Within the scope of the shrinking space design, reliable and accurate sensor function ability is crucial in a wide range of applications - and it is a difficult request.

Within the scope of the shrinking space design, reliable and accurate sensor function ability is crucial in a wide range of applications - and it is a difficult request. However, in addition to other benefits, miniaturization, including narrow size module system) can provide more flexibility for design personnel to locate the components on printed circuit board (PCB), and release the precious circuit board space and to reduce interference.

Medical industry still is the main driver of sensor miniaturization and ultra reliability, because the body's internal applications require minimal, accurate sensors, because they have great application prospect in medical procedures. Arthroplasty (force sensor used in joint replacement) and spinal arthrodesis. In the external use, sensor suppliers must provide flexible installation options, as much as possible to ensure that the sensor is close to the patient and/or liquid (such as drugs, blood or water), so that accurate and precise measurement.

Small, portable medical equipment development, to the hospital in narrow space, also make the nursing staff can quickly and easily transfer the equipment from one patient to another patient. The miniaturization of sensor helps in mobile medical equipment, in the design of wearable technology and handheld instruments to achieve this goal.

Many elements must be integrated to realize this smaller size. In addition to suitable for small size of itself, for example, the end product of physical and packing requirements, budget and technical problems, such as by multiple sensor function integrated into a single small packages to continuously reduce the BOM cost.
 

Puts the development of the medical sensors in the background, let us make a brief introduction of the history of cardiac pacemaker.

Columbia doctors Alberto Vejarano Laverde with Colombia electrical engineer Jorge Reynolds, built the first cardiac pacemaker Pombo cooperation. The 45 kg or 99.2 pounds. And automatically by 12 v batteries, electrode is connected to the heart, and used to keep the 70 - year - old priest Gerardo Florez alive. Once the silicon transistors appeared in the pictures, things become easier. The first fully implantable pacemakers in Sweden in 1958. It is connected with electrodes connected to the heart muscle. It lasted three hours. The second implants make it for two days. The first implantable pacemakers receiver Arne Larsson actually received 26 devices, and died at the age of 86.

Like most electronic products innovation, heart pacemakers is more and more small, function is more and more strong. For example, recent advances include leadless pacemaker devices, and performance of its traditional competitors, and its size is 10% of the traditional equipment, miniature devices directly placed in the patient's heart. This is done through the catheter without surgery. Integration is very high, even in a small state, because it contains active sensors, metabolism and double sensors, sensor to measure temperature, position and the consequences of arrhythmia.
 

Pacemakers and other heart related technology has been developing constantly, because the heart disease is a major cause of death in developed countries, early diagnosis, treatment and maintenance is very important. Biomedical engineers have successfully developed miniature device to open blocked arteries and treatment of cardiovascular disease. However, these tools are still likely to cause infection. Micro sensor will be able to perceive and nanotechnology monitoring biological signals, such as proteins or antibodies in the heart or of the release of inflammatory events.

In addition to the cardiac pacemaker, other announcements for a medical target has also recently published news reports on a regular basis. Fc twente university recently unveiled the world's smallest 1 hand sensor prototype, is used to measure the motor function of patients with rehabilitation. It is smaller than the fingertips, can measure the force applied by your hand. Within this small sensors can be put in gloves and prosthetic devices, can be designed into the bicycle pedal, sole or touch screen. In addition to measuring the total force, sensor can measure the direction of the force f, which is very important for extensive application. The device measuring physical labor involved in the load and the athletes or rehabilitation in patients with performance, as a way to improve the skills, and it has solved the unit is small enough to measure the fingers and objects are caught between the force applied to challenge.

At present, the development of the medical application of sensor miniaturization is quickly out of the lab and into the work a day in the world. Considering human breathing, the need to measure human lungs during breathing and/or external air flow. During conscious sedation, respiratory function in patients with monitoring and evaluation is important, it is a state of relaxation induced by pharmacology, in which patients stay awake during such as dental treatment and cooperation. Understanding of the respiratory cycle can also be used for detection of sleep apnea. Usually, these technologies through along the tube on the side of the positioning of the two ports of the differential pressure sensor to shunt flow of configuration to indirectly measure the breathing tube of flow.

Pressure sensors can be integrated in the design of the many, because they provide a lot of connection and packaging options (SMT, DIP, SIP), as well as the choice of the output (analog or digital). All Sensors series Miniature pressure sensor used in medical instruments and breathing breathing, can save a space and provide high performance. H - GRADE is the company millivolt output high precision version of the pressure sensor (figure 1). They provide calibration of millivolt output, have excellent output performance, reducing the output bias error due to factors such as temperature changes. Suppliers also pointed out that the sensors to provide stability during preheating, and provide stability in a long time. In addition, the sensor using silicon micromachining, stress concentration increase structure, provides a linear output pressure.

This series of sensors used in non corrosive, non ion work such as air, dry gas and other fluid. Output proportional to the power supply voltage of the device, can accept any dc power supply voltage up to + 16 V operation. Features include 0 to 4 "H2O to 0 to 100 PSI pressure range, 0.5% linearity, temperature compensation and zero and range alignment.

Another example of traditional medical applications of sensors is MLX90615SSG - DAA - 000 - TU subminiature Melexis Technologies, intelligent non-contact infrared thermometer (figure 2). For the ear thermometer and fever thermometer, as well as the continuous temperature monitoring, the device is considered to be the world's smallest "smart" infrared thermometer, with a diameter of only 4.7 mm (0.185 inch), height is 2.7 mm (0.106 inch).
 

Signal processing chip integration in transistor appearance packaging, provide fully calibrated thermometer with plug and play. Because of its low noise amplifier, 16 bit ADC and DSP unit, which can realize the high precision and high resolution of the thermometer; For example, in the 30-40 ˚ C key range, precision of + / - 0.1 ˚ C.

In the medical field, the accelerometer is used for monitoring the movement. Used for sports and fitness equipment is an example of the micro sensor of ADI company 3 axis ADXL 335 accelerometer (figure 3).

ADXL335 is a complete 3 axis acceleration measurement system. Its measuring range is at least + 3 g, and includes a built in silicon wafers and polysilicon surface above the signal conditioning circuit micro mechanical sensors, in order to realize the open loop acceleration measurement framework. The output signal is proportional to the acceleration of the analog voltage.

Polysilicon springs will be hanging on a wafer surface structure, and provides the ability to resist acceleration. The deviation of the differential capacitor is used to measure the structure of the differential capacitor by an independent board of fixed and attached to move quality boards. The fixed plate by 180 ° phase-out square-wave driving. Acceleration makes mobile quality deflection and the differential capacitor unbalance, resulting in a sensor output, its amplitude proportional to the acceleration. Phase sensitive demodulation technology is then used to determine the size of the acceleration and direction.
 

Demodulator output amplified by 32 k Ω resistance to outside chip. The user by adding a capacitor to set the signal bandwidth of the device. This filter can improve the measurement resolution and helps prevent aliasing. The device can measure the static acceleration of gravity in the tilt sensor application, as well as sports, impact or vibration caused by the dynamic acceleration.

conclusion

As we have seen sensors play a key role in many medical applications, and more sensor is based on the ongoing miniaturization trend. From a very large cardiac pacemaker to suitable for cardiac pacemaker was an amazing feat, combined with the progress of medical and sensor technology.

Although small, does not always translate into cost-effective, but it can be transformed into a highly integrated and did not reduce the performance, this is very important in medical applications, because it is in size, ease of use, portability and reliability, accuracy and the cost is very important.

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