NFC: what is it, contactless communication module and operating principle

What is NFC?

NFC (Near Field Communication) is a short-range wireless data transmission standard operating at 13.56 MHz. The technology is based on RFID (Radio Frequency Identification) and is backward compatible with ISO 14444 — the standard for contactless smart cards. Data transfer speed is 106, 212 or 424 kbps depending on the selected mode.

Unlike Bluetooth, NFC does not require a pairing procedure — devices exchange data instantly when brought close to each other. The maximum communication distance is 10 cm, which provides natural protection against interception. According to NFC Forum, the technology is supported by more than 3 billion devices worldwide, and this number is growing by 15–20% annually.

The NFC standard is developed by the NFC Forum, a consortium founded by Sony, Philips and Nokia in 2004. The first phone with NFC (Nokia 6131) was released in 2006, but mass adoption began after the release of Android 4.0 (Ice Cream Sandwich) in 2011 and the launch of Apple Pay in 2014. Today, almost all smartphones priced above $150 support NFC.

NFC Operation Modes in a Phone

The NFC controller in a smartphone supports three operating modes, each designed for its own class of tasks. Switching between modes happens automatically depending on the type of interacting device.

Reader/Writer Mode

In this mode, the phone acts as an active reader of NFC tags. When brought close to an NFC tag — a sticker, bracelet or poster — the phone reads data from the tag’s memory. Tags contain from 48 bytes to 32 KB of memory and store URLs, text or commands. Android Beam (replaced by Nearby Share) used this mode to transfer links and contacts.

Peer-to-Peer (P2P) Mode

Two NFC devices exchange data directly. One device acts as the initiator, the second as the target. The LLCP (Logical Link Control Protocol) standard manages the connection, and SNEP (Simple NDEF Exchange Protocol) manages the data format. P2P mode is used for quick transfer of contacts, links or initiating Bluetooth pairing. Speed in P2P mode reaches 424 kbps.

Card Emulation Mode

The phone emulates a contactless smart card — a payment card, transit pass or access badge. An external NFC device (POS terminal, turnstile) interacts with the phone the same way as with a regular plastic card. This mode is used in Apple Pay, Google Pay and Samsung Pay. Payment security is ensured by Secure Element — an isolated chip that stores payment card data.

NFC vs Bluetooth: Technology Comparison

NFC and Bluetooth LE (Low Energy) are two short-range communication technologies that are often compared. NFC wins in connection setup speed (0.1 s) and does not require pairing, but falls short in data transfer speed and range. Bluetooth LE requires pairing (2–5 seconds) but provides speeds up to 2 Mbps and a range of up to 100 meters.

In practice, NFC and Bluetooth do not compete but complement each other. NFC is used for connection initiation (handover): simply bring the phone close to the device so that NFC transmits Bluetooth connection parameters (NFC Bluetooth Handover). After that, devices switch to Bluetooth for fast file or audio streaming transfer.

NFC Hardware Architecture in Smartphones

The NFC module of a smartphone consists of three components: NFC controller, NFC antenna and Secure Element (for secure operations). NFC controller is a separate chip or part of a combined communication module (NFC + Bluetooth + Wi-Fi, e.g. WCN3990 from Qualcomm). It manages the radio interface and exchange protocols.

The NFC antenna is a printed coil on a flexible substrate (FPC) or on the battery case. The antenna size is 20×30 mm, number of turns — 3–5. The antenna connects to the controller through a matching circuit tuned to 13.56 MHz frequency. According to NXP Semiconductors, efficient antenna operation requires precise calculation of inductance and quality factor.

Secure Element (eSE) is a separate cryptographic chip (NXP P71, Samsung S3K) or an isolated area in the SoC (iSE — integrated Secure Element). It stores payment card data and performs cryptographic operations for HCE (Host Card Emulation). Secure Element is isolated from Android/iOS: only the NFC controller has access to it via APDU commands over the SWP (Single Wire Protocol) bus.

// Example APDU command for interacting with Secure Element
const uint8_t SELECT_APDU[] = {
    0x00, 0xA4, 0x04, 0x00,            // CLA, INS, P1, P2
    0x07,                               // data length (7 bytes)
    0xA0, 0x00, 0x00, 0x00,             // RID — registered
    0x03, 0x10, 0x10,                   // PIX — application identifier
    0x00                                // Le — expected response length
};

// Sending command via NFC controller to Secure Element
NfcStatus nfcStatus = sendApdu(SELECT_APDU, sizeof(SELECT_APDU));

NFC Applications in Mobile Devices

NFC in a phone is used in four main scenarios: contactless payment, transportation, access control and task automation. The most widespread application is payment systems: Apple Pay, Google Pay and Samsung Pay. They use Card Emulation mode with HCE (Host Card Emulation) or Secure Element to emulate a bank card.

Transportation systems worldwide (Moscow Metro, London Tube, New York MTA) accept NFC payments through mobile wallets. In Japan, FeliCa technology (Sony) based on NFC has been used for transit, shopping and office access since 2004. Smartphones with FeliCa chips, such as iPhones for the Japanese market, support Suica and PASMO.

NFC Tags allow automating “smart home” scenarios: bring your phone to a tag by the bed — the alarm turns on and notifications turn off. On Android this is implemented via Android Beam / NFC Tools, on iOS — via Shortcuts and NFC triggers. Some smartphones also use NFC for fast charging — the Qi standard uses NFC for charger identification.

Code Example: Reading NFC Tag on Android

Android provides an API for processing NFC tags through the Intent System. When a tag is brought close to the phone, the system creates an intent with the tag, and the application receives data in NDEF (NFC Data Exchange Format) format. Below is an example of an Activity that reads a URL or text from an NFC tag.

class NfcReaderActivity : AppCompatActivity() {

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_nfc)
        handleNfcIntent(intent)
    }

    override fun onNewIntent(intent: Intent) {
        super.onNewIntent(intent)
        handleNfcIntent(intent)
    }

    private fun handleNfcIntent(intent: Intent) {
        if (intent.action == NfcAdapter.ACTION_NDEF_DISCOVERED) {
            val rawMessages = intent
                .getParcelableArrayExtra(NfcAdapter.EXTRA_NDEF_MESSAGES)
            rawMessages?.forEach { rawMsg ->
                val msg = rawMsg as NdefMessage
                msg.records.forEach { record ->
                    val payload = String(record.payload)
                    println("NFC data: $payload")
                }
            }
        }
    }
}

To work with NFC, you need to declare the android.permission.NFC permission in the manifest and configure an intent-filter for ACTION_NDEF_DISCOVERED, ACTION_TECH_DISCOVERED or ACTION_TAG_DISCOVERED. Android automatically filters NFC tags by NDEF record type — this allows the application to respond only to tags with a specific MIME type or URL prefix. Note that the NFC antenna is usually located in the upper part of the phone’s back panel — to read a tag, bring the top of the phone to the tag.