JPH09307487A - Magnetic field communication circuit and communication system using it - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the expansion of a circuit scale by eliminating the necessity of transmission at a data speed in the neighborhood of a self resonance frequency caused by connection similar to a transformer so as to avoid narrowing a communicable position range in spite of miniaturizing an electromagnetic induction coil, and unecessitating special data processing. SOLUTION: When this system is provided with an antenna 1 receiving radio waves, a magnetic impedance element 3 is inserted to the antenna 1 and while radiating a high frequency to the antenna 1 from outside, the fluctuation of a magnetic field based on transmission data is given to the element 3 at the same time. Then the fluctuation of the outputting amplitude of the antenna 1 is demodulated by a wave detection circuit 7 to reproduce transmitted data.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic field communication circuit for performing communication depending on the strength of a magnetic field and a communication system using the magnetic field communication circuit.

[0002]

2. Description of the Related Art Communication circuits utilizing the fluctuation of magnetic field are widely used everywhere. For example, a lift system in a ski resort, a handy terminal of a waitress in a restaurant, or an electronic device such as an ID-TAG. Most of the magnetic field communication is an electromagnetic induction method, which is to transmit data by making two coils face each other and creating a state just like a transformer coupling. The communication circuit that uses the fluctuation of the magnetic field has the following features when compared to the system that uses light or wireless.・ Data communication is possible regardless of dirt. -Communication is possible only within a certain range, and confidentiality is excellent. -It is possible to perform relatively high-speed communication. This is used in various situations in the part where such characteristics can be utilized.

[0003]

However, in the electromagnetic induction type magnetic field communication circuit, the following problems have occurred.・ If the electromagnetic induction coil is downsized, the communicable position range will be narrowed. -To solve the above problems, the coil becomes large and hinders miniaturization. -Because of the same coupling as a transformer, it is necessary to transmit at a data rate near the self-resonant frequency.・ Therefore, special data processing such as Manchester is required, and the circuit scale becomes large. In the present age when miniaturization is spurred in this way, especially these were big problems.

[0004]

In order to solve the above-mentioned problems, a magnetic field communication circuit of the present invention comprises an antenna or a pickup coil for receiving radio waves, and the antenna or the pickup coil has a magnet impedance element (hereinafter referred to as MI). Element) to radiate a high frequency from the outside to the antenna or the pickup coil, and at the same time, to give a magnetic field variation based on the transmission data or the transmission signal to the magnet impedance element, thereby varying the output amplitude of the antenna or the pickup coil. Is configured to reproduce received data or a received signal via a demodulation element.

Further, the present invention as a communication system using the above magnetic field communication circuit of the present invention is a radio wave generating means for generating a high frequency radio wave, and a transmission signal generation for generating a magnetic field which fluctuates based on data or a signal to be transmitted. Means, an antenna or a pickup coil for receiving the high frequency radio wave, and a magnet impedance element connected to the antenna or the pickup coil and changing its impedance by a magnetic field from the transmission signal generating means. The receiving device comprises antenna means and detection means for demodulating the output signal of the antenna means.

[0006]

BEST MODE FOR CARRYING OUT THE INVENTION In the magnetic field communication circuit and communication system of the present invention having the above configuration, when a magnetic field is applied as data to an MI element while a constant radio wave is applied to an antenna or a pickup coil, the impedance of the antenna depends on the magnetic field. The given data is detected by extracting this change, that is, by detecting the signal output from the antenna or pickup coil to which the MI element is connected, and determining the detected output signal. You can do it.

[0007]

Embodiments of the magnetic field communication circuit of the present invention will be described below with reference to the drawings. FIG. 1 is a diagram showing a specific example of the invention. 1 is an antenna element, 2 is a tuning capacitor, 3 is an MI element, 4 and 5 are taps, 6 is a matching capacitor, 7 is a detection circuit, and 8 is an AD converter.

The antenna element 1, tuning capacitor 2, MI element 3, and matching capacitor 6 constitute a loop antenna. The loop antenna is known as an antenna having a high resonance Q. First MI
The simple impedance of the element 3 was measured. The MI element 3 is an element whose impedance changes according to the strength of the magnetic field, and the measured characteristics of the MI element 3 are shown in the Smith chart of FIG. In this measurement, the impedance at 131 MHz, which is the frequency at which the impedance change is large when there is no magnetic field and when the magnetic field is close, is plotted. A on the Smith chart when an external magnetic field is applied
Point B indicates the point when no magnetic field is applied. At the frequency used for this measurement, it was found that the R component was small when the magnetic field was present, but the L component was not so changed.

Using the MI element 3 having this characteristic, as shown in FIG.
The Smith charts of FIGS. 3 and 4 show the characteristics of the antenna when the loop antenna shown in FIG. In the embodiment, the marker frequency is 131 MHz and the frequency width is 200 MHz. FIG. 4 shows the characteristics when a magnetic field is applied, and FIG. 3 shows the characteristics when a magnetic field is not applied. The reflectance VSWR is approximately 1 in FIG. 4 which is a characteristic when a magnetic field is applied, and the VSWR is approximately 4 in FIG. 3 which is a characteristic when a magnetic field is not applied.
That is, when a magnetic field is applied, high frequency transmission can be efficiently performed to the next stage circuit. In this measurement, the loss resistance of the antenna is reduced in the presence of a magnetic field, and at the same time a large amount of change can be obtained by proper matching.

Now, this loop antenna has 131 MHz
The high frequency constant amplitude carrier of is externally applied, and
At the same time, when a varying magnetic field based on the magnetic field data or the transmission signal is applied to the MI element, the amplitude of the antenna output at the taps 4 and 5 changes according to the data or the signal. Therefore, in the detection circuit 7, the antenna output is AM
Transmission data or a transmission signal can be reproduced by performing detection. In the example, AM
Although envelope detection is used for detection, data or signals may be processed by a digital signal processor or AD converter.

After the envelope detection, the AD converter 8 logically judges the transmission data or the transmission signal as in the embodiment. A voltage comparator may be used for the logical judgment. In the above-described embodiments of the magnetic field communication circuit and the communication system of the present invention, as the means for generating the transmission data by the magnetic field, the transmission data by the magnetic field is generated by controlling the current flow / non-current flow through the solenoid. . Therefore, the present invention is not limited to the case where the transmission data or the transmission signal is digital data, and M that the impedance changes depending on the magnitude of magnetism.
The magnetic field communication circuit and the communication system of the present invention can be applied by utilizing the characteristics of the I element and making the transmission data or the transmission signal an analog signal. In this case, the AD converter 8
It goes without saying that it is not necessary to make a logical decision on the output of.

In this embodiment, a copper plate having a width of 5 mm and a length of 116 mm is used for the antenna element 1, the tuning capacitor 2 has a capacitance of 12 pF, and the matching capacitor has a capacitance of 15 pF.

[0013]

With the above structure, the magnetic field communication circuit and communication system of the present invention have the following effects. -By using a frequency with a relatively short wavelength as a carrier, it is possible to achieve miniaturization compared to the electromagnetic induction method. -The envelope detection circuit that requires few parts can be used as the detection circuit on the receiving side, so magnetic field communication is possible with a simple circuit. -The confidentiality can be improved because the data and signals react only to the determined high frequency. -Since high frequency is used as a carrier, it is possible to transmit signals with wide frequency range. -Since there is no effect of the self-resonant frequency of the transformer, extremely low speed to high speed data can be received in the common circuit. -Since the receiving circuit can be composed of only passive elements, there is no waste of energy.

As described above, it is possible to provide a magnetic field communication circuit and a communication system which are small in size and have good characteristics, without the drawbacks of the conventional electromagnetic induction type magnetic field communication circuit. By combining the present invention with a memory element such as an EEPROM, a program or ID can be written from outside the device, and any misalignment after installation, ID change, and program change can be easily performed, and the effect is great.

[Brief description of drawings]

FIG. 1 is an explanatory diagram showing an embodiment of a magnetic field communication circuit and a communication system of the present invention.

FIG. 2 is a Smith chart showing characteristics of the MI element 3 in the embodiments of the magnetic field communication circuit and the communication system of the present invention.

FIG. 3 is a Smith chart showing the characteristics of the antenna when a magnetic field is not applied in the embodiments of the magnetic field communication circuit and the communication system of the present invention.

FIG. 4 is a Smith chart showing the characteristics of the antenna when a magnetic field is applied in the examples of the magnetic field communication circuit and the communication system of the present invention.

[Explanation of symbols]

 1 Antenna Element 2 Tuning Capacitor 3 MI Element 4 Tap 5 Tap 6 Matching Capacitor 7 Detection Circuit 8 AD Converter

Claims (5)

[Claims] 1. A magnetic field communication circuit for transmitting data or signals while simultaneously applying a radio wave to an antenna and a magnetic field to a magnet impedance element. 2. An antenna means comprising an antenna or a pickup coil for receiving radio waves, a magnet impedance element connected to the antenna or the pickup coil, and a detecting means for demodulating an output signal of the antenna means. Magnetic field communication circuit characterized by. 3. The magnetic field communication circuit according to claim 2, wherein the detection means is a detection means using envelope detection. 4. The magnetic field communication circuit according to claim 2, wherein the antenna means is a loop antenna. 5. A radio wave generating means for generating a high frequency radio wave,
A transmitting device including a transmission signal generating unit that generates a magnetic field that fluctuates based on data or a signal to be transmitted, an antenna or a pickup coil that receives the high-frequency radio wave, and the transmission that is connected to the antenna or the pickup coil. It is characterized in that it comprises an antenna means composed of a magnet impedance element for changing its impedance by a magnetic field from the signal generating means, and a receiving device equipped with a detection means for demodulating an output signal of the antenna means. Communications system.