Application of the hottest piezoelectric thin film

2022-08-14
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The application of piezoelectric thin film sensor in life characteristic monitoring

piezoelectric thin film has unique characteristics. As a dynamic strain sensor, it is very suitable for life signal monitoring on the surface of human skin or implanted into human body. Some thin-film elements are sensitive enough to detect human pulse through the coat. This paper will focus on several typical applications of piezoelectric films in life feature monitoring

when you stretch or bend a piece of piezoelectric polyvinylidene fluoride PVDF polymer film (piezoelectric film), an electrical signal (charge or voltage) will be generated between the upper and lower electrode surfaces of the film, which is proportional to the stretching or bending. Generally, piezoelectric materials are sensitive to pressure, but for piezoelectric films, when a small force is applied longitudinally, a large stress will be generated horizontally, while if the same force is applied to a large area of the film, the stress will be much smaller. Therefore, piezoelectric films are very sensitive to dynamic stress, 28 μ The typical sensitivity of m-thick PVDF is 10 ~ 15MV/micro strain (change in parts per million of length)

the term 'dynamic stress' is used because the charge generated by deformation will be lost from the circuit connected to the film, so the piezoelectric film cannot detect static stress. When different levels of prestress need to be detected, this instead becomes the advantage of piezoelectric films. The film only feels the change of stress, and the minimum response frequency can reach 0.1Hz

piezoelectric film is thin, light, very soft, and can work passively, so it can be widely used in medical sensors, especially when it is necessary to detect subtle signals. Obviously, the characteristics of this material are particularly prominent in the case of limited power supply (accounting for 24.6% of the self weight. In some structures, it can even generate a small amount of energy). Moreover, the piezoelectric film is extremely durable and can withstand millions of bending and vibration

contact sensor

using the dynamic strain gauge characteristics of piezoelectric film, the piezoelectric film can be easily fixed directly on the human skin (such as the inner side of the wrist). Precision electronics - the product model of American meas sensor is a general sensor, and one side of the sensor is coated with pressure sensitive adhesive. However, this adhesive has not been certified for biocompatibility. In a short-term test, 3m9842 (polyurethane tape) can be fixed on the skin, and then the piezoelectric film sensor can be pasted on 3M tape

the reason why piezoelectric films can detect very small physical signals and feel large-scale activities is that the piezoelectric response of PVDF films is linear in a considerable dynamic range (about 14 quantities · discussion level of the utilization of carbon fiber composites in construction engineering and Ocean Engineering). In most cases, as long as the bandwidth of the target signal and noise can be clearly distinguished, the small target signal can be collected through the filter

similar sensors have been used in sleep disorder research to detect the movement of chest, leg, eye muscles and skin. In addition, the sensor can be used as an indicator to test the anesthetic effect (neuromuscular conduction) by detecting the response of muscles (such as the muscle between thumb and index finger) to electric shock

acceleration sensor

minisense100 is a standard product of precision electronics. It adopts cantilever design. One end is clamped with a hard PCB board with connecting pins, and the other end is equipped with a mass block

the mass block enables the sensor to react coherently when subjected to vibration. The mass block 'remains stationary', while the film part deforms, resulting in a very high voltage sensitivity (about 1v/g). Other biometric sensors are derived from this component, such as smart badges worn by staff or patients (built-in RF remote sensing equipment with 10 points of significant environmental benefits). The wearer's signal is collected periodically to determine its position and track its status. When the sensor senses that the badge is removed, it will set the badge to sleep; If the sensor senses the movement of any part of the body, muscle tremor, or even pulse vibration, it will wake up the badge

auscultation

many electronic stethoscopes use piezoelectric films as sensor elements because of its durability, high sensitivity and wide bandwidth range. In this application, the sensor elements are usually encapsulated in the traditional metal auscultation head, because the sensor needs to form a 'force' with the body. Once the dynamic pressure signal is converted into an electrical signal, it can be selectively filtered or amplified, played back as an audio signal, judged the specific situation by using more complex calculation methods, or transmitted to a remote base station for further analysis and storage

sensor group

a composite acoustic sensor can monitor multiple points at the same time. Deep breeze uses a sensor group with almost 100 sensors to collect the sound information of patients' inhalation and exhalation. Attach the sensor to the skin surface with a vacuum cover. The collected signals are converted into 'images' of sound after processing, so the air flow in the trachea and lungs can be imaged like cartoons. Any foreign matters and abnormal phenomena are clear in these images. This method is more reliable and safe than X-ray

bed monitoring

piezoelectric film and piezoelectric cable can be installed on the mattress to detect the patient's heartbeat, breathing and body movement. Hoana medical Inc.'s monitoring bed alarm system installs a set of sensors between the mattress and the quilt. When the patient is sitting or lying on the monitoring bed, the sensor can accurately measure and collect the vital characteristics of the patient across the clothes and recent sheets. The flexible switch is used to collect static signals. All dynamic signals of patients are collected by piezoelectric film and converted into corresponding electrical signals, which are displayed on the display beside the hospital bed. When the patient's heart rate and respiratory rate are abnormal, or the patient gets out of bed without authorization, the system can alarm in advance. All this is done by sensors without direct contact with patients

baby breath monitor

infantrust company has developed an assisted parenting product respisense by using the extremely sensitive characteristics of PVDF. Clip the monitor to the position where the diaper is close to the baby's waist to monitor the baby's heartbeat. The piezoelectric film in respisense is in direct contact with the abdominal skin. If the baby is not detected to be active within the set time, the vibration buzzer will be activated, gently stirring the baby to stimulate it to breathe. If the baby still does not respond for a period of time, the alarm will be activated

respiratory thermoelectric monitoring

pvdf is also quite sensitive to the dynamic changes of temperature (28 μ The typical value of m-thick piezoelectric film is 8v/oc). British c-lect medical company has developed a monitor to monitor the respiratory rate. A small piece of piezoelectric membrane element is fixed at the mouth and nose with a mask, and the temperature changes of inhaled and exhaled gases produce strong electrical signals. Even if heated oxygen/air is inhaled, the measurement result is still very accurate. Pippa monitor is powered by battery, and LCD displays the number of breaths per minute

the lip contact sensor made of piezoelectric film uses the same principle to detect the airflow through the mouth or nose. Compared with thermistor, piezoelectric film has high sensitivity, fast response, softness and large detection area

conclusion

from the above application cases, piezoelectric films can replace traditional components to detect and transmit vital signs to medical monitoring systems. It is believed that in the near future, piezoelectric films will be more widely used in treatment and monitoring by virtue of their many advantages. (end)

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