Pengembangan Sensor Cetak Chipless RFID Berbasis Nanokomposit CuNP-rGO-PANI untuk Multi-Analyte Sensing dan Evaluasi Kinerja Nirkabel

Abstract

Sensor cetak berbasis tinta konduktif berperan penting dalam mendukung transformasi digital di sektor manufaktur dan logistik, khususnya pada kemasan cerdas untuk produk sensitif seperti pangan, farmasi, dan elektronik. Sensor ini memungkinkan integrasi fungsi identifikasi dan pemantauan kondisi lingkungan secara nirkabel dengan biaya rendah dan fleksibilitas tinggi. Pendekatan chipless RFID menjadi solusi menjanjikan karena menghilangkan kebutuhan chip aktif, sehingga lebih sesuai untuk produksi masal dan sistem internet of things (IoT) pasif. Namun demikian, kompleksitas desain resonator dan keterbatasan material konduktif cetak masih menjadi tantangan utama, sehingga diperlukan pengembangan material fungsional dan formulasi tinta yang sederhana, stabil, dan mudah diskalakan melalui metode screen printing. Material berbasis grafena memiliki sifat listrik dan mekanik yang unggul, namun kecenderungan restacking antar lembaran reduced graphene oxide (rGO) dapat menurunkan kinerjanya. Dalam penelitian ini, polianilin (PANI) berperan sebagai matriks polimer sekaligus spacer utama yang mencegah restacking rGO dan membentuk struktur berpori, sedangkan nanopartikel tembaga (CuNP) berfungsi sebagai conductive bridge yang memperpendek jalur perkolasi elektron dan meningkatkan konduktivitas listrik. Kombinasi CuNP-Rgo-PANI dirancang sebagai material multifungsi yang berperan sebagai elemen konduktif sekaligus elemen sensitif pada sensor cetak chipless RFID. Penelitian ini berfokus pada pengembangan sensor cetak chipless RFID berbasis nanokomposit CuNP-rGO-PANI dan evaluasi kinerjanya melalui dua aspek utama, yaitu (i) kemampuan sensing multi-analit, yang direpresentasikan oleh respon sensor terhadap amonia (NH3), etanol, dan kelembaban, serta (ii) keandalan pembacaan nirkabel (reading robustness) terhadap variasi jarak baca dan sudut pembacaan. Parameter S11 dan S21 digunakan sebagai indikator perubahan karakteristik resonansi frekuensi tinggi akibat interaksi material dengan analit, bukan sebagai parameter sensing itu sendiri. Respon sensor bersifat near real-time, di mana perubahan sifat listrik nanokomposit dapat terdeteksi secara langsung melalui pergeseran dan atenuasi sinyal resonansi tanpa proses pasca pengolahan yang kompleks. Tahap pertama penelitian mencakup sintesis nanokomposit CuNP-rGO-PANI serta karakterisasi struktural, morfologi, dan interaksi kimia antar komponen. Hasil raman menunjukkan peningkatan rasio ID/IG akibat interaksi CuNP dan proses termal, sementara analisis SEM mengonfirmasi dispersi CuNP berukuran nano dengan ukuran ekuivalen rata-rata 11,48 nm dalam matriks rGO-PANI. Hasil FTIR mengindikasikan adanya interaksi kimia antar komponen, dan stabilisasi CuNP dalam matriks PANI terbukti membantu mengurangi restacking grafena. Hasil ini menegaskan bahwa nanokomposit CuNP-rGO-PANI memiliki potensi tinggi sebagai material tunggal multifungsi yang mampu berperan sekaligus sebagai elemen konduktif dan sensitif dalam sensor cetak chipless RFID. Tahap kedua berfokus pada optimasi formulasi tinta konduktif menggunakan pendekatan response surface methodology-central composite design (RSM-CCD). Hasil penelitian menunjukkan formulasi terbaik pada 74,52% material, 17,40% pengikat, dan waktu curing 10,09 menit, menghasilkan konduktivitas sekitar 5,03 S/cm dan resistansi sekitar 20,12 O dengan validitas model yang tervalidasi secara statistik. Tahap ketiga mengevaluasi kinerja sensor cetak terhadap berbagai analit dan performa pembacaan frekuensi tinggi untuk aplikasi chipless RFID. Sensor menunjukkan resonansi yang stabil di sekitar 8,58 GHz dengan penurunan tajam parameter S11 dan S21, serta mempertahankan respon resonansi yang andal hingga jarak baca sekitar 6,2 cm dan toleransi sudut pembacaan hingga ±30°. Sensor juga menunjukkan kemampuan multi-analyte sensing yang selektif, dengan respons paling kuat terhadap NH3 melalui mekanisme dedoping PANI yang diperkuat oleh rGO dan CuNP, sementara respons terhadap etanol dan kelembaban terdeteksi secara reproducible dan stabil. Secara keseluruhan, perubahan sifat listrik nanokomposit CuNP-rGO-PANI terbukti dapat dimanfaatkan secara efektif sebagai mekanisme sensing dalam sistem pembacaan nirkabel berbasis gelombang mikro untuk aplikasi sensor cetak chipless RFID.

Conductive ink-based printable sensors play an important role in supporting digital transformation in the manufacturing and logistics sectors, particularly in smart packaging for sensitive products such as food, pharmaceuticals, and electronics. These sensors enable the integration of identification and environmental monitoring functions wirelessly at low cost and with high flexibility. The chipless RFID approach is a promising solution because it eliminates the need for active chips, making it more suitable for mass production and passive internet of things (IoT) systems. However, the complexity of resonator design and the limitations of printable conductive materials remain major challenges, requiring the development of functional materials and ink formulations that are simple, stable, and easily scalable through screen printing methods. Graphene-based materials have superior electrical and mechanical properties, but the tendency for reduced graphene oxide (rGO) sheets to restack can reduce their performance. In this study, polyaniline (PANI) acts as both a polymer matrix and a main spacer that prevents rGO restacking and forms a porous structure, while copper nanoparticles (CuNP) function as conductive bridges that shorten the electron percolation path and increase electrical conductivity. The CuNP-rGO-PANI combination is designed as a multifunctional material that acts as both a conductive element and a sensitive element in chipless RFID printed sensors. This study focuses on the development of a printable chipless RFID sensor based on CuNP-rGO-PANI nanocomposites and the evaluation of its performance from two main perspectives: (i) multi-analyte sensing capability, as reflected by the sensor responses to ammonia (NH3), ethanol, and humidity; and (ii) the robustness of wireless readout under variations in reading distance and reading angle. The S11 and S21 parameters are employed as indicators of changes in high-frequency resonance characteristics resulting from interactions between the nanocomposite material and target analytes, rather than serving as direct sensing parameters. The sensor exhibits a near real-time response, wherein changes in the electrical properties of the nanocomposite are directly detected through resonance shifts and signal attenuation without the need for complex post-processing. The first stage of the study involved the synthesis of CuNP-rGO-PANI nanocomposites and comprehensive characterisation of their structural, morphological, and chemical properties. Raman spectroscopy revealed an increase in the ID/IG ratio, attributed to interactions between CuNPs and rGO as well as thermal processing effects. SEM analysis confirmed the homogeneous dispersion of nano-sized CuNPs within the rGO-PANI matrix, with an average equivalent particle size of 11.48 nm. FTIR spectra indicated the presence of chemical interactions among the composite components, while stabilisation of CuNPs within the PANI matrix was found to mitigate graphene restacking. These findings demonstrate that the CuNP-rGO-PANI nanocomposite is a promising multifunctional single material capable of simultaneously serving as both conductive and sensitive elements in printed chipless RFID sensors. The second stage focused on optimising the conductive ink formulation using a Response Surface Methodology–Central Composite Design (RSM–CCD) approach. The optimal formulation was determined to consist of 74.52% nanocomposite material, 17.40% binder, and a curing time of 10.09 minutes, yielding a conductivity of approximately 5.03 S/cm and an electrical resistance of approximately 20.12 O. The developed quadratic model exhibited strong statistical validity, confirming the reliability of the optimisation results. The third stage evaluated the performance of the printed sensor in response to various analytes as well as its high-frequency wireless readout characteristics for chipless RFID applications. The sensor exhibited a stable single resonance at approximately 8.58 GHz, accompanied by sharp decreases in the S11 and S21 parameters. Reliable resonance behaviour was maintained at reading distances of up to approximately 6.2 cm, with angular tolerance extending to ±30°. In addition, the sensor demonstrated selective multi-analyte sensing performance, with the strongest and fastest response observed for NH3, attributed to a PANI dedoping mechanism synergistically enhanced by rGO and CuNPs. Responses to ethanol and humidity were also detected in a reproducible and stable manner. Overall, the observed changes in the electrical properties of the CuNP–rGO–PANI nanocomposite confirm its effective utilisation as a sensing mechanism in microwave-based wireless readout systems for printed chipless RFID sensor applications.