The New Material
Report on the Measurements of a New Material and New Type Magnetometer
1. Introduction
Investigation has been made on the New Material and New Type Magnetometer constructed by Dipl. Ing. István Abonyi. The New Material supposed to be a very high (room temperature) superconductor and as a sensor element of a New Type Magnetometer can provide a very high magnetic field sensitivity comparable to the SQUID based magnetometers.
Preliminary measurements on the New Material have been carried out at ATOMKI**, Debrecen, Hungary and in the Dept. of General Physics, Eötvös University, Budapest, Hungary.
The sensitivity measurement of the New Type Magnetometer was carried out in the Department for SQUID Construction at IPHT Jena, Germany*. They are equipped with the most recent measuring facilities like Hewlett Packard Spectrum Analyzer, and shielded room for high sensitive electric and magnetic measurement.
2. Experimental
2.1 The New Material
The new material, fabricated in tape form, has been investigated by measuring the magnetic susceptibility (in ATOMKI) and electromagnetic wave absorption (at the Dept. of Physics) from 77 K to room temperature.
The tape itself contains a very small amount of this New Material surrounded by very high permeability alloy. Even in the case of any measured peculiarities it made impossible to differentiate between magnetic and superconducting phase transition. This problem needs a more detailed investigation to get a definite determination of the properties of this new material and more developed method of fabrication of the New Material tape for containing much higher density of the New Material.
It must be noted that the New Material as a sensing element can be very useful even if it were not superconducting.
2.2 The New Type Magnetometer
The measurement of the sensitivity of the New Type Magnetometer was carried out in the Department for SQUID Construction. There was a shielded room and the measuring equipment was connected to the magnetometer by special shielded cable. The magnetic field for the measurement was generated by a coil which. was supplied by an Audio Frequency Generator from outside the room. The sensor of the New Type Magnetometer was inside the coil.. Since the magnetic field of the coil is proportional to the current, the intensity of the magnetic field to be applied could be determined from the current provided by the Audio Frequency Generator. The output of the magnetometer was connected to a Hewlett Packard Spectrum Analyzer. It was also outside the shielded room.
At first the sensitivity was tested in the field of 1 nT = 1000 pT in a wide audio frequency range as it can be seen in Fig. 2.2.1 and 2.2.2. The measurements showed that the sensitivity of this first experimental equipment could be in the order of 100 pT in the audio
*IPHT Jena e.V. (Institute for Physics of High Technology) Winzerlaer Str. 10 07745 Jena
**Research Institute for Atomic Physics
frequency range. of 25 – 50 kHz, the sensitivity is limited by the noise, while in Fig. 1.2.3 and 1.2.4 in a narrower frequency band like 1.5 kHz and 400 Hz a few pT magnetic field can be well detected. The narrower the frequency band the less is the noise and due to the less noise the higher is the sensitivity.
3. Comparison the New Magnetometer with the SQUIDs
Superconducting quantum interference devices (SQUIDs) use Josephson effect phenomena to measure extremely small variations in magnetic flux. SQUIDs are operated as either RF or dc SQUIDs. He prefixes RF or dc refers to whether the Josephson junction(s) is biased with an alternating current (RF or a dc current. Flux is normally inductively coupled into the SQUID loop via an input coil, which connects the SQUID to the experiment.
The SQUIDs with the adequate cryostats and electronics are very expensive and they can operate only in a highly sophisticated infrastructure.
There are several application of the SQUIDs because of its high sensitivity to magnetic fields. It can be applied for measuring any other quantities which can be transformed to magnetic field. The most widespread applications of the SQUIDs are showen in Fig. 2.3.1. The possible biomagnetic use of the SQUIDs together with magnetic field strength to be measured are displayed in Fig. 2.3.2.
The biomagnetic application seems to be possible in certain areas as it can be read from the figure where the different biomagnetic signal strength are displayed depending on the application field.
The sensing element of the SQUIDs can be made from either high-temperature superconductor (HTS) or low temperature superconductor (LTS). There are fundamental differences between HTS and LTS sensors. LTS devices have significant advantages and one disadvantage – operating temperature – over HTS devices. Because LTS materials are isotropic it is possible to fabricate devices with three-dimensional structures. That allows crossover and multilayer structures that permit higher sensitivity than single turn devices. HTS crossovers (needed for multilayer coils) require larger dimensions. The effect is that an HTS crossover acts as a Josephson or insulating junction with the addition of significant 1/f noise. The associated flux creep (particularly in HTS) by operating in the mixed state can lea to nonlinearity or hysteretic effects.
The major difference between the RF and dc SQUIDs is that the dc SQUID may offer
Fig. 3.1. Field sensitivities and bandwidths typical for various applications.
The lines indicate the sensitivity of the commercially available SQUIDs.
Fig. 3.2. Typical signal strength and frequency ranges for various biomagnetic signals
Fig. 3.3. Typical design of a fiberglass dewar used for biomagnetic measurements.
lower noise. The cost of the sensitivity can be the complexity of electronics needed to operate a dc SQUID and the difficulty in fabricating two nearly identical Josephson junctions in a single device.
The detection coils because of the thermal shield can not be put directly onto the surface to be measured. The distance between the sample and detection coils (see Tail Spacing in the picture) reduces the actual SQUID sensitivity.
Fig. 2.2.1 Signal-to-noise ratio in a 1000 pT AC field in the 0-25 kHz frequency range
Fig. 2.2.2. Signal-to-noise ratio in a 1000 pT AC field in the 0-50 kHz frequency range
Fig. 2.2.3. Signal-to-noise ratio in a 100 pT AC field in the 0-1500 Hz freq
uency range
Fig. 2.2.4. Signal-to-noise ratio in a 10 pT AC field in the 4800-5200 Hz frequency range
4. Consideration
Since it was the first real trial of the equipment and the sensor material, a higher sensitivity can be expected if a detailed analysis and research work will follow. Owing to recent developments the frequency range of the measuring is already raised to 80 000 measurings per second. This way very low intensity magnetic field has become researchable with significant amount of measuring.
One of the possible applications of the New Material is the measurement of the brain activity and function. Some of the new possibilities:
- The diameter and volume of the sensor made of the New Material compared to the ordinary Magneto-encephalographic equipments, is about five times smaller then the SQUID’s.
- The small volume of the detectors allows increasing in the number of detectors surrounding the brain’s surface.
- The number of the detectors can be increased upto1024 – in contrast with the ordinary MEG system which can use up to maximum 256 SQUIDs.
- The frequency of data acquisition is about 8000 times higher with the new detector system.
- The higher frequency of the data acquisition causes higher signal to the noise level.
- More detector and higher signal to noise ratio can increase the resolution.
- The higher frequency of the data acquisition makes the online functional monitoring of the brain activity possible.
- We have developed a new localization method for the detection of the source of the magnetism.
- Using the new localization method we are able to detect the spatial location of the magnetic source in 3D space.
- The “inverse problem” of the localization when using this method is solved differently from Maxwell’s equation and the Biot-Savart law applied ordinarily.
- The cross section image reconstruction is capable of using the new detector and data acquisition system.
- We are able to measure about few hundred femtotesla (10-15) changes in magnetic field – this is valid for the neurobiological range, while nearly several thousand, synchronously active cells can change the extracranial magnetic field in this magnetic level.
- The detector system is working at room temperature, compared with the MEG equipment’s SQUID detectors, which are working about –258 C° (in case of using superconducting niobium material)
- Using our New Detector we can exclude the outer magnetic noise with a new data acquisition method – the shielding quality of the room is also optimal in lower magnetic permeability level.
NYC, 01/09/2006.
István Abonyi