Site: Advanced Mobile Telecommunication Technology, Inc. (AMTEL)
500-1 Minamiyama Komenoki-cho, Nisshin-sui
Aichi-ken 470-0111, Japan

http://www.denso.co.jp/NEWS/1999/0421a-e.html

Date Visited: 14 October 1998

WTEC Attendees: R. Harris, H. Morishita

Hosts:

BACKGROUND

The headquarters of the Advanced Mobile Telecommunication Technology, Inc. project is at the Denso Research Laboratories in Aichi prefecture. A second site is the Yokohama Laboratory of Alps Electric Co., Ltd. in Kanagawa prefecture. Formed in 1994 with contributions from the Denso (15%), Alps (15%) and JKTC (70%) the company's mission is to "answer the demand for mobile telecommunications and to introduce new technology like high temperature superconductivity into practical applications. AMTEL's goal is "the development of highly efficient mobile telecommunication systems utilizing HTS as the next two generation systems: land mobile telecommunications and mobile satellite telecommunications." The company lists its capital as 2,857.25 million.

The Denso laboratory that this WTEC team visited is very elegant and spacious and not fully used. At this location there are 17 researchers and technicians. At Alps in Yokohama, 4 more researchers consider system design.

The company's work to meet market needs includes the development of both HTS filters and small cryocoolers.

INTERACTIONS WITH JKTC

In their original application to JKTC, AMTEL staff members noted that Denso had been studying HTS for 6 to 7 years and wanted to apply the base technology. Alps already had high frequency technology for cellular phones and wanted to advance its technology. A detailed business plan was submitted. Initial review of the plan was skeptical because it was not believed that such outstanding performance was possible. The application was presented to MPT, which is well aware of the limited spectrum available for cellular phones. Additional skepticism existed because the area of research was wide, and there was much work to do. There was a mid-term review, and there will be a final review. Each year, AMTEL sends a report to JKTC. AMTEL must control expenses but this is reported to be an acceptable requirement. JKTC increases AMTEL's capital three times a year, and each time a progress report must be submitted.

There are other internal reviews by an Engineering Promotion Committee and a Steering Committee. These reviews occur twice a year, using members from AMTEL, Denso and Alps. Both technical and management work are reviewed.

The mid-term review was two years prior to this visit, and AMTEL staff worked hard to prepare for it, submitting a thick report. The review itself lasted one hour with an additional hour for questions. The review was carried out by three professors. AMTEL's staff was not officially told the names of the professors in advance. In Japan if a professor were contacted before the review he would be obligated to try to do good things for the caller. That was deemed too much pressure, and the problem was solved by not revealing the names of the reviewers.

As of 1998, 37 patents had been issued of which 31 were for the cryocooler. A total of 140 patents had been applied for. In Japan patents are issued 2 to 3 years after application.

RECENT R&D RESULTS

Filters are composed of yttrium-barium-copper oxide (YBCO) superconducting films on MgO substrates. Four filters have been designed and tested:

 

Filter 1

Filter 2

Filter 3

Filter 4

Poles

9

15

11

8

Freq. (GHz)

2.6

1.5

0.8

2.0

Filters 1 and 2 were fabricated for the demonstration samples at the mid-term review. Filter 3 is designed as a test for IS-95 cellular telephone base stations, but the tests will be carried out in the laboratory and not on telephone poles as some U.S. companies are doing.

The researchers use Hewlett-Packard design software. Filter 4 was fabricated in niobium as a conceptual test. A bandwidth of 5 MHz or 0.25% was achieved with 90 dB rejection. The passband slope was 30 dB/700 kHz. Responding to a direct question, the researchers compared it with results from the United States, characterizing it as better than those of Conductus or STI, but a little worse than Illinois Superconductor (which uses thallium films).

Filter 3 was demonstrated in a commercially available Stirling cycle refrigerator. AMTEL researchers indicated that in the future they might be more open to collaboration on refrigeration with other companies. They showed a coaxial lead with reduced heat leak because its very thin shield is made of vacuum deposited copper. They have used both MgO and LaO substrates with YBCO. The YBCO is sputter deposited on both sides of the substrate. They achieved a noise figure of 0.5 dB at 840 MHz, which they asserted is 2 dB better than room temperature copper and 1 dB better than copper at 77 K.

The cooler operates at 70 K +/- 0.3 K. A lower temperature would require a bigger cryocooler. The researchers have also developed a pulse tube refrigerator having a capacity of 1 watt, sufficient for 1 filter. They are developing a bigger refrigerator, which was first assembled four days before the visit. It is designed for a 7 watt capacity at 70 K. Compressor resonances were being evaluated at the time of the visit. The researchers acknowledged plans to miniaturize the refrigerator, reducing its size by about half to less than 20 kg. The overall size was about 30 x 30 x 20 cm. They stated that the refrigerator must be quiet to be located in an urban area, where people would object to the noise.

Deposition is carried out in a 4-target off-axis sputtering system having a base pressure of 1 x 10-6 T. The sputtering gas is a 1:1 mixture of Ar and O2. The samples are exposed to air between depositions on the two sides of the substrates.

REFERENCES

AMTEL. n.d. Background of incorporation. AMTEL brochure.

AMTEL. n.d. Copies of viewgraphs from AMTEL presentations.

AMTEL. n.d. HTS for a better tomorrow. AMTEL brochure.

AMTEL. 1998. Answers to questions submitted by WTEC.

Kohara, K., A. Torii, and S. Ito. n.d. Etched plate regenerator for a small cryocooler. Preprint.

Kubota, H. and H. Takeuchi. 1998. Low thermal leakage coaxial cable. Paper EDC-12. Applied Superconductivity Conference.

Nara, K., Y. Hagiwara, and S. Ito. n.d. Measurements of gas temperature in the pulse tube using planar laser Rayleigh scattering method. Preprint.

Takizawa, K., S. Yatsuzuka, Y. Hagiwara, A. Torii and S Ito. n.d. Investigation of displacement and phase shift of the gas piston in a pulse tube refrigerator with a neck tube. Preprint.

Tsuzuki, G., M. Suzuki, N. Sakakibara, and Y. Ueno. 1998. Novel superconducting ring filter. IEEE MTT-S Digest: 379-382.

Ueno, Y., N. Sakakibara, M. Okazaki, and M. Aoki. 1997. High temperature superconducting filters for receiver front-end of mobile telecommunication base station. Advances in Superconductivity X, Proceedings of the 10th International Symposium on Superconductivity (ISS '97). October 27-30, Gifu, Japan: 1131-1136.


Published: September 1999; WTEC Hyper-Librarian