KULIAH -2 KONSEP-KONSEP DASAR Dr.Ir. Sri Pujiyati, M.Si Administrasi dan Jaminan Mutu Pendidikan Fakultas Perikanan dan Ilmu Kelautan Institut Pertanian

KELEBIHAN HIDROAKUSTIK AMAN TERHADAP MANUSIA ATAU BIOTA REAL TIME TINGKAT KEPERCAYAAN TINGGI DAPAT DIGUNAKAN DI BERBAGAI KONDISI PERAIRAN (DALAM/DANGKAL/POLUSI)

KEKURANGAN HARGA ALAT RELATIF MAHAL OPERATOR PERLU KEAHLIAN KHUSUS DEAD ZONE Terjadi tumpang tindih (Overlapping)

Ey-500

PEMBENTUKAN GELOMBANG SUARA Sumber suara : segala sesuatu yang menghasilkan suara. Jenis gelombang suara yang paling sederhana dan paling banyak dikenal dihasilkan oleh permukaan yang bergetar yang bergerak harmonik teratur.

Lab. Akustik dan istrumentasi Apa itu SUARA? Perambatan daerah tekanan tinggi dan rendah yang silih bergantian dan menjauhi sumber suara A sound source can be illustrated as a tube with a piston in the front. The piston is driven by a shaft coupled to a rotating disc producing uniform back and forth movements of the piston. Alternating high and low pressure zones will propagate outwards from the source. This is defined as sound. Increasing the speed of rotation (back and forth movements of the piston) will increase the sound frequency. Increasing the distance (amplitude) of the back and forth movements of the piston will increase the sound intensity. Be aware that sound, in addition to the sound pressure component, also has a kinetic component: the back and forth movements of the water particles. Lab. Akustik dan istrumentasi ITK-FPIK-IPB

Lab. Akustik dan istrumentasi Tekanan Tinggi Perubahan POSISI partikel Parameter Gelombang: Panjang Gelombang (Wavelength) jarak antara dua puncak gelombang Frekuensi (Frequency) f jumlah puncak per detik Kecepatan Suara (Sound Velocity) c jarak yang ditempuh per detik Perioda (Periode) T waktu antara dua puncak Sound speed=wavelength*frequency One period=1/frequency What is the wavelength of a 38 kHz sound? Wavelength=1500 m/s/38 000 periods/s=3,9 cm What is the wavelength of a 10 Hz sound? Wavelength=1500 m/s/10 periods/s=150 m. What is the period of a 38 kHz sound? Period (s)=1/38 000 cycles/s=26 microseconds. With increase in frequency the wavelength becomes shorter. The range of the sound decreases, but the resolution increases. To detect small objects like plankton, a high frequency is needed. The speed of sound in water depends on the temperature (T), salinity (S) and density (D) according to the following formula: c=1448,6+4,618T-0,0523T2+1,25(S-35)+0,017D Hubungan antara parameter gelombang: Lab. Akustik dan istrumentasi ITK-FPIK-IPB

Lab. Akustik dan istrumentasi FREKUENSI SUARA 38 000 Hz (Typical Simrad echosounder frequency) Sound energy 20 Hz 20 000 Hz Infrasonik audible Ultrasonik Fish hearing Human hearing Whale talk Echo sounders Dog hearing Bat orientation Sound is defined as pressure changes ranging in frequency from 20 to 20 000 Hz. These are the frequencies that are audible to humans. Any frequency above the audible range of humans (>20 000 Hz) is called ultrasound, and any frequency below is called infrasound (<20 Hz). Fish can hear frequencies of sound far down in the infrasound area (0.1 Hz) and up to about 500 Hz (some fish like herring up to 4 kHz). Whales communicate from the northern to the southern hemisphere using infrasound (long range). Dogs can hear frequencies of sound above the audible range for humans (up to 40 kHz). Bats are using ultrasound for orientation (transmitting at 25 to 75 kHz) because the resolution of small objects, like obstacles and prey, are increases with increase in frequency. Bats can detect a suspended cotton of 0,3 mm. In hydroacoustics mostly ultrasound is used, but Simrad produces transducers transmitting at 4 kHz for sub bottom analysis. However, more common frequencies for fisheries use are from 38 to 200 kHz. Lab. Akustik dan istrumentasi ITK-FPIK-IPB

Pembentukan Gelombang Suara di Air: Sumber suara adalah transducer yang memiliki lebar beam (beam sorot) dengan pola arah tertentu Frekuensi yang dihasilkan tinggi atau gelombang suara pendek Tipe gelombang suara yang dihasilkan adalah gelombang pulsa Gelombang ultrasonik (tidak dapat didengar oleh manusia/ikan) Mengapa digunakan gelombang suara??

Lab. Akustik dan istrumentasi Intensitas l B A Sound speed=wavelength*frequency One period=1/frequency What is the wavelength of a 38 kHz sound? Wavelength=1500 m/s/38 000 periods/s=3,9 cm What is the wavelength of a 10 Hz sound? Wavelength=1500 m/s/10 periods/s=150 m. What is the period of a 38 kHz sound? Period (s)=1/38 000 cycles/s=26 microseconds. With increase in frequency the wavelength becomes shorter. The range of the sound decreases, but the resolution increases. To detect small objects like plankton, a high frequency is needed. The speed of sound in water depends on the temperature (T), salinity (S) and density (D) according to the following formula: c=1448,6+4,618T-0,0523T2+1,25(S-35)+0,017D Bagaimana intensitas yang di dengar oleh si-A dan si-B? Berapa frekuensi dari sumber suara bila diketahui jumlah putaran sebanyak 100 putaran dalam satu detik dan berapa besar periodenya? Lab. Akustik dan istrumentasi ITK-FPIK-IPB

Intensitas adalah jumlah energi per detik (power) yang lewat melalui satuan luas tertentu tegak lurus terhadap arah pemancaran/perambatan gelombang suara Tekanan “P” adalah tekanan mekanik yang dihasilkan oleh vibrasi permukaan transducer di dalam medium air (micropascal, Newton)

Lab. Akustik dan istrumentasi Dalam prakteknya, digunakan Sound pulse (ping) = lama pulsa (pulse duration) n = jumlah periode dalam satu pulse T = lama dalam satu periode Panjang Pulsa (Pulse Length) The sound pulse is a package of energy sent from the transducer, not as a continuous signal, but as a short pulse repeated at regular intervals. A typical pulse (ping) duration is 1 ms. The number of periods in one pulse of a 38 000 kHz (cycles/s) is than: 0,001s*38 000 cycles/s=38 cycles (periods). The duration of one period of a 38 kHz tone is 26 microseconds. If we have 38 periods in one pulse and each period lasts 26 microseconds, we end up with a pulse duration of 1 ms. A second sound pulse is not transmitted until the echo from the previous is received. With increase in depth there is therefore normally an increase in pulse interval. In an echosounder should have a 200 m range the pulse interval must be 2*200 m/1500 m/s=0,26 s. Echo sounders was first used to determine water depth. If the time delay from transmitted to received signal is 2 s the water depth is? Lab. Akustik dan istrumentasi ITK-FPIK-IPB

Pulse Length (m) vs. Pulse Duration (s) Pay attention to the distinction between pulse length (m) and pulse duration (s). 1,5 m=38 periods = 1 ms Lab. Akustik dan istrumentasi ITK-FPIK-IPB

Lab. Akustik dan istrumentasi DECIBEL (dB) Decibel merupakan satuan pengukuran logaritmik dari nisbah (ratio) dua intensitas, Iterukur and Iacuan : Contoh, jika Iacuan = 1, 10 log 0.001 = - 30 dB 10 log 1 = 0 dB 10 log 1000 = 30 dB A relative scale is convenient to express sound. The decibel scale is such a scale. The intensity of sound in decibels is the log of the ration between two intensities of the actual sound intensity and a reference intensity. Lab. Akustik dan istrumentasi ITK-FPIK-IPB

Decibel selain merupakan rasio intensitas juga merupakan rasio dari power (W) Decibel selain merupakan rasio voltase (V) juga merupakan rasio dari tekanan (P)