Cordless Fetal Transducer System Based On Digital Wireless Technology

Fetal surveillance is an effective method to evaluate the development and safety of the fetus in the womb. A traditional fetal monitor is equipped with probes to monitor fetal heart rate, uterine contraction pressure and fetal movement, etc. The probes are connected to the monitor by cables which cause inconvenience and discomfort to pregnant women and sometimes even affect their physical and psychological health. With a view to this, a study is conducted mainly on how to realize the cordless connection between various probes and the monitor so as to avoid the inconvenience caused by cables. Accordingly, an "one-to-four" cordless fetal transducer system is designed and developed.A comparison study is drawn on recent approaches of short-distance cordless communication technology, especially technology used in nRF24E1 and CC1100. The former is revealed to better satisfy the requirements of power effectiveness and miniaturization, and is thus adopted to realize cordless communication. Research work on design and realization of a cordless fetal transducer system in the paper is described in the following aspects:(1) The cordless communication system, based on nRF24E1, works within the worldwide frequency band between 2.4 to 2.5 GHz, transmits and receives data in the mode of ShockBurst^TM to the fastest speed of 1Mbps. It is characterized by small size, low cost, easy manufacture and matched impedance.(2) The SEND-ACK mode of communication is adopted to guarantee the reliability of communication. In the ShockBurst^TM, the preamble, address and CRC of the data packet are automatically added before transmission and automatically removed after reception.(3) SystemView is applied into the emulational study on PCM coding, which is subsequently conducted on the collected fetal heart rate signals according to the format of data packets of nRF24E1.(4) Replaceable lithium battery is used as the electrical source of the probes. The battery management and charge circuitry are designed on the basis of special IC to guarantee the longevity of battery and convenience of replacement and maintenance.(5) Intelligent detection technology is applied into the design of the receiving base of probes. When the probe is not working, it can be charged in correspondence to the setting of the subsystem; when it is working, the base detects and receives the cordless data signals which are processed by C8051F020 after DA conversion.(6) A multi-probe cordless fetal transducer system is designed to monitor four pregnant womensimultaneously for clinical requirements.There are still some technical problems needed to be solved. For example, some interference would occur among the probes when the system is activated for a while and it might be ascribed to the same launching frequency of the antenna by preliminary judgment.