Development Of TEM Receiver Coil

TEM instruments are currently used in many fields for conductive target detection. A vast territory, many potential users and resources require to conduct a larger number of instruments, but the key point lies in whether the widely used equipment is "useful". Because of the sensitivity and independent software of our own R & D TEM instrument developers have a huge gap between foreign countries'which leads to the less effectiveness of our equipment, therefore limits the commercialization of our TEM instrument. In recent years, several well-known foreign companies such as Canada Geonics geophysical company PROTEM-47, 57,67 as excellent TEM has occupied a large share of the Chinese market. TEM instrument is a kind of high value-added product, a ground equipment sells from at least a hundred of thousands, as many as hundreds of thousands. Therefore, developing and improving the level of our TEM instrument is with high economic value and social benefits. This paper mainly studies the characteristics of the transient electromagnetic receiver coils based on the entire time domain electromagnetic method (including the transmitter and receiver, data acquisition, preprocessing, interpretation software parts), which includes the following several areas:1, Studies on some basic features and theories of the transient electromagnetic signals and the work unit, excitation field source and the actual received signal in detail. Transient electromagnetic signals has the features of large dynamic range, frequency bandwidth, the first field and second field characteristics co-exists. When the emission current turns off, as it is not the ideal periodic rectangular pulse, the received signal makes the TEM a field with secondary market exists at the same time. The first field does not include physical parameters of the information of good conductor, Therefore, TEM analysis of the received signal is mainly the analysis of secondary field. Secondary field generated by alternating magnetic field in the ground is exponentially decay form. Early signal includes the shallow geological information which is with high signal amplitude. Late signal response contains deep geological information and changes quickly. Thus, in order to receive TEM coil which can detect deep geological information should reduce the TEM system noise and make the signal do not advanced by the annihilation of noise .2 Studies of equivalent circuit of the receiving coil TEM, represents a detailed analysis of its time domain response and frequency response on the receiving coil of the electrical parameters (inductance and distributed capacitance), carried out on the receiver coil shield. To study the characteristics of receiver coils in the TEM, we know time-domain characteristics of TEM receiver coil, frequency domain characteristics are matched with the resistance of the coil, adjusting resistance value can match the bandwidth of the receiver coil to obtain the fastest response speed, the best flatness and the best linear phase; receiver coil inductance and coil turns, coil and coil shape cross-sectional area are mainly determined by the coil winding distributed capacitance is determined manner; receiver coils must be shielded to reduce interference on the sensor the impact of the signal, while the coil shield must be grounded, or does not play a role in reducing interference.3, Receiver coil noise on the TEM were derived theoretically and verify its correctness, method of reduce the noise of the program are given, in this basis given the sensitivity of receiver coils; the actual production of TEM receiver coil, the coil of physical parameters on electrical parameters were studied. According to computational amplifier noise model, theoretical formula derived coil noise, and then makes the simulation under PSpice, right derived to verify the noise model, while in the frequency domain for points, got the noise voltage, thus giving the coil sensitivity. In order to reduce system noise, we propose three methods to reduce the noise: Differential input / output time domain signal superposition and binning superposition of their own to improve the coil, then given SNR level. Giving experiment on the winding way, the coil turns, wire diameter, coil cross-sectional area of the coil electrical parameters we could know the information about electric parameters of the coil, while the receiving coil winding the reproducibility was studied too. This method of our situation around, the coil electrical parameters error is very small within the allowable range.4, Tests on TEM receiving coil on the time domain characteristics, frequency characteristics and noise characteristics. In theory, the matching receiver coil to receive the coil resistance should be the critical damping value, but in practice, it is necessary to make the critical damping in the receiving coil in order to make the receiver coil within the bandwidth of the most flat. A series of matches in the receiving coil resistance testing, we found the receiver coil at its best, flat areas, fast response and linear phase matching when the resistance (different resistance coil have different best match value); in time-domain characteristics of the test, because of the slightly larger addition of the matching resistor, making the signal undershoot oscillate in the process (this phenomenon is not critical damping). This could be eliminated by the average method; in the receiver coil noise test, we do research on electromagnetic compatibility of it to identify the smallest system and in order to make the system noise cascade method.