductive or has a dielectric constant different from air. Many types of sens ...

s have found uses in a number of industries and can be efficiently designed on a

printed circuit board A printed circuit board (PCB), also called printed wiring board (PWB), is a Lamination, laminated sandwich structure of electrical conduction, conductive and Insulator (electricity), insulating layers, each with a pattern of traces, planes ...

. A capacitor consist of two parallel electrodes with a capacitance computed as, C =εA/d (1) Where ε is the permittivity of the

dielectric In electromagnetism, a dielectric (or dielectric medium) is an Insulator (electricity), electrical insulator that can be Polarisability, polarised by an applied electric field. When a dielectric material is placed in an electric field, electric ...

medium, ''A'' is the cross sectional area of the electrodes and ''d'' is the distance between them. Liquids have a higher dielectric constant than gas; when an air bubble is in a fluid-filled tube the

capacitance Capacitance is the ability of an object to store electric charge. It is measured by the change in charge in response to a difference in electric potential, expressed as the ratio of those quantities. Commonly recognized are two closely related ...

is reduced and the output voltage rises. The size of the bubble is inversely related to the measured capacitance. Table 1 shows an example of the characteristics of a particular capacitive sensor being researched. Table 1 Example Characteristics of a Particular Capacitive Sensor

Uses in extracorporeal blood circuits

In various medical treatments that use

Extracorporeal An extracorporeal procedure is a medical procedure which is performed outside the body. Extracorporeal devices are the artificial organs that remain outside the body while treating a patient. Extracorporeal devices are useful in hemodialysis and ...

Blood Circuits (ECBC) the detection of air bubbles in the blood is vital for the patient safety. An air bubble in an artery that supplies blood to the heart or brain can cause serious injury or death. In an ECBC the bubble sensor is placed on the arterial pump that is supplying the blood to the heart. Depending on the size of the bubble detected the pump will respond in different ways. The sensors allow the operator to set a size threshold for the size of the bubbles to detect. If the bubbles are below the threshold it is displayed to the user as microbubble activity. When a bubble equal to or greater than the threshold is detected an audio and visual alarm is generated and the arterial pump is stopped, this effectively terminates the

cardiopulmonary bypass Cardiopulmonary bypass (CPB) or heart-lung machine, also called the pump or CPB pump, is a machine that temporarily takes over the function of the heart and lungs during open-heart surgery by maintaining the circulation of blood and oxygen throug ...

. The operator must identify and remove the bubble before bypass can be re-instated.P. Kay and C. M. Munsch, Techniques in Extracorporeal Circulation, CRC Press, 2004.

References

{{reflist Medical equipment Sensors Bubbles (physics)