| Title of Invention | A BROAD BAND TRANSCEIVER FOR MARINE APPLICATIONS |
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| Abstract | A broad band transceiver for marine applications comprising two PZT stacks of four rings each pre-stressed by Be-Cu stress bolt; the tail mass being of reduced length and made of high density Cu-W material; and tuning washers of made of FRP, the thickness of the said Iwashers being variable for achieving fine tuning. |
| Full Text | This invention relates a broad band transceiver for marine application. under water devices and instrument to a radar in air. Sound waves are the only source for communication in sonar is a complementary The known sonar is a low frequency (LF) sonar which has operating frequencies of 6 and 7.5kHz for the use in ship hull operations. i I It is an object of this invention to upgrade this device to operate at lower frequencies than the present without making any alteration in the external configuration of the transducer or stave but only by altering the internal configuration. There are nine individual elements in a single stave and the stave has the following underwater characteristics. This invention intends to lower the operational frequency of a sonar transducer and achieve a broader bandwidth without changing the underwater performance and keeping the external configuration unaltered especially without altering the active materials. There are ways to lower the frequencies by using magnetostrictive materials which have lower sound velocity compared to the piezoceramic (PZT) materials used in the known art, but this is not possible in this case. If the external configuration is changed, this Will lead to a major alteration in the production procedure. On the other hand, lower \ frequencies provide longer range operation using the sa|me sonar system. If the external configuration is changed the individual components in the production of the transducer like aluminum head mass (horn), rubber moulding, stave rack, pigtail assembly, chain connectors, stress bolt among others will need to be changed. This will end up in a major investment in production. Alteration in the external configuration will also lead to an alteration in the ship hull size which is a major expenditure. The fundamental relation for achieving oscillation in a ■-series RLC electronic circuit is given by the equation connecting resonance frequency (/i), L, the inductance and C, the capacitance values. For a particular value of Cb and L , resonant frequency If the capacitance value is doubled, keeping the L value constant, the frequency of the oscillator will get reduced to f\N2 theoretically. Since the resonance frequency of the prior art transducer is 7.5kHz, by doubling the capacitance value, the frequency of resonance should in principle get reduced to 1.5Hi = 5.5 kHz in water. In this formulation, the electro- mechanical equivalence of an electro-acoustic transducer is assumed to be satisfied [1]. t This principle can be mace practical by doubling the number of stacks in the transducer because, the capacitance values are giver by the active PZT material. So if one adds one exactly similar PZT stack retaining the tail mass weight constant and using the same matching coil, it is possible to reduce the resonance frequency of 7.5kHz to 5. 5kHz in water. In the known art, the tail mass material (conventional Tonpilz design, where the active materials are pre-stressed between a head mass and a tail mass using a stress bolt) used is mild steel which has a density of 7.85kg/m3. By selecting a material with higher density, it is possible to reduce the length of the tail mass provided the sound velocity of the material matches to satisfy the lumped mass approximation (sound velocity is assumed to be uniform) of a mechaniqal oscillator The advantages of this invention are: The external configuration of the transducer element and hence the stave itself remain unaltered and a broad band operation in the region 4.5 to 10 kHz can be achieved. Theoretically, a decrease in frequency will ultimately lead to a change in the external dimensions as well as an increase in weight of the transducer. But here the weight of the single element has been reduced by ~200g. Hence total weight remains same and the transducer can be operated with a SL ~208dB in 4.5,6 and 7.5kHz with a driving power of ~lkW. Established production procedure of the known art remains unaltered. A major savings of the investment budget may not occur if any other proposal is adopted for the same purpose. Only the tail mass material I of the known art is replaced by the new copper tungsten material in addition to the new stack assembly. Fine tuning of the transducer can be easily obtained by changing the thickness of | the tuning washers made ot FRP. ] The new PZT stack consislts of eight rings by doubling of four rings. That is, the the original stack consisted the new transducer assemjbly consists of two original stacks (each of four rings) pre-stressed using the original Be-Cu stress bolt as shown in Fig.i The increase in stack length in the proposed transducer inoroooo in otaok longth is compensated by reducing the length of the tail mass to half by using high density Cu-W material of density ~14.50kg/m3. The actual transducer assembly drawing is shown in Fig:2. Item NO.BO and 10x2 are the modified tail mass and stack respectively. All the other ijtem remain the same as in the known art. The transducer assembly is encapsulated using the known pig tail assembly itself for water tight encapsulation following known procedure. Similarly nine individual elsments were assembled in the prior art stave and driven using a suitable power amplifier. The underwater parameter evaluation of the stave was carried out at (National Accreditation Bureau of Laboratories) NABL accredited Acoustic Test Facility (ATF) at NIOT. The altered Tail mass configuration is shown in Fig:3. The experimentally obtained Transmitting Voltage Response (TVR) showing the Broad Band achievement in the frequency range 4.5 to 10| kHz is shown in Fig:4: The broad band nature allows the transducer operation at 4.5, 6 and 7.5kHz using the single stave itself without having a major variation in the required underwater parameters. A comparison of the TVR of the old art transducer and the newly developed is shown in Fig:5. A similar comparison of the receiving sensitivity (RS) of the prior art transducer and the new transducer has also been obtained experimentally. The operation of the transducer gave consistent results during the endurance test conducted for 12h continuously at NIOT and typical results are shown in Table 3.1. In short this invention has the following features: A compact broad band transducer for marine applications such as long range detection and underwater communication. A single transducer stave can operate delivering nearly same out put power (SL~208dB) with a nearly in put electrical power drive of lkW The new stave can be used in the improved sonar performance fo|r old ship hull itself with an marine applications. Savings in the initial investment occur by avoiding a completely different design with an increase in weight as well as an alteration in the external configuration adoption. In addition to the above, the production procedure remains the same which is well advantageous to a production agency. The lumped parameter approximation used in the low frequency transducer is found to be valid in the present invention also. Since in this invention the volume of the active material has been doubled, it is possible in principle to drive the stave with higher capacity power amplifier where limitation will be only on the cavitations limit for a particular depth of operation. Since this is mainly designed for surface ships, a better water tight encapsulate i of the same transducer will lead to a much deeper marine (Operations. An enhancement in the band \kridth without affecting much on the performance is a clear reflection of a better transducer design with an increase in efficiency or the effective coupling factor keff. ! It will be appreciated that various other features of this invention are possible without Ideparting from the scope and ambit of this invention. We Claim: 1. A broad band transceiver for marine applications comprising two PZT stacks of four rings each pre-stressed by Be-Cu stress bolt; the tail mass being of reduced length and made of high density Cu-W material; and tuning washers of made of FRP, the thickness of the said Iwashers being variable for achieving fine tuning. 2. A broad band transceiver for marine applications substantially as herein described with reference to, and as illustrated in, the Accompanying drawings. Table 3.1 Set up details HT Voltage 200 V / 7A LT Voltage 18V/10A Period 20 s No. of cycles 100 Distance between stave and hydrophone 4.395 m |
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| Patent Number | 278301 | |||||||||
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| Indian Patent Application Number | 448/CHE/2008 | |||||||||
| PG Journal Number | 53/2016 | |||||||||
| Publication Date | 23-Dec-2016 | |||||||||
| Grant Date | 20-Dec-2016 | |||||||||
| Date of Filing | 22-Feb-2008 | |||||||||
| Name of Patentee | NATIONAL INSTITUTE OF OCEAN TECHNOLOGY | |||||||||
| Applicant Address | NIOT CAMPUS VELACHERY-TAMBARAM MAIN ROAD, PALLILARANAI CAMPUS, CHENNAI-600100. | |||||||||
Inventors:
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| PCT International Classification Number | H 04 B 1/00 | |||||||||
| PCT International Application Number | N/A | |||||||||
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